bluuebunny/crossref_metadata_2025 huggingface dataset:
Linear unmixing of fine particulate materials: implications for compositional analyses of primitive asteroids
Authors: Lowry Vanessa , Donaldson Hanna Kerri , Campins Humberto , Bowles Neil , Hamilton Victoria
Published: October 2020

Linear least squares unmixing of infrared spectra is a fast and effective way to spectrally estimate the modal mineral abundances of laboratory samples and remotely-sensed surfaces to within 5% on average [e.g., 1]. This technique has been applied to spectra of whole rocks, coarse particulates, meteorites, and the Martian surface to successfully determine modal abundances [e.g., 1-3]. With the recent arrival of NASA’s OSIRIS-REx spacecraft to asteroid 101955 Bennu, the OSIRIS-REx Thermal Emission Spectrometer (OTES) has been providing a wealth of data to interpret using spectral unmixing techniques [e.g., 4].The assumption of linear spectral unmixing allows for the deconvolution of a mixed spectrum if the individual spectra and particle sizes of the pure end members are present within a spectral library. By implementing a weighted linear least squares (WLS) unmixing algorithm, one is able to deconvolve these mixed spectra into areal percentages of each endmember with the underlying assumption that this then corresponds to the volume percentages [e.g., 1-3]. At thermal infrared (TIR) wavelengths, end member spectra of coarse particulates combine linearly due to high absorption coefficients and relatively small mean optical paths, which limits most of the volumetric scattering [e.g., 1-3]. Linearity in the TIR region continues as particle size decreases until the wavelength of light approaches the particle size, at this point particles become optically thin and non-linear behavior (e.g., volumetric scattering) is observed. However, Ramsey and Christensen [1] demonstrated that when unmixing fine particulates (10 – 20 μm) with a spectral library of end members at the same particle size linear unmixing can still be used to estimate modal mineral abundances.In this study we investigate the effectiveness of a linear least squares unmixing approach to estimate mineral abundances for samples dominated by fine particulates (< 38 μm). We use a WLS algorithm and a spectral library of fine particulate pure minerals to unmix spectra of a suite of fine particulate, primitive asteroid analogs. Results from this investigation have implications for the interpretation of spectral observations of primitive asteroids that have a layer of fine particulate regolith.[1] Ramsey M. S. and Christensen P. R. (1998) JGR, 103, 577-596. [2] Hamilton V. E. and Christensen P. R. (2000) JGR, 105, 9717-9733. [3] Rogers A. D. and Aharonson O. (2008) JGR, 113,EO6S14. [4] Hamilton V. E. et al. (2019) Nature Astron., 3, 332-340.
Constraining planet formation around 6-8 M☉ stars
Authors: Veras Dimitri , Tremblay Pier-Emmanuel , Hermes James , McDonald Catriona , Kennedy Grant , Meru Farzana , Gänsicke Boris
Published: October 2020

Identifying planets around O-type and B-type stars is inherently difficult; the most massive known planet host has a mass of only about 3 M⊙ . However, planetary systems which survive the transformation of their host stars into white dwarfs can be detected via photospheric trace metals, circumstellar dusty and gaseous discs, and transits of planetary debris crossing our line of sight.
 
These signatures offer the potential to explore planet formation efficiency and chemical composition for host stars with masses up to the core-collapse boundary at ≈ 8 M⊙ , a mass regime rarely investigated in planet formation theory. Here, we establish limits on where both major and minor planets must reside around ≈ 6–8 M⊙ stars in order to survive into the white dwarf phase. For this mass range, we find that intact terrestrial or giant planets need to leave the main sequence beyond approximate minimum star–planet separations of, respectively, about 3 and 6 au, as shown here:

Further, in these systems, rubble pile minor planets of radii 10, 1.0, and 0.1 km would have been shorn apart by giant branch radiative YORP spin-up if they formed and remained within, respectively, tens, hundreds, and thousands of au, as shown here:

Overall, we find that planet formation around 6 M⊙-8 M⊙ stars may be feasible, and hence we encourage dedicated planet formation investigations for these systems.
Surveying the Trans-Neptunian Solar System with TESS
Authors: Rice Malena , Laughlin Greg
Published: October 2020

In recent years, the observed orbital geometry of extreme trans-Neptunian objects (TNOs) has provided tantalizing evidence predicting the existence of an as-yet undiscovered “Planet Nine.” Combined with orbit stability models, these observations permit a detailed prediction of Planet Nine's properties, with a shrinking parameter space as more of these rare objects are discovered. I will present the first results from a new survey utilizing light curve data from the Transiting Exoplanet Survey Satellite (TESS) to search for TNOs at distances 70-800 au, with a magnitude limit V~22. This survey leverages an innovative new pipeline designed to extract the locations, magnitudes, and 27-day orbital arcs of undiscovered outer solar system objects, including both Planet Nine and the population of extreme trans-Neptunian objects pertinent to the Planet Nine theory, using a blind shift-stacking search along all plausible outer solar system orbits. Together with the extensive sky coverage of the TESS survey, this search will place stringent constraints upon the as-yet undiscovered TNO population, with great potential to either discover Planet Nine or almost entirely rule out its existence.
Juno reveals new insights into Io-related decameter radio emissions
Authors: Martos Yasmina M , Imai Masafumi , Connerney John E.P. , Kotsiaros Stavros , Kurth William S.
Published: October 2020

