EOS

It sounds like the beginning of a joke: What do you get when you put a team of geologists and nurses in the same room? But the answer is no laughing matter for Kentuckians.

Although smoking itself is a well-known health risk—and Kentucky dances around the top spot for cigarette smokers in the United States—smokers who live in a home with radon gas exposure can be 10 times more likely to be diagnosed with lung cancer.

But how prevalent is radon in Kentucky homes? The first step to answering the question is understanding the underlying geology—the source of radon gas. In an innovative collaboration, the Kentucky Geological Survey (KGS) and the Bridging Research Efforts and Advocacy Toward Healthy Environments (BREATHE) research group at the University of Kentucky have created an interactive radon hazard map available to the public.

The map is web based and searchable and merges detailed geologic mapping, radon home test kits, and color-coded hazard values to help residents understand their risk to the clear, odorless, tasteless gas. The researchers hope the map will be a useful tool for both residents and public health experts.

Partnership Forged in Bedrock

The collaboration began about 5 years ago. The University of Kentucky published a news article on researchers in the School of Nursing working on radon exposure. A geologist at KGS (which is also affiliated with the University of Kentucky) saw the story, and his interest was immediately piqued.

“Well, you know, radon comes from rocks, and rocks don’t start and stop at county boundaries.”In the original article, the radon map they were using showed risk at the county level. “Our geologist said, ‘Well, you know, radon comes from rocks, and rocks don’t start and stop at county boundaries,’” said Bill Haneberg, state geologist and director of KGS and lead author of a paper in GeoHealth that detailed the interactive radon mapping project.

Haneberg explained that Kentucky already has exceptionally detailed geologic maps. (“For so many years, the motivating factor for these great maps we have in Kentucky was coal,” he added.) “There was this phenomenal collaborative program between the U.S. Geological Survey (USGS) and the KGS,” he said. From 1960 to 1978, geoscientists mapped the entire bedrock geology of the state at a 1:24,000 scale, and the maps have all been digitized.

Geologists at KGS shared the maps with the BREATHE team. Ellen Hahn, director of BREATHE and a coauthor of the paper, was impressed with their detail and scalability.

“Our initial work was based on 1,000 indoor radon values in northern Kentucky,” Hahn said. The initial collaboration between KGS and BREATHE used this smaller data set and geologic mapping to look for any patterns. “We were looking for statistical correlations between the types of rock formation and indoor radon values that we had from that data set,” she noted. “We did indeed find interesting results from that.” For instance, homes built on limestone, dolostone, and some shales have higher indoor radon concentrations than homes on siltstone, sandstone, and surficial deposits.

Scaling Up the Project

From the northern Kentucky data set, the team then scaled up the project to the entire state. Hahn explained that two companies had been distributing and analyzing home radon kits in Kentucky for more than 20 years. She contacted those companies and asked for historical data, making sure that personal information was kept private—all addresses were changed to coordinates, for instance. In the end, the team ended up with more than 71,000 radon tests across the state.

“It turns out in Kentucky, the highest rate of potential is associated with Mississippian limestones.”The team grouped the indoor radon tests located in a specific geologic formation to look at the values of measured radon. Using the 75th percentile of radon measurements, rock units were color coded for hazard. When a person clicks on the map, a box pops up containing information about the rock unit, measured radon levels, and number of radon kits tested for that formation.

“I think that map is quite cool. It’s really nice to look at, and I think it’s pretty accessible,” said Douglas Brugge, an environmental health professor and chair of the Department of Public Health Sciences at the University of Connecticut. He was not involved in the study. “I think what most people are going to want to do is look for where they live, they’re going to want to zoom in on the map for their locality and get a sense of risk in their area.”

“The highest potential may surprise a lot of people,” said Haneberg, explaining that Kentucky has a lot of uranium-rich, Devonian age black shales. “But it turns out in Kentucky, the highest rate of potential is associated with Mississippian limestones. In fact, if you look at that map, there’s a big red belt going around the edge of the Illinois basin—those are Mississippian limestones, including the same limestones that host Mammoth Cave.” Haneberg noted that Devonian shales, with all of their uranium, came in third.

Credit: BREATHE

The EPA suggests an action level of 4.0 picocuries per liter, meaning that radon remediation should be done on homes that register those radon levels. On the map, the worst rock units for potential radon release were in excess of 16 picocuries per liter. Haneberg pointed out that the map is not a definitive measurement of the radon at an individual home, as that number is influenced by variations in geology and home construction.

Researchers said the map demonstrates the value of cross-disciplinary science. “I think environmental health hazards usually require people who are more on the physical sciences side and people who are on the public health, epidemiology side,” Brugge noted. Although geologists can focus in on the exposure to hazards, public health experts can link the exposure to health concerns and communicate risk to the public.

If the public can understand that the interactive map is a first step in understanding their exposure, then the efforts were successful, said Brugge. “If it motivates [residents] to do testing when they wouldn’t have done it, then that’s a good thing.”

Clear Communication and Collaboration

When communicating with the public, “I think it’s really important to distinguish between hazard and risk—it’s a subtle thing,” said Haneberg. Geologists look for hazards—what is the likelihood of this rock unit releasing radon? Risk, on the other hand, “involves the consequences” of those hazards, he explained.

That’s where the public health experts come in. “We bring the knowledge of disease and how it affects the body…how environmental exposures affect people’s risk of developing the disease,” Hahn noted. “We’re very familiar with prevention of disease through exposures.” Part of that prevention is behavior change—whether that is quitting smoking or adding radon remediation to a house.

The radon mapping and communication strategy saved approximately one premature lung cancer death and between $3.4 million and $8.5 million every year.Hahn and her team have been working on how best to get radon risk information to the public. She said they targeted high-risk counties for their initial outreach efforts. “We invited the Cooperative Extension agents, the health department, and other professionals…to a lunch-and-learn—bring your lunch, and we’ll teach you something about radon.” Each participant got infographics, free radon test kits, and some presentation materials to go out into their communities.

In a related study, Hahn and her colleagues ran an economic analysis to assess the value of using geologic data to help communicate radon risk potentials in Kentucky. They wanted to understand how geologic maps may have reduced lung cancer by fostering increased testing and increased mitigation. “We were able to find that we actually save lives and money,” Hahn said.

They found that the radon mapping and communication strategy saved approximately one premature lung cancer death and between $3.4 million and $8.5 million per year.

—Sarah Derouin (@Sarah_Derouin), Science Writer

Tropical cyclones’ strong winds are associated with ocean mixing and cold wakes. The cold water that is brought to the surface is rich in nutrients and can trigger photosynthesis that can be observed by satellites. Using satellite, Da et al. [2021] show that there are statistically significant trends in sea surface temperature cooling and primary production associated with tropical cyclones in the past 35 years. Furthermore, this tropical cyclone-induced increase in ocean primary production has partially mitigated the overall decline in primary production due to anthropogenic climate change.

Citation: Da, N. D., Foltz, G. R., & Balaguru, K. [2021]. Observed global increases in tropical cyclone-induced ocean cooling and primary production. Geophysical Research Letters, 48, e2021GL092574. https://doi.org/10.1029/2021GL092574

—Suzana Camargo, Editor, Geophysical Research Letters

Environmental conditions are intimately connected with human health outcomes. The COVID-19 pandemic has brought this into sharp focus. Some countries have plentiful data about their populations to inform resource distribution and policy making. Across the continent of Africa, however, comprehensive data on human health and environmental indicators is generally lacking for a variety of reasons, and results in poorer health outcomes and disjointed health interventions. A new special collection on the connections between COVID-19, environmental and human health across continental Africa seeks new data, research, and analysis to improve our understanding.

COVID-19 in Africa

As of mid-June 2021, there were approximately 5.1 million cases and 136,000 deaths associated with COVID-19 in Africa.COVID-19 cases first appeared on the continent of Africa during the spring of 2020, with most of the cases occurring north of the Sahara and in South Africa, plus in Ethiopia.

As of mid-June 2021, there were approximately 5.1 million cases and 136,000 deaths associated with COVID-19, with an estimated case-fatality ratio of 2.64 percent, which is only exceeded by the continent of South America.

South Africa has the highest number of cases and fatalities within the continent, with 1.7 million cases and more than 58,000 fatalities. The top five countries in terms of both the number of COVID-19 cases reported and fatalities reported are South Africa, Morocco, Tunisia, Egypt, Ethiopia. Other countries experiencing high cases and fatalities include Kenya, Nigeria, Algeria, Zambia, Sudan, Nigeria, Zimbabwe, Ghana, and Sudan.

A new wave of COVID-19 first observed in Southern Africa is now spreading across the continent has been linked to the Delta variant.

While the total numbers of COVID-19 cases and fatalities within Africa are considerably lower than in Europe, South America, North America, and Asia, there are reasons to be concerned, which is the motivation behind the call for new research papers for a special collection. These include:

Low and middle-income countries with growing populations that lack critical health facilities and equipment such as intensive care units, ventilators, and health care staff Limited vaccinations have been distributed across the continent and new variants continue to emerge The indirect causal connections between COVID-19 cases, spread, and seriousness have been found on other continents but not necessarily in Africa Limited in situ environmental data requiring the use of remotely sensed measurements. COVID-19 and air pollution

When the first cases began to show up in Africa during March 2020, many governments immediately began to partially or fully shut down activities tied to their economies. Consequently, while atmospheric pollution may have been reduced, many individuals with limited income may have become unemployed during the pandemic.

Air pollution is linked to COVID-19 with greater uncertainty in relation to precipitation and temperature.Our current level of knowledge suggests that air pollution is linked to COVID-19 with greater uncertainty in relation to precipitation and temperature.

In high particulate matter (PM) regions, COVID-19 seriousness and mortality are greater and there is the same dimension of environmental injustice that occurs in communities of color in the United States.

Results also show that COVID-19 transmission (R0) is higher in polluted areas where high long-term exposure to PM2.5 concentrations (composed of sulfate, ammonium, and black carbon) aerosols exceeds healthy standards.

In sub-Saharan Africa, poor air quality occurs at the household level from indoor cooking and heating, at local level from mega-city pollution, and on regional scales from large-scale desert dust and biomass burning during the dry seasons. Aerosols from desert dust are surmised to cause the drive of more premature death relative to biomass burning. During the dry season in West Africa, hazardous dust concentrations are associated with infant mortality, meningitis, and respiratory disease.

A shortage of data and a lack of research

Access to data remains the main obstacle to linking the environment and health in Africa.Access to health and environmental data remain the main obstacles to linking the environment and health in Africa.

During the COVID-19 pandemic, daily COVID-19 cases have been reported in many countries; however, spatially varying data at higher administrative levels within African countries may not be available.

In addition, some countries show a low number of tests per 100,000 persons leading to potential under-sampling, which could be related to available tests or the expense of testing to many low-income citizens.

The lack of research and operational grade in situ measurements of particulate matter and trace gas pollutants is abysmally low throughout the continent. Hence, the use of satellite observations and low-cost PM sensors has introduced novel ways to examine potential relationships between COVID-19 and the environment.

Special collection on the COVID-19 pandemic and environmental conditions in Africa

A new special collection in the journal GeoHealth entitled The COVID-19 pandemic and environmental conditions in Africa is a call to the community to help explore the various aspects of COVID-19 across continental Africa. It also provides a platform for input from scientists in Africa to contribute from their vantage point and across widely varying cultural and environmental settings.

Papers investigating the links between the environment, COVID-19, and health, in general, in Africa are welcomed. Submissions can include recent developments in modeling and forecasting, monitoring, data analysis, weather, climate and air quality variability, epidemiology and COVID-19 related impacts. Manuscripts should be submitted via the GEMS website for GeoHealth.

—Gregory S. Jenkins (gsj1@psu.edu,  0000-0002-0753-3964), The Pennsylvania State University, USA

New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

If exoplanets were comic book characters, the first few ever confirmed would have been greeted with cries of “Zounds!” or “Zowie!” or even “Gadzooks!” Not only were these worlds unlike anything in our own solar system, but they were unlike anything scientists had even pondered. The first two were chunks of rock orbiting a pulsar, the remnant of an exploded star. The next one was a gas giant orbiting at just a fraction of the distance between the Sun and Mercury—so close that the planet’s outer atmosphere was heated to more than 1,500°C.

Astronomers have since added more than 4,000 confirmed exoplanets to the list (although the exact number depends on which list you check). Thousands more await verification.

Most of those worlds fit into a few major categories, some of which are alien to our own neighborhood. According to NASA’s exoplanet catalog, for example, there are more than 1,300 super-Earths, which are pretty much what they sound like—rocky planets a few times the size of Earth. Hundreds more are mini-Neptunes, which are bigger than super-Earths but smaller than Neptune, the Sun’s most distant major planet.

Some exoplanets don’t fit into the major categories, though. They are the oddballs. And like many oddballs, they can be more interesting than the conformists.

Second-Chance Planets

The first two confirmed exoplanets, discovered 3 decades ago, remain among the oddest and rarest of all: “zombie” planets that probably were born after their star died. Both orbit the pulsar PSR B1257+12. A pulsar is a rapidly spinning neutron star, the corpse of a massive star that exploded as a supernova. As the neutron star spins, it emits pulses of energy that form an extremely accurate clock—and provide clues for exoplanet hunters. The tug of an orbiting object alters the timing of the pulses a tiny bit, revealing a planet’s presence.

