The Exosphere as a Boundary: Origin and Evolution of Airless Bodies in the Inner Solar System and Beyond Including Planets with Silicate Atmospheres

In this review we discuss all the relevant solar/stellar radiation and plasma parameters and processes that act together in the formation and modification of atmospheres and exospheres that consist of surface-related minerals. Magma ocean degassed silicate atmospheres or thin gaseous envelopes from planetary building blocks, airless bodies in the inner Solar System, and close-in magmatic rocky exoplanets such as CoRot-7b, HD 219134 b and 55 Cnc e are addressed. The depletion and fractionation of elements from planetary embryos, which act as the building blocks for proto-planets are also discussed. In this context the formation processes of the Moon and Mercury are briefly reviewed. The Lunar surface modification since its origin by micrometeoroids, plasma sputtering, plasma impingement as well as chemical surface alteration and the search of particles from the early Earth’s atmosphere that were collected by the Moon on its surface are also discussed. Finally, we address important questions on what can be learned from the study of Mercury’s environment and its solar wind interaction by MESSENGER and BepiColombo in comparison with the expected observations at exo-Mercurys by future space-observatories such as the JWST or ARIEL and ground-based telescopes and instruments like SPHERE and ESPRESSO on the VLT, and vice versa

Three-Dimensional Modeling of Callisto's Surface Sputtered Exosphere Environment

We study the release of various elements from Callisto's surface into its exosphere by plasma sputtering. The cold Jovian plasma is simulated with a 3D plasma-planetary interaction hybrid model, which produces 2D surface precipitation maps for magnetospheric H+ , O+ , O++ , and S++ . For the hot Jovian plasma, we assume isotropic precipitation onto the complete spherical surface. Two scenarios are investigated: One where no ionospheric shielding takes place and accordingly full plasma penetration is implemented ('no ionosphere' scenario), and one where an ionosphere lets virtually none of the cold plasma but all of the hot plasma reach Callisto's surface ('ionosphere' scenario). In the 3D exosphere model, neutral particles are sputtered from the surface and followed on their individual trajectories. The 3D density profiles show that whereas in the 'no ionosphere' scenario the ram direction is favored, the 'ionosphere' scenario produces almost uniform density profiles. In addition, the density profiles in the 'ionosphere' scenario are reduced by a factor of ~2.5 with respect to the 'no ionosphere' scenario. We find that the Neutral gas and Ion Mass spectrometer, which is part of the Particle Environment Package on board the JUICE mission, will be able to detect the different sputter populations from Callisto's icy surface and the major sputter populations from Callisto's non-icy surface. The chemical composition of Callisto's exosphere can be directly linked to the chemical composition of its surface, and will offer us information not only on Callisto's formation scenario but also on the building blocks of the Jupiter system.Comment: Published in JGR: Space Physic

The moon observed in energetic neutral Atoms: Review of the scientific findings from SARA/CENA on board of Chandrayaan-1

The Sub-keV Atom Reflecting Analyzer (SARA) instrument on board Chandrayaan-1 was exceptionally successful. The instrument not only achieved all its set science goals but also revealed several hitherto unknown and unexpected properties of the solar wind interaction with the lunar surface. SARA’s scientific findings can be divided into two groups based on the nature of the particles detected: The first group contains findings gained from ion measurements (from SWIM, SARA’s ion sensor) whereas the second group contains findings gained from energetic neutral atom (ENA) measurements (from CENA, SARA’s ENA sensor). Here, we present a review of all scientific findings based on ENA measurements. Since the Moon is constantly bombarded by solar wind ions. Until recently, it was tacitly assumed that the ions that impinge onto the lunar surface are almost completely absorbed, with less than 1% reflection, (e.g. Crider and Vondrak, Adv. Space Res., 2002; Feldman et al., JGR, 2000). However, recent observations conducted showed that on average 16% of the impinging solar wind ions are reflected as ENAs (e.g. McComas et al., GRL, 2009; Wieser et al., PSS, 2009; Vorburger et al., JGR, 2013). The energy spectrum of the reflected ENAs is broader than the spectrum of the incident solar wind protons (Futaana et al., JGR, 2012; Harada et al., JGR, 2014), and the characteristic energy is < 50% of the incident solar wind characteristic energy. This hints at multiple scattering processes taking place on the lunar surface. Determination of the ENA angular backscatter function showed that, contrary to expectations, as the solar zenith angle (SZA) increases, particles scatter more toward the sunward direction than in the anti-sunward direction (Vorburger et al., GRL, 2011; Lue et al., JGR, 2016). The ENA reflection ratio is rather featureless over the lunar surface (Vorburger et al., JGR., 2013), showing only strong variations at local crustal magnetic fields due to the interaction of the plasma with so-called mini-magnetospheres (e.g., Wieser et al., GRL, 2010; Vorburger et al., JGR, 2012; Vorburger et al., JGR, 2013). CENA measurements were also used to derive the electric potential above a lunar magnetic anomaly (Futaana et al., GRL, 2012, Järvinen et al. GRL, 2014). Electrical potentials are of scientific interest because they can influence the local plasma and dust environment near the magnetic anomaly. CENA also presented the first-ever measurements of sputtered lunar oxygen (Vorburger et al., JGR., 2012) as well as the first-ever observations of backscattered solar wind helium (Vorburger et al., JGR., 2012). With the backscattered proton signal being unexpectedly large, these signals are small in comparison, but persistent nevertheless. Finally, recent CENA data analyses showed that a significant fraction of the solar wind plasma is able to reach far into the lunar nightside surface: CENA measured a 30 deg broad ENA ring parallel to the terminator, with a total flux equal to ~1.5% of the total dayside flux (Vorburger et al., GR., 2016). These measurements shed light onto the expansion of plasma into voids as they occur in planetary wakes

