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Curiosity looks up, spies Martian double-mooning

Phobos overlaps Deimos in video treat

Curiosity self-portrait at Rocknest in the Gale Crater

Video As Curiosity trundles across the Martian surface, the bulk of NASA's interest has been focused downwards at the ground, but the rover has also been looking up and has captured some remarkable video of the two moons of Mars overlapping each other overhead.

The images captured by the telephoto lens in Curiosity's Mast Camera show Phobos, the largest of Mars' twin moons, eclipsing its smaller and more distant brother Deimos. The rover was able to capture the conjunction on August 1 and beam the data up to the Mars Reconnaissance Orbiter for transmission back to Earth.

NASA knows enough about the orbital paths of the moons to ensure that Curiosity was looking up at the right time, and the new images will be used to calculate their orbits with much greater precision than before, measure their influence on their home planet, and provide a look at the craters of Phobos.

"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," said Mark Lemmon, co-investigator for use of Curiosity's Mastcam.

"We may also get data good enough to detect density variations within Phobos and to determine if Deimos' orbit is systematically changing," he added.

Current measurements suggest that Deimos is moving away from the Martian surface, albeit at a very slow rate. Phobos orbits Mars much closer to the surface, and is to be spiraling inwards. It's thought that it will eventually be broken up and form a planetary ring around Mars. ®

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