Effects of an Intrinsic Magnetic Field on Ion Loss From Ancient Mars Based on Multispecies MHD Simulations. Issue 2 (15th February 2020)

• Record Type: Journal Article
• Authors: Sakata, R.; Seki, K.; Sakai, S.; Terada, N.; Shinagawa, H.; Tanaka, T.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 2(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-15
• Subjects: ancient Mars -- atmospheric evolution -- intrinsic magnetic field -- ion escape -- extreme solar condition; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2019JA026945
• Languages: English
• ISSNs: 2169-9380

Abstract

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. Plain Language Summary: It has been suggested that ancient Mars had an atmosphere thick enough to sustain liquid water on its surface, while present Mars only has a thin atmosphere. Ion loss to space is one of the important processes for the removal of the atmosphere because a younger Mars would have been exposed to much stronger solar activity. Over 4 Ga, Mars had an intrinsic magnetic field like that of the Earth. The existence of an intrinsic magnetic field changes the electromagnetic environment around the planet and affects the ion loss. We investigate the ion loss from Mars at approximately 4.5 Ga, assuming both the strong solar conditions and the existence of an intrinsic magnetic field using numerical simulations. The results show that the existence of the weak dipole field increases the loss of molecular ions such as O2 + and CO2 + . Contrary to the weak intrinsic magnetic field, however, a strong intrinsic magnetic field substantially decreases the loss of molecular ions. The ion loss processes are also affected by the intrinsic magnetic field. These effects of the intrinsic magnetic field are less pronounced for O + loss because of the extended O + corona. Key Points: A weak intrinsic magnetic field increases ion loss rates when the solar wind dynamic pressure exceeds the magnetic pressure (overpressure) The existence of intrinsic magnetic field facilitates cusp outflows enabling more escape of molecular ions (O2 + and CO2 + ) by a factor of 6 In nonoverpressure cases, the ion loss rates decrease by 2 orders for molecular ions, but the effect is mild for O + with extended corona