The Juno spacecraft has been orbiting Jupiter since July 2016 providing stunning new information about the planet and its environment. The new magnetic field model, JRM09, with much improved accuracy near the planet, provides the basis for a better understanding of Io-related decametric radio emissions and implications for auroral processes. Here, we study Io-related DAM events observed by the Juno Waves instrument to estimate the beaming angle, the resonant electron energy and radio source location by forward modeling. The JRM09 magnetic field model is used to better constrain the location and observability of the radio emissions, and characterize the loss cone-driven electron cyclotron maser instability. We obtained good agreement between synthetic and observed arcs. The estimated beaming cone half-angles range from 33° to 85° and the obtained resonant electron energies are up to 23 times higher than previously proposed. Additionally, we quantitatively analyze the higher likelihood of observing groups of arcs originating in the northern hemisphere relative to those originating in the southern hemisphere. This is primarily a consequence of the asymmetry of the magnetic field geometry, observer location, and pitch angles of the electrons at the equator.  
Modeling the past and future activity of the Halleyids meteor showers
Authors: Egal Auriane , Brown Peter , Wiegert Paul , Campbell-Brown Margaret , Rendtel Jürgen , Vida Denis
Published: October 2020

We present a new numerical model of the Eta-Aquariid and Orionid meteor shower. Through the modelling of millions meteoroids released from comet 1P/Halley, we simulate the characteristics of each Eta-Aquariid and Orionid apparition between 1985 and 2050. The modelled showers activity duration, shape, maximum zenithal hourly rates (ZHR) values, and mass distributions are compared with several decades of meteor observations in the optical and radar range. Our simulations suggest that the age of the Eta-Aquariids shortly exceeds 5000 years, while the Orionids are composed of older material. Several Eta-Aquariid outbursts are expected in the future, in particular around 2023-2024 and 2045-2046. The evolution of 1P/Halley's meteoroid streams is strongly influenced by mean motion resonances with Jupiter, that might be responsible of a ~12 year cycle in the Orionids activity variations.
Using the effective recombination coefficient to constrain the positive ion composition in Saturn's ionosphere
Authors: Dreyer Joshua , Vigren Erik , Morooka Michiko , Wahlund Jan-Erik , Buchert Stephan , Waite J. Hunter
Published: October 2020

We combine RPWS/LP and INMS data from Cassini's Grand Finale orbits into Saturn's lower ionosphere to calculate the effective recombination coefficient α300 at a reference electron temperature of 300 K. Assuming photochemical equilibrium at altitudes below 2500 km and using an established method to determine the electron production rate, we derive upper limits for α300 of ∼ 2.5∗10-7 cm3 s-1, which suggest that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients.An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate coefficients > 5∗10-7 cm3 s-1 at an electron temperature of 300 K. The results do not give constraints on the nature of the negative ions.
Low-energy electrons in Saturn’s inner magnetosphere from the Cassini Langmuir Probe
Authors: Xystouris George , Arridge Christopher Stephen , Morooka Michiko , Wahlund Jan-Erik
Published: October 2020

It is known that Enceladus is one of the main mass sources in Saturn’s inner magnetosphere, with other bodies – e.g. Dione, Tethys, Saturn’s rings and atmosphere – thought to play a smaller role. In this study we analysed electron density and temperature as estimated from Cassini’s Langmuir Probe (LP) for the entire duration of the Cassini mission (August 2004 – September 2017).  The main motivation for this work is to understand the impact of Enceladus as a main mass source and search for evidence of additional sources.  We also have been investigating the impact of the spacecraft-plasma interaction, and illumination conditions on the LP current-voltage curves and henceforth on the bulk electron parameters.One particular facet of this work is the discrimination of spacecraft-generated photoelectrons in the current-voltage curves so that they can be excluded from further analysis of the ambient magnetospheric electrons.  To develop a robust algorithm to identify photoelectrons we have been working with data during transitions in and out of shadow caused by two main events: i) when the LP is shadowed by the spacecraft, or ii) during eclipses by Saturn or its moons.With a cleaned data set we focused on analysing data within 0.5RS of the Kronian in the inner magnetosphere (r
Search for Candidate Exogenous Material on Bennu using MapCam and PolyCam Images
Authors: Campins Humberto , Tatsumi Eri , Popescu Marcel , Rizos Juan , Simon Amy , Kaplan Hannah , deLeon Julia , Licandro Javier , DellaGiustina Daniella , Lauretta Dante
Published: October 2020

Introduction: Exogenous material has been reported on asteroids (101955) Bennu and (162173) Ryugu.  The albedo, color, and spectra of six bright boulders on Bennu show that they are distinct from the rest of Bennu’s comparatively dark surface and are likely basaltic material from asteroid (4) Vesta (DellaGiustina et al. 2019; 2020).  Bright boulders identified on asteroid (162173) Ryugu show absorptions near 1 µm but not near 2 µm, suggesting olivine-rich anhydrous silicates (Tatsumi et al., 2019; 2020).Methods: In this work, we used images of Bennu obtained by the MapCam and PolyCam instruments (Rizk et al. 2018; Golish et al. 2020) on NASA’s OSIRIS-REx spacecraft (Lauretta et al. 2017) to search for more potentially exogeneous material on the surface of Bennu.  Results: We identified approximately 50 bright boulders on Bennu with significant x-band (0.85 µm) absorptions, including the six bright boulders previously described in DellaGiustina et al. (2020).  These bright boulders are distributed across Bennu’s surface, concentrated in terrains with larger than average particle size.  The boulders exhibit three main morphologies (homogeneous, heterogenous, and breccia) and three spectral types (reflectance peak at 0.55 µm, flat, and reflectance peak at 0.7 µm). There is some correlation between the morphology and the spectra. More specifically, three of the four boulders with reflectance peaks at 0.55 µm are in the breccia category and one is in the heterogeneous category, whereas all the boulders with reflectance peaking at 0.7 µm fall in the homogeneous and heterogenous categories. Bright boulders with reflectance peaking at 0.55 µm have lower normal albedo than the other two spectral groups, suggesting a different composition and possibly a different origin. An initial comparison with Ryugu (Tatsumi et al. 2019) indicates that Bennu is more abundant in possible exogeneous material.  Discussion: Further analysis of MapCam and PolyCam images has revealed a wider diversity of potentially exogenous lithologies on Bennu, expanding on the findings of DellaGiustina et al. (2020).  We continue our study of this diversity of material on Bennu’s surface to constrain the asteroid’s origin, evolution, and collisional history (e.g., Ballouz et al. 2020).References: DellaGiustina D. et al. (2019) Nat. Astron. 3, 341-351. DellaGiustina D. et al. (2020) Nat. Astron, in revision. Lauretta D. S. et al. (2017) Space Sci. Rev. 212, 925–984. Tatsumi E. et al. (2019) LPI Contribution No. 2132, id.1753. Rizk B. et al. (2018) Space Sci. Rev. 214, 26. Golish D.R. et al. (2020) Space Sci. Rev. 216, 12. Ballouz R.-L. et al. 2020, EPSC abstract.
How much Io material reaches Europa?
Authors: Bagenal Fran , Dols Vincent , Nerney Edward , Crary Frank , Cassidy Tim
Published: October 2020

The plasma interaction with Io’s atmosphere results in at least a ton per second of escaping neutrals. Most of these neutrals supply extended neutral clouds along Io's orbit  and eventually become ionized and accelerated to corotation with Jupiter, populating the Io plasma torus as well as spreading out to fill Jupiter’s vast magnetosphere. About half to two-thirds of the plasma torus ions charge-exchange with the extended neutral clouds  and leave the torus as energetic neutral atoms, passing Europa’s orbit. Energetic neutrals are also produced directly in the plasma-atmosphere interaction, escaping with sufficient speed to reach Europa’s orbit before being ionized. The iogenic ions that are accelerated to high energies in the middle magnetosphere ultimately move back inward, again crossing Europa’s orbit. We present estimates of the fluxes of these various iogenic populations and how much oxygen, sulfur and sodium might be hitting Europa.
Sizes of Particles, Clumps, and Gaps Within the Strong Janus 2:1 and Mimas 5:3 Density Waves from Cassini UVIS Stellar Occultation Data Statistics
Authors: Eckert Stephanie , Colwell Joshua , Jerousek Richard , Esposito Larry
Published: October 2020

The high-speed photometer of Cassini’s Ultraviolet Imaging Spectrograph (UVIS) collected data from stellar occultations across Saturn’s rings at unprecedented high resolution over a wide range of viewing geometries. Because photon counts are described by Poisson statistics, we expect a variance equal to the mean in the absence of intervening ring material. However, most ring ‘particles’ are truly aggregates of smaller particles, ranging from micron-size dust to tens of meter-sized boulders, and if the sizes of these aggregates are not small relative to the field-of-view over a single integration period, they introduce excess variance from which we can glean further information about the sizes of particles and clumps. This is particularly relevant in the A ring, where non-axisymmetric self-gravity wakes are ubiquitous. Larger elongated clumps nicknamed straw have been directly imaged in the troughs of strong density waves (Porco et al., 2005, Science, 307, 1226-1236). In this work we present a survey of the statistical moments of variance and skewness for several ring stellar occultations at two strong density waves from different ring regions, Janus 2:1 and Mimas 5:3, over a variety of viewing angles. The line-of-sight distance from Cassini to the rings affects the measurement area due to the scattered signal and diffraction, and different viewing angles provide measurements of the same ring material with different aspects to potentially reveal the three-dimensional structure of clumps. We calculate an effective particle size per integration area, R, derived by Colwell et al., (2018, Icarus, 300, 150-166) and find similar values for R in both peaks and troughs across density waves as well as within density waves and in adjacent regions. We observe strong statistical similarity between troughs and regions adjoining the waves with overall higher skewness in the A ring, indicating more clumping and greater asymmetry in this region than in the inner B ring region.
The plasma/atmosphere interaction at Io: revisiting the ion/neutral charge-exchange cross-sections and their ion-velocity dependency
Authors: Dols Vincent , Johnson Robert , Bagenal Fran
Published: October 2020

