Volatiles and Refractories in Surface-Bounded Exospheres in the Inner Solar System

Abstract

Volatiles and refractories represent the two end-members in the volatility range of species in any surface-bounded exosphere. Volatiles include elements that do not interact strongly with the surface, such as neon (detected on the Moon) and helium (detected both on the Moon and at Mercury), but also argon, a noble gas (detected on the Moon) that surprisingly adsorbs at the cold lunar nighttime surface. Refractories include species such as calcium, magnesium, iron, and aluminum, all of which have very strong bonds with the lunar surface and thus need energetic processes to be ejected into the exosphere. Here we focus on the properties of species that have been detected in the exospheres of inner Solar System bodies, specifically the Moon and Mercury, and how they provide important information to understand source and loss processes of these exospheres, as well as their dependence on variations in external drivers.

Space Weathering Effects in Troilite by Simulated Solar‐Wind Hydrogen and Helium Ion Irradiation

“…However, while Schläppi et al. ( 2008 ) identify solar‐wind ion sputtering as the dominant mechanism for exospheric production at asteroids 2867 Steins and 21 Lutetia and transient OH and H 2 O has been noted at Ceres; no exosphere has been definitively detected yet around an asteroid (Grava et al., 2021 ). Thus, the potential to identify a thin sulfur‐exosphere sputtered from the surface of Psyche is intriguing.…”

Effects of mercury surface temperature on the sodium abundance in its exosphere

“…While the micrometeoroid impact vaporization is a stochiometric release process that depends mainly on meteoroid velocity, and that hardly explain the observed double peaked spatial distribution and the time variability of the Na exosphere, it seems the main surface release process for refractories peaking mainly at the dawn terminator (e.g. Milillo et al 2020;Grava et al 2021). Ion Sputtering (IS) seems a process that could better be related to the observed distributions and short-term variabilities linked to fluctuation of the impacting solar wind onto the surface.…”

Space plasma physics science opportunities for the lunar orbital platform - Gateway

“…− Ring current and near-Earth plasma sheet monitoring, by imaging of the ENAs produced by charge exchange between the plasma sheet or ring current energetic ions (few ~keV to few ~10 keV) with the geocorona neutral hydrogen atoms, e.g., Brandt et al (2004), Vallat et al (2004, Goldstein et al (2022). − Magnetopause and cusps monitoring by detecting and imaging the SWCX (solar wind charge exchange) soft X-rays produced by charge exchange between highly-charged heavy ions, originating from the solar wind, and the exospheric neutral atoms, e.g., Branduardi-Raymont et al (2012), Branduardi-Raymont et al (2021), Sibeck et al (2018). − Plasmasphere imaging, by resonant scattering of the solar EUV (30.4 nm) by the plasmaspheric He + ions, e.g., Sandel et al (2003), Darrouzet et al (2008), He et al (2016).…”