A brilliant aurora encircles the pole of one of the planets orbiting the pulsar PSR B1257+12 in this artist’s concept. The pulsar is at upper left, and its other two known planets are also in view. Credit: NASA/JPL-Caltech

Astronomers have discovered a handful of other pulsar planets (including a third for PSR B1257+12). Pulsar timing is so precise that it can reveal orbiting objects as small as asteroids, so the dearth of discoveries suggests that pulsar planets are rare.

It’s unlikely that planets could survive a supernova, so astronomers say these must be “second-chance” planets. They may have formed from debris from a pulsar’s destroyed companion star, such as a white dwarf. “If the star is in a binary with a low-mass star or a compact companion, the pulsar irradiates the companion and the companion evaporates,” said Rebecca Martin of the University of Nevada, Las Vegas. “This can lead to a runaway effect where the companion is dynamically disrupted and forms a disk around the neutron star. Planets may form from this disk.”

Hot Jupiters

The first exoplanet found orbiting a star in the prime of life, similar to the Sun, was just as shocking as the pulsar planets (and earned its discoverers a share of the 2019 Nobel Prize in Physics). Exoplanet 51 Pegasi b is roughly half the mass of Jupiter, the giant of our solar system, yet is close enough to its star that it orbits in just 4 days (compared to 12 years for Jupiter). That makes the planet extremely hot.

And 51 Pegasi b is not even the most extreme “hot Jupiter.” Of the few hundred known examples, some are many times Jupiter’s mass, one orbits its planet in just 18 hours, and some are being blasted by so much stellar radiation that their atmospheres are eroding into space. And although 51 Pegasi b was a true oddball when it was discovered, the roster of hot Jupiters has grown so large that these worlds form a category all their own. (A swelter of hot Jupiters, perhaps?)

The exoplanet WASP-79 b (left) is so close to its parent star that its upper atmosphere is as hot as molten glass. Credit: NASA/ESA/L. Hustak (STScI)

Such worlds are hard to explain. Close to a star, temperatures should be too high, and stellar winds should be too strong to allow a planetary core to sweep up enough hydrogen and helium to grow that big.

Most astronomers have hypothesized that hot Jupiters formed farther out in their solar systems and migrated inward. As often happens in comics, though, one character can disrupt the entire narrative. HIP 67522 b, which orbits once every 7 days, belongs to a star that’s only about 17 million years old—hundreds of millions of years younger than most hot-Jupiter hosts. It seems unlikely that the planet could have formed far from the star and then migrated so close in such a short period of time. So scientists may have to go back to the drawing board to explain at least some hot Jupiters.Kepler-51 hosts three planets, all of which are oddballs. They are a few times the mass of Earth but roughly as big as Jupiter. That makes them not much denser than cotton candy.

Cotton Candy Planets

The star Kepler-51 hosts three planets, all of which are oddballs. They are a few times the mass of Earth but roughly as big as Jupiter. That makes them not much denser than cotton candy. The Kepler-51 worlds are among a dozen or so confirmed “super-puff” planets.

Although some hot Jupiters have been puffed up by the heat from their nearby stars, super-puffs are much cooler, noted Jessica Libby-Roberts, a graduate student completing her Ph.D. at the University of Colorado Boulder. That temperature difference means the super-puffs must be inflated by some other mechanism.

Despite their great size, the planets of Kepler-51 are lightweight, so they are roughly as dense as cotton candy. Credit: NASA/ESA/L. Hustak/J. Olmsted (STScI)

Kepler-51 is a relatively young star, so its planets could be puffed up by the internal heat left over from their formation, Roberts said. Other super-puffs could have formed in “a really weird” region of the disk around the star where they could grab a lot of gas in a hurry. However, super-puffs might not be especially puffy at all. Instead, high haze layers or wide bands of rings might make them appear much larger than they really are.

Except for the planets of Kepler-51, most known super-puffs are the most distant members of multiplanet systems, Roberts said. If they really are puffy, then “either super-puffs need to form really far from their stars before migrating inwards, or they need to end up at a distance far enough from their stars to hold on to all that hydrogen-helium atmosphere, or a combination of both,” Roberts said. “There is still a lot to be done in this area.”

Wrong-Way Planets An artist’s concept depicts the retrograde orbit of planet WASP-8 b. Credit: ESO/L. Calçada

Some exoplanets fit into more than one “oddball” category. WASP-17 b, for example, is a super-puff. It’s half as massive as Jupiter but twice as wide, making it one of the largest and cotton-candiest planets yet discovered. It’s also a “wrong-way” exoplanet, orbiting in the opposite direction from its star’s rotation on its axis—one of only a handful of such planets yet seen.

Scientists suggest that WASP-17 b (and other retrograde planets) could have performed an about-face as the result of the gravitational influence of another planet­, through either a single especially close encounter or a more gradual long-range nudge.

Seeing Double

If planet hunters could visit any fictional world of their choosing, there might be a mad dash for Tatooine, the home world of Luke Skywalker. The first Star Wars movie featured an iconic view of Luke watching twin suns set over the desert. Today, any planet found to orbit both members of a binary star is instantly compared to that famous world.

Twin suns set on a Tatooine-like world, which orbits both members of a binary star, in this artist’s concept. Credit: NRAO/AUI/NSF, S. Dagnello

Although quite a few planets are known to orbit one member of a binary, circumbinary planets are about as common as stormtroopers who can shoot straight—astronomers have cataloged roughly a score of them. (One of them, Kepler-64 b, orbits one binary in a two-binary system, giving it four stars).

The known circumbinaries should remain in stable orbits for “at least 100 million years,” according to Jerome Orosz of San Diego State University. Some of the planets even lie within their host stars’ habitable zone, where conditions are most comfortable for life. “It’s obviously more complicated than the habitable zone for a single star,” Orosz said. “In particular, the habitable zone around a binary star moves as the two stars orbit….Keep in mind that the known circumbinary planets are gaseous, with diameters in the range of Neptune’s to Jupiter’s. Those planets probably won’t be habitable. There are no Earth-like planets known to be in circumbinary systems.”

The search for Tatooines in other systems continues, however—perhaps leading to more zowies or zounds in the years ahead.

—Damond Benningfield (damond5916@att.net), Science Writer

New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

The whole field of exoplanet study is frustratingly tantalizing. We now know for sure there are alien worlds. We can see them! Kinda. We see their shadows; we can see their fuzzy outlines. We are so close to the tipping point of having enough knowledge to truly shake our understanding—in the best way, says this space geek—of Earth’s place in the universe.

The first light of the James Webb Space Telescope (JWST) may be what sends us over that exciting edge. In just a few months, the much-delayed launch will, knock on wood, proceed from French Guiana and take around a month to travel to its destination at the second Lagrange point (L2). “This is certainly an exciting time for exoplanet science, with current missions like Hubble and TESS [Transiting Exoplanet Survey Satellite] providing us with new discoveries and future missions like JWST, which promises to provide incredible new data that will answer some of our current questions and also create many new ones,” said Sarah Hörst of Johns Hopkins University, Eos‘s Science Adviser representing AGU’s Planetary Sciences section who consulted on this issue. “The field is moving very quickly right now.”

That’s why our August issue is all about exoplanets—what we know and what awaits us over the launch horizon. Who gets the first peek through JWST? In March, the proposals selected for the first observing cycle were announced. Meet the slate of scientists who will be pointing the telescope at other worlds, and read what they hope to learn in “Overture to Exoplanets.”

As with all new instruments, the data collected from JWST will be pieced together with observations from ongoing missions and other facilities around the world. “Over the last decade, we’ve gotten gorgeous images from the ALMA interferometer in Chile and have seen loads of fine-scale structure, tracing pebbles in planet-forming disks,” says astronomer Ilse Cleeves in our feature article. Hörst found this synergy with ALMA (Atacama Large Millimeter/submillimeter Array) especially intriguing: “Although I’ve thought a lot about what we’ll learn about individual planets, I hadn’t really thought much about what we’ll be able to learn about planet formation process by studying the disks themselves.”

“I’m excited for all the ‘well, that’s weird’ moments. Those are my favorite things in science because that’s when you know that new discoveries are going to be made.”In “The Forecast for Exoplanets Is Cloudy but Bright,” we learn the immense challenge posed by exoplanet atmospheres, when researchers are still struggling to understand the complex dynamics of clouds on our own planet. And in “Exoplanets in the Shadows,” we look at the rogues, the extremes, and a new field being coined as necroplanetology.

What awaits us when the first science results start coming in from JWST and all the coordinated missions next year? “I’m really excited for the unexpected,” says Hörst. “I’m excited for all the ‘well, that’s weird’ moments. Those are my favorite things in science because that’s when you know that new discoveries are going to be made. I’m also really happy for all of my colleagues who have worked so tirelessly for so many years to make JWST happen.”

We’re pretty happy, too, for the scientists long awaiting this day and for the rest of us who eagerly await a wide new window on our mysterious universe.

—Heather Goss (@heathermg), Editor in Chief, Eos

New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

When astronomers gathered to reveal “new planets” at a press conference in January 1996, the world paid attention. Hundreds of journalists and fellow astronomers packed the meeting room, where presenters confirmed the identity of one exoplanet and reported the discovery of two others—the first planets known to orbit other Sun-like stars. The story made the front pages of major newspapers (“Life in Space? 2 New Planets Raise Thoughts,” wrote the New York Times), appeared in magazines (including a Time cover story), and aired on television news (including CNN) soon after.

A quarter of a century later, exoplanets still generate headlines—sometimes. With the number of confirmed planets well beyond 4,000 and more being added to the list almost weekly, however, a sort of exoplanet fatigue has set in. Only the most spectacular discoveries show up in our daily newsfeeds: potentially habitable planets, for example, or “extreme” worlds—those that are especially hot or young or blue or close to our solar system.

Yet some of the topics in the penumbra of exoplanet discussions are just as fascinating as those in the spotlight. They remain in the shadows in part because they involve objects that are rare or that are difficult to find and study with current technology. The recently named field of necroplanetology, for example, studies planets orbiting dead or dying stars, providing the only direct look at the innards of exoplanets. Gravitational microlensing allows astronomers to detect planets at greater distances than once thought possible. Several groups of researchers are developing instruments or small spacecraft to look at Earth as an exoplanet analogue, showing us what our planet would look like to an astronomer many light-years away. And the International Astronomical Union (IAU) has begun the long process of bestowing proper names on exoplanets—a process that simply may not have had enough time to filter into the consciousness of either professional astronomers or the public.

“We’ve discovered a lot of weird things,” said Laura Mayorga, an exoplanet researcher and postdoctoral fellow at the Johns Hopkins University Applied Physics Laboratory (APL). “When we first started studying exoplanets, we found that they got stranger and stranger. They put all of our understanding to the test.… Finding something new throws everything up in the air, and it has to resettle. That makes this a really exciting time.”

Death of a Planet

Although it sounds like something from a Syfy channel original movie, necroplanetology is the newest branch of exoplanet studies—a novelty that involves intrinsically rare targets. The term was coined by Girish Duvvuri, then a student working with Seth Redfield at Wesleyan University in Connecticut, in a 2020 paper. “We’re proud of the name,” said Redfield. “It’s a great way to describe the systems we’re studying. It has a small number of practitioners, but the larger community is just starting to look into this topic.”

The name was originally applied to the study of dead or dying planets around white dwarfs, which are the hot but dead cores of once normal stars. A typical white dwarf is at least 60% as massive as the Sun but only about as big as Earth. The size of white dwarfs makes it easier to detect the remains of pulverized planets as they transit, passing across the face of the star and causing its brightness to dip a tiny bit.

Starlight filtering through an exoplanet’s atmosphere during a transit would reveal its composition. (Astronomers have used the same technique to measure the atmospheres of planets transiting much larger main sequence stars, which are in the prime of life.) “What we started finding first was not whole planets but planetary debris,” Redfield said.

“All those clues made it clear that planets can exist around white dwarfs. They can be destroyed by white dwarfs as well.”In particular, using early observations from the K2 mission of the planet-hunting Kepler space telescope, they found WD 1145+017, a white dwarf about 570 light-years from Earth. The star’s light dipped several times in a pattern that repeated itself every few hours. The researchers concluded that they were seeing the debris of a planet that had been shredded by its star’s gravity—probably chunks or piles of rock surrounded by clouds of dust.

Observations with large ground-based telescopes revealed calcium, magnesium, iron, and other heavy elements in the white dwarf’s spectrum. Such heavy elements should quickly sink toward the core of a white dwarf, where they wouldn’t be detected. Their discovery suggested that the elements had been deposited quite recently, as rubble from a disrupted planet (or planets) spiraled onto the white dwarf’s surface.

“All those clues made it clear that planets can exist around white dwarfs,” said Redfield. “They can be destroyed by white dwarfs as well. The tidal forces are quite extreme, so they can break apart and grind up a planet.… As that material accretes onto the white dwarf, we’re actually learning about the innards of the planets.”

