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Correction to: The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

Wed, 07/17/2019 - 00:00

Correction to: Space Sci. Rev. (2019) 215: 29 https://doi.org/10.1007/s11214-019-0594-x

The article The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta, written by Groussin et al., was originally published electronically on the publisher’s internet portal (currently SpringerLink) on 2 May 2019 without open access. With the author(s)’ decision to opt for Open Choice the copyright of the article changed to © The Author(s) 2019 and the article is forthwith distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits use, duplication, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license and indicate if changes were made.

Coronal Mass Ejections over Solar Cycles 23 and 24

Mon, 07/01/2019 - 00:00
Abstract

We present a statistical analysis of solar coronal mass ejections (CMEs) based on 23 years of quasi-continuous observations with the LASCO coronagraph, thus covering two complete Solar Cycles (23 and 24). We make use of five catalogs, one manual (CDAW) and four automated (ARTEMIS, CACTus, SEEDS, and CORIMP), to characterize the temporal evolutions and distributions of their properties: occurrence and mass rates, waiting times, periodicities, angular width, latitude, speed, acceleration and kinetic energy. Our analysis points to inevitable discrepancies between catalogs due to the complex nature of CMEs and to the different techniques implemented to detect them, but also to large areas of convergence that are critically important to ascertain the reliability of the results. The temporal variations of these properties are compared to four indices/proxies of solar activity: the radio flux at 10.7 cm (F10.7), the international sunspot number (SSN), the sunspot area (SSA), and the total magnetic field (TMF), either globally or separately in the northern and southern hemispheres in the case of the last three. We investigate the association of CMEs with flares, erupting prominences, active regions and streamers. We find that the CME occurrence and mass rates globally track the indices/proxies of solar activity with no time lag, prominently the radio flux F10.7, but the linear relationships were different during the two solar cycles, implying that the CME rates were relatively larger during SC 24 than during SC 23. However, there exists a pronounced divergence of the CME rates in the northern hemisphere during SC 24 as these rates were substantially larger than predicted by the temporal variation of the sunspot number. The distribution of kinetic energy follows a log-normal law and that of angular width follows an exponential law implying that they are random and independent. The distribution of waiting time (WTD) has a long power-law tail extending from 3 to 100 hr with a power-law index which varies with the solar cycle, thus reflecting the temporal variability of the process of CME formation. There is very limited evidence for periodicities in the occurrence and mass rates of CMEs, a striking feature being the dichotomy between the two hemispheres. Rather weak correlations are present among the various CME parameters and particularly none between speed and acceleration. The association of CMEs with flares and erupting prominences involves only a few percents of the overall population of CMEs but the associated CMEs have distinctly larger mass, speed, kinetic energy and angular width. A more pronounced association is found with active regions but the overwhelming one is with streamers further confirmed by the similarity between the heliolatitudinal distribution of CMEs and that of the electron density reconstructed from time-dependent tomographic inversion. We find no evidence of bimodality in the distributions of physical parameters that would support the existence of two classes, particularly that based on speed and acceleration, the distributions thus favoring a continuum of properties. There exists an excess of narrows CMEs which however does not define a special class. These narrow CMEs are likely associated with the ubiquitous mini-filaments eruptions and with mini flux ropes originating from small magnetic bipoles, the disruption mechanisms being similar to those launching larger CMEs. This supports the concept that CMEs at large arise from closed-field coronal regions at both large and small scales.

In-Orbit Commissioning of Czech Nanosatellite VZLUSAT-1 for the QB50 Mission with a Demonstrator of a Miniaturised Lobster-Eye X-Ray Telescope and Radiation Shielding Composite Materials

Mon, 07/01/2019 - 00:00
Abstract

This paper presents the results of in-orbit commissioning of the first Czech technological CubeSat satellite of VZLUSAT-1. The 2U nanosatellite was designed and built during the 2013 to 2016 period. It was successfully launched into Low Earth Orbit of 505 km altitude on June 23, 2017 as part of international mission QB50 onboard a PSLV C38 launch vehicle. The satellite was developed in the Czech Republic by the Czech Aerospace Research Centre, in cooperation with Czech industrial partners and universities. The nanosatellite has three main payloads. The housing is made of a composite material which serves as a structural and radiation shielding material. A novel miniaturized X-Ray telescope with lobster-eye optics and an embedded Timepix detector represents the CubeSat’s scientific payload. The telescope has a wide field of view. VZLUSAT-1 also carries the FIPEX scientific instrument as part of the QB50 mission for measuring the molecular and atomic oxygen concentration in the upper atmosphere.

