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The Mass Spectrum Analyzer (MSA) will perform in-situ observations of ions and magnetic fields around Phobos as part of the Martian Moons eXploration (MMX) mission to investigate the origin of the Martian moons and physical processes in the Martian environment. MSA consists of an ion energy mass spectrometer and two magnetometers which will measure velocity distribution functions and mass/charge distributions of low-energy ions and magnetic field vectors, respectively. For the MMX scientific objectives, MSA will observe solar wind ions, those scattered at the Phobos surface, water-related ions generated in the predicted Martian gas torus, secondary ions sputtered from Phobos, and escaping ions from the Martian atmosphere, while monitoring the surrounding magnetic field. MSA will be developed from previous instruments for space plasma missions such as Kaguya, Arase, and BepiColombo/Mio to contribute to the MMX scientific objectives.

The so-called ‘PacMan’ features on the leading hemispheres of the icy Saturnian moons of Mimas, Tethys and Dione were initially identified as anomalous optical discolorations and subsequently shown to have greater thermal inertia than the surrounding regions. The shape of these regions matches calculated deposition contours of high energy plasma electrons moving opposite to the moon’s orbital direction, thus suggesting that electron interactions with the grains produce the observed anomalies. Here, descriptions of radiation-induced diffusion processes are given, and various sintering models are considered to calculate the rate of increase in the contact volume between grains in an icy regolith. Estimates of the characteristic sintering timescale, i.e. the time necessary for the thermal inertia to increase from that measured outside the anomalous regions to that within, are given for each of the moons. Since interplanetary dust particle (IDP) impact gardening and E-ring grain infall would be expected to mix the regolith and obscure the effects of high energy electrons, sintering rates are compared to rough estimates of the impact-induced resurfacing rates. Estimates of the sintering timescale determined by extrapolating laboratory measurements are below ∼0.03 Myr, while the regolith renewal timescales are larger than ∼0.1 Myr, thus indicating that irradiation by the high energy electrons should be sufficient to form stable thermal anomalies. More detailed models developed for sintering of spherical grains are able to account for the radiation-induced anomalies on Mimas and Tethys only if the regoliths on those bodies are relatively compact and composed of small (≲ 5 µm) grains or grain aggregates, and/or the grains are highly non-spherical with surface defect densities in the inter-grain contact regions that are much higher than expected for crystalline water ice grains at thermal equilibrium. These results are consistent with regolith thermal conductivity models which can only be reconciled with spacecraft observations if the contacts between grains are assumed to have much lower thermal conductance than predicted for idealized grains. The strength of the anomalies on Tethys and Dione appear to be limited by E-ring grain infall, while on Mimas IDP gardening limits the strength of the anomaly. The smaller flux of more deeply penetrating high energy (>1 MeV) electrons on Dione can account for the small thermal inertia differences measured there. Determining regolith sintering rates and the corresponding effect on thermal conductivity can, in principle, provide an independent constraint on the regolith grain geometries and exposure timescales for icy bodies.

Far more definitive information on composition is required to resolve the question of origin for the Martian moons Phobos and Deimos. Current infrared spectra of the objects are inconclusive due to the lack of strong diagnostic features.Definitive compositional measurements of Phobos could be obtained using in-situ X-ray, gamma-ray, or neutronspectroscopy or collecting and returning samples to Earth for analysis. We have proposed, in lieu of those methods, toderive Phobos and Deimos compositional data from secondary ion mass spectrometry (SIMS) measurements by calibratingthe instrument to elemental abundance measurements made for known samples in the laboratory. We describe thePhobos/Deimos Regolith Ion Sample Mission (PRISM) concept here. PRISM utilizes a high-resolution TOF plasma composition analyzer to make SIMS measurements by observing the sputtered species from various locations of the moons' surfaces. In general, the SIMS technique and ion mass spectrometers complement and expand quadrupole mass spectrometer measurements by collecting ions that have been energized to higher energies, 50-100 eV, and making measurements at very low densities and pressures. Furthermore, because the TOF technique accepts all masses all the time,it obtains continuous measurements and does not require stepping through masses. The instrument would draw less than10 W and weigh less than 5 kg. The spacecraft, nominally a radiation-hardened 12U CubeSat, would use a low-thrust SolarElectric Propulsion system to send it on a two-year journey to Mars, where it would co-orbit with Deimos and then Phobos

© 2017 Elsevier Inc. Prof. Thomas Orlando is currently a professor in the Georgia Institute of Technology (GIT) School of Chemistry and Biochemistry and an adjunct professor in the GIT School of Physics. He serves as director of the GIT Center for Space Technology and Research and as principal investigator (PI) of the NASA Solar System Exploration Research Virtual Institute Center on Radiation Effects on Volatiles and Exploration of Asteroids and Lunar Surfaces (REVEALS). Prof. Carol Paty and Dr. Esther Beltran are deputy PIs, and Dr. Brant Jones and Prof. Stephen Robinson are science theme leaders. Orlando, Jones, Paty, and Schaible focus on understanding radiation effects on the regolith and the solar-wind formation of volatiles. Profs. Valeria La Saponara, John Reynolds, and Robinson focus on mitigating health risks by developing nanocomposites for spacesuits and habitats. Prof. Phillip First explores 2D materials for radiation detection. Collectively, the efforts will help facilitate future human exploration of near-Earth destinations.

International audience; We present new results for ion irradiation experiments performed on fragments of the Tagish Lake (TL) meteorite. These experiments were focused on (a) quantifying the effect of the solar wind on spectral reflectance and (b) identifying the parent bodies of TL within the Asteroid Belt and or Jupiter Trojans. In the visible and near-infrared, we observe a flattening and brightening of the reflectance with progressive irradiation; in the mid-infrared, we observe a small shift towards longer wavelengths of the main emission feature at 10 mu m consistent with what is observed in silicates, likely caused by amorphization. We evaluated possible parent bodies for Tagish Lake by comparing its total reflectance in the visible and spectral changes in the 0.4-25 mu m range with available measurements for main belt asteroids and Jupiter Trojans (asteroid data includes measurements from the WISE, SMASS and Spitzer surveys as well as IRTF observations). The low reflectance of TL compared to asteroid albedos shows that TL-like bodies are very rare among Jupiter Trojans (\textless0.02% of the total population) and that they exist in a very small proportion (\textless4.5% of the total population) among main belt asteroids, where only one asteroid, 368 Haidea, was found to match both TL's spectrum and reflectance. Additionally, TL-like bodies would be preferentially located in the outer Asteroid Belt (2.85-3.3 AU) further away from the Sun than the average current location of most Ch- and Cgh-types, these objects being the likely parent bodies of CM-type chondritic meteorites. It thus appears that the location of both meteorite groups (TL and CM) must be different, with TL having formed further away from the Sun than CMs. We find that there are by far more parent bodies of CM than TL-like meteorites, which still remains to be understood. (C) 2013 Elsevier Inc. All rights reserved.