SPRG Seminars
March 5, 2013:
"Modeling of the Sputtering Efficiency for Martian Atmosphere"
Yung-Ching Wang, Space Science Laboratory, University of California at Berkeley
The formation of a hot corona with the related escape rate of the oxygen atoms is an important issue affecting the evolution of the Marian atmosphere. While the dissociative recombination process appears to dominate the non-thermal escaping rate of the oxygen atoms, atmospheric sputtering by the re-impact of the pickup exospheric ions could have played a role in earlier epochs and at solar maximum in the present epoch. Due to the orientation of the interplanetary magnetic fields and the shielding of the crustal fields near Mars surface, the pickup ions may re-impact the atmosphere with a variety of angles, energies, and spatial distributions. While night-side sputtering is suggested to occur based on modeling (Li et al., 2011), the sputter component due to pickup ion impacts on the oxygen corona can be distinguished from other ejection mechanisms, such as dissociative recombination. In preparation for the Maven mission, we performed a Monte Carlo model of the upper atmosphere coupled to a molecular dynamic calculation for the molecular collisions developed by Leblanc and Johnson (2002) to study the cascade sputtering effects in the region of the Martian exobase. Different incident angle and energy spectrum of the impact ions were tested. Further calculations with more realistic pickup ion impact distributions will be performed based on the numerical results of a 3D Monte Carlo Pickup Ion Transport model, which includes the electromagnetic backgrounds from the 3D multi-species MHD simulations (Y. Ma et al., 2004; Y. Ma and A. F. Nagy, 2007).