Such a planet may have been born far from its host star and migrated close enough to be destroyed. Astronomers know that such migrations are possible because they have discovered a few hundred “hot Jupiters”: worlds as massive as the largest planet in the solar system but so close to their stars that their upper atmospheres are heated to hundreds or thousands of degrees. Some of these planets are being eroded by stellar radiation and winds, perhaps marking the beginning of the end for worlds that could be subjects for future necroplanetologists.

Stars That Take a Dip

Despite expectations of a bounty of such white dwarf systems, Redfield said, they seem to be rare. (A recent study found evidence of one intact giant planet around one white dwarf.) Astronomers have found evidence of similar processes at work around main sequence stars, though.

The best-known example is KIC 8462852 (also known as Boyajian’s Star), about 1,470 light-years from Earth. Large, but irregular, dips were discovered in the brightness of the star, which is bigger, hotter, and brighter than the Sun. Possible explanations for the decrease included the panels of a “megastructure” built by an advanced civilization orbiting the star—an idea (since abandoned) that generated plenty of headlines.

Astronomers have discovered other examples of “dipper” stars as well. Edward Schmidt, a professor emeritus at the University of Nebraska–Lincoln, reported 15 slow dippers, whose light varies over long timescales, in study released in 2019. He said he plans to publish details on 17 more in an upcoming paper.

One or more moons could be snatched away as a planet falls into its star. The planet essentially hands its moons to the star—they’re orphaned exomoons.The stars all have similar masses and temperatures, which suggests that their dipping patterns share a common explanation, Schmidt said. “It could be caused by disintegrating planets—that looks promising so far.” He’s looking through published spectra of the stars to see whether their surfaces are polluted by the residue of planets, which could solidify the idea.

A couple of systems discovered by Kepler seem to add credence to the hypothesis. Kepler-1520b, for example, shows dips in luminosity of up to 1.3%. A ground-based study found that the dimming is caused in part by clouds of dust grains, providing “direct evidence in favor of this object being a low-mass disrupting planet,” according to 2015 paper. And K2-22, discovered in Kepler’s K2 mission, appears to be a disintegrating planet more massive than Jupiter but only 2.5 times the diameter of Earth.

Another study suggested a slightly altered explanation for Boyajian’s Star and other dippers: disintegrating exomoons. Researchers suggested that one or more moons could be snatched away as a planet falls into its star. “The planet essentially hands its moons to the star—they’re orphaned exomoons,” said Brian Metzger, one of the study’s authors and a physicist at Columbia University and senior research scientist at the Flatiron Institute.

Stellar radiation could be eroding the surviving moons, releasing solid grains of material that then form a clumpy disk around the star. So the young field of necroplanetology may need a new subfield: necrolunarology.

A Second Chance at Life

For some planets, though, the death of a star isn’t necessarily the end—it may be the beginning. The first confirmed exoplanets, discovered 3 decades ago, orbit a pulsar, a dead star whose composition is more exotic than a white dwarf. A pulsar is a rapidly spinning neutron star, the collapsed core of a massive star that exploded as a supernova. As the neutron star spins, it emits pulses of energy that form an extremely accurate clock. The gravitational tug of a companion alters the timing of the pulses a tiny bit, revealing the presence of an orbiting planet.

The first identified pulsar planets orbit PSR B1257+12. Astronomers have since discovered a handful of others, but most searches have come up empty. An examination of more than a decade of observations made by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), a project that is using pulsar timing to hunt for gravitational waves, for example, found no evidence of planets around a set of 45 fast rotating pulsars. The search could have revealed planets as light as the Moon in orbital periods of 1 week to almost 5 years, said Erica Behrens, a graduate student at the University of Virginia who conducted the study during an internship at the National Radio Astronomy Observatory.

This artist’s view shows a brilliant aurora on one of the planets of the pulsar PSR 1257+12, energized by the pulsar itself (top left). The system’s other two confirmed planets also are in view. Credit: NASA/JPL-Caltech

“Since we’ve seen so few, it seems like they’re pretty rare,” Behrens said, which may explain why they’ve received so little attention since the early discoveries. “They must have formed after the star has blown up. No planet that existed while the star was still living would be able to survive the supernova.”

Theoretical work hints that instead of supernova survivors, pulsar planets may be “zombies,” born from the debris of companion stars.

Metzger and Ben Margalit, also of Columbia, have suggested, for example, that the companion could be a white dwarf. The extreme gravity of the neutron star tears the white dwarf apart—perhaps in a matter of seconds—and the debris forms a disk around the pulsar. Some of the material in the disk falls onto the neutron star while the outer edge of the disk expands and cools. Solid material in those precincts may condense to form solid bodies, which then merge to make planets.

The scenario would explain the frequency of pulsar planets, which is roughly equal to the frequency of neutron star–white dwarf binaries, Metzger said. It would not, however, explain the birth of a pulsar planet that’s been discovered in a globular cluster, where the density of stars is extremely high. “You’d have to invoke more exotic interactions,” which scientists are still trying to model, he said.

A Rogues’ Gallery of Exoplanets

Although most exoplanets have been discovered through transits or radial velocity measurements, which detect a back-and-forth shift in the wavelengths of starlight caused by the pull of orbiting planets, a few stragglers have been found through other methods. Such methods are difficult to apply, or they’re looking for objects or phenomena that are rare, so they’ve yielded far fewer discoveries than the most favored methods.

Astrometry, for example, precisely measures a star’s position to detect tiny wobbles caused by the gravitational tug of orbiting planets. Such measurements are hard to make and have yielded only one or two discoveries. However, astronomers expect observations by the Gaia spacecraft, which is plotting the positions and motions of more than 1 billion stars, to yield thousands of new Jupiter-sized exoplanets in relatively wide orbits, which would create a whole new population for study.

The most successful of the lesser known techniques, however, has been gravitational microlensing which has revealed more than 100 planets. “It’s very complementary to other techniques,” said Matthew Penny, an astronomer at Louisiana State University. “You get an instant detection of some very distant planets that would take decades to find with other techniques.”

This diagram shows how microlensing reveals a planet orbiting a star. Credit: NASA, ESA, and K. Sahu (STScI)

Gravitational microlensing relies on general relativity, which posits that if a star or planet passes in front of a more distant star, the intervening object’s gravity bends and magnifies the background star’s light, creating a double image. If the alignment is perfect, it creates a bright circle of light known as an Einstein ring. (The same technique is used on a larger scale to study galaxies and quasars billions of light-years away.)

The length and magnification of a lensing event allow astronomers to calculate the intervening object’s mass and, in the case of a planet, its distance from its star. Astronomers have measured planet-star separations of up to more than 10 astronomical units (AU), which is far wider than with other techniques.

Microlensing can reveal planets that are thousands of light-years away (the current record holder, according to the NASA Exoplanet Archive, is at 36,500 light-years, many times farther than planets discovered with other techniques). Microlensing allows astronomers to study planets in regions of the Milky Way well beyond our own stellar neighborhood, including the central galactic bulge.

Perhaps most important, microlensing is the only technique that can reveal rogue planets, which travel through the galaxy alone, unmoored to any star.

A rogue planet glides through the galaxy alone in this artist’s impression. Credit: NASA/JPL-Caltech

Rogues might form as stars do, from the gravitational collapse of a cloud of gas and dust. That process would form only massive planets—a minimum of 5 times the mass of Jupiter, Penny said. “So far,” however, he explained, “the main results are that there are not a lot of free-floating giant planets out there,” with only a handful of confirmed discoveries to date.

Most rogues probably form from the disk of material around a star, then escape. “It could be an interaction between planets,” Penny said. “If you form a lot of planets in a disk, the disk keeps order until it dissipates. But once the damping effect of the disk is gone, all hell breaks loose,” and gravitational battles can sling planets into interstellar space. There may be billions of these smaller castaway worlds.

Although three searches are dedicated to finding planetary microlensing events, they’re restricted by daylight, clouds, and the other disadvantages of looking at stars from the ground.

As with astrometry discoveries and the Gaia mission, though, a space telescope may greatly expand the numbers of confirmed exoplanets. The Nancy Grace Roman Space Telescope, which is scheduled for launch later in the decade, could find 1,400 bound exoplanets and 300 rogues during its lifetime, Penny said. The telescope’s mirror will be the same size as that of Hubble Space Telescope, but with a field of view 100 times wider. That field of view will allow Roman to see a large area toward the galactic bulge—the preferred target for microlensing planet searches. Current plans call for it to scan the region six times for 72 days per session.

“It’s the ideal platform for doing microlensing because you can never predict when a lensing event will occur, and planetary events are very short,” Penny said.

One Telescope, Many Exoplanet Studies

Roman is expected to help with other exoplanet studies as well. As a technology demonstration, it will carry a coronagraph, which blocks the light of a star, allowing astronomers to see the light of planets directly. “It’ll try to get down to Jupiter-like exoplanets that are closer than Jupiter is now,” said Mayorga. “It might get as close as 1 AU for a Sun-like star.”

Current images of exoplanets, whether from telescopes in space or on terra firma, generally cover a single pixel. To better understand those pictures, scientists use the planets of our solar system as exoplanet analogues. In essence, they take the beautiful pictures of Earth and the other worlds that fill Instagram pages and squish them down to a pixel. “That sets a ground truth for the weird things we find in the universe,” Mayorga said. “It allows us to connect that disk-integrated light to the underlying cloud bands or continents or oceans. It’s the only place we can make that connection.”

Mayorga and colleagues used Cassini images snapped during a flyby of Jupiter as one analogue. They saw how the planet’s brightness and color changed as viewed under different Sun angles or as the Great Red Spot rotated in and out of view.

Several teams are developing missions or instruments that would use Earth as an exoplanet analogue. Mayorga, for example, is involved with a concept known as Earth transit observer, a proposed CubeSat mission that would watch Earth from L2, a gravitationally stable point in space roughly 1.5 million kilometers beyond Earth. Transits of the Sun would reveal the composition of our planet’s atmosphere, including its many “biomarkers,” such as oxygen, ozone, and methane.

Another mission, LOUPE (Lunar Observatory for Unresolved Polarimetry of Earth), would monitor Earth in both optical and polarized light from an instrument that hitches a ride on a lunar orbiter or lander.

“Measuring the linear polarization of a planet over a range of time yields a wealth of information about atmospheric constituents and clouds, as well as surface features like vegetation, water, ice, snow, or deserts,” said Dora Klindžić, a member of the mission team and a graduate student at Delft University of Technology and Leiden Observatory. “By observing Earth from a distance where we can reasonably pretend we are an outsider looking at the Earth, such as from the Moon, we can learn how a planet richly inhabited with life and vegetation appears when observed from another faraway planet. In a way, we are looking at ourselves to know others.”

Interstellar Probe could provide that type of understanding from an even more distant perspective. The proposed spacecraft could travel up to 1,000 AU from the Sun to study interstellar space and would look back toward the planets of the solar system. “Ten, 20, 30 years into the mission, we would have observations of the solar system from outside looking in, as if we were flipping the telescope and taking a look at a planetary system we do know,” said Michael Paul, project manager for the mission study at APL. “Tying that with in situ data we have for Mercury, Venus, Mars, Earth, Jupiter, Saturn will better inform the models we have of other planetary systems.”

No Tatooines Here

Give an object a good name, and people are likely to pay attention. “The fact that [Boyajian’s Star] has this special name means that there aren’t many other objects like it,” said Redfield. Perhaps with catchier names, the “unsung” planets and techniques, which can produce some of the most thought-provoking discoveries, will gain their share of the spotlight.

The three exoplanets discussed at the January 1996 press conference, for example, were designated 51 Pegasi b, 47 Ursae Majoris b, and 70 Gamma Virginis b—the names of the parent stars followed by the letter b. Astronomers have used that naming scheme ever since, with extra planets in a system assigned the letters c, d, e, and so on, on the basis of the order of discovery.

The system works well, although the names get a little confusing when the star has only a long catalog designation; no one’s going to be enchanted by 2MASS J21402931+1625183 A b, for example. And such “telephone book” designations are hardly going to appeal to the public, which regularly sees planets with names like Tatooine and Vulcan and Gallifrey in movies and TV shows.

So the IAU has conducted two international competitions that have produced proper names for more than 140 exoplanets. In the most recent project, 112 countries held individual contests, with each country proposing the name for one planet and its star.

“It was great to tap into the public imagination,” said Eric Mamajek, cochair of the naming campaign steering committee and deputy chief scientist for NASA’s Exoplanet Exploration Program. “I was blown away by the ones that made it through the campaign. The names all have stories.”

Astronomers have been slow to adopt the names, though. The names don’t show up in most of the major online catalogs, for example. “Those phone book names take on the intimacy of a proper name for most astronomers,” said Redfield. “I know that HD 189733 b [an exoplanet he’s studied] is just a bunch of numbers, but for me it has the power of a proper name. I call it ‘189.’ We’re on a nickname basis.”

“I think it will be a long process,” said Mamajek. “It may take a new generation—people who grew up reading these names in textbooks.”

Perhaps that new generation will recognize the first exoplanet confirmed around a Sun-like star not as 51 Pegasi b but as Dimidium or the first pulsar planets not as PSR B1257+12 b and c but as Draugr and Poltergeist.