The Io Torus plasma is mostly composed of singly and multi-charged S and O ions. These ions interact with the neutrals of Io’s atmosphere (S, O, SO2 and SO) through symmetrical (i.e. O+ + O => O + O+) and asymmetrical (i.e. S++ + O => S + O++) charge-exchanges. Charge-exchange cross-sections were estimated in Johnson & Strobel, 1982 and McGrath & Johnson, 1989 at 60 km/s (the plasma corotation velocity in Io’s frame), and are used in numerical simulations of the torus/neutral cloud interaction (i.e. Delamere and Bagenal, 2003).Dols et al., 2008 proposed numerical simulations of the multi-species chemistry interaction at Io using these cross-sections at 60 km/s. The plasma/atmosphere interaction at Io is strong and the flow velocity and ion temperature are drastically reduced close to Io (v < 10 km/s). Thus, velocity-dependent charge-exchange cross-sections are critical for such numerical simulations and their effect on the local plasma and neutral supply at Io should be explored.We propose to revisit the calculation of ion/neutral charge-exchange cross-sections following Johnson & Strobel, 1982’s approach for plasma velocities relevant to the local interaction at Io (V=10-120 km/s). More sophisticated calculations were proposed in McGrath & Johnson, 1989 but both publications offered very few details about their procedure.We will illustrate the effect of using velocity-depend charge-exchange cross-sections in numerical simulations of the multi-species plasma/atmosphere interaction at Io.More generally, this presentation aimed at providing an incentive for the community to expand the work of McGrath & Johnson, 1989. Johnson & Strobel, Charge-exchange in the Io torus and exosphere, JGR, 87,1982McGrath & Johnson, Charge exchange cross sections for the Io plasma torus, JGR, 94, 1989Delamere & Bagenal, Modeling variability of plasma conditions in the Io torus, JGR, 108, 2003Dols, Delamere, Bagenal, Kurth, Paterson, A multi-species chemistry model of Io’s local interaction with the plasma torus, JGR, 113, 2008
A Search for Solar Cycle Variability in the Nightside Ionosphere of Mars
Authors: Girazian Zachary , Halekas Jasper
Published: October 2020

The nightside ionosphere of Mars is mainly produced by a combination of electron impact ionization and day-to-night ion transport. The relative contribution of these two sources, and their variability over the solar cycle, has not been well established. To address this issue, we use Mars Atmosphere and Volatile EvolutioN (MAVEN) observations to search for cyclical variability in nightside ion densities over the solar cycle. We find that nightside densities (O+ in particular) were significantly higher during solar maximum (2014) than during solar minimum (2019). Our results suggest that, similar to the nightside ionosphere of Venus, day-to-night transport of O+ ions is more prominent during solar maximum.
ESCAPADE: Coordinated multipoint measurements of Mars' unique hybrid magnetosphere
Authors: Lillis Robert , Curry Shannon , Luhmann Janet , Ma Yingjuan , Barjatya Aroh , Whittlesey Phyllis , Livi Roberto , Larson Davin , Xu Shaosui , Russell Christopher , Fowler Christopher , Brain David , Thiemann Ed , Withers Paul , Modolo Ronan , Harada Yuki , Berthomier Matthieu
Published: October 2020

Multi-spacecraft missions after 2000 (Cluster II, THEMIS, Van Allen Probes, and MMS) have revolutionized our understanding of the causes, patterns and variability of a wide array of plasma phenomena in the terrestrial magnetospheric environment. ESCAPADE is a twin-spacecraft Mars mission concept that will similarly revolutionize our understanding of how solar wind momentum and energy flows throughout Mars’ magnetosphere to drive ion and sputtering escape, two processes which have helped shape Mars’ climate evolution over solar system history. ESCAPADE will measure magnetic field strength and topology, ion plasma distributions (separated into light and heavy masses), as well as suprathermal electron flows and thermal electron and ion densities, from coordinated elliptical, 200 km x ~7000 km orbits. ESCAPADE are small spacecraft (
A depletion of ammonia and water by storms in the deep atmosphere of Jupiter
Authors: Guillot Tristan , Stevenson David J , Bolton Scott J , Li Cheng , Atreya Sushil K , Becker Heidi N , Brown Shannon T , Ingersoll Andrew P , Janssen Michael A , Orton Glenn S , Levin Steven M , Steffes Paul G , Wong Mike
Published: October 2020

Microwave observations by the Juno spacecraft have shown that, contrary to expectations, the concentration of ammonia is still variable down to pressures of tens of bars in Jupiter. While mid-latitudes show a strong depletion, the equatorial zone of Jupiter has an abundance of ammonia that is high and nearly uniform with depth. In parallel, Juno determined that the Equatorial Zone is peculiar for its absence of lightning, which is otherwise prevalent most everywhere else on the planet. We show that a model accounting for the presence of small-scale convection and water storms originating in Jupiter’s deep atmosphere accounts for the observations. At mid-latitudes, where thunderstorms powered by water condensation are present, ice particles may be lofted high in the atmosphere, in particular into a region located at pressures between 1.1 and 1.5 bar and temperatures between 173K and 188K, where ammonia vapor can dissolve into water ice to form a low-temperature liquid phase containing about 1/3 ammonia and 2/3 water. We estimate that, following the process creating hailstorms on Earth, this liquid phase enhances the growth of hail-like particles that we call ‘mushballs’. Their growth and fall over many scale heights can effectively deplete ammonia, and consequently, water to great depths in Jupiter’s atmosphere. In the Equatorial Zone, the absence of thunderstorms shows that this process is not occurring, implying that small-scale convection can maintain a near homogeneity of this region. We predict that water, which sinks along with ammonia, should also be depleted down to pressures of tens of bars. Except during storms, Jupiter's deep atmosphere should be stabilized by the mean molecular weight gradient created by the increase in abundance of ammonia and water with depth.  This new vision of the mechanisms at play, which are both deep and latitude-dependent, has consequences for our understanding of Jupiter’s deep interior and of giant-planet atmospheres in general.
Uranus and Neptune are key to understand planets with hydrogen atmospheres
Authors: Guillot Tristan
Published: October 2020

