ESA Science & Technology - Global Mars-solar wind coupling and ion escape

Publication date: 04 August 2017

Authors: Ramstad, R., et al.

Journal: Journal of Geophysical Research
Volume: 122
Issue: 8
Page: 8051-8062
Year: 2017

Copyright: © 2018 American Geophysical Union

Loss of the early Martian atmosphere is often thought to have occurred due to an effective transfer of the solar wind energy through the Martian induced magnetic barrier to the ionosphere. We have quantified the coupling efficiency by comparing the power of the heavy ion outflow with the available power supplied by the upstream solar wind. Constraining upstream solar wind density n_sw, velocity v_sw, and EUV intensity I_EUV/photoionizing flux F_XUV in varying intervals reveals a decrease in coupling efficiency, k, with solar wind dynamic pressure as k ∝ p_dyn^-0.74±0.13 and with F_XUV as k ∝ F_XUV^-2.28±0.30. Despite the decrease in coupling efficiency, higher F_XUV enhances the cold ion outflow, increasing the total ion escape rate as Q(F_XUV) = 10¹⁰(0.82 ± 0.05)F_XUV. The discrepancy between coupling and escape suggests that ion escape from Mars is primarily production limited in the modern era, though decreased coupling may lead to an energy-limited solar wind interaction under early Sun conditions.