Author Information

Damond Benningfield (damond5916@att.net), Science Writer

New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

The long-awaited launch of the James Webb Space Telescope ( JWST) is finally in sight. Astronomers around the world are anticipating the wealth of information the flagship will gather on everything from the oldest galaxies in the universe to the birthplaces of stars and planets.

“It really is a Swiss army knife telescope with a huge range of applications,” said Elisabeth Matthews, an astronomer at Observatoire de Genève in Switzerland.

JWST, built by a team of more than 1,200 people from 14 countries, will collect infrared (IR) light across a broad range of wavelengths. That makes it ideally suited to studying exoplanets, which bury most of their secrets deep in the infrared spectrum. In this way, among many others, JWST will build on the legacies of the Hubble and Spitzer space telescopes, both of which astronomers have used to make revolutionary leaps in our understanding of distant worlds, although neither telescope was designed to do so. JWST’s instruments, on the other hand, were designed with exoplanets in mind.

The observatory is scheduled to launch by the end of this year, and exoplanet scientists have long been planning what they want to look at first. In 2020 they submitted their proposals to the telescope’s science team, and the selections for JWST’s first observing cycle were announced in March. (An observing cycle is 1 year, or 8,760 hours, of observing time.) More than 20% of JWST’s time during its first observing cycle will be dedicated to understanding exoplanets.

The unifying theme across the exoplanet observing programs? “One word: diversity.”The unifying theme across the exoplanet observing programs? “One word: diversity,” said Stefan Pelletier, an astronomy doctoral student at Université de Montréal. “All bases are being covered in terms of science cases as well as instrument and observing configurations.”

The list of principal investigators (PIs) and coinvestigators on the accepted programs is also more diverse across many axes of identity than space telescope programs have been in the past. Compared with a recent round of Hubble proposals, a higher percentage of PIs who are women and also PIs who are graduate students will make the first JWST observations.

It’s a testament to the hard work by the team at the Space Telescope Science Institute, Matthews said, “both in making sure [members of] the exoplanet community are able to understand the telescope and design good science experiments for it and also in ensuring that the proposals for these science experiments have been carefully and equitably judged.”

Andrew Vanderburg, an astronomer at the University of Wisconsin–Madison, added, “It’s awesome that the [dual anonymous] peer review—where the reviewers don’t know who wrote the proposals, and vice versa—makes it possible for young scientists with good ideas to be awarded time on the world’s most powerful observatory from day one.”

Prologue: A Shakedown Cruise

JWST promises to be a game changer for understanding how and what types of planets form and what makes them habitable, but for this first cycle it’s unknown how the telescope’s performance will measure up to expectations. “The reviewers very much wanted a robust ‘shakedown cruise,’” said Peter Gao, an exoplanet scientist at the University of California, Santa Cruz. “Several proposals focused on new and interesting observing methods and science cases that are sure to be the testing grounds for similar, larger, and more elaborate proposals in the next cycles.”

The selected exoplanet observations tend to stay well within the telescope’s expected limitations. “JWST time is very precious, so for the first cycle it is understandable that emphasis was put on programs that are ‘safe’ in that they are almost guaranteed to generate good results,” said Alexis Brandeker, an astronomer at Stockholm University. Some observations might be “risky” in that the scientists aren’t sure what they’ll find, but if they do find something, they’ll get a good look at it.

On the science side, there’s variety both in the types of planets targeted for observations and in the types of observations being made. “These include the measurement of mineral cloud spectral features as a way to probe the composition of exoplanet clouds, exploring asymmetries in the dawn and dusk limbs of exoplanets during transits, eclipse mapping, and getting a sense of which rocky exoplanets host atmospheres,” Gao said.

And on the target side, “there is a nice balance between some of the first exoplanets to be characterized, like HD 189733 b, and weird exoplanets whose observations were difficult to interpret, like 55 Cancri e,” said Lisa Đặng, a physics graduate student at McGill University in Montreal. Instead of making limited observations of a wide range of planets, most of the selected exoplanet programs seek to observe one or a few planets in great detail.

Lights Up on a Familiar Scene

In this first observing cycle, “we are going after a lot of known exoplanets that we have observed in the past, so there aren’t many unexplored targets,” Đặng said. “This makes absolute sense since it will be the first time we are going to use these instruments in space and we don’t really know what challenges we will have to deal with yet.”

“There are some really interesting planets…that we already have tantalizing glimpses of from Hubble and Spitzer data,” said Hannah Wakeford, an astrophysicist at the University of Bristol in the United Kingdom. Wakeford, for example, will be targeting a well-studied, but still mysterious, hot Jupiter, HD 209458 b. “The data we currently have from Hubble tell us there is something in this atmosphere, and my program aims to show that it is clouds made from magnesium silicates (glass),” she said.

In 2007, astronomers used the Spitzer Space Telescope to create the first global temperature of an exoplanet, the hot Jupiter HD 189733 b. With JWST, astronomers plan to make a map of this planet’s hot spots (yellow) and cold spots (blue) not just in 2D, but also in 3D. Credit: NASA/­JPL­Caltech/H. Knutson (Harvard-Smithsonian cfa)

Tiffany Kataria, a planetary scientist at NASA Jet Propulsion Laboratory in Pasadena, Calif., is part of one of the five programs studying HD 189733b, a hot Jupiter so normal that it’s called canonical. “This planet was one of the first exoplanets whose atmosphere was observed with the Spitzer and Hubble space telescopes, yet there is still much we don’t know about the properties of its atmosphere,” she said. Kataria will make a 3D map of the planet’s glowing dayside to study its wind and temperature patterns, “which tells us a great deal about the physical processes taking place in the atmosphere.”

Néstor Espinoza’s target is hot Jupiter WASP-63 b and, more specifically, its sunrise and sunset. The program “aims to try to detect, for the first time, the infrared atmospheric signatures of the morning and evening limbs of a hot gas giant exoplanet…. It goes in the direction of exploring atmospheric structure of these distant exoplanets in 3D.” Espinoza is an astronomer at the Space Telescope Science Institute in Baltimore, Md.

Plenty of smaller planets reside among the old favorites that JWST will study, including the Earth-sized lava world 55 Cancri e. Brandeker’s program will examine changes in light when the glowing, molten planet passes behind its star. “We hope to see if consecutive eclipses show the same or different faces of the planet,” he said. Planets that orbit close to their stars are assumed to be tidally locked, having the same hemisphere always facing the star. If 55 Cancri e rotates faster or slower than it orbits, “this assumption, often taken for granted, can be questioned also for other planets. This in turn has major implications for how planets are heated, i.e., one side versus all sides.”

Another old favorite is the sub-Neptune GJ 1214 b, the target of one of Eliza Kempton’s observing programs. “Through a combination of mid-IR transmission spectroscopy, plus thermal emission and secondary eclipse observations, we aim to get a clearer picture of the atmospheric composition and aerosol properties of this enigmatic world,” she said.

“The overlap with existing observations is not a main motivator because we expect JWST to perform so much better than existing facilities,” said Kempton, an exoplanet astronomer at the University of Maryland in College Park. “But it will certainly be reassuring to see that the JWST data do agree with prior observations, and the level of agreement will help us to contextualize all data taken previously with facilities like Hubble and Spitzer.”

The surface of 55 Cancri e is probably molten, as seen in this artist’s illustration. Astronomers will use JWST to better understand how the surface heats up. Credit: ESA/Hubble, M. Kornmesser, CC BY 4.0

Newest among the old favorites soon to be studied by JWST is the TRAPPIST-1 system, which excited astronomers and the public alike when it was discovered to have seven possibly rocky Earth-sized planets.

“JWST has a small chance of finding biosignatures on TRAPPIST-1 planets …but a very good chance of telling us which molecules dominate the atmosphere and whether there are clouds.”A grand total of eight different programs will look at these planets’ atmospheric properties. “With this program,” said Olivia Lim, an astronomy doctoral student at Université de Montreal and PI for the program, “we are hoping to determine whether the planets have an atmosphere or not, at the very least, and if they do host atmospheres, we wish to detect the presence of molecules like [carbon dioxide, water, and ozone] in those atmospheres. This would be an important step in the search for traces of life outside the solar system.”

“JWST has a small chance of finding biosignatures on TRAPPIST-1 planets,” said Michael Zhang, “but a very good chance of telling us which molecules dominate the atmosphere and whether there are clouds.” Zhang is an astronomy graduate student at the California Institute of Technology in Pasadena.

Planetary Plot Twists

Some exoplanets just don’t fit inside the box as neatly as other exoplanets do, and astronomers are really hoping that JWST will help them understand why that is. Kataria leads the program to study one of these oddballs, HD 80606 b.

“HD 80606 b is an extreme hot Jupiter, and that’s saying something, given that hot Jupiters are pretty extreme to begin with!” Kataria said. “This Jupiter-sized exoplanet is on a highly eccentric, or elliptical, orbit and experiences a factor of greater than 800 variation in flux, or heating, throughout its 111-day orbit.”

“Most of the time it spends at relatively temperate distances,” Brandeker added, “but once every 111 days it swooshes very closely by the star in a few days [and] gets ‘flash heated.’”

The flash heating that HD 80606 b experiences once every 111 days likely creates intense storms and unexpected weather patterns, which JWST will monitor. These computer models of those weather patterns are based on Spitzer data taken during a 2007 flash heating event. (Blue represents colder bulk atmosphere, and red represents warmer winds.) Credit: NASA/­JPL­Caltech/G. Laughlin (UCO/Lick Observatory)

Studying HD 80606 b’s atmosphere as it heats and cools “will really help us examine the pure physics behind atmospheric energy transport, which is important for all worlds,” Wakeford said.

Kataria is also a coinvestigator on a program to make a 3D atmospheric map of a different oddity, WASP-121 b, a gas giant so hot that it bleeds heavy metals into space and orbits so close to its star that it’s shaped like a football. WASP-121 b is one example of a “super-puff” planet: These planets are roughly the size of Jupiter but far less massive, which makes their density closer to that of cotton candy. Pelletier will be looking at another super-puff, WASP-127 b. “Our hope is to gain a better understanding of the carbon budget on a planet vastly different from anything we have in our solar system,” he said.

What’s the most important thing to learn about super-puff planets? “Basically anything!” according to Gao, whose program will target super-puff Kepler-51 b. “All previous attempts at characterizing super-puff atmospheres have yielded featureless spectra and therefore very little information. If our observation is anything but a flat line, then we will have learned so much more than what we now know about these mysterious objects. It really is a fact-finding mission.”

M Dwarfs’ Breathtaking Aria

M dwarf stars are the smallest and most common stars in the universe, and astronomers have found that they host plenty of planets. Rocky habitable planets around these stars are easier to find using the two most prevalent methods—transits and radial velocity—but whether those planets can host atmospheres is still debated.

“I think the Cycle 1 observations will teach us a ton about whether rocky planets around M dwarfs can keep their atmospheres,” said Laura Kreidberg, director of research into the atmospheric physics of exoplanets at the Max Planck Institute for Astronomy in Heidelberg, Germany. “This is one of the most fundamental questions about where life is most likely to arise in the universe. There are tons of these small planets around small stars”— more than 1,500 are known so far—“but they experience more high-energy radiation over their lifetimes, so it’s not known whether they can keep their atmospheres. No atmosphere [is] bad news for life!”

The small rocky planet LHS 3844 b depicted in this illustration has been confirmed to have no atmosphere, so JWST will be able to study its surface composition. Credit: NASA/­JPL­Caltech/R. Hurt, IPAC

Both of Kreidberg’s observing programs will target rocky planets around M dwarfs. “One of the planets [LHS 3844 b] is already known to not have an atmosphere, so the goal of this program is to study the planet’s surface composition—what type of rock it’s made of—and search for any hints of volcanic activity, which could produce trace amounts of sulfur dioxide.”

Kreidberg is also looking at TRAPPIST-1 c, “which is very close to Venus in temperature. For that planet, I’m searching for absorption from carbon dioxide, to test whether the planet has a thick, Venus-like atmosphere or whether the atmosphere has been lost.”

“While we have made many models of atmospheric loss for small planets,” Gao said, “this will be our first real test of these theories. Will we find out that most characterizable rocky planets don’t actually have atmospheres and that our modeling efforts for their climates and habitability are futile? Or will we see a much more diverse set of atmospheric states? The results of these studies will be interesting and informative for future cycles regardless of what we find.”

Small-Planet Showstoppers

About half of JWST’s exoplanet-specific observing time will be dedicated to studying worlds smaller than Neptune. “This tells me without a doubt that the community is overwhelmingly interested in the little guys,” Gao said. These planets might be rocky (if they’re small enough) or could have a rock-ice core and a thick atmosphere.

“The large program on sub-Neptune and super-Earth atmospheres led by Natasha Batalha and Johanna Teske is especially exciting to me because it will provide us with a systematic survey of a class of planets that is not present in our solar system and was not readily observable with previous facilities,” Kempton said. “The potential for this program to unlock greater insight into the atmospheres of small planets is quite high.”

