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I. Temperatures of polar ice deposits on mercury and the moon. II. Jovian atmospheric dynamics from Galileo imaging

Citation

Vasavada, Ashwin R. (1998) I. Temperatures of polar ice deposits on mercury and the moon. II. Jovian atmospheric dynamics from Galileo imaging. Dissertation (Ph.D.), California Institute of Technology. https://resolver.caltech.edu/CaltechTHESIS:01282013-083854060

Abstract

Locations on Mercury that produce ice-like radar responses lie within impact craters that have very cold, permanently shaded floors. The retention of possible ice deposits is determined largely by their temperature. We present model- calculated temperatures of flat surfaces and surfaces within bowl-shaped and flatfloored polar impact craters. Our model includes appropriate insolation cycles, realistic crater shapes, multiple scattering of sunlight and infrared radiation, and depth and temperature-dependent regolith thermophysical properties. Unshaded water ice deposits are rapidly lost to sublimation on Mercury and the Moon. Meter-thick deposits of water ice are stable to evaporation over the age of the solar system if located in the permanently shaded portions of flat-floored craters within 10° latitude of the poles of either planet. Results for craters associated with radar features on Mercury are consistent with stable water ice deposits if a thin regolith layer thermally insulates the lowest latitude deposits, reducing sublimation rates. A regolith cover also is a diffusion barrier, reduces losses from sputtering, impact vaporization, and exposure to H Lyα, and is implied independently by the radar observations. Impact craters near the lunar poles contain colder permanently shaded regions than those on Mercury.

During the first six orbits of the Galilee spacecraft's prime mission, the Solid State Imaging system acquired multispectral image mosaics of Jupiter's Great Red Spot, an equatorial belt/zone boundary, a "5-µm hotspot" similar to the Galilee Probe entry site, and two of the classic White Ovals. We present mosaics of each region approximating their appearance at visible wavelengths and showing cloud height and opacity variations. The local wind field is derived by tracking cloud motions between multiple observations of each region with time separations of roughly one and ten hours. Vertical cloud structure is derived in a companion paper by Banfield et al.(1998). Galilee's brief, high-resolution observations complement Earth-based and Voyager studies, and offer local meteorological context for the Galileo Probe results. Images taken one hour apart reveal small, rapidly changing, high cloud features possibly analogous to terrestrial thunderstorms. Our results show that the dynamics of the zonal jets and large vortices have changed little since Voyager, with a few exceptions. We detect a cyclonic current within the center of the predominantly anticyclonic Great Red Spot. The zonal velocity difference between 0°s and 6°S has increased by 20 m s^(-1). We measure a strong northeast flow approaching the hotspot. This flow indicates either massive horizontal convergence or the presence of a large anticyclonic vortex southeast of the hotspot. The current compact arrangement of two White Ovals and a cyclonic structure greatly perturbs the zonal jets in that region.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Planetary Science and Electrical Engineering
Degree Grantor:California Institute of Technology
Division:Geological and Planetary Sciences
Major Option:Planetary Sciences
Minor Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Ingersoll, Andrew P.
Group:Astronomy Department
Thesis Committee:
  • Unknown, Unknown
Defense Date:18 May 1998
Record Number:CaltechTHESIS:01282013-083854060
Persistent URL:https://resolver.caltech.edu/CaltechTHESIS:01282013-083854060
ORCID:
AuthorORCID
Vasavada, Ashwin R. 0000-0003-2665-286X
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:7447
Collection:CaltechTHESIS
Deposited By: Benjamin Perez
Deposited On:28 Jan 2013 17:07
Last Modified:02 Dec 2020 02:39

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