Photochemical escape of oxygen from Mars: A comparison of the exobase approximation to a Monte Carlo method

Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars

“…Several hot O transport models have been constructed to simulate this, including two-stream, Monte Carlo, and DSMC (Direct Simulation Monte Carlo) models [e.g., Nagy and Cravens, 1988;Ip, 1990;Kim et al, 1998;Hodges, 2000;Hać, 2009, 2014;Valeille et al, 2009aValeille et al, , 2009bValeille et al, , 2010aValeille et al, , 2010bYagi et al, 2012;Lee et al, 2013;Gröller et al, 2014]. But these photochemical escape rate calculations vary by about 2 orders of magnitude as summarized in Table 3 of Fox and Hać [2009], and there is a lack of direct observational constraint on photochemical escape models.…”

Modeling of Venus, Mars, and Titan

“…Monte Carlo simulations have been used to describe exospheric hot oxygen density and escape produced by the dissociative recombination of O + 2 ions (Hodges 2000;Krestyanikova and Shematovich 2005;Cipriani et al 2007;Chaufray et al 2007;Valeille et al 2009a;Fox and Hac 2009) and sputtering Johnson 2001, 2002;Cipriani et al 2007;Chaufray et al 2007). The main inputs of Monte Carlo models are the thermosphericionospheric background and collisions cross-sections between hot oxygen atoms and thermospheric species (mainly CO 2 and thermal O).…”

“…To describe Mars' hot oxygen corona, which is produced by O + 2 dissociative recombination, first a realistic O + 2 density profile, electron temperature profile, and a neutral density profile (to calculate collisions) are assumed to compute the production rates of hot oxygen. Cipriani et al (2007), Krestyanikova et al (2005) and Fox and Hac (2009) assume a spherically symmetry O + 2 and neutral density profile based on 1D photochemical models (Krasnopolsky 2002;Fox and Hac 2009). To describe sputtering, Leblanc and Johnson (2001) only need neutral density profiles, taken from Zhang et al (1993), and include a day/night asymmetry in the temperature profile.…”

“…The addition of one vibrational quantum adds about 0.23 eV to the exothermicity (Fox and Hac 1997). The vibrationally excited states of O + 2 ions are controlled by ion-neutral reactions in the thermosphere (Fox and Hac 1997) and their altitude distributions have been modeled in the Martian ionosphere by Fox and Hac (2009) at a 60 • solar zenith angle (see also Futaana et al 2011, this issue). The production rates from Mehr and Biondi (1969) and Peverall et al (2001) are displayed in Fig.…”

“…In Monte Carlo models, the hot oxygen atoms simulated by "representative" particles or test particles, which are followed along their trajectory. This approach uses more realistic 2D or 3D thermospheric-ionospheric environments (Hodges 2000;Leblanc and Johnson 2002;Chaufray et al 2007;Valeille et al 2009aValeille et al , 2009b or realistic cross sections to describe the collision between hot oxygen atoms and the background atmosphere (Krestyanikova and Shematovich 2005;Cipriani et al 2007;Fox and Hac 2009). The collision cross sections of hot oxygen and cold thermospheric species are crucial parameters, as shown by several studies (Shizgal 1999a;Johnson et al 2000;Cipriani et al 2007;Fox and Hac 2009;Lichtenegger et al 2009).…”