GeoSpace: Earth & Space Science

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Ancient Moon rock provides evidence of giant lunar impact 4.3 billion years ago

Wed, 10/16/2019 - 14:15

New research finds evidence of an ancient impact 4.3 billion years ago on the Moon, churning rock up to the lunar surface.
Credit: NASA.

By Abigail Eisenstadt

An Apollo 16 lunar rock sample shows evidence of intense meteorite bombardment on the Moon 4.3 billion years ago, according to new research. The results provide new insights for the Moon’s early history, showing lunar impacts were common throughout the Moon’s formation than previously thought.

When the Moon first formed, its surface was covered in a sea of molten rock called the lunar magma ocean. This magma ocean eventually cooled and formed the rocks that make up the lunar crust and mantle.

A new study in AGU’s Journal of Geophysical Research: Planets analyzed a Moon rock from the Apollo 16 mission and found the rock cooled quicker than expected. The results suggest that 4.3 billion years ago a previously unidentified impact event forced the rock from the depths of the slowly cooling lunar crust to the surface.

“Something hit the Moon while the rocks were still at high temperatures, excavated the rock from depths in the lunar crust, and then it cooled quickly after that,” said Naomi Marks, a geochemist at Lawrence Livermore National Laboratory in Livermore, California and lead author of the new study.

Many planetary scientists had previously accepted the idea that the Moon had a relatively peaceful existence following its creation until the Late Heavy Bombardment, a period when the Moon was intensely pelted by meteorites and asteroids 4.0 billion to 3.8 billion years ago. But scientists have been questioning the accuracy of this theory. The new results add to growing evidence that the theory may be incorrect by identifying a major impact outside of the theory’s timeframe, according to the study’s authors.

“We are fairly confident that that the age is recording an impact, which means that there were significant impacts outside of the Late Heavy Bombardment period,” Marks said.

Understanding ancient lunar impacts could help scientists uncover more information about the early Moon’s formation and its surroundings.

Clast 3A refers to the area sampled from the anorthosite rock called 60016. The rock shown here was brought back during the Apollo 16 mission.
Credit: AGU.

Forming rocks from magma

The Moon is thought to have originated from debris created by a collision between an ancient Mars-sized planet and Earth. During its initial period of formation, the Moon’s surface was an ocean of magma. Eventually, heavier elements began to sink to the depths of the ocean, forming the solid lunar core around 4.4 billion years ago. Then the outer layer comprised of lighter material began to rise to the top and cool. This formation of the lunar crust is estimated to have taken between 10 million and 250 million years.

Studying the lunar crust allows scientists to learn more about the Moon’s origins and evolution. One type of lunar surface rock, called anorthosites, are responsible for the Moon’s bright white color and were once thought to be the oldest rocks on the lunar surface.

In the new study, Marks and her colleagues wanted to use anorthosites to estimate how long it took for the lunar magma ocean to cool and solidify into rocks. They took a sample from a previously unexamined anorthosite collected by the Apollo 16 mission and analyzed isotopes produced by the radioactive decay of elements within the rock to determine when it cooled to certain temperatures.

They found the rock went from around 855 degrees Celsius (1,571 degrees Fahrenheit) to roughly 250 degrees Celsius (482 degrees Fahrenheit) within a few thousand years – an unusually quick cooling rate in the scheme of other planetary timescales. The rapid cooling indicates a major impact likely propelled rock out of the lower crust to the surface, where it rapidly cooled into anorthosite alongside other rocks, according to the authors.

The study provides good evidence for a large impact on the Moon 4.3 billion year ago, adding to many decades of research on lunar chronology, said Kevin McKeegan, a planetary scientist at the University of California, Los Angeles in Los Angeles, California, who was unaffiliated with the study.

Evidence for the ancient lunar impact reveals how tumultuous the Moon’s early period was, helping scientists understand more about its formation and composition, according to Marks.

— Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Radioactive chlorine from nuclear bomb tests still present in Antarctica

Tue, 10/15/2019 - 20:27

New research finds some glaciers in Antarctica are still releasing radioactive chlorine-36 created during 1950s nuclear weapons tests.
Credit: NASA/Joe MacGregor.

By Abigail Eisenstadt

Antarctica’s ice sheets are still releasing radioactive chlorine from marine nuclear weapons tests in the 1950s, a new study finds. This suggests regions in Antarctica store and vent the radioactive element differently than previously thought. The results also improve scientists’ ability to use chlorine to learn more about Earth’s atmosphere.    

Scientists commonly use the radioactive isotopes chlorine-36 and beryllium-10 to determine the ages of ice in ice cores, which are barrels of ice obtained by drilling into ice sheets. Chlorine-36 is a naturally occurring radioactive isotope, meaning it has a different atomic mass than regular chlorine. Some chlorine-36 forms naturally when argon gas reacts with cosmic rays in Earth’s atmosphere, but it can also be produced during nuclear explosions when neutrons react with chlorine in seawater.

Nuclear weapons tests in the United States carried out in the Pacific Ocean during the 1950s and the 1960s caused reactions that generated high concentrations of isotopes like chlorine-36. The radioactive isotope reached the stratosphere, where it traveled around the globe. Some of the gas made it to Antarctica, where it was deposited on Antarctica’s ice and has remained ever since.

Other isotopes produced by marine nuclear bomb testing have mostly returned to pre-bomb levels in recent years. Scientists expected chlorine-36 from the nuclear bomb tests to have also rebounded. But new research in AGU’s Journal of Geophysical Research: Atmospheres finds the Vostok region of Antarctica is continuing to release radioactive chlorine into the atmosphere. Since naturally produced chlorine-36 is stored permanently in layers of Antarctica’s snow, the results indicate the site surprisingly still has manmade chlorine produced by bomb tests in the 1950s and in the 1960s.

“There is no more nuclear chlorine-36 in the global atmosphere. That is… why we should observe natural chlorine-36 levels everywhere,” said Mélanie Baroni, a geoscientist at the European Centre for Research and Teaching in Geosciences and the Environment in Aix-en-Provence, France, and co-author of the new study.

Studying the chlorine’s behavior in Antarctica can improve ice dating technology, helping scientists better understand how Earth’s climate evolved over time, according to the study’s authors.

In the new study, Baroni and her colleagues examined chlorine emissions in different parts of Antarctica to better understand how chlorine behaves over time in areas where annual snowfall is high versus areas where snowfall is low. The researchers took ice samples from a snow pit at Vostok, a Russian research station in East Antarctica that receives little snow accumulation, and compared them to ice samples from Talos Dome, a large ice dome roughly 1400 kilometers (870 miles) away that receives a lot of snow accumulation every year.  

Vostok and Talos Dome are both shown on this map of Antarctica. Vostok is still releasing anthropogenic chlorine-36 into the atmosphere.
Credit: AGU.

The researchers tested samples from both sites for concentrations of chlorine-36 and determined how much chlorine was present in Vostok’s ice from 1949 to 2007 and how much was in Talos Dome’s ice from 1910 to 1980.

The results showed chlorine-36 in Talos Dome ice has gradually decreased over time, holding only four times the level of natural chlorine-36 level, in 1980. However, the Vostok ice showed very high levels of chlorine-36, with the top of the snow pit reaching levels of 10 times the expected natural concentration in 2008.

The consistently higher levels suggest the Vostok snowpack is still releasing radioactive chlorine from the 1950s and 1960s marine nuclear bomb tests. The amount of radioactivity is too small to have an effect on the environment, but the results are surprising because a different radioactive isotope produced by nuclear tests had already returned to pre-bomb levels in Vostok, according to the study’s authors. They had hypothesized chlorine-36 would behave similarly.

They also compared the Vostok ice samples with samples from the same site taken in 1998. Measuring the depth of each sample, they found chlorine-36 had moved closer to the surface of the snowpack, which was surprising, according to Baroni. The chlorine was not only spreading to the atmosphere from the firn surface of the snowpack, but moving up from the snowpack’s depths, meaning the chlorine is more mobile scientists previously thought.

Scientists are currently planning to drill for a 1.5 million-year-old ice core in the Antarctic and understanding how Vostok releases manmade chlorine-36 could improve how scientists use the isotope to glean data from the ancient ice core, Baroni said.

Determining how manmade nuclear chlorine-36 moves in low snow accumulation zones over the last century could serve as a microcosmic example for how natural chlorine-36 has built up in snowpacks over the last 1 million years, according to the study authors. The results give more information to future scientists using the isotope to date ancient ice and uncover Earth’s past climate, according to the study.

— Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Extreme solar storms may be more frequent than previously thought

Fri, 10/04/2019 - 14:00

By Abigail Eisenstadt

Researchers propose in a new study why an extreme solar storm in 1859 was so damaging to Earth’s magnetic field. They compared the storm with other extreme storms in history, suggesting this storm is not likely unique.

The September 1859 Carrington Event ejected concentrated solar plasma towards Earth, disrupting the planet’s magnetic field and leading to widespread telegraph disturbances and even sporadic fires. New research in AGU’s journal Space Weather indicates storms like the Carrington Event are not as rare as scientists thought and could happen every few decades, seriously damaging modern communication and navigation systems around the globe.

“The Carrington Event was considered to be the worst-case scenario for space weather events against the modern civilization… but if it comes several times a century, we have to reconsider how to prepare against and mitigate that kind of space weather hazard,” said Hisashi Hayakawa, lead author of the new study and an astrophysicist at Osaka University in Osaka, Japan and Rutherford Appleton Laboratory in the United Kingdom.

This visualization depicts what a coronal mass ejection might look like like as it interacts with the interplanetary medium and magnetic forces. Credit: NASA / Steele Hill

The Carrington Event is one of the most extreme solar storms observed in the last two centuries and was caused by a large coronal mass ejection, an emission of plasma from the Sun’s outmost atmosphere. Depending on a coronal mass ejection’s strength and trajectory, it can significantly distort Earth’s magnetic field, causing an intense magnetic storm, global auroras and damaging any technology that relies on electromagnetic waves.

Scientists previously thought events like the Carrington Event were very rare, happening maybe once a century. They knew the Carrington Event caused low-latitude auroras and failure of telegraph equipment throughout the globe, but they had mostly studied records from the Western Hemisphere, leaving a considerable data gap in the Eastern Hemisphere.

