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Deimos ( Dee-Mos) is the second of two moons orbiting Mars. It is considered the second moon because it is much farther away from Mars than the first moon, Phobos. It is still a bit strange compared to our Moon which is generally round and follows a set pattern around the Earth.

Deimos was discovered by Asaph Hall, the same day in 1877 as the discovery of Phobos. His discovery was the first time anyone had seen the two moons of Mars, though some astronomers had written about their possible existence before.

Deimos is as unique and interesting as Mars itself, and therefore there are quite a few fun facts to be learned. Here are some of the most interesting:


  • Like an Asteroid – Deimos is a fairly small moon and looks a lot more like an asteroid than a real moon. Its largest measurement is 15 kilometers and is made with the same kind of rock and minerals that are found on both asteroids and meteorites
  • Where Did It Come From? – Because Deimos is made from the same materials as many asteroids, some scientists think that both Deimos and Phobos used to be asteroids in the asteroid belt. Another theory is that Mars was once surrounded by many rocks the same size and shape as Deimos that have disappeared over time.
  • Craters – Deimos has far fewer craters than its brother moon Phobos. The two biggest craters are about 1 and 2 kilometers across and are named Swift and Voltaire. The names come from famous writers who once wrote about the possible existence of moons around Mars. Jonathan Swift actually wrote that there were two moons well before they were actually discovered.
  • Distance from Mars – Deimos is a lot farther from Mars than Phobos. In fact, it is so far from Mars that it looks like a star in the sky most of the time. From some places on Mars, you wouldn’t even be able to see Deimos at all.
  • When Does it Rise? – Deimos rises in the east and sets in the west, but it does so at a strange speed. Instead of rising every night like our moon, Deimos rises only once every 2.7 days.
  •  In Front of the Sun – Solar eclipses on Earth are rare. When they happen, we get fairly excited and it is reported in the news for days. However, on Mars, Deimos regularly passes in front of the sun. Since it is so small, it only appears as a small black dot, but it has been recorded multiple times by landers on Mars.