Open AccessHeavy‐ion flux enhancement in the vicinity of the Martian ionosphere during CIR passage: Mars Express ASPERA‐3 observations
Author(s) -
Hara T.,
Seki K.,
Futaana Y.,
Yamauchi M.,
Yagi M.,
Matsumoto Y.,
Tokumaru M.,
Fedorov A.,
Barabash S.
Publication year - 2011
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2010ja015778
Subject(s) - martian , mars exploration program , solar wind , ionosphere , atmosphere of mars , physics , flux (metallurgy) , ion , atmospheric sciences , geophysics , computational physics , astrobiology , plasma , materials science , quantum mechanics , metallurgy
A characteristic heavy‐ion signature observed in the vicinity of the Martian ionosphere during passages of Corotating Interaction Region (CIR) structures in solar wind is reported. We analyzed data obtained by the IMA/ASPERA‐3 onboard the Mars Express (MEX) from September to October 2007. We compared the solar wind velocity at Mars derived from a shifted Maxwellian fitting to the IMA data with time‐shifted Advanced Composition Explorer satellite data taken at ∼1 AU to the Martian orbit. Using the derived solar wind velocity, we identified four CIR structures passing through Mars quasiperiodically. Coinciding with the CIR passages, the IMA observed heavy‐ion flux enhancement in the vicinity of the Martian ionosphere. The heavy‐ion energies reach ≥100 eV and sometimes up to approximately several kiloelectron volts. Observed ion velocity distribution functions show that they are mainly precipitating toward the Martian ionosphere. The flux of the precipitating ions is typically 10 5 –10 6 (10 4 –10 5 ) cm −2 s −1 for the energy range of 50–500 eV (≥500 eV) and it becomes by one order of magnitude higher in one event. While the flux level is consistent with a previous model prediction of sputtering ions, the intermittent occurrence of the heavy‐ion precipitation differs from conventional expectation of constant precipitation. These results suggest that the efficiency of the sputtering process in the Martian atmospheric escape is highly variable with dynamic solar wind variations.