Fate of Ice Grains in Saturn's Ionosphere. Issue 2 (8th February 2018)

• Record Type: Journal Article
• Authors: Hamil, O.; Cravens, T. E.; Reedy, N. L.; Sakai, S.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 2(2018)
• Page Start: 1429
• Page End: 1440
• Publication Date: 2018-02-08
• Subjects: Saturn -- ring rain -- energy crisis -- ice grains -- ionosphere -- sublimation; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024616
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: It has been proposed that the rings of Saturn can contribute both material (i.e., water) and energy to its upper atmosphere and ionosphere. Ionospheric models require the presence of molecular species such as water that can chemically remove ionospheric protons, which otherwise are associated with electron densities that greatly exceed those from observation. These models adopt topside fluxes of water molecules. Other models have shown that ice grains from Saturn's rings can impact the atmosphere, but the effects of these grains have not been previously studied. In the current paper, we model how ice grains deposit both material and energy in Saturn's upper atmosphere as a function of grain size, initial velocity (at the "top" of the atmosphere, defined at an altitude above the cloud tops of 3, 000 km), and incident angle. Typical grain speeds are expected to be roughly 15–25 km/s. Grains with radii on the order of 1–10 nm deposit most of their energy in the altitude range of 1, 700–1, 900 km, and can vaporize, depending on initial velocity and impact angle, contributing water mass to the upper atmosphere. We show that grains in this radius range do not significantly vaporize in our model at initial velocities lower than about 20 km/s. Key Points: Nanosized ice grains impacting Saturn's upper atmosphere deposit energy and/or water mass which may account for observation We model the fate of in‐falling ice in the upper atmosphere of Saturn, tracking the deposited energy/mass from individual grains With Cassini data, we can potentially determine the possible impact of "ring rain" on the energy and water mass discrepancy at Saturn