In the new study, Hayakawa and his colleagues wanted to improve reconstructions of the Carrington event and compare this event with other extreme storms. They organized an international collaboration and compiled historical observations of auroras during the storm from the Eastern Hemisphere and Iberian Peninsula to fill the gaps in their knowledge from studying only the Western Hemisphere records.

The researchers collected observations of the storm’s auroras from the Russian Central Observatory, Japanese diaries, and newspapers from Portugal, Spain, Australia, New Zealand, Mexico and Brazil. They then compared these observations to previous reports of the storm from the Western Hemisphere, like ship logs, contemporary scientific journals, and more newspapers.

An image from NASA’s Solar Dynamic Observatory shows a giant sunspot present in 2014. The sunspot spanned 80,000 miles. Credit: NASA/SDO

The researchers also analyzed several unpublished sunspot drawings made by European astronomers during the 1859 storm. Analyzing these drawings allowed them to determine where on the Sun the storm originated and track how the sunspot group grew and shrank over time.

The newly recovered historical documents suggest the Carrington sunspot group had probably launched multiple outbursts from early August to early October, including a preceding solar storm in late August 1859. The researchers estimate this event happened around August 27th, 1859 and sent out separate coronal mass ejections that were strong enough to impact Earth’s magnetic field. The August storm may have played a role in making the September Carrington Event so intense.

After reconstructing the storms around the Carrington Event, the researchers compared the solar storm to other storms in 1872, 1909, 1921, and 1989 and found two of them – those in 1872 and 1921 – were comparable to this event. The 1989 event caused a serious blackout throughout all of Quebec, Canada. This means events like the Carrington may not be as legendary and elusive as once thought, and scientists need to consider the hazards of such events more seriously than before, according to Hayakawa.

“While the 1859 storm was certainly one of the most extreme events, this seems at best comparable to the 1872 storm and 1921 storm in terms of its intensity,” he said. “So, the Carrington event is no longer something unique. This fact may require us to reconsider the occurrence frequency of this kind of ‘worst-case scenario’ of space weather events.”

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Shape of volcanic ash influences contamination of water sources in volcanically active regions

Thu, 10/03/2019 - 14:00

By Abigail Eisenstadt

Contaminants from volcanic eruptions leach into water at different rates depending on the shape of the volcanic ash particles, according to new research that could enhancing scientists’ ability to predict water quality risk in volcanically active regions.

Volcanic ash consists of microscopic fragments of solidified magma propelled from volcanic eruptions. When a volcano erupts, ash can travel great distances. In the short term, ash can contaminate vegetation, surface water, soils and groundwater with heavy metals like copper, cadmium and arsenic and non-metal contaminants like fluorine.

These contaminants can enter the food chain in a process known as bioaccumulation. Bioaccumulation occurs when organisms ingest and store contaminants that they cannot metabolize. These contaminants can become more concentrated as they travel up the food chain, poisoning livestock and humans. Bioaccumulation of heavy metals can cause some cancers, while bioaccumulation of non-metals like fluorine can cause skeletal damage.

Kilauea, a famous Hawaiian volcano, erupts lava and basaltic ash that has high concentrations of fluorine. Credit: M. Patrick, USGS. Public domain.

A new study in AGU’s journal GeoHealth finds ash particles’ surface area controls how quickly ash leaches contaminants into the water. The more bubbles a particle has – or the more porous it is – the larger its surface area. Ash with more bubbles leaches faster, because it has more surface for water to permeate.

The results suggest particle structure can affect water quality, improving geologists’ ability to predict how environments might respond to volcanic explosions. Understanding how ash types influence the way contaminants dissolve in water enables scientists to predict the health hazards imposed by water contamination in regions with frequent volcanism, according to the study’s authors.

“The first couple of hours are when water is the most contaminated and the leaching rates decline afterwards. However, the long term, repeated eruptions can lead to bioaccumulation,” said Candace Wygel, a geologist who conducted the research while a graduate student at Lehigh University in Bethlehem, Pennsylvania. Wygel, now a geologist at Roux Environmental Engineering and Geology D.P.C. in New York City, New York, is the lead author of the new paper.

Measuring bubble concentration

Previous studies of volcanic ash assumed each particle was uniformly spherical and compact. This method didn’t account for how porous some types of ash are. For example, particles from andesitic ash, a type of volcanic ash with medium-grained crystals and medium silica content, may have many microscopic bubbles. Each bubble increases the surface area of the ash sample. More water can touch the sample and dissolve its contaminants.

In addition, different types of volcanic ash have unique concentrations of elements and contaminants. Basaltic ash, a type of volcanic ash low silica content, contains more metals than andesitic ashes. However, since andesitic ash has more bubbles, it leaches what it has faster. Scientists knew chemical composition influenced what volcanic ash leached, but Wygel and her colleagues suspected particle structure also impacts ashes’ leaching rate.

“We wanted to see how the morphology of the ash impacted leaching into the environment,” Wygel said.

The left image is andesitic ash from the Turrialba volcano. Its high porosity gives it a larger surface area. The right image is basaltic ash from Kilauea. Its smooth and spherical appearance shows its reduced surface area. Credit: AGU

In the new study, the researchers collected samples from four volcanoes in Hawaii, Costa Rica, Alaska and Iceland. Each volcano erupted primarily basaltic or andesitic ash. The researchers measured each sample’s total surface area and accounted for bubbles inside the ash. They found the samples had surface areas about three times larger than when they were measured with the standard geometric method.

They found ash particles with larger surface areas leached metals faster. Over seven days, water eroded the particles, making their surface areas smaller and changing their leaching rates. The researchers took surface area measurements at different points in time to observe how ashes’ leaching rates changed from water weathering.

Andesitic ash from the Costa Rican volcano, Turrialba, had the highest leaching rate, attributed to its high concentrations of bubbles. Turrialba’s ash initially leached contaminants fastest. However, basaltic ash from the Hawaiian volcano, Kilauea, leached the greatest concentrations of metals. The results suggest ashes’ leaching rate and chemical composition affect environments in tandem.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

The post Shape of volcanic ash influences contamination of water sources in volcanically active regions appeared first on GeoSpace.

Water distribution affects exoplanets’ habitable zone

Tue, 10/01/2019 - 14:00

By Abigail Eisenstadt

Earth-like exoplanets with dry tropical regions can remain habitable at a closer distance to their host star than previously thought, a new study suggests.

Earth is an example of an aqua planet that maintains its water in a habitable zone. This image of Earth taken by the spacecraft Galileo shows its vast Pacific Ocean. Credit: NASA/JPL

Because life on Earth requires liquid water, researchers looking for life beyond Earth’s solar system search for exoplanets that orbit their star within a “habitable zone” where the planet is neither frozen in ice nor completely dry.

Distance to the central star, thickness of the atmosphere, and the amount of water on a planet can affect where its habitable zone lies. The new research in AGU’s Journal of Geophysical Research: Planets, finds where water is distributed on land also impacts how close some types of planets can be to their central star without losing all their water.

The new study finds land planets, which have equal to or less than 10 percent of the volume of Earth’s water, can remain habitable at a closer distance to their host star if most of their water is at the planet’s poles. This means the habitable zone for these types of planets may be different than previously assumed.

“Our results showed the inner edge of the habitable zone is not a single, sharp boundary, but a border whose location changes depending on the planetary surface environment,” said Takanori Kodama, an astrophysicist at the University of Bordeaux in Bordeaux, France, and lead author of the new study.

Water in the habitable zone

The amount of water a planet has limits how close it can be to the heat of its star. Water vapor in the air traps heat like a greenhouse, insulating the planet and making its surface much warmer than it normally would be.

Warmer temperatures and more surface water both cause more water vapor to enter a planet’s atmosphere. If more heat is coming into the atmosphere in the form of solar radiation than the amount of heat that is being expelled as outgoing planetary radiation, the planet gets hotter. This causes more evaporation and more water vapor, subsequently trapping more heat and causing a runaway greenhouse cycle.

On habitable planets, incoming solar radiation and outgoing planetary radiation are balanced.

“Small differences in the amount of water cause significant differences in planets’ climates,” Kodama said.

Mars is an example of a potentially Earth-like planet that lost its liquid water and atmosphere. Credit: NASA/JPL/USGS

Aqua planets, like Earth, have narrow habitable zones because their water-heavy atmospheres limit outgoing planetary radiation while insulating solar radiation, creating a buildup of heat. Land planets have a wider habitable zone, because they have less water in their atmospheres.

Kodama previously established the total amount of water a land planet has can affect how close it can be to its central star before the amount of water vapor thickens the atmosphere and sends the planet into a runaway greenhouse state. After this water vapor threshold is reached, all the planet’s water eventually disappears through evaporation caused by heat accumulation.

The new study examines how water distribution on land planets influences how close they can exist to their host star without entering a runaway greenhouse state. The new results indicate that how close a planet can be to its host star and remain habitable also depends on the planet’s surface water distribution in addition to its overall amount of water. Land planets with drier equators can live closer to their stars.

The researchers used three-dimensional models to simulate the different ways a set volume of water on land planets could be distributed. In one model, the water was distributed closer to the planet’s poles. In the other, water was scattered away from the poles.

They found land planets with more water at their equator have wetter atmospheres, sending them into a greenhouse state. Land planets with water near their poles have drier atmospheres around their tropical regions, because the water vapor does not circulate up to the equator. Those land planets can maintain their water when they are closer to their central stars.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Historic earthquakes suggest Trans-Mexican Volcanic Belt’s quiet regions are active

Wed, 09/25/2019 - 14:00

By Abigail Eisenstadt

Seemingly low-hazard seismic regions in Mexico have experienced multiple, strong earthquakes since the 1500s, new research finds, suggesting the regions have many unmapped, active fault lines. The areas are inside the Trans-Mexican Volcanic Belt, home to roughly 40 percent of Mexico’s population, who may be unaware of the land’s seismic history.

New research collected archival records documenting the belt’s historic earthquakes, converting the historic reports into numerical data. The new study in the AGU Journal Tectonics found there have been at least 16 large earthquakes during the past 450 years in areas of the belt previously believed to be dormant, challenging an existing understanding of the belt’s behavior.

“Instrumental seismology spans a little over 100 years, but this phenomenon takes place at geological times. If we want to understand what’s really happening in the Earth… then we really need to go back and see what’s happened,” said Gerardo Suárez, a seismologist at the National Autonomous University of Mexico in Mexico City, Mexico, and lead author of the new study.

The red region is the Trans-Mexican Volcanic Belt, which reaches from the Gulf of Mexico to the Pacific Ocean. Credit: Soleincitta; CC Attribution-Share Alike 3.0 Unported (CC BY-SA 3.0); No changes made.

The Trans-Mexican Volcanic Belt is a 1000-kilometer (621-mile) long volcanically tectonic active region stretching from the Gulf of Mexico to the Pacific Ocean across Central and South Mexico. It is home to many urban centers, including Mexico City.

Seismic hazard is the probability that an earthquake could occur in a region over a specific time frame. Scientists assumed that the seismic hazard in the Trans Mexican Volcanic belt was low because there were not many documented earthquakes.

Even if a region hasn’t had earthquakes for a century, it still could be seismically active. Suárez suspected the belt’s areas without visible faults, like its central and western region, could have had earthquakes in the past because missionaries, colonial government officials and Aztec codices recorded descriptions of tremors, landslides and fractures in the region. Before the widespread use of earthquake recording equipment, earthquakes in the past are identifiable only through written accounts.

Understanding the history of earthquakes inside the Trans Mexican Volcanic belt could help alert people living in the region to the potential seismic hazard there, according to the study’s authors.

Black dots represent the historic earthquakes used in the study. Each dot has the year and magnitude of the earthquake listed next to it. Credit: AGU

Using history to find hidden fault lines

The researchers collected historical records from Mexican archives, using them to classify individual earthquakes from 1568 to 1920. They selected 16 earthquakes with enough recorded sites and reported damage to qualify for the study.

An Aztec codex called the Anales de Tlatelolco, for example, recorded seismic activity for more than four days in 1575. One of the villages where the earthquake was felt, named Zacaetotlán, is nowhere to be found in modern Mexico. Another manuscript hints that Zacaetotlán was a pre-Hispanic settlement found near a volcano in the belt’s central region. The town’s ruins have never been found.

In another example, a 7.6-magnitude earthquake struck the state of Michoacán in 1858. Its epicenter was in a city called Morelia in the center of the volcanic belt. Documents from the time attest to its devastating aftermath in the state. The same earthquake also struck Mexico City roughly 200 kilometers (124 miles) away. The city hall and other government buildings were damaged, as well as aqueducts.

Suárez and his colleagues converted the archival testimonies into numerical values using the Modified Mercalli Intensity Scale, a seismologic method that ranks earthquakes by the intensity of the damage or by how it was felt by the population. Earthquakes that are “severe” might move furniture, while “violent” earthquakes cause building collapse. The scale helped the scientists use the reports of damage to assign each earthquake an intensity data point and then estimate the magnitude and epicenter using a numerical approach.

Results showed earthquakes have happened throughout the Trans-Mexican Volcanic Belt, even in areas thought to be geologically inactive. These earthquakes were particularly common in the central and western regions of the volcanic belt. Several of them are associated with blind faults, or faults that aren’t visible on the Earth’s surface, according to the study.

“We should expect earthquakes throughout the volcanic belt even in areas where we have not yet been able to map active tectonic faults,” Suárez said.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Ice islands on Mars and Pluto could reveal past climate change

Mon, 09/23/2019 - 16:51

By Joshua Rapp Learn

Many of the craters of Mars and Pluto feature relatively small ice islands unattached to their polar ice caps.

These ice islands could be records of past climate change on Mars and Pluto, and could also provide clues about the workings of Martian water and ice, said Mike Sori, a planetary scientist at the University of Arizona and the lead author of a new study in AGU’s Journal of Geophysical Research: Planets detailing the new findings.

Examples of crater deposits from the daytime THEMIS IR mosaic in the southpolar region of Mars. (a) circumpolar crater filling deposits in an unnamed crater (b) “Stacked” circumpolar crater filling deposits in South crater. (c) Marginal deposit in Elim crater. (d) The south polar layered deposits overprinting an unnamed crater. (e) Irregular deposit in unnamed crater. (f) West-east topographic profile from MOLA data through the circumpolar crater filling deposits in (a), with location represented by the dashed line in (a). (From Sori, et al., 2019, JGR: Planets)

Most previous work on ice on Mars had examined the northern polar ice cap on the planet, where other researchers noticed that small domes of ice dozens of miles across persisted inside craters beyond the reach of the main ice sheet.

Sori wanted to see if these features were unique to the planet’s north pole, and to find out more about these understudied features.
“It’s a mountain within a hole,” he said.

Locations of circumpolar crater filling deposits (dark blue points), marginal deposits (black points), and irregular deposits (light blue points) on a southern polar projection of elevation represented by MOLA-derived colored shaded relief. (From Sori, et al., 2019, JGR: Planets)

The study’s authors used different types of instruments from orbiting space craft to examine these features, including images showing the features and topography maps made by the Mars Orbiter Laser Altimeter (MOLA).

They found 104 large impact craters that had deposits inside, including 31 with relatively circular, domed ice cones in craters in the southern polar region. The other craters had more irregular deposits.

Sori and his co-authors focused on the 31 more regular ice cones for this work since they were most confident that these formations were composed mostly of frozen water.

HiRISE images of circumpolar crater filling deposits, shown as insets in daytime THEMIS IR mosaics. (a) Enhanced color portion of HiRISE image ESP_031749_1080 showing dunes on the circumpolar crater filling deposits in Richardson crater (89 km crater diameter, 72.5ºS, 180.2ºE). (b) Enhanced color portion of HiRISEimage ESP_057439_1075 showing layer exposures of the circumpolar crater filling deposits in Burroughs crater (110 km crater diameter, 72.3ºS, 116.6ºE). (From Sori, et al., 2019, JGR: Planets)

“They don’t appear as bright white stuff in images, so it’s not super obvious that they’re ice if you just look at them,” he said.

Once the study authors determined these ice mountains seemed to be a recurring process on Mars, they widened their study to see if they could find similar features elsewhere in the solar system. They looked at Pluto, which has a big bright ice sheet called Sputnik Planitia.

Even though Pluto’s ice is made of frozen nitrogen, the ice sheets were about the same size: about 1,000 kilometers in diameter and a few kilometers thick. Pluto also has similar crater topography.

Map of five outliers of nitrogen ice within impact craters on Pluto. Labels are to the lower left of each crater on a LORRI image mosaic. Topography data comes from New Horizons stereo images (Schenk et al., 2018).

While the available images of Pluto aren’t as good as those of Mars, Sori and his colleagues measured five craters with ice deposits in an area roughly the same distance from Pluto’s main ice sheet as those they found on Mars.

“Broadly speaking it was reasonably similar,” Sori said, adding that the researchers couldn’t measure topography on Pluto as well due to poorer data.

The shapes aren’t exactly dome-shaped on Pluto either, but Sori said it’s still interesting that Pluto’s ice islands are deposited in craters.
“There’s some sort of climate reason or topography reason why holes in the ground are good place for ice to go,” he said.

The researchers aren’t totally sure why this is, but Sori said that in Mars’ southern polar region the ice islands are usually to the west of the center of the craters, which is the way the wind blows there.

“Wind has to play some sort of role,” Sori said.

View of the 102-km-diameter South Crater on Mars, which hosts a large mound of ice. Image made using NASA’s Solar System Treks (https://trek.nasa.gov) and Viking Orbiter Imaging Systems with 5 times vertical exaggeration. (Courtesy of Michael Sori)

How or why the ice islands form is also a mystery. For example, researchers don’t know if craters collect ice or retain ice. They found a few of the ice mounds that are still connected a little to the main ice sheet on Mars, and it’s possible that the other ice mounds were once part of the main ice sheet. If so, this would mean the ice sheets were once bigger on Mars and Pluto, and that they are gradually declining, with the craters retaining some small amount of the ice that once covered them.

While Earth doesn’t have many craters like Pluto or Mars, Sori said there is a crater in Greenland that has an ice mound connected still to the main ice sheet, and that it may be part of the same phenomenon happening on Mars and Pluto.

Joshua Learn is a freelance science writer. Follow him on Twitter: @JoshuaLearn1

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New study complicates theory that ancient impact pierced Moon’s crust

Mon, 09/23/2019 - 14:00

By Abigail Eisenstadt

The moon’s largest and oldest impact crater likely doesn’t have minerals from below the lunar crust on its surface, complicating a theory that an ancient massive impact event pierced the Moon’s crust during the crater’s formation, a new study finds.

A study published earlier this year analyzed the way lunar materials reflect light to determine that a basin-forming impact that formed an ancient massive crater, the South Pole-Aitken basin, caused minerals from deep inside the Moon’s mantle to rupture the Moon’s surface. If mantle materials breached the lunar crust, studying them could yield significant clues about the Moon’s history.

Now, new research in the AGU journal Geophysical Research Letters reexamined the same data, acquired by the Chinese spacecraft Chang’E 4’s rover, which landed in the crater in January 2019. The new study finds the crater’s crust mainly consists of a common lunar crustal mineral not detected in earlier analyses. The new results suggest the basin floor may not have exposed lunar mantle material as previously reported.

This image of the Moon was taken by the International Space Station. Sometimes the far side of the Moon is called the “dark side,” but in reality both sides of the Moon have two weeks of sunlight followed by two weeks of darkness. Chang’E 4 landed on the far side of the Moon that never faces Earth. Credit: Fernando Echeverria

“We are not seeing the mantle materials at the landing site as expected,” said Hao Zhang, a planetary scientist at the China University of Geosciences, Wuhan, China, and a co-author of the new study. 

The new study complicates theories about how the oldest, largest crater on Moon formed, adding to the body of knowledge about the Moon’s history.

Dating the South Pole-Aitken basin

Images show wrinkles in the Aitken Crater.
Credit: NASA/GSFC/Arizona State University

The South Pole-Aitken basin is considered one of the largest craters in the Solar System and the oldest on the Moon. The basin is 2,500 kilometers (1,553 miles) in diameter and runs roughly 13 kilometers (8 miles) deep. The basin resides on the Moon’s far side, the enigmatic area facing away from Earth. It was untouched until Chang’E 4’s landing in the crater in January 2019.

Although scientists haven’t radiometrically dated the basin’s age yet, some estimates place its formation at 4.2 billion years ago.

