Cosmic dance of Mars' moons Phobos and Deimos caught on camera

NASA says sky-watching cameras on its Curiosity rover captured images of Mars' moon Phobos passing directly in front of the Red Planet's other moon Deimos. No previous images from missions on the surface of Mars have ever caught one moon eclipsing the other, the space agency reported. Large craters on Phobos -- the larger of the two moons at about 14 miles wide -- are clearly visible in the images captured by the unmanned Curiosity's mast camera of it eclipsing the smaller Deimos. Deimos is about 7.5 miles wide; both Phobos and Deimos are thought to be asteroids that have been captured by Mars' gravity. The observations will help provide more precise knowledge of the moons' orbits, researchers said. "The ultimate goal is to improve orbit knowledge enough that we can improve the measurement of the tides Phobos raises on the martian solid surface, giving knowledge of the martian interior," Mark Lemmon of Texas A&M, a co-investigator using Curiosity's mast camera, said. "We may also get data good enough to detect density variations within Phobos and to determine if Deimos' orbit is systematically changing." The orbit of Phobos is very slowly getting closer to Mars, the researchers said, while the orbit of Deimos may be slowly getting farther from the Red Planet.