Correction to: Hard X-Ray/Soft Gamma-Ray Experiments and Missions: Overview and Prospects

Wed, 06/26/2019 - 00:00

Correction to: Space Sci. Rev. (2017) 212: 429–518 https://doi.org/10.1007/s11214-017-0426-9

This article was published with erroneous information in the last statement of the first paragraph on page 448. Please find in this document the correct paragraph that should regarded as the final version by the reader.

The Konus results were outstanding. Concerning GRBs, we wish to mention the important discovery, within single GRBs, of a time-resolved correlation between luminosity and peak energy (interpreted as bremsstrahlung temperature) of the EF(E) spectrum (Golenetskii et al. 1983), and the earliest evidence of an isotropic distribution of the GRB positions in the sky (Mazets et al. 1981; Mazets and Golenetskii 1988) (see Fig. 4). Other key results concern the discovery on 5 March 1979 of the first pulsating burst, later called Soft Gamma Ray Repeater (SGR), from the supernova remnant N49 in the Large Magellanic Cloud (Mazets et al. 1979b): SGR 0526-66. Konus detected a total of 16 recurrent bursts from this source (Golenetskii et al. 1984) and obtained the earliest detections of the famous SGR 1806-20 and SGR 1900+14 (Mazets et al. 1979a).

Experimenting with Mixtures of Water Ice and Dust as Analogues for Icy Planetary Material

Mon, 06/24/2019 - 00:00
Abstract

Due to its abundance and unique properties, water is a major actor in the formation and evolution of many planetary surfaces as well as a sensitive and reliable tracer of past geologic and climatic processes. Water ice is found in variable abundance at the surfaces of many Solar System objects, from the floor of permanently shadowed craters at the poles of Mercury to large fractions of the surfaces of several trans-Neptunian objects. With few exceptions, water is not found in pure form but associated to contaminants of various nature and concentration. These associations and the nature of the mixing and segregation processes that affect and control them are key for our understanding of some of the most important aspects of planetary evolution processes. The observation and characterization of water ice at the surface of Solar System objects is therefore among the primary scientific objectives of many space missions. The quantitative interpretation of remote sensing data in terms of surface composition and physical properties requires the use of complex physical models that rely on experimental data in two different ways. First, the models require as inputs the fundamental properties of the pure materials, such as the optical or dielectric constant. Second, the models can only be fully tested if their results are confronted to actual measurements performed on samples whose complexity comes close to the one encountered on natural planetary surfaces but which are nevertheless well-enough characterized to serve as reference. Such measurements are challenging as macroscopic ice-rich samples prepared as analogues of icy planetary surfaces tend to be unstable, the ice component being prone to metamorphism and phase change. The questions of the reproducibility of the samples and the relevance of the measurements are therefore critical. The Ice Laboratory at the University of Bern has been set up in 2010 to overcome some of these difficulties. We have developed protocols to prepare, store, handle and characterize various associations of ice with mineral and organics contaminants as analogues of different types of icy Solar System surfaces. The aims of this article are to present the context and background for our investigations, describe these protocols and associated hardware in a comprehensive way, provide quantitative characterization of the samples obtained using these protocols and summarize the main results obtained so far by experimenting with these samples. The current state and possible future evolutions of this project are then discussed in the context of the next generation of space missions to visit icy objects in the Solar System and longer term perspectives on future observations of protoplanetary discs and exoplanetary systems.

