HR: 12:05h
AN: P22C-04    [Abstracts]
TI: Cassini Composite Infrared Spectrometer (CIRS) Observations of Iapetus' Thermal Emission, and Implications for the Hemispheric Asymmetry
AU: * Spencer, J R
EM: spencer@boulder.swri.edu
AF: Southwest Research Institute, 1050 Walnut St. Suite 300, Boulder, CO 80302, United States
AU: Pearl, J C
EM: John.C.Pearl.1@gsfc.nasa.gov
AF: NASA Goddard Spaceflight Center, Greenbelt Rd, Greenbelt, MD 20771, United States
AU: Segura, M
EM: msegura@cirsrss.gsfc.nasa.gov
AF: NASA Goddard Spaceflight Center, Greenbelt Rd, Greenbelt, MD 20771, United States
AU: Team, C
EM: John.C.Pearl.1@gsfc.nasa.gov
AB: During the flyby of Iapetus on September 10th 2007, The Composite Infrared Spectrometer (CIRS) on the Cassini Saturn orbiter spacecraft will provide high-resolution maps of thermal emission from the dark leading hemisphere at night, and from the bright terrain and the bright/dark transitional region on the trailing hemisphere during the day. These data, combined with daytime observations of the dark hemisphere from January 2005, will provide a much improved picture of diurnal temperature variations on Enceladus, allowing comparison of the thermal inertias of the dark and bright terrains. The temperature data will also yield improved constraints on the stability of H₂O ice and other ices on the different terrains on Iapetus, perhaps shedding light on the peculiar distribution of bright and dark terrain on this satellite. The bright terrain on Iapetus is concentrated on the trailing hemisphere but extends over the poles onto the leading hemisphere, while the dark terrain, centered on the leading hemisphere, extends around the equator onto the trailing side. Our 2005 model (Spencer et al. 2005, Division for Planetary Sciences Meeting, Cambridge, abstract #39.08) explains the shape of this boundary in terms of modification of a simple exogenic leading/trailing asymmetry by ice migration. Ice is proposed to sublime from the warm, dark leading hemisphere and collect in the polar regions, which become brighter, while bright low-latitude regions on the trailing hemisphere may experience sufficient ice sublimation to darken by formation of a surface lag deposit. CIRS observations of the daytime temperatures of the bright terrain at low latitudes will determine whether this terrain is indeed warm enough for significant ice sublimation, thus providing a test of the sublimation model.
DE: 5410 Composition (1060, 3672)
DE: 5422 Ices
DE: 5470 Surface materials and properties
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting