The terrain where Phoenix set its three legs is relatively flat with polygon-shaped patterns in the ground likely caused by the expansion and contraction of underground ice.

菲尼克斯放置三个支架的地形相对来说比较平坦，地面上多角形图案看起来好像是由于地下永冻土的扩张和收缩形成的。

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The Burke-Gilman Trail follows the relatively flat terrain of an abandoned spur line of the Burlington Northern Railroad.

BBC: Cycling Seattle��s Burke-Gilman Trail

Sol 1, as the days are known on Mars, was a busy time for the three-legged lander, which set down Sunday in relatively flat terrain cut by polygon-shaped fissures.

NPR: Phoenix Sends Color Photos of Mars to NASA