Effects of an Intrinsic Magnetic Field on Ion Loss From Ancient Mars Based on Multispecies MHD Simulations

Abstract

Ion loss to space has played an important role in atmospheric escape and climate change on Mars because of intense solar activity during a younger, more active phase of the Sun. Although the existence of an intrinsic magnetic field on ancient Mars is also a key factor in ion loss, its effect remains unclear. Based on multispecies magnetohydrodynamics (MHD) simulations, we investigated processes and rates of ion loss from Mars under extreme solar conditions and the existence of a dipole field with different strengths. The effects of a dipole field on ion loss depend on whether the dipolar magnetic pressure is strong enough to sustain the solar wind dynamic pressure. When the dipole field is existent but weak, it facilitates the cusp outflow and increases the loss rates of molecular ions (O2+ and CO2+) by a factor of 6 through the high‐latitude magnetotail. When the dipole field is strong enough, the loss rates of molecular ions are decreased by 2 orders of magnitude, and peaks of the escape flux are located near the equatorial plane due to the magnetic reconnection in the northern‐dusk or southern‐dawn lobe regions. The pickup process on the extended oxygen corona created by the strong EUV flux contributes to the total O+ loss. Therefore, the effects of the dipole field are less pronounced for O+. Under more moderate solar EUV conditions, the effects on O+ loss can be stronger and thus contribute to climate change.

Did Mars Possess a Dense Atmosphere During the First $\sim400$ Million Years?

“…However, Sakata et al (2020) very recently presented a follow-up study in which they applied the same model to simulate the effect of an intrinsic magnetic field around ancient Mars of different field strengths on atmospheric escape. As input, they used again the same model atmospheres by Kulikov et al (2007), EUV flux, and solar wind characteristics as in the previously discussed study by Terada et al (2009).…”

“…For cases, where the intrinsic magnetic field is strong enough to sustain the solar wind dynamic pressure, the escape rates plummet by two orders of magnitude, indicating that a sufficiently strong intrinsic magnetic field provides a shield for ancient Mars against strong atmospheric escape (Sakata et al, 2020). Sakata et al…”

“…Since the simulations by Sakata et al (2020) are based on the background atmosphere of Kulikov et al (2007), as mentioned before, it has again to be noted that the infrared cooling of CO2 in the thermosphere. Consequently, this would lead to a significantly expanded upper atmosphere (see also Fig.…”

“…-What role did non-thermal escape processes played on Mars during the first ~400-600 million years (Terada et al, 2009;Lammer et al, 2013;Amerstorfer et al, 2017;Zhao et al, 2017;B. M. Jakosky et al, 2018;Dong et al, 2018a;Sakata et al, 2020)? In case Mars had an intrinsic magnetic field early on (Acuna et al, 1999;, was it decreasing or increasing atmospheric escape (e.g., Blackman and Tarduno, 2018;Gunell et al, 2018;Egan et al, 2019)?…”

Non-thermal escape of the Martian CO$_2$ atmosphere over time: constrained by Ar isotopes

“…The same atmospheric profiles as in Boesswetter et al (2010) (i.e. assuming no dissociation of the CO 2 molecules) were also used by Terada et al (2009) and Sakata et al (2020) and are therefore not accurate (Tian et al, 2009;Scherf & Lammer, 2021). By using the impact rates of exospheric O + and C + ions we also calculate the corresponding sputter escape rates for O, CO 2 , CO, C, 36 Ar, and 38 Ar.…”