Gaspra, Deimos and Phobos
This montage shows asteroid 951 Gaspra (top) compared with Deimos (lower left) and Phobos (lower right), the moons of Mars. The three bodies are shown at the same scale and nearly the same lighting conditions.
Gaspra is about 17 kilometers (10 miles) long. All three bodies have irregular shapes due to past catastrophic conditions. However, their surfaces appear remarkably different, possibly because of differences in composition but most likely because of very different impact histories.
The Phobos and Deimos images were obtained by the Viking Orbiter spacecraft in 1977; the Gaspra image is the best of a series obtained by the Galileo spacecraft on October 29, 1991.
