Discovery of Phobos

Phobos is the larger and closer of the two small moons of Mars and was discovered in August 1877 by the American astronomer Asaph Hall, working at the United States Naval Observatory in Washington with a large refracting telescope. Hall found it just days before spotting the smaller moon Deimos, after he had searched persistently for Martian satellites during a close approach of the planet. Phobos is an irregular, heavily cratered body only a few tens of kilometres across, and it orbits closer to its planet than any other known moon, circling Mars in about seven and a half hours. Because its orbit is slowly shrinking, it is expected to break up or crash into Mars in tens of millions of years. The name comes from the Greek word for fear.

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