HR: 1340h
AN: P13C-1429    [Abstracts]
TI: Painting Iapetus White
AU: * Ip, W
EM: wingip@astro.ncu.edu.tw
AF: Institute of Astronomy, National Central University, 300 Jhongda Road, Jhongli, 32054, Taiwan
AB: One of the intriguing features of Iapetus is about the remarkable dichotomy of its surface albedo distribution with the leading hemisphere being very dark (albedo about 0.05) and the trailing hemisphere being relatively bright (about 0.5). This factor of 10 difference in the surface albedos has been generally interpreted to be the result of collection of collisional ejecta from Phoebe which is also very dark (about 0.06). Being moving outside Iapetus"orbit in retrograde direction, such mechanism certainly has its distinct advantage. The first close encounter of the Cassini spacecraft in September, 2007, will bring many new measurements and insights. We would like to take this opportunity to explore a different scenario. That is, the surface material of Iapetus was initially as dark as Phoebe and the albedo dichotomy actually came from the surface impact and accretion of large amount of icy materials emitted from the inner Saturnian region during the formation of the Saturn system. For this to happen, an intrinsic magnetic field of Saturn much stronger than the present value would be required so that the water-group ions can be trapped inside the partially rotating magnetosphere containing the orbit of Iapetus. In case this possibility of reverse-coating can not be ruled out by theoretical models and scaling arguments, it would have interesting implication on the origin of Iapetus itself.
DE: 2732 Magnetosphere interactions with satellites and rings
DE: 6055 Surfaces
DE: 6060 Radiation and chemistry
DE: 6275 Saturn
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting