One of only two Martian moons, Phobos has been described as no more than a tiny rock. NASA also notes that Phobos is on a collision course with Mars. As NASA writes, "Phobos is nearing Mars at a rate of 1.8 [meters] every hundred years; at that rate, it will either crash into Mars in 50 million years or break up into a ring." It has a six-mile gouge in it called the Stickney crater, which experts believe was caused by a meteorite impact. Phobos is named for one of the mythical sons of the Greek god Ares, who is the Greek equivalent of the Roman god Mars.