Signatures of sputtering at Mars: the first evidence?

Abstract : One of the potential drivers of Mars' past atmospheric evolution is its escape to space following Mars' interaction with the solar radiation flux and solar wind. To understand how the solar mass and energy can lead to the erosion of the atmosphere is one of the main goals of the Mars Atmosphere and Volatile Evolution MissioN (MAVEN mission. Among the erosion processes that may have been dominant at Mars is sputtering, where neutrals can escape via collisions with heavy planetary ions that are picked up by the solar wind and precipitate back into Mars' upper atmosphere This flux of precipitating heavy ions has been clearly observed by MAVEN. However, so far, no signature of the expected effects of these precipitating ions has been identified in Mars' atmosphere or exosphere. A challenge in this regard is that present-day sputtering enhancement of the upper atmosphere is expected to be weak compared to the other sources including various heating episodes and photochemical processes, especially the dissociative recombination of ionospheric O2+. We will here describe a possible approach to disentangle the effect of the sputtering from other known sources of Mars' exosphere in Neutral Gas and Ion Mass Spectrometer (NGIMS/MAVEN) measurements of the exosphere by analyzing the height profiles of elements other than O. This novel approach could be applicable to future missions to other planetary atmospheres where sputtering is occurring, and if successful, would be the first observation of sputtering at Mars.