Science Opportunities offered by Mercury's Ice-Bearing Polar Deposits

n/

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Modeling of Possible Plume Mechanisms on Europa

Plumes spewing water high above Europa's surface have been inferred from several observation campaigns in the past decade. Whereas the occasional existence of plumes on Europa has thus been confirmed, the origin of the plumes remains uncertain. Most notably, it is still unclear whether the inferred plumes are of oceanic origin, possibly containing information about the ocean's habitability, or if they are of surficial nature, offering information on the highly processed surface instead. In this study, we use a Monte-Carlo model to analyze three different plume models, two of which are surficial (near-surface liquid inclusion and diapir), and one of which originates in the sub-surface ocean (oceanic plume). We analyze all relevant Lyman- and OI 1304 A emission mechanisms to determine the three models' emission profiles. These profiles are then compared to the Hubble Space Telescope/Space Telescope Imaging Spectograph measurements presented by Roth, Saur, etal.(2014, https://doi.org/10.1126/science.1247051) with the goal of determining which ab initio model fits these measurements best. Our analyses show that all three models investigated produce similar Lyman- and OI 130.4nm emission profiles, with differences being perceivable only on scales well below the HST resolution and sensitivity. Since none of the models contradict the Roth, Saur, etal.(2014, https://doi.org/10.1126/science.1247051)observations, none of them can be ruled out as being the acting force behind the observed plumes. The currently available optical measurements are thus not sufficient to determine the physical nature of Europa's plumes, identification of which can only be achieved through higher resolution images or in situ measurements

Chemical and Isotopic Composition Measurements on Atmospheric Probes Exploring Uranus and Neptune

So far no designated mission to either of the two ice giants, Uranus and Neptune,exists. Almost all of our gathered information on these planets comes from remote sensing.In recent years, NASA and ESA have started planning for future mission to Uranus andNeptune, with both agencies focusing their attention on orbiters and atmospheric probes.Whereas information provided by remote sensing is undoubtedly highly valuable, remotesensing of planetary atmospheres also presents some shortcomings, most of which can beovercome by mass spectrometers. In most studies presented to date a mass spectrometerexperiment is thus a favored science instrument forin situcomposition measurements onan atmospheric probe. Mass spectrometric measurements can provide unique scientific data,i.e., sensitive and quantitative measurements of the chemical composition of the atmosphere,including isotopic, elemental, and molecular abundances. In this review paper we presentthe technical aspects of mass spectrometry relevant to atmospheric probes. This includesthe individual components that make up mass spectrometers and possible implementationchoices for each of these components. We then give an overview of mass spectrometersthat were sent to space with the intent of probing planetary atmospheres, and discuss threeinstruments, the heritage of which is especially relevant to Uranus and Neptune probes,in detail. The main part of this paper presents the current state-of-art in mass spectrometryintended for atmospheric probe. Finally, we present a possible descent probe implementationin detail, including measurement phases and associated expected accuracies for selectedspecies