On the properties of O + and O 2+ ions in a hybrid model and in Mars Express IMA/ASPERA-3 data: A case study

Abstract

We have performed a numerical simulation to analyze the energy spectra of escaping planetary O + and O 2 + ions at Mars. The simulated time–energy spectrograms were generated along orbit no. 555 (June 27, 2004) of Mars Express when its Ion Mass Analyzer (IMA)/ASPERA-3 ion instrument detected escaping planetary ions. The simulated time–energy spectrograms are in general agreement with the hypothesis that planetary O + and O 2 + ions far from Mars are accelerated by the convective electric field. The HYB-Mars hybrid model simulation also shows that O + ions originating from the ionized hot oxygen corona result in a high-energy ( E>1 keV) O + ion population that exists very close to Mars. In addition, the simulation also results in a low-energy ( E<0.1 keV) planetary ion population near the pericenter. In the analyzed orbit, IMA did not observe a clear high-energy planetary ion or a clear low-energy planetary ion population near Mars. One possible source for this discrepancy may be the Martian magnetic crustal anomalies because MEX passed over a strong crustal field region near the pericenter, but the hybrid model does not include the magnetic crustal anomalies.