Effects of the IMF Direction on Atmospheric Escape From a Mars‐like Planet Under Weak Intrinsic Magnetic Field Conditions

Abstract

The planetary intrinsic magnetic field is critical when considering the atmospheric escape from planets. The strength of the intrinsic magnetic field particularly affects the interaction between solar wind and terrestrial-type planets (e.g., Chassefière & Leblanc, 2004; Seki et al., 2001), and it changes the escape mechanism. The terrestrial global magnetic field has also experienced strength changes (e.g., Guyodo & Valet, 1999) and recurring reversals over 4.6 billion years (Gyr) that could have affected the atmospheric composition of planets. It is believed that ancient Mars had a global intrinsic magnetic field of interior origin and the magnetic field decayed by ∼3.9 Gyr ago (Acuña et al., 1999). One of the pieces of evidence that ancient Mars had an intrinsic field is the existence of a "crustal magnetic field" (Acuña et al., 1999). Present-day Mars has a remanent magnetism in the crust mainly in the southern hemisphere, which is called the crustal magnetic field. The relationship between planetary climate change and the existence of intrinsic magnetic fields is an interesting research topic. It is considered that Mars had maintained a warm and wet climate until ∼4 Gyr ago (e.g., Goldspiel & Squyres, 1991; Jakosky et al., 1994; Malin & Edgett, 2003). However, the atmosphere and water were lost, resulting in only a thin Martian atmosphere. A recent model study suggests that Mars lost a large portion of the atmosphere within 500 million years of its origin (Lammer et al., 2013). The atmospheric escape can be separated into the neutral and ion escape. The neutral escape channels include the Jeans escape and hydrodynamical escape associated with the escape of relatively light species such as hydrogen,

The Impact and Mechanism of the Magnetic Inclination Angle on O+ Escape from Mars

“…In spite of the considerable transport channel controlled by the vertical magnetic field lines, the effects of ion supply and solar wind energy transfer on ion escape cannot be neglected. The supply of ions can be affected by ionization efficiency (e.g., Dubinin et al 2017b;Cui et al 2018), whereas the energy input may control by the interplanetary magnetic field direction (e.g., Weber et al 2020;Sakai et al 2021) and solar wind conditions (e.g., Nilsson et al 2011;Ramstad et al 2015;Ramstad & Barabash 2021). However, this study only considers the typical solar wind conditions as well as the strength and direction of the interplanetary magnetic field.…”

Multispecies MHD Study of Ion Escape at Ancient Mars: Effects of an Intrinsic Magnetic Field and Solar XUV Radiation

“…The IMF orientation strongly influences the interactions between the solar wind and the magnetosphere at magnetized planets. Recently, Sakai et al (2021) studied ion escape from present Mars with a weak dipole field under three different IMF direction cases, the northward IMF parallel to the dipole at subsolar, the Parker spiral IMF, and the southward IMF antiparallel to the dipole at subsolar cases. They found that the IMF orientation changes the ion escape channels and ion escape rates.…”

“…We used a three‐dimensional global multispecies MHD model REProduce Plasma Universe‐Planets (REPPU‐Planets) introduced by previous papers (Sakai et al., 2018, 2021; Sakata et al., 2020; Terada, Kulikov et al., 2009; Terada, Shinagawa, et al., 2009). The multispecies model solves the continuity equations for densities of ion species in addition to the MHD equations, that is, the continuity equation for the total density, the conservation equation for the momentum, the conservation equation for the energy, and the induction equation for the magnetic field.…”

Observations and Modeling of Martian Auroras

“…The escape rates of these atoms will help to understand the formation of hot oxygen corona and ENAs in the exosphere of Mars. The ENAs are produced by charge exchange reactions between solar wind protons and hydrogen atoms (Galli et al 2008;Milillo et al 2009;Haider and Masoom 2019;Sakai et al 2021). The hot oxygen corona is produced due to dissociative recombination of O + 2 (Zhao and Tian 2015;Cravens et al 2017).…”