自從土衛八Iapetus被發現以來，其對比鮮明且不對稱分布的反照率(Albedo)一直是爭議點。在2004年的觀測中，卡西尼(Cassini)探測船拍攝到許多前所未見的清晰影像，引導我們重新審視這顆中等大小的冰質衛星--Iapetus。其中，表面溫度的測量，對於了解Iapetus上揮發性冰物質之昇華經歷與傳輸過程，有著特殊地位。例如，在假設外球層存在的前提下，我們有興趣去探討一些氣體分子：氧氣、二氧化碳等等之可能的時間變化與表面濃度分布。為了達到此目的，首先根據不對稱分布之反照率建立了表面溫度模型。然後，在模擬這些氣體分子在Iapetus表面彈跳的過程中，將此表面溫度模型應用於Monte Carlo彈道模型中。這個數值模擬模型，目的是為2007年卡西尼探測船飛掠Iapetus之觀測，提供一個預測結果。 Because of its remarkable asymmetry in its surface albdeo distribution, Iapetus has been the focus of attention since its first discovery. The Cassini observations in 2004 have given us a new view of this icy satellite of medium size. The measurements of the surface temperature are of particular value for the understanding of the sublimation history and surface transport of volatile ice on Iapetus. For example, we are interested in knowing the possible time variations and surface distributions of the O2, CO2 and other gas molecules if a tenuous exosphere can exist. For this purpose, a thermal model with the albedo asymmetry has been constructed. The computed surface temperature distribution is used as input to a Monte Carlo model of the ballistic transport of the gas molecules across the surface of Iapetus. This numerical simulation is performed in preparation of the close encounter observations with Iapetus by the Cassini spacecraft in 2007.