Small planets all start from a collection of dust and gas. How much material a future planet starts with determines how much additional gas it can attract and how much of that gas it will keep when it heats up. Planets that end with a large gaseous envelope are termed mini-Neptunes, and those with only a small amount of gas are deemed super-Earths. Credit: NASA/Ames Re-search Center/­JPL­Caltech/R. Hurt

“These planets are so small that they’re beyond the reach of current technology, so anything JWST discovers will be a big improvement on what we know,” Zhang said. “For small planets like GJ 367 b, my target, and 55 Cancri e, we basically don’t know anything, so we’ll learn the first thing about them. Do they have atmospheres? If so, are they carbon dioxide, oxygen, or exotic metal atmospheres made of sodium and silicon oxide?”

One of Espinoza’s programs will focus on super-Earth K2-141 b, a planet only slightly larger and more massive than Earth but much, much hotter. “Depending on the properties of this exoplanet like the presence or not of an atmosphere, the flux change during its orbit around the star should give rise to very different signals, which will enable us to infer what this exoplanet’s exterior is made of,” said Espinoza.

If K2-141 b does have an atmosphere, it might not be the one it started with. Lisa Đặng aims to find out. Rocky planets as hot as that one “are thought to have lost any primordial atmosphere but, instead, could sustain a thin rock vapor atmosphere [that] outgasses from the mantle,” she said. Does the atmosphere stick around or rain back down? “With our observations we are hoping to detect molecular signatures of the atmospheric constituents and also obtain a map of the planet’s atmosphere and surface.”

Ballad of Planets and Disks

JWST should build upon discoveries made not only by space telescopes like Hubble and Spitzer but also by ground-based observatories like the Atacama Large Millimeter/submillimeter Array (ALMA). These observations will probe the birthplaces of planets: the disks of dust and gas around young stars. “Over the last decade, we’ve gotten gorgeous images from the ALMA interferometer in Chile and have seen loads of fine-scale structure, tracing pebbles in planet-forming disks,” said Ilse Cleeves, an astronomer at the University of Virginia in Charlottesville. “Some of the structures likely trace planets in formation, and so it’ll be very exciting to see what JWST uncovers, both in terms of patterns in the disk and perhaps even the drivers—protoplanets—themselves!”

Matthews added that “if JWST is able to successfully detect planets in these disks, it will be an important confirmation of our understanding of how planets interact with disks.” If no planets appear in the disks, astronomers will have to rethink how, and whether, planets shape disks.

A few of the first observations with JWST will seek to map out how planet-forming disks distribute their water and other materials that are essential for life. This artist’s illustration shows where water ice may exist in a ­planet-­forming disk. Credit: A. Angelich (NRAO/AUI/NSF)/ALMA (ESO/NAOJ/NRAO), CC BY 4.0

Cleeves will be studying planet-forming disks to understand how they give rise to habitable planets. “How common are habitable planets? Availability of water is a natural place to start, but we don’t have great observational constraints on how much water is present or the distribution of water in disks. We are looking forward to mapping out water ice in a nearby disk that happens to be posing in front of a host of background stars.” If a star’s light passes through a part of the disk that has ice, the ice will imprint a spectroscopic signal on the light. With so many background stars, Cleeves said, they’ll be able to say not just whether ice is present, but also where.

The makings of a world well suited for life go beyond the presence of water, however, and Melissa McClure’s three observing programs will look for them. We’ll “trace how the elemental building blocks of life—like carbon, hydrogen, oxygen, nitrogen, and sulfur—evolve between molecular clouds, where they freeze out on dust grains as ices, and protoplanetary disks, where these ices are incorporated into forming planetesimals and, ultimately, planets,” she said. “I think that within a few years we will have an understanding of how much water terrestrial planets typically have and whether they inherited that water from their birth locations in their disks or if cometary delivery was necessary.” McClure is an assistant professor and a Veni Laureate at Leiden Observatory in the Netherlands.

“This planet orbits close enough to the white dwarf that it could not have originally orbited there before the star’s death. So how did it get there?”A perhaps underrecognized component of JWST’s observing capabilities is the coronagraph that will allow direct imaging of exoplanet systems, meaning that the telescope will see light emitted by the planet itself. Coupled with JWST’s infrared capabilities, the telescope will be able to observe planets much older and colder than is currently possible. That’s Matthews’s aim. “Eps Indi Ab is similar in age to the solar system and is similarly far from its star as Jupiter is from the Sun. Because JWST is able to image much further into the infrared than Earth-based telescopes and because old planets are brighter at these very long wavelengths, our project provides a unique opportunity to study a truly Jupiter-like planet outside the solar system,” she said.

Sometimes planets survive their star’s demise, as is the case of WD 1856+534 b, a gas giant planet that orbits the slowly cooling corpse of a star, also known as a white dwarf. In this case, the planet’s survival presents a puzzle. “This planet orbits close enough to the white dwarf that it could not have originally orbited there before the star’s death. So how did it get there?” asked Andrew Vanderburg, whose program will target this system.

Bridge to Act II

Once the “shakedown cruise” is complete, Hannah Wakeford would like to see JWST used to study more worlds the size of Jupiter, Saturn, and Neptune. “There is so much we can learn that we can’t even get from our own solar system giant planets,” she said, “so it is, in my opinion, a low-risk, high-reward scenario.”

“The very first exoplanetary observations to be made by JWST are going to be a big jump into the known unknown…. As the title of an album of one of my favorite rock bands would say, ‘Expect the unexpected.’”On Vanderburg’s wish list: “Disintegrating planets. These will be great probes of the interior compositions of planets, so I hope we will get observations of them in the future.”

Cleeves called the first cycle “a great place to start. I have a feeling, though, that the most interesting next projects are those that we haven’t anticipated yet, so I’m really looking forward to the first couple of years with JWST, grappling with the data and finding those unexpected puzzles.”

Espinoza agreed. “I’m almost convinced features will show up in the data that we will perhaps not be able to explain right away,” he said. “As such, the very first exoplanetary observations to be made by JWST are going to be a big jump into the known unknown…. As the title of an album of one of my favorite rock bands would say, ‘Expect the unexpected.’”

Author Information

Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

The first time scientists measured the atmosphere of an exoplanet—a planet outside our solar system—they found something unexpected in the signal. It was 2001, and the Hubble Space Telescope was trained on HD 209458 b, a recently discovered gas giant roughly the size of Jupiter.

When astronomers looked for the presence of sodium in light waves shining through the planet’s atmosphere as it crossed in front of its star, there was a lot less of it than they thought there would be, said Hannah Wakeford, a lecturer in astrophysics at the University of Bristol in the United Kingdom. “From the very first measurement of an exoplanet atmosphere, there was evidence that something else was happening, something else was there blocking the light.”

The most compelling theory for what that something could be? Massive banks of dark, hot clouds. “Clouds are essentially liquid or solid droplets or particles that are suspended in a gaseous atmosphere,” said Wakeford. But because the planet is so hot—5 times hotter than Earth—those droplets couldn’t be made of water, as they are on Earth.

In the 2 decades since analyzing the atmosphere of HD 209458 b, astronomers have discovered more than 4,000 exoplanets. Using spectroscopy, they have measured the atmospheres of more than 100 of those objects, and it looks like many of them are cloudy. The way those extraterrestrial clouds behave and the exotic things they could be made of—liquid sand, iron, even rubies—are stretching scientists’ ideas of what terms like clouds, rain, and snow even mean in the context of the universe.

“Clouds are everywhere,” said Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Germany. “And to have any hope of understanding what’s going on in [exoplanet] atmospheres, we have to understand the clouds.”

Mushballs and Methane Lakes

The trouble is, clouds are complicated. Even on Earth, clouds are difficult to model (one reason weather forecasts can still lack accuracy.) Their complexity arises partly because they are simultaneously very small and very large: made up of microscopic water droplets yet so vast they can cover more than two thirds of Earth’s surface. Another reason is that there are so many kinds of clouds, and they behave in complex ways, explained atmospheric physicist David Crisp at the Jet Propulsion Laboratory, California Institute of Technology.

Clouds are “ubiquitous; they can form in many different kinds of environments, and there are many processes associated with their formation,” Crisp said.

On Earth, clouds take many forms, like these cirrus and stratocumulus clouds. Their variety and ubiquity make them difficult to account for in climate models. Credit: NASA

And they’re not made only of water, either. Most cloud particles start growing on condensation nuclei—a speck of dust or a grain of salt. And although most earthly cloud droplets are spherical and liquid, those that make up cirrus clouds are hexagonal ice crystals.

Clouds can frustrate scientists’ ability to see clearly, whether they are gazing at the heavens from the ground or peering back at Earth from space. In the 1980s, Crisp helped build the camera in the Hubble Space Telescope and now leads a NASA team that uses orbiting satellites to measure the dangerous levels of carbon dioxide accumulating in Earth’s atmosphere. “I’ve learned to hate clouds from both sides now,” he joked.

Clouds mess with models predicting future climate change, he said, because they simultaneously warm and cool the planet, depending in part on whether their droplets are mainly liquid or mainly ice. In general, low-lying, mostly liquid clouds provide shade and reflect solar energy back into space, whereas high-altitude, frozen cirrus clouds trap infrared radiation emitted by Earth’s continents and oceans and intensify surface heating. This duality has long frustrated exoplanet cloud watchers, too—scientists scrutinize cloud signals to better understand how or whether clouds are heating the atmosphere below them.

Scientists are still trying to understand whether, at a global level, those cooling and warming effects cancel each other out and how that balance could change in the future. (One recent study even suggested that at carbon dioxide levels of around 1,200 parts per million, global cloud cover could become unstable and dissipate, dramatically accelerating warming.)

“We’ve dropped a few dozen probes into the atmosphere of Venus. But you know, if you measured Earth’s atmosphere with only a dozen instruments, how much would you know about the Earth?”Despite the uncertainties, we know a lot more about Earth’s clouds than we do about those on other planets and moons of our solar system. It was only in the 1970s, for instance, that scientists figured out that Venus is enveloped in clouds of sulfuric acid. “This stuff will strip paint—and just about anything else,” said Crisp. Space missions to Venus have dropped mass spectrometers into the planet’s atmosphere that, “even though sulfuric acid is not very nice to our mass spectrometers,” have managed to send back data about the chemical makeup and concentrations of several cloud layers.

Jupiter’s atmosphere has been sampled too, and has been found to contain swirling ammonia clouds. Recent flybys of the tops of these clouds by NASA’s Juno mission identified mushballs—Jovian hailstones formed out of water-ammonia slush enrobed in an ice crust—that fall through the planet’s atmosphere. On the way down, these mushballs collide with upward moving ice crystals and electrify the clouds, causing shallow, high-altitude lightning visible from space.

The thick atmosphere of Saturn’s moon Titan glows in this composite image made with both vis-ible and ultraviolet light. On Titan, the rain, rivers, and lakes are made of liquid methane and ethane. Credit: NASA

Thanks to the Cassini spacecraft, we know that the atmosphere on Titan, the largest of Saturn’s moons, is largely made up of nitrogen, like Earth’s. There are seasons, monsoons, and wild windstorms. But Titan’s mountains are made of solid ice, and instead of a water cycle, it has a hydrocarbon cycle: On Titan, the rain, rivers, and lakes are made of methane and ethane.

But many questions remain when it comes to solar system weather. For example, we don’t know how deep into Jupiter the mushballs fall before they evaporate and rise again, said Wakeford. There are mysterious long-chain hydrocarbons floating high in the atmosphere of Titan too. “We have absolutely no idea how they got there; it’s baffling.”

What knowledge we do have is drawn from the briefest of snapshots, added Crisp. “We’ve dropped a few dozen probes into the atmosphere of Venus. But you know, if you measured Earth’s atmosphere with only a dozen instruments, how much would you know about the Earth? These planets are big places, and they have complicated climates—quite as complicated as ours.”

A Lead Blanket or Gems and Jewels

The challenges of analyzing extraterrestrial clouds are magnified when it comes to exoplanets. We can’t send a probe laden with instruments to any of them or record detailed images of their surfaces.

All we have is light, said Heather Knutson—the light coming from a far-off star. “We know there’s a planet in orbit around it, and we can indirectly infer some basic things about that planet, but it’s really a sort of poor man’s camera,” said Knutson, an astronomer at the California Institute of Technology

“If we’re going with the X-ray analogy, clouds are sort of like a lead blanket over the planet.”When an exoplanet passes in front of its star—an event called a transit—astronomers can measure the way light passes through the planet’s atmosphere on its way to us. Measuring how opaque the atmosphere is at different wavelengths of light (transit spectroscopy) offers clues to its composition. Kreidberg used an X-ray analogy to explain how it works: “Our bodies are opaque in optical light. If you shine a flashlight at a person, you can’t see through them. But if you look in the X-rays, you can see through the skin, but not through the bones.”

In the same way that our skin differs from our bones, molecules in planetary atmospheres are opaque or transparent at different wavelengths. “Whether it’s water or methane or oxygen or carbon dioxide, they have distinct opacity at different wavelengths of light,” said Kreidberg. “So if the planet looks a little bit bigger at a particular wavelength, then we can work backward from that to try to infer what’s in its atmosphere.”

https://eos.org/wp-content/uploads/2021/07/Exoplanet_Animation_Transit_Depth_vs_Wavelength_ipod_lg.m4v

But clouds get in the way of that process, said Knutson. “If we’re going with the X-ray analogy, clouds are sort of like a lead blanket over the planet. You see something that looks very featureless.”

