Martian corona: Nonthermal sources of hot heavy species

Abstract

[1] We have studied the production of hot O and C atoms, and hot CO 2 and CO molecules in the Martian upper atmosphere and exosphere by dissociative recombination (DR) of O 2 + and CO + ions, and sputtering of the atmosphere by incident O + pick-up ions. Production and collisional thermalization of the hot particles in the upper atmosphere are described by using a unique Monte Carlo test particle approach to simulate both nonthermal processes. Velocity distributions, atmospheric loss rates, and density profiles are derived for suprathermal O, C, CO, and CO 2 at low and high solar activity. At high solar activity the hot oxygen escape rate estimated from DR of O 2 + is found to be less than two times the sputtering rate. Sputtering is found to efficiently populate the corona with molecular species such as CO and CO 2 at high solar activity and also to produce a carbon escape rate that is comparable to that derived from the major photochemical sources. Dissociation of CO 2 molecules by the impacting pick-up ions flux are found to produce about 50% of the sputtered exospheric oxygen density at high solar activity. Collisions of the background atmospheric gas with hot O atoms produced by DR of O 2 + produce densities of hot CO 2 and CO molecules larger than 10 2 cm À3 for altitudes lower than 1000 km, at both high and low solar activity. Interestingly, the hot CO 2 density scale height is observed to be process dependent. The hot oxygen energy distributions associated with sputtering and DR near the exobase are also found to follow distinct decreasing energy laws. We suggest that the effects of the solar zenithal angle (SZA), crustal magnetic fields, and atmospheric tides on the ionospheric structure may produce exospheric signatures.

The Aeronomy of Mars: Characterization by MAVEN of the Upper Atmosphere Reservoir That Regulates Volatile Escape

“…Both 1-D and 3-D exosphere models, with widely varying complexity, have recently been used to simulate the hot atomic O distribution as well as the corresponding escape fluxes and global escape rates (e.g. Kim et al 2001;Hodges 2002;Krestyanikova and Shematovitch 2005;Cipriani et al 2007;Chaufray et al 2007;Valeille et al , 2009bValeille et al , 2010aValeille et al , 2010bYagi et al 2012). Fox and Hać (2009) also compute hot O escape fluxes and global escape rates.…”

Modeling and Simulating Flowing Plasmas and Related Phenomena

“…Cravens 1986;Kimmel et al 1987;Luhmann et al 1988;McKenzie et al 1994), Mars (cf. Cipriani et al 2007;Cravens et al 2002;Kallio et al 1997;Kallio and Koskinnen 1999), Venus (cf. Luhmann Kecskemety and Cravens 1993) and Titan (cf.…”

Neutral Upper Atmosphere and Ionosphere Modeling

“…Both 1D models (based upon 2-stream calculations and Liouville's equation) plus multi-dimensional Monte Carlo particle trajectory models have been employed in these exospheric simulations. Recent 1D spherical Monte Carlo models have been constructed by Cipriani et al (2007), extending the original work of Hodges (2000) to include hot O, C, CO 2 and CO. They also have examined more carefully the relative sources of dissociative recombination and atmospheric sputtering (Luhmann and Kozyra 1991) by O + pickup ions.…”