Recent results from the MAVEN Langmuir Probe and Waves instrument suggest higher than predicted electron temperatures (Te) in Mars' dayside ionosphere above ~180 km in altitude. Correspondingly, measurements from Neutral Gas and Ion Mass Spectrometer indicate significant abundances of O2+ up to ~500 km in altitude, suggesting that O2+ may be a principal ion loss mechanism of oxygen. In this article, we investigate the effects of the higher Te (which results from electron heating) and ion heating on ion outflow and loss. Numerical solutions show that plasma processes including ion heating and higher Te may greatly increase O2+ loss at Mars. In particular, enhanced Te in Mars' ionosphere just above the exobase creates a substantial ambipolar electric field with a potential (eΦ) of several kBTe, which draws ions out of the region allowing for enhanced escape. With active solar wind, electron, and ion heating, direct O2+ loss could match or exceed loss via dissociative recombination of O2+. These results suggest that direct loss of O2+ may have played a significant role in the loss of oxygen at Mars over time.

a b s t r a c tA goal of Cassini's extended mission is to examine the seasonal variations of Saturn's magnetosphere, moons, and rings. Recently we showed that the thermal plasma between the main rings and Enceladus exhibited a time dependence that we attributed to a seasonally variable source of oxygen from the main rings (Elrod, M.K.

We investigate the complex interaction between Saturn's magnetosphere and Titan's upper ionosphere using ion data acquired by the Cassini Plasma Spectrometer (CAPS) during the T40 encounter. Bounds on ion-group abundances at altitudes between~2733 and~12,541 km are determined by fitting mass spectra with model functions derived from instrument calibration data. The spectra are dominated by H + , H 2 + , H 3 + , and two hydrocarbon groups with mass ranges 12-19 and 24-32 amu, respectively. Notably, this constitutes the first reported observation of H 3 + in Titan's exosphere. These measurements are discussed in the context of data from the CAPS electron spectrometer (ELS) and the Ion and Neutral Mass Spectrometer (INMS), which fortuitously sampled the ionospheric outflow during the T40 encounter at altitudes between~2225 and~3034 km. The CAPS data reveal a composition that is constitutively similar to that sampled by INMS, with hydrocarbon ions first observed as far as~11,000 km from Titan and increasing in density by more than an order of magnitude along Cassini's inbound trajectory.In addition, we juxtapose the CAPS ion data with numerical results from three different interaction models and show that it is consistent with the location of the field-draping boundary described by Ulusen et al. (2012) and the Saturnward ion tail predicted by Sillanpää et al. (2006).

<p align="justify"><span lang="en-US">Airless planetary bodies’ surfaces, such as the Moon’s or Mercury’s, are composed of porous regoliths which interact directly with the impinging solar wind. In the case of the Moon, this incoming flux of solar protons has been observed to be partially neutralized and backscattered as Energetic Neutral Atoms (ENA) with reflection coefficients believed to be ranging between </span><span lang="en-US">⁓</span><span lang="en-US">0.1 and 0.2 depending on the study and/or the measurement. Such a large range of reflection coefficients reflects the diversity in the regolith’s interactions with the solar wind and underlines the lack of understanding of the lunar regolith and its influence on the particles impacting it.</span></p> <p align="justify"><span lang="en-US">The ENA flux is thought to depend on the structure of the upper regolith layer and the solar wind characteristics. By using a model combining a Monte Carlo approach to describe a solar proton’s journey through the lunar surface, with molecular dynamics to characterize its interactions with the regolith’s grains, we highlighted key parameters which influence the backscattered ENA flux and analyzed their roles in these interactions. To describe the structure of the lunar regolith we used the open-source code LAMMPS Molecular Dynamics Simulator, which allows a realistic description of grain-on-grain contacts using a Johnson-Kendall-Roberts (JKR) contact model. The porosity of the modeled regolith is shown to be dictated by the surface energy of the grains. By considering silicate grains and a realistic range of surface energy for this material, we studied regoliths’ porosities ranging from ~0.5 to 0.85. This work showed that a large porosity favors deeper penetration of the protons inside the regolith, which increases the number of collisions, and thus the energy lost by the impinging protons and their absorption. By accounting for particular directions of observation with respect to the solar wind direction, we showed that the angular distribution of the backscattered ENA is anisotropic. We here used IBEX observations and its characteristic 90° observation angle as a demonstration of the influence of this anisotropy. We finally analyzed the effects of both the energy distribution of the hydrogen atoms after a collision with a grain and the solar wind properties on the ENA energy flux spectrum shape. The modelled spectrum was also compared to the observations of Chandrayaan-1. This work aims for a better understanding of the interactions ongoing at this interface and intents to look into the possibility to deduce information on the surface structure solely from ENA flux measurements.</span></p>