Still, on the basis of the planet’s average atmospheric temperature—something astronomers can estimate from the brightness of the star and the planet’s distance from it—it’s possible to infer what those clouds are likely to be made of because of the varying temperatures at which different molecules condense from gas into liquid.

And the vast range of possible temperatures is something that distinguishes exoplanets from those in our solar system, said Nikku Madhusudhan, an astrophysicist and exoplanet scientist at the University of Cambridge. “Because of that vast range, you allow for a much wider range of chemical compositions [than in the solar system]. A lot more chemistry can happen.”

An artist’s impression of the gas giant HAT-P-7 b. Astronomers detected strong winds and cata-strophic storms and suspect that the clouds could be made of corundum, the mineral that forms rubies and sapphires. Credit: Mark Garlick/ University of Warwick

Here on Earth, with an average temperature of 290 K, clouds are made mostly of water. The atmospheres of some exoplanets, between 400 K and 900 K, are warm enough to condense salts and sulfides into clouds. At around 1,400–2,000 K (a third as hot as the Sun), we would expect to see clouds of molten silicates—the material that makes up the volcanic sand on some of Earth’s beaches and is used in the production of glass. On an even hotter planet like WASP-76b, which is estimated to reach 2,400 K, clouds are likely made of liquid iron. And the atmospheres of the hottest known exoplanets—giant, 2,500+ K ultrahot Jupiters orbiting very close to their stars—are the right temperature for clouds made of corundum, a crystalline form of aluminum oxide that forms rubies and sapphires on Earth.

“These are quite literally the gems and jewels that we have here on Earth forming clouds and lofted high into the atmospheres of Jupiter-sized worlds that are lit glowing from their star,” said Wakeford. She remembered walking through the Hall of Gems in London’s Natural History Museum after learning this, trying to imagine the crystals molten and forming clouds. “It just blew my mind.”

Metallic Monsoons

WASP-76 b made headlines in 2020 when a team of European researchers published a paper suggesting it had not only clouds of iron but iron rain as well.

Artwork imagining the nightside of WASP-76 b, a hot Jupiter exoplanet with clouds of iron—and possibly even iron rain. Credit: ESO/M. Kornmesser

“We see the iron, and then we don’t see the iron. So it has to go somewhere, and the physical process that we expect is rain.”Like our own Moon and many planets that orbit very close to a star, WASP-76 b is tidally locked, meaning one side of the planet always faces the star (dayside) and the other always faces away (nightside). Researchers found evidence of iron atoms in the atmosphere of WASP-76 b’s hotter dayside but not on the cooler nightside, which they argued meant that the iron must be condensing into liquid droplets as wind carries the atoms around the planet. “We see the iron, and then we don’t see the iron. So it has to go somewhere, and the physical process that we expect is rain,” said Kreidberg, who was not involved in the study. “This is some of the most convincing evidence I have ever seen for exoplanet weather.”

But Caroline Morley, an astrophysicist at the University of Texas at Austin, cautioned that the phenomenon could be more complex. Recent studies, including one co-authored by Kreidberg, have examined the microphysics of how iron droplets form, finding that the substance’s high surface tension means that it doesn’t easily condense from a gas to a liquid. There might be some other processes involved in WASP-76 b’s iron phenomenon, Morley said—perhaps the iron interacts with some other chemicals in the planet’s atmosphere, which helps it form a cloud.

“Statistically, I believe that there are exoplanets where it is raining right now,” she said. “But I think that we have not seen smoking gun evidence for rain on other planets yet.”

Crisp agreed. “Clouds we’ve detected. Rain and snow have not yet been detected—but I’d be surprised if they weren’t there. Those are logical outcomes of the systems we see.”

Metaphorical Meteorology

So when astronomers talk about possible rain on exoplanets, is it really what we would think of as rain? What do the concepts of rain and clouds even mean in the context of distant space? To some extent, it’s all a metaphor, said Wakeford.

“We have to be open to the fact that the complexity in nature may greatly surpass our imagination at the present time.”On Earth, the terms rain, clouds, and snow all apply almost exclusively to one substance: water. “Water is one of the most amazing materials in the universe,” Wakeford said, but not all substances behave like water when experiencing differences in pressure or temperature. “So when we frame these very alien clouds and rain and snow in that [water-based] context, it puts things in our minds that aren’t exactly what the physics is.”

For instance, words like snow and hail can be a bit misleading when you talk about solid particles in an atmosphere that’s hotter than a lava flow. “I tend to use rain instead of snow,” Wakeford said, “because snow to us evokes a temperature, a coldness. Rain is something that can define many different types of conditions, whereas snow for us is very much a cold thing. And this is not what’s happening here on some of these planets that are so incredibly hot.”

An imagined movie poster for the exoplanet HD 189733 b, a cobalt-blue hot Jupiter with winds approaching 8,700 kilometers per hour and rain of molten glass. Credit: NASA-JPL/Caltech

Still, Wakeford thinks a smattering of poetic license is justified to bring the public along on the journey and capture people’s imaginations. “If you start by saying, ‘It’s raining drops of glass on these planets’—that’s a starting point. I can use that; I’ve got [your attention] now. Then we can build on that and get a deeper understanding.”

When it comes to actually doing the research, though, scientists should be both circumspect and open-minded, said Madhusudhan. Although it can sometimes help to extrapolate from what we’re discovering about Earth’s clouds to these faraway planets, for instance, it’s important to remember that these worlds are so exotic that it’s possible there are processes going on in their atmospheres that we haven’t even considered. “The biggest mistake we could make is to try to simplify the complexity of exoplanetary systems just to fit a narrative.”

We may go on to discover kinds of weather we don’t even have words for, said Madhusudhan. “We have to be open to the fact that the complexity in nature may greatly surpass our imagination at the present time.”

Peering into the Infrared

So far, everything we know about clouds on exoplanets has been based on what Madhusudhan calls indirect inference: “It’s a bit more real than philosophical but a bit less real than an actual observation.” But the launch of the international James Webb Space Telescope ( JWST) near the end of this year promises to give astronomers the chance to make direct observations of exoplanet clouds for the first time.

JWST will keep Earth between it and the Sun and is designed to look at the longer wavelengths of infrared light. “Planets are easier to study in the infrared,” said Knutson. The telescope will make faraway objects look brighter than they do in visible light and will be better able to detect molecules in exoplanet atmospheres. It should also advance our understanding of alien weather.

“When you go to midinfrared, the composition of a cloud droplet starts to matter—the way that it scatters light is different for different cloud species,” said Knutson. “So we might, for the first time, directly measure what the clouds are made of.”

Morley is leading a team that will use JWST to examine a cold exoplanet called WISE J085510.83−071442.5 to test for the presence of water ice clouds and see whether they are changing as the planet rotates, implying that there are storm systems and weather. “That would give us real evidence, for the first time, that there’s water ice forming in a planet outside of the solar system,” Morley said.

Wakeford, meanwhile, will have a chance to train the telescope on HD 209458 b, the very first planet that 20 years ago was assumed to have clouds of magnesium silicate. JWST will give her a chance to prove (or disprove) that assumption with direct measurements.

Overall, “I think we think about clouds more broadly than anybody has thought about clouds in human history,” said Morley. “And we’re just on the cusp of being able to get a huge amount of really detailed information about those clouds. It’s a really exciting time to be in this field.”

Author Information

Kate Evans (@kate_g_evans), Science Writer

The properties of suspended sediments are difficult to measure in the field, yet characterizing these materials is essential to successful monitoring and management coastal and estuarine environments. To overcome the challenges of estimating the relative proportions of sand and mud in mixed sediment environments, Pearson et al. [2021] developed a new methodology. This is achieved by comparing the response of simultaneous optical and acoustic measurements, in both laboratory experiments and in application to field measurements on the ebb-tidal delta of a major inlet.

The important contribution in this paper is the development of a new indicator, the “sediment composition index”, that can be used to directly predict the relative fraction of sand in suspension. This approach may prove to be widely useful in gaining deeper understanding of material transport in the coastal ocean by improving estimates of sediment flux and increasing confidence in the interpretation of observations.

Citation: Pearson, S. G., Verney, R., van Prooijen, B. C., Tran, D., Hendriks, E. C. M., Jacquet, M., & Wang, Z. B. [2021]. Characterizing the composition of sand and mud suspensions in coastal and estuarine environments using combined optical and acoustic measurements. Journal of Geophysical Research: Oceans, 126, e2021JC017354. https://doi.org/10.1029/2021JC017354

—Ryan P. Mulligan, Editor, JGR: Oceans

Climate change has found its way into courtrooms around the world more and more often in recent years: Plaintiffs have brought more than 1,500 cases of climate litigation since 1986, and an increasing number of cases are filed each year.

“The power of the courts as a force of climate action really should no longer be in dispute.”“In the last few years we’ve seen lawsuits in the Netherlands, Germany, Ireland, Belgium, and elsewhere that have shown that successful climate litigation is possible,” said Rupert Stuart-Smith, who researches climate systems and policy at the University of Oxford’s Sustainable Law Program in the United Kingdom. In most of those cases, courts ruled that a country or a company’s climate targets or progress toward meeting those targets needed to be significantly improved. “The power of the courts as a force of climate action really should no longer be in dispute.”

However, climate litigation has failed more often than not to hold greenhouse gas emitters accountable for climate-related impacts like flooding and damage from drought or wildfires. For lawsuits that try to establish a causal link between a defendant’s emission and the impacts on plaintiffs, Stuart-Smith and his team sought to understand why those types of cases tend to fail.

“Why aren’t these cases winning?” he asked. “What is the evidence that is being used in these cases, how does that compare to the state of the art in climate science…and how have the courts interpreted it?”

A Failure to Make the Connection

The researchers examined 73 cases across 14 jurisdictions worldwide that made a claim that a defendant’s emissions negatively impacted the plaintiffs. In those cases, courts did not dispute the general idea that greenhouse gases cause climate change. “What was more of a challenge,” Stuart-Smith said, “was establishing a causal relationship between greenhouse gas emissions of an individual entity…and specific impacts on a specific location.” Making that causal connection is key for the success of climate litigation, he said, and is the goal of climate attribution science, or science that quantifies the extent to which climate change alters an event.

“The evidence submitted and referenced in these cases does lag considerably behind the state of the art in climate science.”However, 73% of the cases the team examined did not bring forward peer-reviewed climate attribution science as evidence. Of the 54 cases that claimed that an extreme weather event caused the impacts suffered by plaintiffs, 26 claimed that climate change caused the extreme weather event but did not provide evidence of that claim. Six more did provide such evidence, but that evidence did not quantify how much more likely or how much worse climate change made the extreme weather event.

“We found that there is a clear role for attribution science evidence in these lawsuits,” Stuart-Smith said. In the few cases where climate science was submitted as evidence, “the evidence submitted and referenced in these cases does lag considerably behind the state of the art in climate science. And as a result…the evidence provided was not sufficient to overcome causation tests.”

Of the 73 cases they examined, only 8 have been successful so far. (Thirty-seven are pending, and 28 have been dismissed.) The researchers suggest that “growing use of attribution science evidence which is specific to the impacts experienced by plaintiffs…could overcome some of the key hurdles to the success of climate-related lawsuits.” These results were published in Nature Climate Change in June.

Establishing a Dialogue

Not every extreme weather event is caused by or made worse by climate change, but an increasing number of them are: Anthropogenic climate change has been making hurricanes, drought, and wildfires stronger and more frequent; has been tied to worsening health conditions around the world; and has started a climate refugee crisis. As recently as a decade ago, Stuart-Smith pointed out, climate science wasn’t advanced enough to claim that climate change caused any single extreme weather event, but that is no longer the case. For example, the World Weather Attribution initiative, an international collaboration of climate scientists, has already established that the June 2021 extreme heat wave in the North American Pacific Northwest “was virtually impossible without human-caused climate change” and that “this heatwave was about 2°C hotter than it would have been if it had occurred at the beginning of the industrial revolution.”

“We need better paths of communication between the legal and scientific communities.”This study highlights that “we need better paths of communication between the legal and scientific communities,” Stuart-Smith said. Lawyers need to be able to explain to climate scientists what type of evidence will be helpful and ensure that the claims they’re bringing forward are actually attributable to climate change. Climate scientists, too, need to consider providing evidence to litigators as “an opportunity to make one’s research relevant to important ongoing issues in the courts.…It’s got to come from both sides.”

Although climate attribution cases haven’t been very successful in the past, “it doesn’t seem farfetched anymore to suggest that future cases will force companies to pay compensation to communities impacted by climate change,” either after damage is already done or as communities try to mitigate or adapt to future impacts, Stuart-Smith said. “But that is only going to be the case if…the evidence submitted to courts clearly substantiates the alleged relationship between the defendants’ emissions and the impacts suffered by plaintiffs.”

—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer

For a successful result, managed retreat should not be considered a last resort, and the process should start today.The idea of moving from places endangered by rising seas, dangerous temperatures, or wildfires is a personal, communal, and national decision. The response at each level is based on which risks are tolerable and whose values are prioritized. But adaptation measures can provide a road map for how a person, a community, or even a country can proceed. Such road maps are laid out in papers recently published in a special issue of Science. The gist: For a successful result, managed retreat should not be considered a last resort, and the process should start today.