Scientists theorized the South Pole-Aitken basin-forming event ruptured the lunar crust, because of how deep the basin is today. Crustal topographic maps estimate the crust only extends 30 kilometers (19 miles) beneath the crater, whereas the rest of the lunar crust is 40 kilometers (25 miles) thick on average.

The Moon was once covered in molten magma oceans. Over time, these cooled and separated into crust and mantle layers distinguished by many characteristics, including their mineral composition. Clinopyroxene, orthopyroxene, and olivine are all minerals associated with the Moon’s mantle. They occasionally appear on the surface of the Moon, but large concentrations of them in a region could signal that the mantle once punctured the crust.

Testing the crustal composition

Spectroscopy is the study of how matter interacts with light. Minerals absorb specific wavelengths of light and color, which gives them unique signatures. Astrophysicists perform different types of spectroscopy to determine the composition and concentration of different materials on planetary bodies and their regions, based on these unique signatures.

Previous research published in May in the journal Nature found concentrations of clinopyroxene, orthopyroxene, and olivine in the crater – amounts high enough to seemingly confirm the theory that the mantle had once breached the crust. The Nature study analyzed spectroscopic soil data from Chang’E 4 and processed the data using a series of functions. This process allowed them to identify the mathematically best fitting mineral for each’s spectra compositions.

Zhang and his colleagues also analyzed spectroscopic data acquired by instruments on Chang’E 4’s rover after the spacecraft landed in the crater. They used a technique that compared the rover’s documented reflections of light and color from the lunar surface to a database of known minerals. The database accounted for minerals’ particle size, the way the minerals interact with light, and how they respond to space weathering – changes to the soil surface caused by solar wind irradiation and bombardment from tiny particles that the Moon’s surface experiences.

This different process allowed the researchers to detect and measure the amount of plagioclase in the crater. Plagioclase is a mineral created from cooling lava. It’s also one of the most common rocks on the Moon’s surface. The results showed plagioclase made up 56-72% of the crater’s composition, making it the majority mineral. The high concentration of plagioclase suggests the lunar crust was not pierced by an ancient impact.

The new study also found the landing site on the crater had concentrations of 9-28% orthopyroxene, 4-19% clinopyroxene, and 2-12% olivine. Although The three minerals are in the basin, they are not present at high enough amounts to prove an impact event once broke the crust, according to the study’s authors.

The new study complicates the certainty of earlier findings and points towards a need for continued research on the far side’s lunar surface, according to Zhang.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Study Tallies Huge Hidden Health Costs from Climate Change

Wed, 09/18/2019 - 17:43

Climate change is taking a huge toll on Americans’ health, so much so that it could constitute a public health crisis, a new study by the Natural Resources Defense Council (NRDC) and the University of California, San Francisco (UCSF), suggests.

The study, published in the AGU journal GeoHealth, finds that Americans endured more than $10 billion in health costs from 10 climate-sensitive events in 2012. That stunning toll likely has continued, or risen, in recent years with the increasing impacts from climate change.

But these enormous public health costs are rarely, if ever, tallied in government analyses, which typically address property, agriculture and infrastructure losses from major severe weather events—leaving out the deaths, hospitalizations, emergency department visits, outpatient medical care, prescribed medications, and lost wages associated with those events.

“Climate change represents a major public health emergency. But its destructive and expensive toll on Americans’ health has largely been absent from the climate policy debate,” said study lead author Dr. Vijay Limaye, a scientist in NRDC’s Science Center. “Our research shows that health-related costs added at least another 26 percent to the national price tag for 2012 severe weather-related damages.

“This continuing untold human suffering and staggering cost is another reason we must take assertive action to curb climate change now. Cutting greenhouse gas pollution and expanding clean energy, while also investing in preparedness and climate adaptation, is the prescription for a safer, healthier future.”

The new analyzed national and state-collected health surveillance data across a wide range of 10 types of climate-sensitive events around the country in 2012.

The analysis examined costs from wildfires in Colorado and Washington; ozone air pollution in Nevada; extreme heat in Wisconsin; infectious disease outbreaks of tick-borne Lyme disease in Michigan and mosquito-borne West Nile Virus in Texas; extreme weather in Ohio; Hurricane Sandy in New Jersey and New York; allergenic oak pollen in North Carolina; and Harmful Algal Blooms on the Florida coast.

Those events resulted in at least $10 billion in health-related costs from about 900 deaths, 21,000 hospitalizations, 18,000 emergency room visits, and 37,000 outpatient encounters.

Among key findings from NRDC’s case studies:

  • Wildfires in Colorado and Washington led to 419 premature deaths, 627 hospital admissions and $3.9 billion in total health costs.
  • West Nile virus in Texas led to 89 premature deaths, 1,628 hospital admissions and $1.1 billion in total health costs.
  • Ozone air pollution in Nevada led to 97 premature deaths, 114 hospital admissions and $898 million in total health costs.
  • Hurricane Sandy in New York and New Jersey led to 273 premature deaths there and in other states, 6,602 hospital admissions and $3.1 billion in total health costs.

Since 2012, annual temperatures have continued to rise, and the five hottest years on record globally have all been in the last five years. While the U.S. experienced 11 billion-dollar weather disasters in 2012, that total was exceeded in 2016, 2017, and 2018, according to data gathered by the National Oceanic and Atmospheric Administration (NOAA). The NOAA annual extreme weather cost estimates do not include health costs.

“Our research signals that all told, there could be tens to hundreds of billions of dollars in health costs already from recent climate-related exposures nationwide,” said study co-author Dr. Kim Knowlton, senior scientist at NRDC. “It’s clear that failing to address climate change, and soon, will cost us a fortune, including irreversible damage to our health.”

The report estimated that more than two-thirds of the illness costs were paid for by Medicare and Medicaid. That aligns with research showing that older adults and the economically-disadvantaged are among those most vulnerable to harm from climate change.

Finally, while the report shows a sizable impact on public health, its authors note the true costs are likely substantially higher but cannot be fully evaluated due to incomplete health surveillance and environmental monitoring.

Improvements could be made with increased funding for the U.S. Centers for Disease Control and Prevention’s Climate-Ready States and Cities Initiative and National Environmental Public Health Tracking Network, to support expanded, coordinated tracking and monitoring of climate-sensitive health harms and environmental disruptions related to climate change. Leadership is also needed for a coordinated federal effort to track the economic impacts of climate change on public health.

This post was originally published on the NRDC website

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New study suggests gigantic masses in Earth’s mantle untouched for more than 4 billion years

Wed, 09/18/2019 - 16:00

By Abigail Eisenstadt

Ancient, distinct, continent-sized regions of rocks, isolated since before the collision that created the Moon 4.5 billion years ago, exist hundreds of miles below the Earth’s crust, offering a window into the building blocks of our planet, according to new research.

The new study in the AGU Journal Geochemistry, Geophysics, Geosystems used models to trace the location and origin of volcanic rock samples found throughout the world back to two solid continents in the deep mantle. The new research suggests the specific giant rock regions have existed for 4.5 billion years, since Earth’s beginning.

This image shows the divisions between Earth’s layers. The ancient, continent-sized rock regions encircle the liquid outer core. Credit: Lawrence Livermore National Laboratory

Previously, scientists theorized that separated continents in the deep mantle came from subducted oceanic plates. But the new study indicates these distinct regions may have been formed from an ancient magma ocean that solidified during the beginning of Earth’s formation and may have survived the massive Moon-creating impact.

Determining the masses’ origin reveals more details about their evolution and composition, as well as clues about primordial Earth’s history in the early Solar System, according to the study’s authors.

It’s amazing that these regions have survived most of Earth’s volcanic history relatively untouched, said Curtis Williams, a geologist at the University of California, Davis, in Davis, California and lead author of the study.

Looking inward

The mantle is a layer of rock, stretching 2,900 kilometers (1,802 miles) down inside the Earth. Earth’s molten, liquid, metallic core lies beneath the mantle. The core-mantle boundary is where the solid mantle meets the metallic liquid core.

Scientists knew from past seismic imaging studies that two individual rock bodies existed near the core-mantle boundary. One solid rock body is under Africa and the other is under the Pacific Ocean.

Seismic waves, the vibrations produced by earthquakes, move differently through these masses than the rest of the mantle, suggesting they have distinct physical properties from the surrounding mantle. But geologists couldn’t determine whether seismic waves moved differently through the core-mantle continents because of differences in their temperature, mineral composition or density, or some combination of these properties. That meant they could only hypothesize about the separate rocky masses’ origin and history.

“We had all of these geochemical measurements from Earth’s surface, but we didn’t know how to relate these geochemical measurements to regions of Earth’s interior. We had all of these geophysical images of the Earth’s interior, but we didn’t know how to relate that to the geochemistry at Earth’s surface,” Williams said.

Primitive material and plumes

Williams and his colleagues wanted to determine the distinct masses’ origin and evolution to learn more about Earth’s composition and past. To do this, they needed to be able to identify samples at Earth’s surface with higher concentrations of primitive material and then trace those samples back to their origins.

Scientists often take rock samples from volcanic regions like Hawaii and Iceland, where deep mantle plumes, or columns of extremely hot rock, rise from the areas near the core, melt in the shallow mantle and emerge far from tectonic fault lines. These samples are made of igneous rock created from cooling lava. The study’s authors used an existing database of samples and also collected new samples from volcanically active areas like the Balleny Islands in Antarctica.

Geologists can measure specific isotopes in igneous rocks to learn more about the origin and evolution of the Earth. Some isotopes, like Helium-3, are primordial, meaning they were created during the Big Bang. Rocks closer to Earth’s crust have less of the isotope than rocks deeper underground that were never exposed to air. Samples with more Helium-3 are thought to come from more primitive rocks in the mantle.

The researchers found some of the samples they studied had more Helium-3, indicating they may have come from primitive rocks deep in the Earth’s mantle.

The researchers then used a new model to trace how these primitive samples could have gotten to the Earth’s surface from the mantle. Geological models assume plumes rise vertically from deep within the mantle to the Earth’s surface. But plumes can move off course, deflected, due to various reasons. The new model took into account this plume deflection, allowing the study’s authors to trace the samples back to the two giant masses near the core-mantle boundary.

