Publisher Information: KTH KTH, Rymd- och plasmafysik Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA.;NYU, New York, NY 10012 USA.;New York Univ Abu Dhabi, Abu Dhabi, U Arab Emirates.;Univ Bern, Bern, Switzerland. NASA, Goddard Space Flight Ctr, Greenbelt, MD USA. NYU, New York, NY 10012 USA.;Univ Virginia, Charlottesville, VA USA. Univ Oxford, Oxford, England.;Open Univ, Milton Keynes, England. Univ Bern, Bern, Switzerland. Univ Bern, Bern, Switzerland. Univ Bern, Bern, Switzerland. Johns Hopkins Univ, Appl Phys Lab, Laurel, MD USA. New York Univ Abu Dhabi, Abu Dhabi, U Arab Emirates. Univ Bern, Bern, Switzerland.;CALTECH, Jet Prop Lab, Pasadena, CA USA. American Geophysical Union (AGU) 2022
نبذة مختصرة : We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope from sublimated H2O and radiolytically produced H-2 using the Direct Simulation Monte Carlo method. The spatial morphology of this corona produced via photoelectron and magnetospheric electron-impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O-2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark nonice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H-2 component can reproduce the observation, and is also capable of producing the enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument, providing the first evidence of H-2 in Callisto's atmosphere. The range of H-2 surface densities explored, under a variety of conditions, that are consistent with these observations is similar to(0.4-1) x 10(8) cm(-3). The simulated H-2 escape rates and estimated lifetimes suggest that Callisto has a neutral H-2 torus. We also place a rough upper limit on the peak H2O number density (less than or similar to 10(8) cm(-3)), column density (less than or similar to 10(15) cm(-2)), and sublimation flux (less than or similar to 10(12) cm(-2) s(-1)), all of which are 1-2 orders of magnitude less than that assumed in previous models. Finally, we discuss the implications of these results, as well as how they compare to Europa and Ganymede.
QC 20230309
Processing Request
No Comments.