Surface Morphology of Comets and Associated Evolutionary Processes: A Review of Rosetta’s Observations of 67P/Churyumov–Gerasimenko

Wed, 06/12/2019 - 00:00
Abstract

Comets can be regarded as active planetary bodies because they display evidence for nearly all fundamental geological processes, which include impact cratering, tectonism, and erosion. Comets also display sublimation-driven outgassing, which is comparable to volcanism on larger planetary bodies in that it provides a conduit for delivering materials from the interior to the surface. However, in the domain of active geological bodies, comets occupy a special niche since their geologic activity is almost exclusively driven by externally supplied energy (i.e. solar energy) as opposed to an internal heat source, which makes them “seasonally-active” geological bodies. During their active phase approaching the Sun, comets also develop a transient atmosphere that interacts with the surface and contributes to its evolution, particularly by transporting materials across the surface. Variations in solar energy input on diurnal and seasonal scale cause buildup of thermal stresses within consolidated materials that lead to weathering through fracturing, and eventually mass-wasting. The commonly irregular shapes of comets also play a major role in their evolution by leading to (1) non-uniform gravitational forces that affect material movement across the surface, and (2) spatially heterogeneous outgassing patterns that affect the comet’s orbital dynamics and lead to tidal stresses that can further fracture the nucleus. In this chapter, we review the surface morphology of comet 67P/Churyumov–Gerasimenko as well as its seasonal evolution as viewed by Rosetta from August 2014 to September 2016, their link to various processes, and the forces that drive surface evolution.

Dimensionality, Coordinate System and Reference Frame for Analysis of In-Situ Space Plasma and Field Data

Tue, 05/28/2019 - 00:00
Abstract

In the analysis of in-situ space plasma and field data, an establishment of the coordinate system and the frame of reference, helps us greatly simplify a given problem and provides the framework that enables a clear understanding of physical processes by ordering the experimental data. For example, one of the most important tasks of space data analysis is to compare the data with simulations and theory, which is facilitated by an appropriate choice of coordinate system and reference frame. While in simulations and theoretical work the establishment of the coordinate system (generally based on the dimensionality or dimension number of the field quantities being studied) and the reference frame (normally moving with the structure of interest) is often straightforward, in space data analysis these are not defined a priori, and need to be deduced from an analysis of the data itself. Although various ways of building a dimensionality-based (D-based) coordinate system (i.e., one that takes account of the dimensionality, e.g., 1-D, 2-D, or 3-D, of the observed system/field), and a reference frame moving along with the structure have been used in space plasma data analysis for several decades, in recent years some noteworthy approaches have been proposed. In this paper, we will review the past and recent approaches in space data analysis for the determination of a structure’s dimensionality and the building of D-based coordinate system and a proper moving frame, from which one can directly compare with simulations and theory. Along with the determination of such coordinate systems and proper frame, the variant axis/normal of 1-D (or planar) structures, and the invariant axis of 2-D structures are determined and the proper frame velocity for moving structures is found. These are found either directly or indirectly through the definition of dimensionality. We therefore emphasize that the determination of dimensionality of a structure is crucial for choosing the most appropriate analysis approach, and failure to do so might lead to misinterpretation of the data. Ways of building various kinds of coordinate systems and reference frames are summarized and compared here, to provide a comprehensive understanding of these analysis tools. In addition, the method of building these systems and frames is shown not only to be useful in space data analysis, but also may have the potential ability for simulation/laboratory data analysis and some practical applications.

Titan as Revealed by the Cassini Radar

Tue, 05/21/2019 - 00:00
Abstract

Titan was a mostly unknown world prior to the Cassini spacecraft’s arrival in July 2004. We review the major scientific advances made by Cassini’s Titan Radar Mapper (RADAR) during 13 years of Cassini’s exploration of Saturn and its moons. RADAR measurements revealed Titan’s surface geology, observed lakes and seas of mostly liquid methane in the polar regions, measured the depth of several lakes and seas, detected temporal changes on its surface, and provided key evidence that Titan contains an interior ocean. As a result of the Cassini mission, Titan has gone from an uncharted world to one that exhibits a variety of Earth-like geologic processes and surface-atmosphere interactions. Titan has also joined the ranks of “ocean worlds” along with Enceladus and Europa, which are prime targets for astrobiological research.

