A Tenuous, Collisional Atmosphere on Callisto
A tenuous, collisional atmosphere on Callisto Shane R. Carberry Mogana;b;c;∗, Orenthal J. Tuckerd, Robert E. Johnsone;f , Audrey Vorburgerg, Andre Gallig, Benoit Marchandh, Angelo Tafunii, Sunil Kumarc, Iskender Sahina, Katepalli R. Sreenivasana;b;f aTandon School of Engineering, New York University, New York, USA; bCenter for Space Sci- ence, New York University Abu Dhabi, Abu Dhabi, UAE; cDivision of Engineering, New York University Abu Dhabi, Abu Dhabi, UAE; dNASA Goddard Space Flight Center, Maryland, USA; eUniversity of Virginia, Virginia, USA; f Physics Department, New York University, New York, USA; gPhysikalisches Institut, University of Bern, Bern, Switzerland; hHigh Per- formance and Research Computing Center, New York University Abu Dhabi, UAE; iSchool of Applied Engineering and Technology, New Jersey Institute of Technology, New Jersey, USA Abstract A simulation tool which utilizes parallel processing is developed to describe molecu- lar kinetics in 2D, single- and multi-component atmospheres on Callisto. This expands on our previous study on the role of collisions in 1D atmospheres on Callisto composed of radiolytic products (Carberry Mogan et al., 2020) by implementing a temperature gradient from noon to midnight across Callisto's surface and introducing sublimated water vapor. We compare single-species, ballistic and collisional O2,H2 and H2O at- mospheres, as well as an O2+H2O atmosphere to 3-species atmospheres which contain H2 in varying amounts. Because the H2O vapor pressure is extremely sensitive to the surface temperatures, the density drops several orders of magnitude with increasing distance from the subsolar point, and the flow transitions from collisional to ballistic accordingly. In an O2+H2O atmosphere the local temperatures are determined by H2O near the subsolar point and transition with increasing distance from the subsolar point to being determined by O2.
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