The combination of the isotope information and the new model allowed the researchers to determine the composition of the two giant masses and theorize how they may have formed.

Understanding the composition of specific rock masses near the core-mantle boundary helps geologists conceptualize ancient Earth-shaping processes that led to the modern-day mantle, according to the study’s authors.

“It’s a more robust framework to try and answer these questions in terms of not making these assumptions of vertically rising material but rather to take into account how much deflection these plumes have seen,” Williams said.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Scientists identify weather event behind extreme cold in Europe and Asia during February 2018

Tue, 09/17/2019 - 14:00

By Abigail Eisenstadt

Researchers have identified a weather event that caused an unusually extreme cold wave to hit Europe and Asia during the winter of 2018, which could help atmospheric scientists better predict similar events in the future, according to a new study.

A wave of extremely cold air hit Eurasia in late February 2018, lasting for a month while temperatures broke record lows across Europe. The extreme cold came from a splitting of a cluster of air high above the Arctic, called the polar vortex.

Weather forecast models didn’t anticipate the stratospheric warming in 2018 until the start of February – only 12 days before it happened – which prevented the models from anticipating the extreme cold that followed.

Now, a new study in AGU’s Journal of Geophysical Research: Atmospheres finds a cyclone-induced chain of events warmed the stratosphere and caused the Arctic polar vortex to split in two, causing the extreme cold.

The information could help weather forecasts detect stratospheric warmings earlier and anticipate future cold waves, according to the study’s authors.

The top panel shows how some forecasts anticipated the sudden stratospheric warming, while the bottom shows what other forecasts anticipated. Ultimately, the warming appeared similar to the top panel forecasts’ predictions.
Credit: AGU

A trigger for sudden warmings

The stratosphere is the second layer of Earth’s atmosphere. It is typically cool, arid, and home to the Arctic polar vortex, a body of circulating cold air around Earth’s North Pole. If the stratosphere warms, the polar vortex weakens and splits in two, which can cause outbreaks of cold weather across the Northern Hemisphere.

To predict sudden warming events in the stratosphere, past research mostly studied how the troposphere — the lowest layer of the atmosphere and where Earth’s weather occurs — behaved on average prior to events in the stratosphere. But these models did not always catch how temporary weather patterns in the troposphere influenced the stratosphere.

In the new study, researchers tested their hypothesis that a chain of events in the troposphere caused the sudden stratospheric warming and subsequent splitting of the polar vortex. They first looked at weather forecast data in the days and weeks leading up to the sudden stratospheric warming event. They saw the forecasts only seemed to accurately predict the event when they captured a cyclone over Greenland and a high-pressure air mass over Scandinavia in the days before the stratospheric warming.

The weather sequence was a “trigger snap” that caused the vortex to split, said Simon Lee, an atmospheric scientist at the University of Reading in the United Kingdom and lead author of the new study. When the polar vortex split, a cluster of cold air around the Arctic pole dispersed and traveled southward toward Eurasia.

A satellite image of European extreme cold snap documents widespread snowfall throughout Eastern Europe. The image is of a past vortex-related cold wave during 2010. Credit: ESA, CC BY-SA 3.0 IGO

The research team also looked at historic weather data and found the same series of events has caused sudden stratospheric warmings in the past. They found these unusual weather patterns occurred 49 times between 1979 and 2017 and foreshadowed 35% of the stratospheric warmings in this period.

“It’s one mechanism that potentially explains a third of these events historically,” Lee said. “That just one event in the Atlantic has contributed to a third of them is quite surprising.”

Looking for changes in this particular air mass over Greenland and Scandinavia could improve weather forecasters’ ability to predict extreme cold outbreaks, adding to atmospheric scientists’ knowledge about sudden stratospheric warming events, according to the study authors.

Knowing when and how this weather pattern occurs gives scientists an ability to say what weather will be like in weeks and months in the future, Lee said.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Lightning flashes illuminate storm behavior

Thu, 09/12/2019 - 15:38

By Mary Caperton Morton

Anybody who has ever tried to photograph lightning knows that it takes patience and special camera equipment. Now, a new study is using those brief but brilliant flashes to illuminate cloud structures and shed light on storm cell behavior, giving weather forecasters new tools for predicting lightning hazards.

The new technique is “essentially lightning-based tomography, similar to a medical x-ray,” said Michael Peterson, an atmospheric physicist at Los Alamos National Labs in New Mexico and author of the new study, published in AGU’s Journal of Geophysical Research: Atmospheres.

“Using lightning flashes as the light source, we can identify contrasts in cloud layers that are indicative of dense regions, such as ones that might be laden with hail,” he said.

A comparison of GLM imagery products for a large thunderstorm over South America. The total energy measured by GLM in (a) differs from the idealized energy distribution in (b), and this difference forms the basis of the thundercloud imagery product in (c) that highlights the texture of the uppermost cloud layer (north) as well as long horizontal lightning flashes behind the thunderstorm core (south). Credit: Michael Peterson/LANL

Peterson drew upon data gathered by the Geostationary Lightning Mapper (GLM) on NOAA’s GOES satellites. The GLM was designed to measure total lightning activity and provide that data to forecasters in real-time, but the products used in operations are only a small portion of GLM’s capabilities.

“I think we’re past the days of only using flash rates to characterize the lightning hazard,” Peterson said. “We can learn a lot by examining how the flashes evolve and by observing how their optical emissions interact with the clouds.”

Other teams have studied reflections and scattering in thunderclouds, but they tend to rely on computer models of simulated clouds that have simplified cloud shapes such as cylinders or horizontal planes.

“In the real world, storms are a lot more complex. We can learn a lot more about storm behavior by working with actual data observations gathered from actual storms,” Peterson said.

This deeper dive into the GLM data can also help identify storm systems that may produce especially dangerous lightning, like horizontal flashes that can seem to strike out of the blue, Peterson said.

“When lighting strikes sideways, it can strike the ground well after the storm has already passed, when it may seem safe to go back outside,” he said. These long horizontal flashes stand out clearly in the new imagery product, improving situational awareness, he added.

The next step will be to combine the GLM’s optical imagery with radio-frequency measurements to construct a more three-dimensional view of the lightning and storm clouds.

“Right now, you can’t tell for certain if you’re seeing a cloud-to-ground flash or an intercloud flash with the optical data,” Peterson said. “Radio-frequency measurements can provide altitude information, and that will allow us to make more accurate assessments about where the optical lightning emissions are coming from and how they’re being transmitted through the clouds.”

Mary Caperton Morton is a freelance science writer. 

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Lightning ‘superbolts’ form over oceans from November to February

Tue, 09/10/2019 - 19:00

By Hannah Hickey

The lightning season in the Southeastern U.S. is almost finished for this year, but the peak season for the most powerful strokes of lightning won’t begin until November, according to a newly published global survey of these rare events.

The new study maps the location and timing of “superbolts” — bolts that release electrical energy of more than 1 million Joules, or a thousand times more energy than the average lightning bolt, in the very low frequency range in which lightning is most active. Results show that superbolts tend to hit the Earth in a fundamentally different pattern from regular lightning, for reasons that are not yet fully understood.

The study was published Sept. 9 in the Journal of Geophysical Research: Atmospheres, a journal of the American Geophysical Union.

This map shows the frequency of lightning strikes of all sizes measured by the World Wide Lightning Location Network, with pink being the highest values. Lightning occurs most often over land, with a few so-called “lightning chimneys” that include the Southeastern U.S. and the islands of Southeast Asia. Credit: World Wide Lightning Location Network

“It’s very unexpected and unusual where and when the very big strokes occur,” said lead author Robert Holzworth, a University of Washington (UW) professor of Earth and space sciences who has been tracking lightning for almost two decades.

Holzworth manages the World Wide Lightning Location Network, a UW-managed research consortium that operates about 100 lightning detection stations around the world, from Antarctica to northern Finland. By seeing precisely when lightning reaches three or more different stations, the network can compare the readings to determine a lightning bolt’s size and location.

The network has operated since the early 2000s. For the new study, the researchers looked at 2 billion lightning strokes recorded between 2010 and 2018. Some 8,000 events — four millionths of a percent, or one in 250,000 strokes — were confirmed superbolts.

“Until the last couple of years, we didn’t have enough data to do this kind of study,” Holzworth said.

The dots represent superbolts, lightning with an energy of at least 1 million Joules. Red dots are particularly large superbolts, with an energy of more than 2 million Joules. Superbolts are most common in the northeast Atlantic and the Mediterranean Sea, with smaller concentrations in the Andes, off the coast of Japan, and near South Africa. Credit: Holzworth et al./Journal of Geophysical Research: Atmospheres

The authors compared their network’s data against lightning observations from the Maryland-based company Earth Networks and from the New Zealand MetService.

The new paper shows that superbolts are most common in the Mediterranean Sea, the northeast Atlantic and over the Andes, with lesser hotspots east of Japan, in the tropical oceans and off the tip of South Africa. Unlike regular lightning, the superbolts tend to strike over water.

“Ninety percent of lightning strikes occur over land,” Holzworth said. “But superbolts happen mostly over the water going right up to the coast. In fact, in the northeast Atlantic Ocean you can see Spain and England’s coasts nicely outlined in the maps of superbolt distribution.”

“The average stroke energy over water is greater than the average stroke energy over land — we knew that,” Holzworth said. “But that’s for the typical energy levels. We were not expecting this dramatic difference.”

Robert Holzworth stands with a test lightning sensor on the roof of a UW building. The pipe contains an antenna that detects the electrical frequencies generated by lightning. Seattle’s actual detector is on the roof of a neighboring building. Credit: Dennis Wise/University of Washington

The time of year for superbolts also doesn’t follow the rules for typical lightning. Regular lightning hits in the summertime — the three major so-called “lightning chimneys” for regular bolts coincide with summer thunderstorms over the Americas, sub-Saharan Africa and Southeast Asia. But superbolts, which are more common in the Northern Hemisphere, strike both hemispheres between the months of November and February.

The reason for the pattern is still mysterious. Some years have many more superbolts than others: late 2013 was an all-time high, and late 2014 was the next highest, with other years having far fewer events.

“We think it could be related to sunspots or cosmic rays, but we’re leaving that as stimulation for future research,” Holzworth said. “For now, we are showing that this previously unknown pattern exists.”