Uranus and Neptune are the last unexplored planets of the Solar System. I show that they hold crucial keys to understand the atmospheric dynamics and structure of planets with hydrogen atmospheres. Their atmospheres are active and storms are believed to be fueled by methane condensation which is both extremely abundant and occurs at low optical depth. This means that mapping temperature and methane abundance as a function of position and depth will inform us on how convection organizes in an atmosphere with no surface and condensates that are heavier than the surrounding air, a general feature of gas giants. Using this information will be essential to constrain the interior structure of Uranus and Neptune themselves, but also of Jupiter, Saturn and numerous exoplanets with hydrogen atmospheres. Owing to the spatial and temporal variability of these atmospheres, an orbiter is required. A probe would provide a reference profile to lift ambiguities inherent to remote observations. It would also measure abundances of noble gases which can be used to reconstruct the history of planet formation in the Solar System. Finally, mapping the planets’ gravity and magnetic fields will be essential to constrain their global composition, structure and evolution.
The fast rotation of Orcus obtained from TESS measurements
Authors: Kiss Csaba , Pál András , Szakáts Róbert , Marton Gábor , Müller Thomas
Published: October 2020

(90482) Orcus is one of the largest Kuiper belt objects, with one known, relatively large satellite, Vanth. There have been several ~10-20h rotation periods reported in the literature for Orcus, with considerable uncertainty. Here we report on recent measurements of Orcus with the TESS Space Telescope providing a light curve period of 7 h, the fastest rotation among those large trans-Neptunian objects for which the rotation is not expected to cause a distorted, triaxial ellipsoid shape, like in the case of Haumea. While moons of large Kuiper belt objects are usually assumed to be formed from an original large body via collisions, the fast rotation may point to a scenario in which Vanth was captured from a nearby heliocentric orbit early in the history of the Solar system, and subsequent tidal evolution led to the present, nearly circular orbit. In this sense the Orcus-Vanth system is peculiar, as the present rotational characteristics and satellite orbits of all other large Kuiper belt objects are consistent with a collisional origin. 
Exploring changes in dust particles size distribution on Mars during 2018 Global Dust Storm with a 3D Global Climate Model
Authors: Bertrand Tanguy , Kahre Melinda , Wilson John , Wolff Mike , Haberle Robert M , Montmessin Franck , Urata Richard , Hartwick Victoria , Kling Alex , Brecht Amanda , Steakley Kathryn , Batterson Courntey
Published: October 2020

The 2018 Global Dust Storm (GDS) has been observed on Mars from the surface and from orbit. Here we focus on the surface temperatures measured locally by REMS/MSL in Gale crater and column dust IR opacities observed globally by Mars Climate Sounder on-board Mars Reconnaissance Orbiter  (MCS/MRO) (e.g. Montabone et al., 2020). Recent modeling efforts of the 2018 GDS highlight that climate models do not simultaneously capture both the evolution of surface temperatures and the decay rate of global column dust opacities, which suggests that significant changes in dust particle sizes may occur during the dust storm (e.g. Bertrand et al., 2020, Montabone et al., 2020). These models typically assume a constant lifted dust particle size—with size evolution occurring in the atmosphere but only because of gravitational sedimentation. For instance, simulations with sufficiently large particles sizes to yield reasonable decay/sedimentation rates also provide excessive radiation fluxes at the surface, with excessive surface temperatures during peak dust loading. One possible way to improve the agreement between the simulations and the observations is to allow the dust particle sizes to change more significantly in time and/or space during the simulated GDS.  Particle size evolution toward large radius during GDSs is supported by several observations (e.g. Elteto and Toon, 2010, Lemmon et al., 2019). Different mechanisms could take place during dust storms to shift the dust particle distribution towards a larger effective radius: (1) the lifted particle size at the surface could change due to different active reservoirs or due to depletion of small particles as the storm increases in intensity and (2) the particle size in the atmosphere could change more significantly due to Brownian coagulation (production of large particles by the collisions induced by Brownian motions of the particles in the gas and subsequent sticking together of small particles) and gravitational coagulation (accretion through sedimentation, Murphy et al., 1990, Jacobsen et al., 1999, Montmessin et al., 2002, Fedorova et al., 2014).  Previous studies have explored the impact of coagulation processes and concluded that coagulation only affects smaller particles (
Correcting the Atmospheric Refraction of Fireball Observations at Low Elevation Angles and Significance of the Correction
Authors: Visuri Jaakko , Lyytinen Esko , Sievinen Janne , Gritsevich Maria
Published: October 2020

We introduce a new atmospheric refraction correction method which allows to retrieve fireball position with high accuracy without the need to consider at which distance from the observer or height above the Earth's surface the fireball is situated.Traditional refraction correction is valid for objects positioned at infinite distance and it overcompensates when an object is situated inside the atmosphere. In this numerical study the overcompensated correction is reduced by artificially increasing the observing site height above the sea level, called the delta-z correction. We use analytically derived formula for the delta-z correction with different refraction models and compare these results to the numerical solution where light ray is traced through the atmosphere. Ray tracing technique is implemented on the finely meshed atmospheric layers in order to derive value of the correction.We parametrize the viewing angle and the fireball height above sea level in order to define whether this delta-z correction is significant or negligible. Significance is defined by studying the errors caused by the observed horizontal altitude, height of the fireball above the sea-level, and height of the observing site. We find that the delta-z correction should be performed if a fireball is observed within 20 degrees altitude above the horizon or with negative altitudes. We also find that delta-z correction is always accurate if fireball is situated 20km or higher above the sea level and hence it can be safely applied in processing of all observational cases of fireballs.
Electron-induced radiolysis and sputtering on the surface of icy moons: insights from laboratory experiments
Authors: Galli André , Cerubini Romain , Rubin Martin , Pommerol Antoine , Vorburger Audrey , Wurz Peter , Ligterink Niels F.W. , Oza Apurva , Thomas Nicolas
Published: October 2020

