October 14, 2014

Mass composition of the escaping plasma at Mars

Carlsson E., Fedorov A., Barabash S., Budnik E., Grigoriev A., Gunell H., Nilsson H., Sauvaud J.-A., Lundin R., Futaana Y., Holmstrom M., Andersson H., Yamauchi M., Winningham J.D., Frahm R.A., Sharber J.R., Scherrer J., Coates A.J., Linder D.R., Kataria D.O., Kallio E., Koskinen H., Sales T., Riihela P., Schmidt W., Kozyra J., Luhmann J., Roelof E., Williams D., Livi S., Curtis C.C., Hsieh K.C., Sandel B.R., Grande M., Carter M., Thocaven J.-J., McKenna-Lawler S., Orsini S., Cerulli-Irelli R., Maggi M., Wurz P., Bochsler P., Krupp N., Woch J., Franz M., Asamura K., Dierker C.

Summary: Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO+2/O+ and O+2/O+. The following ratios averaged over all events and energies were identified: CO+2/O+ = 0.2 and O+2/O+ = 0.9. The values measured are significantly higher, by a factor of 10 for O+2/O+, than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O+, followed by O+2 and CO+2. We estimate the loss of CO+2 to be 4.0 — 1024 s-1 (0.29 kg s-1) by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found. © 2005 Elsevier Inc. All rights reserved.