![Phobos, one of two satellites of Mars. The sunlit feature on the upper left is the crater Stickney; …[Credits : Photo NASA/JPL/Caltech (NASA photo # PIA01333)]](http://media-2.web.britannica.com/eb-media/91/21191-004-E0A2C157.jpg)
Phobos, one of two satellites of Mars. The sunlit feature on the upper left is the crater Stickney; numerous smaller craters are visible elsewhere on the satellite’s surface. The grooved lines around the crater may be fracture lines, remnants of the same collision that produced Stickney. This image was taken by the Mars Global Surveyor spacecraft.
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