Co-authors of the new study are Michael McCarthy, Abram Jacobson, James Brundell and Craig Rodger. 

Hannah Hickey is a science writer for the University of Washington News. 

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New research provides better look at ocean plate under Central America

Fri, 09/06/2019 - 19:00

By Anselme F.E. Borgeaud, Kenji Kawai and Robert J. Geller

Convection in Earth’s mantle is the “engine” driving plate tectonics. Hot material rises to the Earth’s surface from the boundary between the planet’s core and mantle, at a depth of about 3000 kilometers. Cold material then flows downward due to oceanic tectonic plates sinking into the mantle at subduction zones on the Earth’s surface.

Seismologists have long sought to understand this convection cycle by imaging subducting slabs as they descend into Earth’s depths at oceanic trenches. To do this they have used a technique called seismic tomography, which is similar to a medical ultrasound scan.

A new study in AGU’s Journal of Geophysical Research: Solid Earth, used a new, higher resolution, tomographic technique called waveform inversion to image the oceanic plate subducting beneath Central America, the Cocos plate. This allowed resolution of finer details than previous work.

The new findings contribute to improving our understanding of the dynamics of slabs as they reach the bottom of the upper mantle at a depth of about 670 kilometers below the Earth’s surface and help scientists better understand the convection cycle driving plate tectonics.

The new study used records of S-wave (seismic shear wave) triplications from earthquakes in Central America recorded at the USArray, a large array of seismic receivers deployed from 2004 to 2015 in the contiguous US. Waveform triplications occur when several S-waves that travel along slightly different paths arrive at an observatory at almost the same time. The complex waveforms are difficult to interpret using traditional travel-time tomography, but can be readily analyzed by waveform inversion to extract all available information on the structure around depths of 670 kilometers.

Central America is a geologically interesting region because of the large variations in the age of the Cocos plate at the trench, from about 2 million years old to the north, at about the latitude of Mexico City, to about 30 million years old to the south, at about the latitude of Costa Rica, with an age jump of about 10 million years across a past fracture zone called the Tehuantepec Ridge beneath southern Mexico.

Ocean floor ages for the Cocos plate (and other plates in the Pacific) subducting beneath the North-America and Caribbean plates. Location of the Tehuantepec Ridge is shown by the purple dashed curve.

Oceanic plates at the Earth’s surface cool with increasing age, which means that older plates are both denser and have higher viscosity when they enter the oceanic trench; they thus can sink more easily into the mantle than younger plates. The 3-D S-velocity model obtained by this study shows that variations in the age of the plate along the trench correlate well with variations in the shape of the slab at depth, suggesting that there are local variations in density and viscosity of the Cocos slab at depth due to variations in age.

The study also identified the presence of a possible upwelling of warm material, called a “plume,” rising from the lower mantle beneath the northern part of the Cocos slab, which could also affect how the Cocos slab sinks into the upper mantle.

Left: Vertical sections through the inferred tomographic images showing significant deformation of the Cocos slab to the north (blue region in top panel), but not to the south (bottom panel). Right: Map view of structure from 370-410 km depth, showing a possible tear in the Cocos slab. (Note: Velocities are relative to the average global velocity at each depth.)

Furthermore, the inferred images reveal that the Cocos slab possibly tears at a depth of about 400 kilometers along the Tehuantepec Ridge. This might be explained by the difference in density of the Cocos slab north and south of the Tehuantepec Ridge, and by the fact that the Tehuantepec Ridge is probably a weak zone in the slab, which should facilitate tearing. Comparison with surface geological evidence also indicates that this tear occurred about 10 million years ago, which implies an average sinking rate of slabs in the upper mantle of about 4 centimeters per year. This can be used to place constraints on the viscosity of the upper mantle in this region.

Previous studies have shown large regional variability in the dynamics of slabs as they reach the bottom of the upper mantle. In the near future, it should be possible to apply the methods of this study to other subduction zones in order to better understand the physical causes behind the variability of subduction.

Anselme F.E. Borgeaud, Kenji Kawai and Robert J. Geller are associated with the Department of Earth and Planetary Science, School of Science, University of Tokyo, Tokyo, Japan. Borgeaud is currently at the Institute of Earth Sciences, Academia Sinica, Taipei, Taiwan. They are the authors of the research being reported.

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Making sense of Saturn’s impossible rotation

Thu, 09/05/2019 - 18:08

By Larry O’Hanlon

Saturn may be doing a little electromagnetic shimmy and twist which has been throwing off attempts by scientists to determine how long it takes for the planet to rotate on its axis, according to a new study.

Discovering the length of a day on any planet seems like a straightforward task: Find some feature on the planet and clock it as it rotates around once. Or, if it’s a gas giant like Jupiter, which has no solid surface features, scientists can listen for periodic modulations in the intensity of radio signals created within the planet’s rotating magnetic field.

And then there is Saturn, which for decades has defied attempts to pin down out its exact rotation period. Now a new study in AGU’s Journal of Geophysical Research: Space Physics may have finally unveiled the gas giant’s trick for hiding its rotation, and provide the key to giving up its secret.

The new research shows how seasonal changes on Saturn may be confusing attempts by scientists to calculate its exact rotation period.

A planet’s rotation period is one of the fundamental facts about a planet, along with its size, composition, orbital period and other facts that not only describe a planet but help to explain its behavior, history and even provides clues to its formation.

Saturn eclipses the Sun, as seen by the Cassini spacecraft. NASA

Coy Saturn
Saturn emits only low-frequency radio patterns that are blocked by Earth’s atmosphere, make it difficult to study Saturn’s rotation from the Earth’s surface. In contrast, Jupiter emits radio patterns at higher frequencies that allowed radio astronomers to work out its rotation period before the space age got well under way.

It wasn’t until spacecraft were sent to Saturn that scientists were able to collect data about its rotation. Voyagers 1 and 2 sent home the first hints of Saturn’s rotation in 1980 and 1981. They detected a modulation of radio intensity that suggested the planet rotated once every 10 hours and 40 minutes.

“So that was what was called the rotation period,” said Duane Pontius of Birmingham-Southern College in Alabama and a co-author of the new study.

When the Cassini spacecraft arrived at Saturn 23 years later to study the planet for 13 years, it found something astonishing.

“In about 2004 we saw the period had changed by 6 minutes, about 1 percent,” Pontius said.

But how does an entire planet change the speed of its rotation in 20 years? That’s the sort of change that takes hundreds of millions of years. Even more mysterious was Cassini’s detection of electromagnetic patterns that suggested the planet’s rotation is different in the northern and southern hemispheres.

“For a long time, I assumed there was something wrong with the data interpretation,” Pontius recalled. “It’s just not possible.”

Seasons of Saturn
To find out what was really going on, Pontius and his co-authors started by looking at how Saturn is different from its closest sibling, Jupiter.

A mechanical analog model of what might be happening with the northern and southern hemispheres of Saturn’s atmosphere and magnetospheric plasma to create misleading signals of how fast the planet is rotating. The “brake” is the slowing of plasma as it flies further from the planet, in the same way a spinning dancer’s arms move slower when they are outstretched than when they are held close to the body. From E. L. Brooks, et al, 2019, JGR: Space Physics.

“What does Saturn have that Jupiter lacks, beside the obvious rings?” Pontius asked. The answer: seasons. Saturn’s axis is tilted about 27 degrees, similar to Earth’s 23-degree tilt. Jupiter has barely any tilt at all – just 3 degrees.

The tilt means the northern and southern hemispheres of Saturn receive different amounts of radiation from the Sun depending on the season. The different doses of ultraviolet light affect the stripped-down atoms – called plasma – at the edge of Saturn’s atmosphere.

According to the model being proposed by Pontius and his colleagues, the variations in UV from summer to winter in the different hemispheres affects the plasma so that it creates more or less drag at the altitudes where it encounters the planet’s gaseous atmosphere.

That difference in drag makes the atmosphere slow down, which is what sets the period seen in the radio signals.
Change the plasma seasonally, and you change the period of the radio emissions, which is what is seen on Saturn.

The new model provides a solution to the puzzle of Saturn’s impossible changing rotation periods. It also shows that the observed periods are not the rotation period of Saturn’s core, which remains unmeasured.

Pontius presented the model earlier this year at a meeting of Saturn scientists and said it was well received. Now he hopes that other researchers will take the next step to refine the model by exploring how well it fits with 13 years of Saturn data collected by Cassini.

Larry O’Hanlon (@earth2larryo) is a freelance science writer and manages the AGU Blogosphere. 

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Mercury’s ancient magnetic field likely evolved over time

Tue, 09/03/2019 - 14:00

By Abigail Eisenstadt

Mercury’s ancient magnetic poles were far from the location of its poles today, implying its magnetic field, like Earth’s, changed over time, a new study says.

Some planets have metallic liquid cores. Scientists generally believe a planet’s magnetic field comes from its metallic core’s fluid motions. The magnetic field creates a magnetosphere that surrounds the planet. Earth’s magnetosphere blocks a lot of cosmic and solar radiation, allowing life to exist.

Mercury is the other body in the Solar System besides Earth with a confirmed molten core able to generate a magnetic field.

A color-enhanced image of Mercury’s terrain taken by MESSENGER. Credit: NASA / JHU Applied Physics Lab / Carnegie Inst. Washington

New research published in the AGU’s Journal of Geophysical Research: Planets finds Mercury’s ancient magnetic poles, called paleopoles, have shifted throughout its past. The new study also suggests Mercury’s magnetic legacy may be more complicated than previously thought.

Studying other planets’ magnetic fields helps scientists understand how magnetic fields evolve, including on Earth. Observing other metallic cores’ behavior helps scientists understand more about the initial formation and subsequent maturation of planets in the Solar System.

Scientists know Mercury evolved over time but cannot definitively say how it did, said Joana S. Oliveira, an astrophysicist at the European Space Agency’s European Space Research and Technology Centre in Noordwijk, the Netherlands, and lead author of the study.

Magnetic turmoil in the Solar System
Changes in the magnetic field are not specific to Mercury. Earth’s magnetic North Pole drifts roughly 55 to 60 kilometers (34 to 37 miles) per year while its magnetic South Pole drifts roughly 10 to 15 kilometers (six to nine miles). Its magnetic field orientation has flipped more than 100 times in the course of its 4.5 billion years.

