Mars Curiosity rover captures video of Martian moons

NASA's Mars Curiosity rover has captured remarkable images of one of the planet's two moons eclipsing the other.

The images were taken on August 1 by the rover's Mast Camera (Mastcam) instrument. The sequence shows Phobos, the larger of the two moons, passing in front of Deimos, which is about half its size. NASA says it's the first time the phenomenon has been observed from the Martian vantage point.

The Curiosity rover landed on Mars one year agothis month, and has been sending back fascinating pictures, video and scientific data ever since.

Mastcam co-investigator Mark Lemmon of Texas A&M University says the rover's observations could help shed light on the orbits of the Martian moons. "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," he said. "We may also get data good enough to detect density variations within Phobos and to determine if Deimos' orbit is systematically changing."

The two moons were long thought to be asteroids that got captured in Mars' orbit. However, some scientists believe they are actually chunks of Mars itself that broke off as the result of an ancient cosmic collision.

Phobos measures just under 7 miles across, and its shape is more elongated than spherical. It orbits about 3,700 miles from the surface of Mars, and it's slowly drawing in closer to the red planet. Astronomers believe that in another 50 million years or so, the two could collide.

Deimos is not quite 4 miles in diameter, and its orbit is much more distant -- more than 12,400 miles from Mars. It may be slowly drifting even farther away.

The two moons were unknown until 1877, when they were spotted by American astronomer Asaph Hall.