AbstractThe surfaces of Jupiter's icy moons are continually irradiated by charged particles from the Jovian plasma environment. This irradiation triggers chemical reactions in the surface ice and also acts as an atmospheric release process. Remote observations, theoretical modelling, and laboratory experiments must be combined to understandthis plasma-ice interaction. Here, we present new experiment results concerning the chemistry of irradiated water ice samples relevant for icy moons and other icy objects in the solar system. IntroductionThe University of Bern is developing the neutral gas mass spectrometer for ESA's Jupiter Icy moons Explorer (JUICE, Grasset et al. 2013), planned to reach the Jupiter system in 2029. We therefore strive to fill knowledge gaps about the basic physics of the surfaces and atmospheres of Jupiter’s icy moons before the arrival of JUICE. We combine the available facilities for developing and calibrating mass spectrometers and ion/electron spectrometers (Marti et al. 2001) with the sample preparation techniques and diagnostics of the Planetary Imaging Group (Pommerol et al. 2019).Experiment setupTo study the effects of electrons irradiating water ice, we subjected a variety of ice samples (thin amorphous ice films and macroscopic samples of porous ice with customizable grain size) to an electron beam of energies between 200 eV and 10 keV at pressures and temperatures representative for the surfaces of Jupiter's icy moons. The physical and optical properties of these macroscopic ice samples make them realistic analogues for planetary surfaces beyond the ice line. The effect of chemical impurities in the water ice, such as NaCl, can also be investigated. The particles released from the ice were monitored with a newly designed time-of-flight (TOF) mass spectrometer and (in the case of the water ice film) with a microbalance. Preliminary resultsElectron irradiation of pure water ice results mostly in the creation and release of H2 and O2 from H2O in a stoichiometric 2:1 ratio, which is in agreement with the results based on an older quadrupole mass spectrometer (Galli et al. 2018). This seems to hold true for any type of water ice sample, independent of grain size and crystallinity. We also derive upper limits for rare radiolysis products (such as OH and H2O2) and the time scales for the build-up and release of radiolysis products. The O2 release lags behind the immediate H2 release by typically ~ 10 s and is reminiscent of the time-dependent sputtering yield of O2 from water ice upon ion irradiation (Teolis et al. 2005). This delayed O2 release has implications for the O2/H2O ratio observed at the surface of icy objects in the solar system, such as Ganymede, Europa, Callisto (Calvin et al. 1996, Spencer and Calvin 2002), and 67P/Churyumov-Gerasimenko (Bieler et al. 2015).
Understanding our global heliosphere with UV observations: Unique opportunities on Interstellar Probe
Authors: Provornikova Elena , Brandt Pontus , Roelof Ed , Katushkina Olga , Baliukin Igor , Mayyasi Majd , Koutroumpa Dimitra , Mandt Kathleen
Published: October 2020

Solar Lyman-a emission re-radiated from H atoms incoming to the heliosphere from interstellar medium is a powerful tool to probe globally plasma properties both at the heliosphere boundary and near the Sun. H Lyman-α line profiles reflect velocity distributions of low energy H atoms in the heliosphere which hold information about the plasma near the heliopause. H Lyman α intensities as observed at 1 AU serve as diagnostic of global properties of the solar wind. In this talk we will review what we have learned about the global heliospheric interaction from H Lyman-a observations from inside the heliosphere on SWAN/SOHO, Voyages/UVS and New Horizons/Alice missions. Outward trajectory of Interstellar Probe going through the outer heliosphere to the interstellar medium (ISM) up to 1000 AU enable unique science opportunities to explore global interaction between the solar wind and local ISM by observing for the first time Lyman-a emission from outside of the heliosphere. We will report a progress of UV working group in outlining primary science questions on the nature of the global heliosphere and Local Interstellar Cloud, planning observation strategy, measurement requirements and synergies with planetary UV observations for potential KBO fly-by.
Meteor pairs and groups in Geminid meteor shower
Authors: Koten Pavel , Čapek David
Published: October 2020

The existence of the pairs and larger groups of the meteors was already investigated in several papers. Recent statistical analyses of radar or optical data on several meteor showers provided rather negative results. Nevertheless, some level of groupings is possible, especially among young streams.When digitalizing older videotapes obtained during the 2006 Geminid campaign, we found a relatively higher number of meteors that appear in pairs. Therefore we investigated this observational result in more detail.Statistically, when observing Geminid meteor shower, we could expect 1.4 randomly paired meteors per 1 hour assuming ZHR = 100 and the maximum gap between meteors of 1 second. There were recorded 9 pairs during 3.5 hours of observation. Therefore at least some of them cannot be statistically random pairs. Moreover, a triplet of meteors detected within 1 second is well above the statistical threshold for random appearance.In this talk, we will provide more detailed analyses of all the cases as well as some possible scenarios of their origin.
The importance of the evolutional processes in the study of lava tube analogues: the case of La Corona tube (Lanzarote)
Authors: Tomasi Ilaria , Massironi Matteo , Meyzen Christine , Pozzobon Riccardo , Sauro Francesco , Penasa Luca , Martínez-Frías Jesùs , Mateo Medero Elena
Published: October 2020