Scientists use rocks to study how planets’ magnetic fields evolve. Igneous rocks, created from cooling lava, can preserve a record of how the magnetic field looked at the time the rocks cooled assuming they held magnetic materials. The rocks’ cooling magnetic material aligns with the core’s field. This process is called thermoremanent magnetization. Geologists analyzed igneous rocks to determine Earth’s last magnetic field flip was roughly 780,000 years ago.

Earth and the Moon are the only case studies scientists have for changes in planetary bodies’ magnetic poles, because there are no rock samples from other planets.

“If we want to find clues from the past, doing a kind of archaeology of the magnetic field, then the rocks need to be thermoremanent magnetized,” Oliveira said.

MESSENGER’s descent trajectory across the surface of Mercury, with crater locations circled in white. Credit: AGU

Using planetary archaeology to uncover Mercury’s magnetic history
Past research studied Mercury’s present-day magnetic field, but there was no way to study the crustal magnetic field without low-altitude observations. Then in 2015, the spacecraft MESSENGER began its descent into Mercury’s surface. It collected three months of low-altitude information about Mercury during its descent. Some of that information revealed details about Mercury’s crustal magnetization. The new study examined these different crustal regions to extrapolate Mercury’s ancient core magnetic structure.

“There are several evolution models of the planet, but no one has used the crustal magnetic field to obtain the planet’s evolution,” Oliveira said.

MESSENGER’s low-altitude data from its descent path detected ancient craters with different magnetic signatures than most of the terrain MESSENGER observed. The researchers believed the craters, which were formed roughly 4.1 to 3.8 billion years ago, might hold clues about Mercury’s paleopoles.

Craters are more likely to have thermoremanent magnetized rocks. During their formation, the energy from an impact causes the ground to become molten, giving magnetic material a chance to realign with the planet’s current magnetic field. As that material solidifies, it preserves the direction and position of the planet’s magnetic field like a snapshot in time.

Oliveira and her colleagues used spacecraft observations from five craters with magnetic irregularities. They suspected those craters were formed during a time with a different magnetic field orientation than that of today. They modeled Mercury’s ancient magnetic field based on the crater data to estimate the potential locations for Mercury’s paleopoles. The area MESSENGER passed over and recorded during its demise was limited, so scientists could only use inflight measurements from part of the Northern Hemisphere.

Paleopole surprises
The researchers found Mercury’s ancient magnetic poles were far from the planet’s current geographic South Pole and could have changed throughout time, which was unexpected. They expected the poles to be clustering at two points closer to Mercury’s rotational axis at the geographic north and south of the planet. However, the poles were randomly distributed and were all found in the Southern Hemisphere.

The paleopoles do not align with Mercury’s current magnetic North pole or geographic South, indicating the planet’s dipolar magnetic field has moved. The results reinforce the theory that Mercury’s magnetic evolution was very unlike Earth’s or even other planets in the Solar System. They also suggest the planet may have shifted along its axis, in an event called a true polar wander where the geographic locations of the North and South Poles change.

Earth has a dipolar field with two poles, but Mercury has a dipolar-quadrupolar one with two poles and a shift in the magnetic equator. Its ancient magnetic field could have looked like either of these, or even been multipolar with “field lines like spaghetti,” according to Oliveira. There is no way to tell without multiple physical rock samples from Mercury, she said.

Oliveira hopes the new Mercury mission, BepiColombo, will gather more magnetic field data and potentially narrow the study’s conclusions.

Abigail Eisenstadt is a science writing intern at AGU. Follow her on twitter @aeisenstadt1

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Researchers find new ways for coral reef ecosystems to grow

Thu, 08/29/2019 - 14:21

By Keith Randall

For the first time, a team of scientists have found that microscopic organisms from the open ocean are helping coral reef grow. The discovery underscores the vulnerability of reefs and their  importance as indicators of the health of the open ocean in a changing climate.

The researchers examined Hawaii’s Kāneʻohe Bay barrier reef and microscopic particles called particulate organic matter, or POM, which includes phytoplankton. Their results suggest that POM from the open ocean helps provide energy for a coral reef ecosystem to grow.

“An important distinction that we make in this paper is that we are looking at ’oceanic POM’ that comes from offshore and is brought onto the reef by currents and waves,” said Kathryn Shamberger, an assistant oceanography professor at Texas A&M and coauther of a study appearing in the AGU journal Geophysical Research Letters

Aerial view of Kualoa Point and Chinamans Hat at Kaneohe Bay, Oahu, Hawaii. Getty Images

“Coral reef organisms make a lot of POM that the reef feeds on, and it has been known for a long time that feeding on ‘reef POM’ is important for keeping the reef ecosystem healthy,” Shamberger said. “More recent studies have shown that coral reefs also feed on ‘oceanic POM’ and what is new here is that our results show this external food source might be helping the reef grow. We used carbon isotopes to distinguish between oceanic POM and reef POM.”

Calcification is the process by which marine organisms make calcium carbonate skeletons and shells. Calcification (mainly by corals and coralline algae) is what builds the three-dimensional structures of coral reefs that provide the habitat for the entire ecosystem.

“Coral reefs are constantly being eroded and broken down by waves, currents and reef organisms,” Shamberger said. “The reef has to calcify fast enough to maintain the reef structure under all of these destructive processes, so faster calcification can be beneficial for the ecosystem.”

In many areas of the ocean, the calcification of corals and other organisms creates reefs that protect coastal communities, produce attractive white sand beaches, and create habitats for thousands of species that live on coral reefs.

Coral reefs often serve as an indicator of healthy ocean conditions. Studies show that even though they cover less than 1 percent of the ocean, coral reefs are one of the most diverse ecosystems on the planet and are home to at least one-fourth of all marine life.

The more oceanic POM that is supplied to the reef, the more food the reef has to consume, and the more it calcifies, said Andrea Kealoha, currently of the University of Hawaii-Maui, and lead author of the paper. 

“A couple studies have hypothesized that this is the case, and when we feed corals POM in the lab, they calcify more. However, our work is the first study to show this is happening in the field,” Keahola said.

Shamberger said that previous studies have shown that climate change is an important factor in the decline of coral reefs.

The studies show that climate change is already harming coral reefs, especially through ocean warming, but also from other climate change effects including ocean acidification and storm intensification, she said.

“Another effect on the ocean is that climate change is making the surface waters in parts of the open ocean less productive. Fewer nutrients are making it to the surface of the open ocean, and this means fewer phytoplankton are able to grow. Since phytoplankton are the base of the food web in the ocean, fewer of them means fewer of everything else, from other plankton to fish, etc., Shamberger said.

Shamberger said the study shows that coral reefs may also need phytoplankton from the open ocean (oceanic POM) to calcify and grow fast enough to maintain the reef structure and thus, the entire ecosystem. She said it proves that “climate change causing a decrease in open ocean productivity could also result in slowing coral reef growth, adding to the many stressors coral reefs are under. Alternatively, coral reefs that have a plentiful supply of oceanic POM may be able to maintain their growth better under climate change stressors.”

Shamberger also noted that the big picture of the study is twofold: First, to understand the sensitivity of coral reefs to climate change, researchers have to study the nearby open ocean in addition to coral reef waters; and second, the results may help coral reef researchers identify reefs that are particularly sensitive or resilient to climate change, which could help prioritize the resilient reefs for other types of conservation, for example, reducing fishing pressure and land-based pollution.

“Less oceanic POM means less food supplied to the reef, and coral reef growth may decline. However, our results also suggest that oceanic POM may help reefs continue to calcify and grow, even under stressors like ocean acidification,” Kealoha said.

The original version of this post was posted on the Texas A&M website. It was adapted and shared with permission.  

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Upper Nile will experience more water scarcity due to hotter, drier periods

Wed, 08/28/2019 - 13:00

By Joshua Rapp Learn

An increase in hotter, drier years in the coming decades due to climate change may worsen water scarcity issues in the Upper Nile Basin, according to new research.

These impacts are likely to cause an increase in agricultural failure in Ethiopia and may potentially lead to civil strife, according to the authors of a new study published in Earth’s Future, a journal of the American Geophysical Union.

Hippos (those round rock-like objects in the center) and Nile monitor lizards at the source of the Blue Nile by Lake Tana in Bahir Dar, Ethiopia. Credit: Joshua Learn

Richard Clark/Dartmouth College. Nile River map credit is: Jacques Descloitres, NASA/GSFC

“This region is already on the verge of water scarcity,” said Ethan Coffel, a post-doctoral researcher in geography and earth sciences at Dartmouth College in Hanover, New Hampshire, and the lead author of the new study. He added that the region’s population is also growing rapidly, adding to the potential for problems down the road.

Climate models generally agree that rainfall will increase by roughly 10 percent by 2080 in the regions around the upper branches of the Nile River. As a result, some have predicted water scarcity, or water availability per capita, will decrease in the area in coming decades.

But Coffel and his co-authors looked deeper at the models and found that while rainfall will increase on average, projections show years experiencing year-long average temperatures hotter than 22 degrees Celsius (71.6 degrees Fahrenheit) and below about 106 millimeters (4.2 inches) of rain per year will double or triple in frequency by 2080. Such high average temperatures currently only occurs one of every five years in the area.

What this means in practice is that the rainier years will experience more rain, but the dry, hot years will be drier and hotter.

Lake Tana, the source of the Blue Nile. Credit: Joshua Learn

“You just get more extremes. You’ll get more floods and you’ll also get more droughts,” Coffel said.

Beyond just predicting hot and dry periods, the scientists wanted to see what the human impacts of future climate change will be. Since most of the region’s agriculture is rain-fed, years experiencing less precipitation will experience more water scarcity, especially when combined with higher numbers of people. Coffel said the population in the area is projected to double by 2100.

Less rain means also means higher crop variability and a higher chance of crop failure, Coffel said.

The researchers looked at periods of past crop yields in Ethiopia, the country for which they had the longest dataset, and correlated them with dry and hot periods. They found nearly every year with bad crop yields was hot and dry.

A bridge over the Blue Nile in Ethiopia. Credit: Joshua Learn

While there may have been other reasons than just the weather responsible for bad crop yields, Coffel said the data shows a clear correlation.

Furthermore, while civil strife can result in crop failure, Coffel pointed out agricultural shortages can also lead to political problems.

“Agricultural failure drives societal changes that may encourage conflicts,” he said.