Interplanetary Dust, Meteoroids, Meteors and Meteorites

Tue, 05/21/2019 - 00:00
Abstract

Interplanetary dust particles and meteoroids mostly originate from comets and asteroids. Understanding their distribution in the Solar system, their dynamical behavior and their properties, sheds light on the current state and the dynamical behavior of the Solar system. Dust particles can endanger Earth-orbiting satellites and deep-space probes, and a good understanding of the spatial density and velocity distribution of dust and meteoroids in the Solar system is important for designing proper spacecraft shielding. The study of interplanetary dust and meteoroids provides clues to the formation of the Solar system. Particles having formed 4.5 billion years ago can survive planetary accretion and those that survived until now did not evolve significantly since then. Meteoroids and interplanetary dust can be observed by measuring the intensity and polarization of the zodiacal light, by observing meteors entering the Earth’s atmosphere, by collecting them in the upper atmosphere, polar ices and snow, and by detecting them with in-situ detectors on space probes.

The GOES-16 Spacecraft Science Magnetometer

Thu, 05/16/2019 - 00:00
Abstract

Since their inception in the 1970s, the NOAA Geostationary Operational Environmental Satellite (GOES) system has monitored the sources of space weather on the sun and the effects of space weather at Earth. These observations are important for providing forecasts, warnings and alerts to many customers, including satellite operators, the power utilities, and NASA’s human activities in space. The GOES magnetometer provides observations of the geomagnetic field, which can be the first indication that significant space weather has reached Earth. In addition, the magnetic field observations are used to identify and forecast the severity of the space weather activity. This paper reviews the capabilities of the GOES-16 magnetometer (MAG) and presents initial post-launch calibration/validation results including issues found in the data. The GOES-16 MAG requirements and capabilities are similar to those for previously flown instruments, measuring three components of the geomagnetic field but with an improved sampling rate of 10 samples/second. The MAG data are low-pass filtered with a 2.5 Hz cutoff compared to the 0.5 Hz cutoff of previous GOES magnetometers. The MAG is composed of two magnetometers, an inboard (closer to spacecraft bus) and outboard (on tip of boom) magnetometer. Presented are the science and instrument requirements, ground and initial on-orbit instrument calibration and data validation. The on-orbit analysis found magnetic contamination along with temperature dependency effects that resulted in unexpected instrument noise and decreased accuracy, with the issues generally more significant on the inboard magnetometer. The outboard sensor was used for initial analysis of MAG performance. Preliminary comparison, excluding arcjet firing periods, between the outboard magnetometer and the GOES-14 magnetometer found a statistical difference of 5 nT at \(3\sigma \) for the total field. This comparison does not consider inaccuracies in the GOES-14 magnetometer. Future studies will focus on optimizing the outboard sensor performance.

Explosive Magnetotail Activity

Thu, 05/16/2019 - 00:00
Abstract

Modes and manifestations of the explosive activity in the Earth’s magnetotail, as well as its onset mechanisms and key pre-onset conditions are reviewed. Two mechanisms for the generation of the pre-onset current sheet are discussed, namely magnetic flux addition to the tail lobes, or other high-latitude perturbations, and magnetic flux evacuation from the near-Earth tail associated with dayside reconnection. Reconnection onset may require stretching and thinning of the sheet down to electron scales. It may also start in thicker sheets in regions with a tailward gradient of the equatorial magnetic field \(B_{z}\) ; in this case it begins as an ideal-MHD instability followed by the generation of bursty bulk flows and dipolarization fronts. Indeed, remote sensing and global MHD modeling show the formation of tail regions with increased \(B_{z}\) , prone to magnetic reconnection, ballooning/interchange and flapping instabilities. While interchange instability may also develop in such thicker sheets, it may grow more slowly compared to tearing and cause secondary reconnection locally in the dawn-dusk direction. Post-onset transients include bursty flows and dipolarization fronts, micro-instabilities of lower-hybrid-drift and whistler waves, as well as damped global flux tube oscillations in the near-Earth region. They convert the stretched tail magnetic field energy into bulk plasma acceleration and collisionless heating, excitation of a broad spectrum of plasma waves, and collisional dissipation in the ionosphere. Collisionless heating involves ion reflection from fronts, Fermi, betatron as well as other, non-adiabatic, mechanisms. Ionospheric manifestations of some of these magnetotail phenomena are discussed. Explosive plasma phenomena observed in the laboratory, the solar corona and solar wind are also discussed.