The Need for Adaptation Actions

Some degree of relocation is going to be necessary, said climate adaptation scientist Marjolijn Haasnoot of Deltares and Utrecht University in the Netherlands, lead author of one of the Science papers. Already, global average annual sea level rise has more than doubled its 20th-century rate to 3.6 millimeters. By 2100, sea-level rise may be 10-20 millimeters per year and seas could reach up to 1-2 meters above 2000 levels; seas will continue to rise beyond 2100.

So how much response will be necessary, and how do we do it?

Responding to rising seas—or other effects of the climate crisis, like wildfires and unlivable temperatures—requires adaptation. That response could look like resistance (e.g., building seawalls), accommodation (e.g., putting infrastructure on stilts), avoidance (limiting new development in hazardous locations), advance (building out into hazardous areas), or retreat, wrote Katharine Mach from the University of Miami and A. R. Siders from the University of Delaware in their Science paper. Retreat in the most basic sense means relocating homes and infrastructure in harm’s way. “Each adaptation action represents a distinct value-laden decision about what to preserve, purposefully change, or allow to change unguided,” Mach and Siders noted.

But strategic or managed retreat likely includes several different adaptation strategies, like relocating infrastructure and people, as well as restricting development and building protective barriers. Each adaptation action is probably going to be part of a community’s plan to deal with encroaching hazards, Mach said.

Water spills over from the Lafayette River in Norfolk, Va., after high tide even when there is no rain. Credit: Skyler Ballard/Chesapeake Bay Program, CC BY-NC 2.0

Haasnoot also added that managed retreat will look different in different places. That’s why she and her colleagues created a road map to help break managed retreat into bite-sized pieces—manageable, adaptable steps that align with goals like economic development, environmental conservation, and social justice. The Dynamic Adaptive Policy Pathways, or DAPP, approach is already being used by decisionmakers to address threats from rising seas in the Netherlands, United Kingdom, and New Zealand, Haasnoot said.

The authors break down retreat into three stages: a preparation or planning stage, an active retreat stage, and a cleanup stage. The planning stage alone can take decades, Haasnoot said. Within each stage are short-term, medium-term, and long-term plans and actions that should be adaptable as conditions change, she said. For example, she said, a community might start with declaring no-build zones for new development, then over time, relocate households in risky areas as opportunities arise and not allow new families to move in.

Community Engagement

Community engagement is of paramount importance.… Plans need to be “owned” by each community.At every step along the way, Haasnoot said, community engagement is of paramount importance. Mach agreed, adding that any plans need to be “owned” by each community.

The government in Miami-Dade County in Florida, a region at exceptionally high risk from rising seas, has developed a coalition to address sea level rise adaptation strategies, Mach said. The current strategy is a 40-year plan to adapt to 60 centimeters of sea level rise. Miami-Dade’s long-term planning is “impressive,” Mach said, and involves years of community action.

But there’s a problem, said Julie Maldonado, associate director of the Livelihoods Knowledge Exchange Network, who was not involved in any of the recent Science studies. “There isn’t just one Miami, for example.” Understanding who and what constitutes a “community” is important, she said, as is “recognizing that ‘community’ does not equal geography, but also people’s deep ties and connection to place.” Although decisionmakers might consider a whole city or county—say, the city of Miami or Miami-Dade County—one community, the county and city are made up of many diverse communities with their own leaders and cultures. So there can’t be a “homogenized approach to relocation, as if one size fits all,” Maldonado said. Relocation plans cannot be a one-directional engineered resettlement. The process needs to be community driven, with community leaders front and center on the decisionmaking team, not just another stakeholder, she said. And that’s often not happening.

Some communities are being told they need to leave, to abandon their homes and their lands, “with their sovereign rights and self-determination being ignored, rather than guiding the decisions as rightsholders,” Maldonado said. And then where do they go? What happens in the full cycle of the resettlement? Where are the funding mechanisms to support the full process? she questioned.

Challenging Plans

Although learning from other places that have successfully implemented adaptation and even relocation plans while forging community collaborations is worthwhile, road maps must be considered with caution. They can fall into a “check-the-box approach,” Maldonado said, where outside entities might say, “We held a public meeting, so we did community engagement. Check.” But that’s not real, authentic engagement, she said, and any relocation plan that’s equitable needs to be a collaboration that includes, and is guided by, each affected community’s values and is community led.

A prolonged, strategic, managed retreat can be equitable, Mach said, as opposed to relocation after disasters, which usually isn’t. In the United States, most government buyouts of homes occur after disaster strikes. Even if the government gives a homeowner the value of the home predisaster, that is probably not sufficient for replacement, she said. Elsewhere, “people are forced to relocate out of informal settlements often without access to jobs or other basic needs.” These situations need to be avoided, Mach said.

Managed retreat is not easy, and some days it’s hard to be optimistic, Mach said. But “so many capable, brilliant, passionate people are working on this that it gives me hope,” she said. “And for adaptations, on a fundamental level, when things get bad, people dig deep and figure out solutions. That [also] gives me hope.”

—Megan Sever (@MeganSever4), Science Writer

24 July 2021: This article has been updated with changes throughout.

The mechanisms that generate streamflow are controlled by complex interactions between the climate and physiography of a catchment. Streamflow generation is critical for understanding the pathways and processes by which catchments produce stream and river flow. Therefore, identifying the dominant streamflow mechanisms operating in a catchment has important considerations for watershed management. However, there is no simple guidance beyond conceptual frameworks like the classic Dunne diagram to identify the dominant streamflow generation mechanisms for a catchment without a detailed field study.

Wu et al. [2021] developed a data-driven analysis to classify catchments based on characteristics from continuous rainfall and streamflow records and related those characteristics with climatic and physiographic properties to deduce dominant streamflow generation mechanisms of 432 catchments in the US. The analysis extended the conceptual framework of the Dunne diagram to a quantitative synthesis providing regional patterns of dominant streamflow generation mechanisms. The hope is that with a better understanding of potential streamflow generation mechanisms for a catchment, hydrologic model selection, process representation and accuracy will improve.

Citation: Wu, S., Zhao, J., Wang, H., & Sivapalan, M. [2021]. Regional patterns and physical controls of streamflow generation across the conterminous United States. Water Resources Research, 57, e2020WR028086. https://doi.org/10.1029/2020WR028086

—Kevin McGuire, Associate Editor, Water Resources Research

Mitigating climate change will require both reduced emissions and increasing carbon sinks. Nature-based Climate Solutions (NCS) refers to efforts to conserve ecosystems that could serve as effective carbon sinks to help mitigate climate change. But what if projected climate change renders these same ecosystems vulnerable to loss of carbon storage rather than gain?

Coffield et al. [2021] use several complementary statistical approaches to evaluate the projected permanence of carbon stored in forests and other wildlands of California. They project that several proposed areas for ambitious expansion of NCS may not be able to support carbon-rich forests at the end of this century.

In a companion Viewpoint piece, Anderegg [2021] explains the need to understand these risks when promoting NCS. He argues that NCS still has good potential, but it must be paired with significant emissions reductions to be a viable contributor to overall climate mitigation.

Citation: Coffield, S., Hemes, K., Koven, C. et al. [2021]. Climate-driven limits to future carbon storage in California’s wildland ecosystems. AGU Advances, 2, e2021AV000384. https://doi.org/10.1029/2021AV000384

—Eric Davidson, Editor, AGU Advances

This is an authorized translation of an Eos article. 本文是Eos文章的授权翻译。

火山猛烈喷发，火山灰和气体喷涌而出。热浆迅速上升到大气中，各种大气动力学相互作用，形成了火山云的组成、高度和辐射特性。火山云反射太阳辐射，给地球降温，导致极端天气，并延缓全球变暖，但科学家一直想知道火山物质在喷发后是如何演化和解析自身的。到目前为止，对强烈火山喷发初期阶段的观测还很少，而用于研究火山喷发影响的传统气候模型无法捕捉这一初始阶段的很多细节。

在一项新的研究中，Stenchikov等人对区域大气化学模型WRF-Chem进行了修改，以便更好地捕捉火山云发展的初始阶段。研究人员对1991年菲律宾皮纳图博火山爆发进行了模拟研究，他们假设，随着喷发的喷射流，大量的火山碎屑被送入平流层下部。他们进行了25公里网格间距的模拟，考虑到二氧化硫(SO2)、灰、硫酸盐和水蒸气的同时注入。此外，他们还考虑了包括气态二氧化硫在内的所有烟羽成分的辐射加热和冷却效应。

研究人员发现，局部加热起着至关重要的作用，影响着火山云的初始演化过程，分离成层，然后分散或落到地面。他们的新模型显示，在火山爆发后的第一周，火山云以每天1公里的速度上升到大气中，最初是由于火山灰对太阳的吸收，后来是由于硫酸盐气溶胶对太阳和陆地辐射的吸收。

研究人员指出，他们的发现可能对许多应用有帮助，从航空安全到了解气候和地球工程技术。(Journal of Geophysical Research: Atmospheres, https://doi.org/10.1029/2020JD033829, 2021)

-科学作家Sarah Derouin

This translation was made by Wiley. 本文翻译由Wiley提供。

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New Telescope, New Worlds • Exoplanets in the Shadows   • Overture to Exoplanets   • The Forecast for Exoplanets Is Cloudy but Bright   • “Earth Cousins” Are New Targets for Planetary Materials Research   • Oddballs of the Exoplanet Realm   • Thousands of Stars View Earth as a Transiting Exoplanet   • Taking Stock of Cosmic Rays in the Solar System   • Gap in Exoplanet Size Shifts with Age   • Unveiling the Next Exoplanet Act  

The Milky Way is home to billions of stars and probably an even larger number of planets. To search for these planets, scientists watch for minute, but periodic, dips in a star’s light, the telltale signature of a planet passing in front of its host star. And now a team of astronomers has turned that search homeward.

Lisa Kaltenegger and Jackie Faherty calculated the number of stars whose past, present, or future vantage points in space afford a look at Earth passing in front of the Sun. The planets that orbit these roughly 2,000 stars, some of which have additionally been bathed in human-made radio waves, are poised to spot Earth, the researchers suggest.

Turning the Tables

Astronomers have confirmed the existence of more than 4,000 extrasolar planets, and we’re now turning the tables, said Kaltenegger, an astronomer at Cornell University in Ithaca, N.Y. “It’d be interesting to know if someone could have seen us.”

Kaltenegger and Faherty, an astrophysicist at the American Museum of Natural History in New York City, mined data collected by the European Space Agency’s Gaia mission. The Gaia spacecraft, launched in 2013, is conducting the most precise survey to date of the motions and positions of more than a billion stars in the Milky Way. “It’s the greatest kinematic and astrometric catalog of our time,” said Faherty.

A Thin Ring in Space

The researchers honed in on stars within the so-called Earth transit zone, a ring-shaped region of space created by projecting Earth’s orbit around the Sun outward into the cosmos. Any stars—and, by extension, the planets orbiting them—located within this zone see Earth passing in front of the Sun. Astronomers on Earth have exploited this geometry, known as a transit, to detect thousands of far-away planets.

Recent studies of Earth’s transit zone have typically focused on the stars within it right now, said René Heller, an astrophysicist at the Max Planck Institute for Solar System Research in Germany not involved in the research. In 2016, Heller and a colleague published a study defining Earth’s transit zone and showing that roughly 80 stars could currently see Earth transiting the Sun. “We didn’t care too much about the temporal aspect,” he said.

But Kaltenegger and Faherty have now considered the changing vantage points of stars over time, into and out of Earth’s transit zone. That’s an important distinction, said Heller, because stars are in constant motion around the center of the galaxy. A solar system that observes Earth as transiting now might not have the same view in the future, he said.

Kaltenegger and Faherty restricted their analysis to the roughly 331,000 stars in the Gaia Catalog of Nearby Stars. These stars, all within roughly 300 light-years of Earth, are the best candidates for follow-up study given their relative proximity, said Faherty.

Past, Present, and Future Viewpoints

The researchers then propagated the motions of these stars backward and forward in time. At each annual time step over a 10,000-year window, they determined whether a star fell within Earth’s transit zone. The researchers found that 313 stars were in this zone in the past, 1,402 are in it currently, and 319 will enter it in the future. (Seventy-five of the closest stars in the sample receive yet another tip-off to Earth’s presence: These worlds are close enough to us to have already been bathed in human-produced radio waves.)

Astronomers already know that 7 of these 2,034 stars host planets—17 are known thus far, including 7 in the TRAPPIST-1 system. Many more, if not most, of the remaining stars likely also have their own planets, all of which could see Earth passing in front of the Sun. To get a handle on the total number of rocky, habitable planets potentially orbiting these stars, Kaltenegger and Faherty conservatively estimated that 25% of stars host such a planet. That means that more than 500 planets could witness Earth transiting the Sun, the team concluded.

These results were published in Nature in June.

Future observations in the search for extraterrestrial life ought to target these worlds, said Faherty. They’re the ones closest to us and most likely to have spotted Earth, she said. “These are our best shots.”

