First in situ evidence of Mars nonthermal exosphere

François Leblanc (1) , M. Benna (2, 3) , Jean-Yves Chaufray (1) , Antoine Martinez (1) , R. Lillis (4) , S. Curry (4) , M. K. Elrod (2) , P. Mahaffy (2) , Ronan Modolo (1) , J.G. Luhmann (4) , B. Jakosky (5)

1 HELIOS - LATMOS
2 GSFC - NASA Goddard Space Flight Center
3 UMBC - University of Maryland [Baltimore County]
4 SSL - Space Sciences Laboratory [Berkeley]
5 LASP - Laboratory for Atmospheric and Space Physics [Boulder]

Dedicated in‐situ measurements of Mars' exospheric Ar density by NGIMS/MAVEN highlight profiles displaying two slopes altitude variation. Below 230 km, the Ar density is characterized by scale height of 13.5 ± 1.7 km and above 400 km by scale height of 156 ± 25 km. A comparison with the model HELIOSARES suggests that the most probable origin of the Ar non‐thermal component is the collisional interaction, below the exobase, between the atmospheric Ar and the non‐thermal O atoms produced by the dissociative recombination of O₂⁺. These measurements therefore provide a new approach to constrain one of the main source of Mars' atmospheric escape. They also lead to set up an upper limit on the efficiency of pickup ion sputtering at Mars. The comparison with HELIOSARES suggests that NGIMS detection sensitivity might allow a positive detection of this mechanism if more measurements at high altitude deep in the nightside are performed.

Domaines: Astrophysique [astro-ph]

François Leblanc, M. Benna, Jean-Yves Chaufray, Antoine Martinez, R. Lillis, et al.. First in situ evidence of Mars nonthermal exosphere. Geophysical Research Letters, 2019, 46 (8), pp.4144-4150. ⟨10.1029/2019GL082192⟩. ⟨insu-02078150⟩