The way projected population increases will affect and be affected by future water scarcity still has a lot of uncertainties, Coffel said, since water scarcity could be a limiting factor on population increases. While the agricultural data they looked at was only long enough to analyze in Ethiopia, Coffel said these problems are likely to ring true in other countries in the upper Nile like Uganda and South Sudan.

The projected changes may also affect international relations, since countries downriver on the Nile like Egypt already have disputes with Ethiopia over dam construction and water usage.

“If you have increased water scarcity in the region in general, everybody will be more inclined to try to keep as much as they can,” Coffel said.’

The fabled carwash at the source of the Blue Nile. Credit: Joshua Learn

Joshua Rapp Learn (@JoshuaLearn1) is a freelance science writer.

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Streaks in Aurora Found to Map Features in Earth’s Radiation Environment

Tue, 08/27/2019 - 20:45

By Mara Johnson-Groh

A special kind of streaked aurora has been found to track disturbances in near-Earth space from the ground. Known as structured diffuse aurora, it was recently discovered, with the help of NASA spacecraft and instruments, that these faint lights in the night sky can map the edges of the Van Allen radiation belts — hazardous concentric bands of charged particles encircling Earth.

When the Van Allen belts undulate in shape and size — which they do in response to incoming radiation from the Sun as well as changes from Earth below — they can envelop satellites in unexpected radiation. The new discovery, reported in the AGU journal Geophysical Research Letters, will help us better track the edges of the belts — and the more we know about how the belts are changing, the more we can mitigate such effects.

 

 

A white light camera at Poker Flat shows the structured diffuse aurora, that mark the edge of the Van Allen radiation belt as it dances across the night sky. Using a combination of instruments and spacecraft, scientists were able to determine where the electrons causing the aurora had originated. Credits: NASA/Nithin Sivadas

The road to linking these auroras to the Van Allen belts began with a blob seen in radar data.

Scientists spotted the unexpected blob, caused by an excess of electrons, in radar data from Poker Flat, a research facility and rocket range in Alaska – and they set out to find its origin. Using a group of instruments — including NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, NOAA-17 (a low-Earth orbit spacecraft), and radar and optical instruments on the ground at Poker Flat — the scientists were able to track back to the electrons’ source.

 

An unexpected blob, circled in green, seen in radar data from Poker Flat sparked the research leading to the discovery of the structured diffuse aurora as maps of the edge of the outer Van Allen belt. Credits: NASA/Nithin Sivadas

They did this by looking at the energies of the electrons. Electrons coming from the outer Van Allen belt have high energies that decrease farther away from Earth. The scientists worked out where these electrons had been by mapping their trajectories and working backwards. Measurements from the NOAA-17 satellite along the trajectory confirmed that the streaked aurora, which was visible during the blob event, ultimately maps to the edge of the outer Van Allen belt.

 

This illustration shows the white-light observations of the fine structure in the aurora superimposed over Alaska. The dots signifying electrons are color coded to show their origins, with red dots indicating electrons from the radiation belts and blue from further out. Credits: NASA/Google Earth/Nithin Sivadas

The scientists found the electrons had been knocked loose from the outer Van Allen belts as Earth’s magnetic environment was squeezed before the onset of what’s known as a substorm — a space weather event on the night side of Earth triggered by an onslaught of charged particles from the Sun. Eventually, the electrons made their way down into the atmosphere, where they manifested as streaks in the aurora.

 

his schematic of the Van Allen belts’ structure, shows the region of the structured diffuse aurora and the outer edge of the Van Allen belts that it maps. Credits: NASA’s Goddard Space Flight Center/ Historic image of Van Allen Belts courtesy of NASA’s Langley Research Center/ Nithin Sivadas

Scientists will now be able to watch structured diffuse aurora from the ground in real-time to better understand how the edge of the outer Van Allen belt is changing — something that previously could only be done intermittently by waiting for a spacecraft to fly under the belt.

This post was originally published at the NASA’s Goddard Space Flight Center website

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Cluster and XMM-Newton pave the way for SMILE

Tue, 08/27/2019 - 14:45

A joint European-Chinese spacecraft, SMILE is currently scheduled for launch in 2023. It will be placed in a highly inclined, elliptical orbit around Earth, which will take it as far as 120 000 km from our planet.

Cluster and XMM-Newton observing Earth’s magnetosphere. Credit: ESA/ATG medialab

One of its primary objectives will be to observe the Sun-Earth connection, particularly the interactions on Earth’s dayside between the solar wind – a flow of charged particles streaming from the Sun into interplanetary space – and the magnetosphere of our planet.

The magnetosphere is an invisible magnetic bubble that shields the planet from the non-stop, but variable, bombardment of solar particles – mainly protons and electrons.

Science with SMILE. Credit: ESA/ATG medialab

SMILE will carry four instruments to observe this ever-changing celestial battlefield: a light ion analyser, a magnetometer, a soft X-ray imager, and an ultraviolet aurora imager.

 

The soft X-ray imager, which is designed to detect and image low energy X-rays, will observe the outer regions of Earth’s magnetosphere for up to 40 hours per orbit.

These regions include the magnetosheath, which lies behind the bow shock, where the flow of solar wind particles is dramatically slowed down, and the magnetopause, which is the outer boundary of Earth’s magnetosphere.

Of particular interest to scientists who are preparing for the SMILE mission is the density of neutral hydrogen atoms near the magnetopause. This is where the signal at low-energy X-rays, or soft X-ray signal, is expected to reach its peak.

ROSAT all-sky X-ray image at 0.25 keV. Credit: Max-Planck-Institut für extraterrestrische Physik (MPE) and S. L. Snowden

The X-rays are generated when highly charged particles from the solar wind collide with hydrogen atoms in Earth’s magnetic environment – a process known as solar wind charge exchange. When the hydrogen density and solar wind flux are higher than average, the result is a stronger emission of soft X-rays. At such times, SMILE will be able to provide frequent, high-resolution X-ray images and movies of the interaction region.

The resulting images – the first of their kind – will help scientists understand the large-scale interactions between the outer magnetosphere of our planet and the solar wind. By searching for the soft X-ray peak, SMILE will trace the motion of the magnetopause and reveal some of the secrets of how magnetic field lines snap and reconnect on a global scale.

XMM-Newton looking though Earth’s magnetosheath. Credit: Courtesy J. A. Carter

In order to improve our understanding of what happens when the solar wind charge exchange process occurs, scientists in Europe, China and the United States are utilising data from satellites such as ESA’s XMM-Newton X-ray observatory and the Cluster quartet of satellites flying through Earth’s magnetosphere. The data enable them to study actual soft-X-ray measurements made in near-Earth space, and to simulate what SMILE is likely to observe.

In 2019, Hyunju Connor of University of Fairbanks, Alaska, USA, and Jennifer Carter, University of Leicester, UK, published a paper in the AGU journal JGR: Space Physics, in which they investigate neutral hydrogen density at distances from Earth of about 64 000 km – the average distance of the subsolar magnetopause – using XMM-Newton observations in soft X-rays.

XMM-Newton is an astrophysics observatory designed to study highly energetic phenomena across the cosmos, such as black holes and remnants of supernova explosions, which shine brightly in X-rays. The satellite follows a highly elliptical, 48-hour orbit around Earth.

While XMM-Newton’s targets lie well beyond our planet, the line of sight of its X-ray imagers may sometimes pass through Earth’s dayside magnetosheath, resulting in a diffuse soft X-ray emission in the foreground of the observation.

This emission is usually regarded as an unwanted contaminant by astrophysicists, but it provides an opportunity for plasma scientists, who have been analysing these data for many years, to investigate solar wind charge exchange events in the outer magnetosphere. These studies are now proving of value during preparations for the SMILE mission.

Joint Cluster and XMM-Newton observations. Credit: Courtesy H. K. Connor & J. A. Carter (2019)

In their paper, Connor and Carter examined 103 time-variable solar wind charge exchange emission events that astronomers had detected during nearly 9 years of XMM-Newton X-ray observations. Among the top 10 strongest events, they found two occurrences on 4 May 2003 and 16 October 2001 for which there were also magnetosheath data available from the Cluster spacecraft and the Japanese Geotail satellite, as well as solar wind data from NASA’s ACE and WIND spacecraft, part of the OMNI mission.

For these events, the scientists compared these in situ measurements with simulations generated using a computer model known as the Open Geospace Global Circulation Model, or OpenGCCM, which uses solar wind data as input. The in situ data were crucial to verify the validity of the model.

After confirming a good agreement between the modelled and observed density in the magnetosheath, the scientists were able to determine the density of neutral hydrogen particles near the magnetopause. They found that the estimated neutral density was high enough to produce strong soft X-ray signals, confirming that SMILE should provide exciting new images of the dynamic Sun-magnetosphere interaction.

The scientists are now carrying out statistical analysis on a wider sample of XMM-Newton data, in order to achieve a more comprehensive characterisation of dayside neutral hydrogen densities, taking into account variations in solar activity.

Meanwhile, another 2019 paper in JGR: Space Physics led by Tianran Sun of the National Space Science Centre in Beijing, China, presented simulations of the soft X-ray emission on the dayside magnetopause and the cusps under various solar wind conditions.

These simulations are helping to predict the behaviour of a wide range of phenomena relevant to SMILE’s soft X-ray imager observations, such as changes in the X-ray flux or in the magnetopause location, depending on the incoming solar wind flux. In parallel, these studies are also supporting the development of the methodology that will be used to reconstruct the 3D structure and location of the magnetopause from the 2D images that the SMILE soft X-ray imager will obtain.

REFERENCES

Connor, H.K., & Carter, J.A. (2019). Exospheric neutral hydrogen density at the nominal 10 RE subsolar point deduced from XMM-Newton X-ray observationsJ. Geophys. Res.: Space Phys., 124, 1612– 1624. https://doi.org/10.1029/2018JA026187

Sun, T.R., Wang, C., Sembay, S.F., Lopez, R.E., Escoubet, C.P., Branduardi-Raymont, G., et al. (2019). Soft X-ray imaging of the magnetosheath and cusps under different solar wind conditions: MHD simulationsJ. Geophys. Res.: Space Phys., 124, 2435–2450. https://doi.org/10.1029/2018JA026093

This post was originally published on the ESA website

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