Local Manifestations of Cometary Activity

Thu, 05/02/2019 - 00:00
Abstract

Comets are made of volatile and refractory material and naturally experience various degrees of sublimation as they orbit around the Sun. This gas release, accompanied by dust, represents what is traditionally described as activity. Although the basic principles are well established, most details remain elusive, especially regarding the mechanisms by which dust is detached from the surface and subsequently accelerated by the gas flows surrounding the nucleus.

During its 2 years rendez-vous with comet 67P/Churyumov-Gerasimenko, ESA’s Rosetta has observed cometary activity with unprecedented details, in both the inbound and outbound legs of the comet’s orbit. This trove of data provides a solid ground on which new models of activity can be built. In this chapter, we review how activity manifests at close distance from the surface, establish a nomenclature for the different types of observed features, discuss how activity is at the same time transforming and being shaped by the topography, and finally address several potential mechanisms.

The Thermal, Mechanical, Structural, and Dielectric Properties of Cometary Nuclei After Rosetta

Thu, 05/02/2019 - 00:00
Abstract

The physical properties of cometary nuclei observed today relate to their complex history and help to constrain their formation and evolution. In this article, we review some of the main physical properties of cometary nuclei and focus in particular on the thermal, mechanical, structural and dielectric properties, emphasising the progress made during the Rosetta mission. Comets have a low density of \(480 \pm 220~\mbox{kg}\,\mbox{m}^{-3}\) and a low permittivity of 1.9–2.0, consistent with a high porosity of 70–80%, are weak with a very low global tensile strength \(<100\)  Pa, and have a low bulk thermal inertia of \(0\mbox{--}60~\mbox{J}\,\mbox{K}^{-1}\,\mbox{m}^{-2}\,\mbox{s}^{-1/2}\) that allowed them to preserve highly volatiles species (e.g. CO, CO2, CH4, N2) into their interior since their formation. As revealed by 67P/Churyumov-Gerasimenko, the above physical properties vary across the nucleus, spatially at its surface but also with depth. The broad picture is that the bulk of the nucleus consists of a weakly bonded, rather homogeneous material that preserved primordial properties under a thin shell of processed material, and possibly covered by a granular material; this cover might in places reach a thickness of several meters. The properties of the top layer (the first meter) are not representative of that of the bulk nucleus. More globally, strong nucleus heterogeneities at a scale of a few meters are ruled out on 67P’s small lobe.

The Modular Multispectral Imaging Array (MMIA) of the ASIM Payload on the International Space Station

Tue, 04/16/2019 - 00:00
Abstract

The Modular Multispectral Imaging Array (MMIA) is a suite of optical sensors mounted on an external platform of the European Space Agency’s Columbus Module on the International Space Station. The MMIA, together with the Modular X- and Gamma- ray Sensor (MXGS), are the two main instruments forming the Atmosphere-Space Interactions Monitor (ASIM). The primary scientific objectives of the ASIM mission are to study thunderstorm electrical activity such as lightning, Transient Luminous Emissions (TLEs) and Terrestrial Gamma-ray Flashes (TGFs) by observing the associated emissions in the UV, near-infrared, x- and gamma-ray spectral bands. The MMIA includes two cameras imaging in 337 nm and 777.4 nm, at up to 12 frames per second, and three high-speed photometers at 180–230 nm, 337 nm and 777.4 nm, sampling at rates up to 100 kHz. The paper describes the MMIA and the aspects that make it an essential tool for the study of thunderstorms. The mission architecture is described in Neubert et al. (Space Sci. Rev. 215:26, 2019, this issue) and the MXGS instruments in Østgaard et al. (Space Sci. Rev. 215:23, 2019, this issue).

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