Rhea 土卫五(中英)

Rhea is the fourteenth of Saturn¹'s known satellites  and the second largest:

　　orbit: 527,040 km from Saturn

　　diameter: 1530 km

　　mass: 2.49e21 kg

　　In Greek mythology² Rhea was the sister and wife of Cronus (Saturn) and the mother of Demeter, Hades (Pluto), Hera, Hestia, Poseidon (Neptune), and Zeus (Jupiter).

　　Discovered by Cassini in 1672.

　　Though somewhat larger, Rhea is otherwise very similar to Dione. They both have similar compositions, albedo features and varied³ terrain⁴. Both rotate synchronously⁵ and have dissimilar leading and trailing hemispheres.

　　Rhea is composed primarily of water ice with rock making up less than 1/3 of its mass.

　　The leading hemisphere is heavily cratered⁶ and uniformly bright. Like Callisto, the craters⁷ lack the high relief features seen on the Moon and Mercury.

　　On the trailing hemisphere there is a network of bright swaths on a dark background and few visible craters.

　　Rhea's history is probably very similar to Dione's.

　　Rhea（土卫五）是土星已知卫星中距土星第十四近的一颗，且为第二大：

　　公转轨道：距土星 527,040 千米

　　卫星直径：1530 千米

　　质量：2.49e21 千克

　　在希腊神话中，瑞亚是Cronus（萨图恩）的妹妹兼妻子，Demeter，哈迪斯 (普路托)，赫拉，Hestia，波寒冬(尼普顿)和宙斯 (朱庇特)的母亲。

　　它于1672年被卡西尼发现。

　　虽然稍微大一些，土卫五与Dione（土卫四）有些类似。它们的组成相似，反照率特征相似，有不同地形。二者都自转同步，但面向公转方向的半球不同。

　　土卫五主要由混合着冰水的岩石组成，其占卫星总质量的三分之一不到。

　　面向公转的半球环形山遍布，但亮度一致。就像木卫四，缺少在月球和水星上所具有的环形山周围地势有明显起伏的特征。

　　另一个半球上，在黑暗的背景中，一条条纹组成一个网状，可见的环形山较少。

　　土卫五的历史可能与土卫四的相似。