Among the variety of earth analogues, what surely stand out are lava tubes.A lava tube is a type of lava cave formed by a low-viscosity lava flow that can develop 1) forming a continuous and hard crust, which forms a roof above the still flowing lava stream (over-crusting), or 2) slipping between pre-existing lava flows (inflation). The resulting structure constitutes among the most efficient thermal structures on Earth, because of their capacity of thermal insulation isolated lava flows can travel over long distances across lava fields.Lava tubes, which on Earth are typical features of lava fields encountered in intracontinental plateaus and volcanic-shield islands (slopes
Structure of enormous cloud cover seen in Venus' night-side by Akatsuki/IR2
Authors: Satoh Takehiko , Vun Choon Wei , Horinouchi Takeshi , Sato Takao M.
Published: October 2020

The spatial and temporal structures of "Enormous Cloud Cover" (ECC), seen in 2.26- and 1.735-µm Venus' night-side images acquired by Akatsuki/IR2, are investigated. The data were acquired on 18th and 27th August 2016 and have been processed newly-developed "Restoration by Deconvolution" (RD) method that effectively removes contaminating light spread from the intense day crescent. Spectral radiances are compared between ECC and "seemingly normal" area (BC = Background Clouds). Attenuation by ECC is stronger at 2.26 µm (~70 to 80 %) than at 1.735 µm (~50 %) due primarily to lower single-scattering albedo of cloud particles at 2.26 µm. Detailed radiative-transfer analyses suggest the followings:A possible scenario to explain these observational characteristics, strong upwelling region near the western end (front of propagating feature), pushing H2SO4 vapor to condensate in high altitudes. After the region of strongest upwelling propagates away, the cloud particles gradually sediment or are pulled back by downwelling motion of atmosphere.Details of data analysis, interpretation of phenomena with comarison to numerical simulations will be presented.
Will the PIC approach cure the heliosphere modeling?
Authors: Ratkiewicz Romana
Published: October 2020

To push the boundaries of space science, we first need to know more about the real boundary for Terrestrials in space that is heliopause. The heliopause separates solar wind from interstellar matter. This boundary surrounds and contains our heliosphere, the space ruled by the Sun. The state of our current knowledge of the heliosphere, despite a big step forward in the last half-century, requires further work to answer extremely important and at the same time basic science questions. One of the still unsolved and most fundamental question is the structure and shape of the heliosphere. In this paper we shortly discuss selected heliosphere  created so far models and we initite consideration of hybrid-kinetic model using a PIC approach for modeling the heliosphere. 
NOMAD on ExoMars Trace Gas Orbiter: One Martian year of observations
Authors: Vandaele Ann Carine , Daerden Frank , Thomas Ian R. , Aoki Shohei , Depiesse Cédric , Erwin Justin , Neary Lori , Piccialli Arianna , Ristic Bojan , Robert Séverine , Trompet Loïc , Viscardy Sébastien , Willame Yannick , Mason Jon , Patel Manish , Bellucci Giancarlo , Lopez-Moreno Jose-Juan
Published: October 2020

The NOMAD (“Nadir and Occultation for MArs Discovery”) spectrometer suite on board the ExoMars Trace Gas Orbiter has been designed to investigate the composition of Mars' atmosphere, with a particular focus on trace gases, clouds and dust. The instrument probes the ultraviolet and infrared regions covering large parts of the 0.2-4.3 µm spectral range [1,2], with 3 spectral channels: a solar occultation channel (SO – Solar Occultation; 2.3–4.3 μm), a second infrared channel capable of nadir, solar occultation, and limb sounding (LNO – Limb Nadir and solar Occultation; 2.3–3.8 μm), and an ultraviolet/visible channel (UVIS – Ultraviolet and Visible Spectrometer, 200–650 nm).Since its arrival at Mars in April 2018, NOMAD performed solar occultation, nadir and limb observations dedicated to the determination of the composition and structure of the atmosphere. Here we report on the different discoveries highlighted by the instrument during its first full Martian year of observations: investigation of the 2018 Global dust storm and its impact on the water uplifting and escape, on temperature and pressure increases within the atmosphere; dust and ice clouds distribution; ozone measurements; dayglow observations; detection of HCl vertical profiles and in general advances in the analysis of the spectra recorded by the three channels of NOMAD.References[1] Vandaele, A.C., et al., 2015. Planet. Space Sci. 119, 233-249.[2] Vandaele et al., 2018. Space Sci. Rev., 214:80, doi.org/10.1007/s11214-11018-10517-11212.
Investigating physical and chemical mechanisms in planetary atmospheres and their impacts on the observables
Authors: Rengel Miriam , Reiners Ansgar , Cont David , Gapp Cyril , Khaimova Jessica , Lara Luisa M. , Shulyak Denis , Yan Fei
Published: October 2020

