Io's Atmospheric Freeze-out Dynamics in the Presence of a Non-condensable Species
- University of Texas at Austin, Department of Aerospace Engineering, 210 E. 24th St. W.R. Woolrich Laboratories, 1 University Station C0600 Austin, Tx. 78712 (United States)
One dimensional direct simulation Monte Carlo (DSMC) simulations are used to examine the effect of a trace non-condensable species on the freeze-out dynamics of Io's sulfur dioxide sublimation atmosphere during eclipse and egress. Due to finite ballistic times, essentially no collapse occurs during the first 10 minutes of eclipse at altitudes above {approx}100 km, and hence immediately after ingress auroral emission morphology above 100 km should resemble that of the immediate pre-eclipse state. In the absence of a non-condensable species the sublimation SO2 atmosphere will freeze-out (collapse) during eclipse as the surface temperature drops. However, rapid collapse is prevented by the presence of even a small amount of a perfect non-condensable species due to the formation of a static diffusion layer several mean free paths thick near the surface. The higher the non-condensable mole fraction, the longer the collapse time. The effect of a weakly condensable gas species (non-zero sticking/reaction coefficient) was examined since real gas species may not be perfectly non-condensable at realistic surface temperatures. It is found that even a small sticking coefficient dramatically reduces the effect of the diffusion layer on the dynamics. If the sticking coefficient of the non-condensable exceeds {approx}0.25 the collapse dynamics are effectively the same as if there was no non-condensable present. This sensitivity results because the loss of non-condensable to the surface reduces the effective diffusion layer size and the formation of an effective diffusion layer requires that the layer be stationary which does not occur if the surface is a sink. As the surface temperature increases during egress from eclipse the sublimating SO2 gas pushes the non-condensable diffusion layer up to higher altitudes once it becomes dense enough to be collisional. This vertical species stratification should alter the auroral emissions after egress.
- OSTI ID:
- 21254950
- Journal Information:
- AIP Conference Proceedings, Vol. 1084, Issue 1; Conference: 26. international symposium on rarified gas dynamics, Kyoto (Japan), 20-25 Jul 2008; Other Information: DOI: 10.1063/1.3076442; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0094-243X
- Country of Publication:
- United States
- Language:
- English
Similar Records
Theoretical studies of Io's atmosphere
A SPITZER TRANSMISSION SPECTRUM FOR THE EXOPLANET GJ 436b, EVIDENCE FOR STELLAR VARIABILITY, AND CONSTRAINTS ON DAYSIDE FLUX VARIATIONS