—Katherine Kornei (@KatherineKornei), Science Writer

Earth’s largest earthquakes happen on subduction zone megathrusts, and destructive tsunamis often accompany strong shaking. These earthquakes almost always have a puzzling seismic signature; the shallow parts of megathrust ruptures cause tsunamis but mostly emit low-frequency seismic waves that cause less damaging shaking. However, the deeper parts of the ruptures excite high-frequency waves that are especially dangerous to the built environment. Past studies have suggested that this dichotomy results from different fault properties with depth. However, Yin and Denolle [2021] show that rupture characteristics are very different nearer to the Earth’s surface than at greater depth, which causes the change in seismic signatures. The authors note that their use of more realistic Earth models enables them to capture complex interactions between seismic waves and near surface geology in dynamic rupture simulations that reproduce observations.

Citation: Yin, J. & Denolle, M. [2021]. The Earth’s surface controls the depth-dependent seismic radiation of megathrust earthquakes. AGU Advances, 2, e2021AV000413. https://doi.org/10.1029/2021AV000413

—Tom Parsons, Editor, AGU Advances

North America’s Basin and Range Province is home to some of the most extreme environments on the continent, including Death Valley. Stretching from the Wasatch Mountains in Utah to the Sierra Nevada in California and into northwestern Mexico, this area experiences near-constant drought and extreme summer heat.

The Basin and Range Province is also seismically active. For example, the 1887 Sonoran earthquake in the southern Basin and Range caused extensive damage and dozens of deaths. However, deformation rates in the southern Basin and Range are hard to quantify because of few young faults and infrequent seismic events. Furthermore, the adjacent San Andreas and Gulf of California fault systems of the Pacific–North America plate boundary can mask strain rates in the southern Basin and Range.

In a new paper, Broermann et al. explored deformation in a large area including Arizona, New Mexico, and southern portions of Utah and Colorado, within the southern Basin and Range and the Colorado Plateau. The authors observed crustal motion using the EarthScope Plate Boundary Observatory. The array of GPS sensors, seismometers, and other instruments monitor seismology and the tectonic plates underlying North America. The authors used the data to develop models of crustal surface velocity and strain rates in the study area. They concluded that accumulated strain in the crust is the primary driver of future continental earthquakes.

The authors separated the effects of the plate boundary and fluctuating impacts of coseismic and postseismic deformation on strain rates in the region. The results revealed three distinct regions with unique characteristics: a western region, an eastern region, and the Colorado Plateau interior block. Each area differs in the strain rate and motion it experiences, which can affect the probability of future earthquakes. For example, the western region features higher strain rates and an approximately east–west principal axis. In contrast, the eastern region has lower strain rates and a more west–southwest trending axis.

The highest strain rate in the study area includes southwestern Arizona, an expanse with sparse faults and low seismicity. The high strain rate in the region may indicate a potential for future large-magnitude earthquakes, although strain accumulation may be reduced through other processes. (Journal of Geophysical Research: Solid Earth, https://doi.org/10.1029/2020JB021355, 2021)

—Aaron Sidder, Science Writer

This is an authorized translation of an Eos article. Esta es una traducción al español autorizada de un artículo de Eos.

Cada primavera, el fitoplancton florece en el océano. Estos organismos unicelulares y fotosintéticos extraen dióxido de carbono de la atmósfera y producen oxígeno, formando así parte de un sistema de captación de carbono conocido como bomba biológica.

Los modelos numéricos y satelitales que se utilizan ampliamente suponen que la producción primaria y la producción comunitaria neta (o la cantidad neta de carbono removida de la atmósfera a través de la bomba biológica) son mayores en los ecosistemas dominados por el plancton mayor a 20 micrómetros, conocido como microplancton, y menores en aquellos dominados por el plancton de menos de 2 micrómetros, conocido como picoplancton. Sin embargo, el papel del plancton entre esos tamaños, conocido como nanoplancton, se ha ignorado en gran medida. Ahora Juranek et al. demuestran que el nanoplancton puede desempeñar un papel más importante de lo que se pensaba.

El equipo estudió la relación entre el tamaño y la productividad en una región de la Zona de Transición del Pacífico Norte (NPTZ), una zona subtropical-subpolar del tamaño de una cuenca, caracterizada por fuertes gradientes físicos, químicos y ecológicos. Los miembros del equipo llevaron a cabo tres transectos en la NPTZ en la primavera o principios del verano de 2016, 2017 y 2019, cruzando una rasgo conocido como el frente de clorofila de la zona de transición, donde las tasas de producción de la comunidad neta fueron hasta 5 veces más altas que las del sur de la zona de transición.

Los autores utilizaron una combinación de enfoques para caracterizar el tamaño y la diversidad del plancton de 0.5 a 100 micrómetros de diámetro. Estas mediciones se compararon con las tasas de productividad determinadas tanto por un método basado en la incubación como por el seguimiento de la relación entre el oxígeno disuelto y el argón en el agua de mar, que está relacionada con la producción neta de carbono orgánico.

Estos flujos de datos coordinados revelaron un vínculo fuerte y no identificado anteriormente entre la variación de la producción neta de la comunidad y la biomasa del nanoplancton. Con ayuda de la modelización, los autores sugieren que tanto los factores ascendentes, como el suministro de nutrientes, como los descendentes, como el pastoreo de depredadores por tamaños específicos, contribuyen a la importancia del nanoplancton en la zona de transición.

Según los investigadores, los modelos que no tienen en cuenta este plancton de tamaño medio pueden subestimar la producción primaria y la eficacia de la bomba biológica. Comprender el papel del nanoplancton será fundamental para que los científicos entiendan cómo puede afectar el cambio climático al ciclo del carbono en el futuro. (Global Biogeochemical Cycles, https://doi.org/10.1029/2020GB006702, 2020)

—Kate Wheeling, Escritora de ciencia

Although many things about ancient animals’ lives remain a mystery, paleoecologists are able to find out a lot about food webs that existed thousands of years ago by studying the carbon isotopes present in the animals’ bones and teeth.

Humans are changing the isotopic signature of the atmosphere and, subsequently, of the oceans.But humanity’s continual burning of fossil fuels has made this carbon isotope analysis tricky. By burning fossil fuels, said Washington Department of Fish and Wildlife marine biologist Casey Clark, humans are actually changing the isotopic signature of the atmosphere and, subsequently, of the oceans.

This human-induced change is called the Suess effect, named for physical chemist Hans Suess, who first noted this effect in work published in 1955. Scientists have to account for this effect if they want to accurately analyze ancient isotopes. But, said Clark, there isn’t necessarily a lot of agreement about the best way to perform this correction, and different techniques may be used in different subfields, which can make it difficult to compare results from different studies.

That’s why Clark and a team of researchers from the University of Alaska Fairbanks, the University of Washington, the University of Minnesota, and Idaho State University collaborated to create SuessR, a free, customizable tool that will allow researchers to easily and consistently perform region-specific corrections for the Suess effect. A paper introducing the new tool was published earlier this year in the journal Methods in Ecology and Evolution.

Eric Guiry, a biomolecular archaeologist at the University of Leicester, said this tool could make data analysis easier for many scientists. “What I think is interesting about the program is that it should be a user-friendly way of doing [the Suess correction], which has been a bit of an obstacle. I think that there’s a fairly steep learning curve if you want to do a more nuanced and accurate Suess correction for your data. So in the past a lot of people just kind of had a one-size-fits-all approach.… Doing something that’s more bespoke to your region and aware of the kinds of complications you should be incorporating—that takes quite a bit of effort and background knowledge, so this should help people get over that hurdle.”

Modern-Day Ecology

Clark and the research team found measurable differences in the magnitude of the Suess effect when comparing data over a span of just 8 years.Clark explained that correcting for the Suess effect is becoming increasingly important in ecological research, in addition to paleoecological research, where it is more widely used. That’s because the magnitude of the Suess effect is growing exponentially over time. Although the change in the magnitude of the Suess effect might have been undetectably small for a 10-year data set collected in the 1970s, that’s no longer the case. Clark and the research team found measurable differences in the magnitude of the Suess effect when comparing data over a span of just 8 years in a recent data set.

Clark said that being able to properly correct for the Suess effect has major implications for how we understand what’s happening in our oceans today. For example, he said there has been a long-term decline in carbon isotope ratios in some marine systems, but there has been some disagreement about how those declines should be interpreted.

“One of the conclusions that’s been drawn, particularly for the Bering Sea and the North Pacific, is that a long-term decline in carbon isotope ratios is actually indicative of a decline in primary production,” he said. “Some people have said this is an indication that the ocean overall is becoming less productive around here. And that has huge implications—for how many salmon we can expect to see in the future and what will food webs’ structures look like and how much food will there be feeding these systems.”

However, upon reanalysis of these data sets, Clark said it seems that a substantial amount of this decline in carbon isotope ratios is actually due to the Suess effect and that primary productivity is likely not declining nearly as much as some have suggested. The Suess effect, therefore, is not just an abstract concept, but a key piece of our understanding as we try to answer important questions about conservation and food production.

Future Directions

Clark doesn’t see the present iteration of SuessR as the final version of the tool. Instead, he hopes it will become a project shared by the scientific community, with many people from all over the world contributing data and suggestions for improvement.

SuessR currently includes built-in corrections for four regions in the North Atlantic and North Pacific, but Clark wants to add more, as the Suess effect can vary somewhat across regions, especially across different latitudes.

—Hannah Thomasy (@HannahThomasy), Science Writer

In August 2018, Alex Normandeau was on a research cruise in the Southwind Fjord of Canada’s Baffin Island, attempting to study landslides on the seafloor. Normandeau, a research scientist at the Bedford Institute of Oceanography in Dartmouth, Nova Scotia, was aboard the CCGS Hudson collecting bathymetry data and core samples of the seafloor when the crew spotted an iceberg. “We took a bunch of photos and didn’t think anything of it at the time,” Normandeau remembered.

A year later, Normandeau and his colleagues determined that the same iceberg may have initiated a new submarine landslide. Scientists had never shown that icebergs could cause landslides before. Their findings were published in June in Nature Geoscience.

An Iceberg Aground

Submarine landslides can threaten sea life, cause tsunamis, and damage infrastructure such as subsea Internet cables.

Despite these risks, scientists don’t fully understand the causes of submarine landslides. In some cases, earthquakes are the culprits. But because most of the ocean floor is irregularly mapped, it is difficult to know when landslides occur and link them with a causal event.

When the researchers returned to Southwind Fjord in 2019, they learned a new landslide had occurred since their previous visit, providing a rare opportunity to look within a short time window and determine what might have caused it.

“We were hoping for something like this. But to see it happen? It was a lot of luck.”Because no earthquakes had occurred within 300 kilometers of Southwind Fjord, the researchers looked for other mechanisms. By comparing the bathymetry data from their two visits to the fjord, they found an intriguing piece of evidence. They noticed a characteristic pit left when an iceberg impacts the seafloor—right at the initiation point of the landslide, known as a head scarp. Using satellite images from Sentinel-2, they realized that the iceberg they saw the year before eventually ran aground. A few days later, it capsized and slammed into the ocean floor, regrounding several meters away.

NGeo: Iceberg gouging of continental slopes can initiate submarine landslides, potentially far from the iceberg source region@SediAlex; @GSC_CGC; @NRCan; @ClarkGRichards; @DCalvinCampbellhttps://t.co/TMZfbscUlc pic.twitter.com/bS9T7DQk6q

— Nature Geoscience (@NatureGeosci) June 24, 2021

“We interpret that it’s that impact that created the landslide because when you look at where the iceberg regrounded, that’s exactly where the landslide head scarp is,” said Normandeau. “We were hoping for something like this. But to see it happen? It was a lot of luck.”

For further evidence that the iceberg initiated the landslide, the researchers went back to the core samples they collected in 2018 near the landslide but before it occurred. By analyzing the sediment composition and the slope of the seafloor, they found that the sediment in the area was stable under gravitational load, but the estimated load of the iceberg would have been enough to initiate the slide.

Morelia Urlaub, a marine geoscientist at GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, who wasn’t involved in the study, is researching ways to monitor the seafloor and identify new landslides. She said that when researching submarine landslides, researchers must be in the right place at the right time. “That’s what I found fascinating about this iceberg study. They basically caught one,” Urlaub said. “The study is important because it brings up a new mechanism and because the observation is good as it gets.”

Iceberg Impacts Run Deep

After discovering the landslide in Southwind Fjord, the researchers explored maps of the seafloor in other locations. They found several other iceberg pits at landslide head scarps. “The most surprising result was off the continental slope of Nova Scotia,” Normandeau said. “They’re much bigger [landslides] than what we see in the fjords.” Normandeau hypothesizes that when there was an ice sheet in the region around 20,000 years ago, big icebergs broke off and impacted the seabed, causing landslides. He’s hoping to address this hypothesis in future research.

As climate change causes more icebergs to break off the existing ice sheets, understanding the risks that icebergs pose could mitigate damage to new infrastructure projects. In Canada, there is a push to connect northern communities with subsea Internet cables, which would be especially at risk. But icebergs can also travel thousands of kilometers, potentially causing landslides far from the Arctic. “It’s important to be aware of the triggering mechanisms when we’re planning seafloor infrastructure,” Normandeau said. The gouges left when icebergs collide with the seafloor might be only the tip of the problem.

—Andrew Chapman (@andrew7chapman), Science Writer