Hot oxygen and carbon escape from the martian atmosphere

Abstract

The escape of hot O and C atoms from the present martian atmosphere during low and high solar activity conditions has been studied with a Monte-Carlo model. The model includes the initial energy distribution of hot atoms, elastic, inelastic, and quenching collisions between the suprathermal atoms and the ambient cooler neutral atmosphere, and applies energy dependent total and differential cross sections for the determination of the collision probability and the scattering angles. The results yield a total loss rate of hot oxygen of 2.3 − 2.9 × 10 25 s −1 during low and high solar activity conditions and is mainly due to dissociative recombination of O + 2 and CO + 2 . The total loss rates of carbon are found to be 0.8 and 3.2×10 24 s −1 for low and high solar activity, respectively, with photodissociation of CO being the main source. Depending on solar activity, the obtained carbon loss rates are up to ∼ 40 times higher than the CO + 2 ion loss rate inferred from Mars Express ASPERA-3 observations. Finally, collisional effects above the exobase reduce the escape rates by about 20-30% with respect to a collionless exophere.

Photochemical escape of oxygen from early Mars

“…In comparison, oxygen escape rates at exobase from DR of CO 2 + are found to be 1.3 Â 10 25 and 1.1 Â 10 25 s À1 for low and high solar activity conditions respectively (Gröller et al, 2014). Note that DR of CO 2 + has been deemed unimportant in most previous works on photochemical escape of oxygen.…”

“…Many workers have studied photochemical escape of oxygen from present Mars Cipriani et al, 2007;Fox, 1993;Fox andHać , 2009, 2014;Gröller et al, 2014;Hodges, 2000;Kim et al, 1998;Krestyanikova and Shematovich, 2006;Lammer and Bauer, 1991;Shematovich, 2013;Valeille et al, 2010;Yagi et al, 2012;Zhang et al, 1993). Fox and Hać (2009) considered isotropic and forward scattering in the center-of-mass frame in a 3D Monte Carlo Model.…”

Nonthermal dissipation of the Martian neutral upper atmosphere

“…Therefore, the thermal escape of heavy carbon and oxygen atoms cannot be efficient [1,2]. As is well known, in photochemical processes occurring in the upper atmospheres of terrestrial planets, atoms and molecules carrying excess kinetic energies are pro duced [3].…”

“…atoms [2]. The escape from the atmosphere plays a sig nificant role in Martian evolution and, probably, by virtue of changes in the supplies of volatile substances on Mars have promoted long term variations of the planet's climate [4].…”

“…There fore, to estimate the escape velocity, we need to calcu late the kinetics and the transport of suprathermal atoms in the transition region of the Martian upper atmosphere from the thermosphere (where collisions dominate) to the exosphere (where collisions are, vir tually, absent) [3]. At present, the photochemical ori gin escape of heavy atoms from the upper atmosphere of Mars is actively being studied (see, e.g., [2,[5][6][7][8][9][10]). …”