Each day we feature a different image or photograph of our fascinating universe, along with a brief explanation written by a professional astronomer. Pictured above is Deimos , the smallest moon of Mars . In fact, Deimos is the smallest known moon in the Solar System measuring only 9 miles across. Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler , the astronomer who derived the laws of planetary motion.
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