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New Images of the Martian Moons: Phobos and Deimos

Article written: 27 Nov , 2007
Updated: 26 Dec , 2015
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With a fleet of spacecraft orbiting Mars, and rovers crawling across its surface, there’s a flood of images of the Red Planet. It’s nice to know the scientists working on those missions can take the time to look elsewhere every now and then. So today, let me present to you some images of the Martian moons: Phobos and Deimos.

The two images of the Martian moons were captured by the Compact Reconnaissance Imaging Spectrometer for Mars on board NASA’s Mars Reconnaissance Orbiter. Both images were captured while spacecraft was over Mars’ night side, and the ground below was dark.

In order to reorient away from Mars to view the moons, MRO had to turn off its normal nadir-viewing geometry.

The image of Phobos (on the top) was captured on October 23, and shows features as small as 400 metres (1320 feet) across. The image of Deimos was captured on June 7, and shows features as small as 1.3 km (0.8 miles) across.

Phobos is only 21 km (13 miles) across, and orbits Mars once every 7 days, 39 minutes. Because the moon orbits Mars faster than it rotates, Phobos would appear to travel backwards across the sky from an observer on the ground. This is just an illusion, though. Even though it’s tiny, Phobos orbits so closely that it would appear to be 1/3rd the size of our own moon in the sky.

Deimos is even smaller – 12 km (7.5 miles) – but it orbits more distantly than Phobos. It takes 1 day, 6 hours and 17 minutes to orbit the planet. Deimos isn’t large enough that you could make out any features from the surface of Mars. Instead, it would just look like a bright star in the night sky.

The first ever spacecraft observations of the Martian moons were made by Mariner 9 and the Viking Orbiter spacecraft. They found the moons to have very low reflectivity, and appeared to be similar in structure to carbonaceous chondrite meteorites. This led to the commonly held view that the moons are captured asteroids.

Original Source: MRO News Release


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