In the framework of the Priority Programme “Exploring the Diversity of Extrasolar Planets” (SPP 1992) of the German Research Foundation (DFG) we carried out the project “The key physical-chemical processes determining the Composition and Temperature of (exo)planetary atmospheres”. Characterizing the atmospheres of extrasolar planets is a new frontier in exoplanetary science, is dependent on observations and interpretation toolkits. The project intends addressing a key question in current exoplanetary atmospheric research: what are and how do the key chemical and physical processes determine the atmospheric composition and temperature of exoplanets?Here we will review key novel results and scientific achievements obtained with emphasis on:(1) A feasibility study on retrieving the vertical temperature distribution and abundances from ground-based high-resolution spectroscopy in the near-infrared, test case: VLT/CRIRES+.(2) Studies of some mechanisms/effects on spectra, composition and temperature: atmospheric chemistry and dynamic under intensiveirradiation, clouds/hazes effect on the transmission spectrum of mildly irradiated exoplanets, and kinetics-related disequilibrium processes.(3) A look to the composition of the atmosphere of Jupiter, an archetype of gas giants,  as seen by Herschel/PACS.
V band photometry of asteroids from the All-Sky Automated Survey for Supernovae
Authors: Hanus Josef , Pejcha Ondrej , Shappee Ben
Published: October 2020

The All-Sky Automated Survey for Supernovae (ASAS-SN) currentlyoperates 24 small-aperture telescopes distributed around the globe toautomatically survey the entire visible sky every night down to aboutg~18 mag. Between 2013 and 2018, the survey used a V filter withlimiting magnitude V~17. Although primarily hunting for supernovae andother transients, asteroids are common intruders in the ASAS-SN'simages. Here we present efforts to analyze the sparsely sampled V-bandphotometry extracted from the ASAS-SN images for >10,000 asteroidsthat get brighter than V~17 mag. The data span years 2013-2018 andsample up to 7 consequent apparitions for each asteroid. We providedetails about the photometry extraction and calibration, photometryaccuracy, and various statistics such as the typical number of datapoints per asteroid as a function of the brightness. Finally, we analyze the photometric data with the lightcurve inversion method andderive rotation periods, spin axis directions, and shapes for a sampleof studied asteroids. We discuss the typical amount of data sufficientfor a successful shape model determination. We compare derivedphysical properties with those available in the literature to illustrate the reliability of the ASAS-SN photometry.
Energetic proton depletion near Io: atmospheric charge exchange and inhomogeneous magnetic and electric fields
Authors: van Buchem Christiaan , Huybrighs Hans , Blöcker Aljona , Dols Vincent , Witasse Olivier , Miguel Yamila
Published: October 2020

The flux of energetic protons (80 keV-1.04 Mev) near the Galilean moons was measured by the Energetic Particle Detector (EPD) on the Galileo mission (1995 - 2003). Near Galilean moon, such as Io and Europa, depletions of the energetic proton flux, of several orders of magnitude, were observed.Such energetic proton depletions can be caused by the precipitation of these particles onto the moon's surface or charge exchange with the neutral atmosphere. In order to interpret the depletion features in the EPD data, a Monte Carlo particle tracing code has been developed by (H. L. F. Huybrighs et al., 2020; Hans L. F. Huybrighs et al., 2017; Hans Leo Frans Huybrighs, 2018). The expected flux of the energetic ions is simulated under different scenarios, for three Galileo flybys of Io (I24, I27, and I31), including with and without an atmosphere and inhomogeneous magnetic and electric fields. By comparing the simulated distribution to the EPD data, the cause of the depletion features can be investigated.The following causes of energetic proton depletion near Io are identified:Some depletions are consistent with atmospheric charge exchange for flybys I24, I27, and I31.
Some of depletions coincide with the inhomogeneous fields produced in the MHD model by (Dols et al., 2012) for flybys I24, I27, and I31.
For I24 the depletions are consistent with a two component atmosphere: a dense low scale height atmosphere and an extended corona described by a low surface density but a large scale height as presented by (Blöcker et al., 2018).
Furthermore, latitudinal and longitudinal dependencies in the atmospheric models for Io are investigated for all three aforementioned flybys.BibliographyBlöcker, A., Saur, J., Roth, L., & Strobel, D. F. (2018). MHD Modeling of the Plasma Interaction With Io’s Asymmetric Atmosphere. Journal of Geophysical Research: Space Physics, 123(11), 9286–9311. https://doi.org/10.1029/2018JA025747
Dols, V., Delamere, P. A., Bagenal, F., Kurth, W. S., & Paterson, W. R. (2012). Asymmetry of Io’s outer atmosphere: Constraints from five Galileo flybys. Journal of Geophysical Research: Planets, 117(E10). https://doi.org/10.1029/2012JE004076
Huybrighs, H. L. F., Roussos, E., Blöcker, A., Krupp, N., Futaana, Y., Barabash, S., et al. (2020). An Active Plume Eruption on Europa During Galileo Flyby E26 as Indicated by Energetic Proton Depletions. Geophysical Research Letters, 47(10). https://doi.org/10.1029/2020gl087806
Huybrighs, Hans L. F., Futaana, Y., Barabash, S., Wieser, M., Wurz, P., Krupp, N., et al. (2017). On the in-situ detectability of Europa’s water vapour plumes from a flyby mission. https://doi.org/10.1016/j.icarus.2016.10.026
Huybrighs, Hans Leo Frans. (2018). A search for signatures of Europa’s atmosphere and plumes in Galileo charged particle data. Retrieved from http://arxiv.org/abs/1812.11215