Changing Planet

Probe to Attempt Nearest-Ever Flyby of Mars’s Largest Moon on Sunday

NASA Mars Reconaissance Orbiter snapped this high resolution image of the Martian moon Phobos back in 2008. Credit: NASA/JPL/University of Arizona
NASA Mars Reconnaissance Orbiter snapped this high resolution image of the Martian moon Phobos back in 2008. Credit: NASA/JPL/University of Arizona

As Europe’s Mars Express celebrates 10 years in orbit around the Red Planet it’s getting set to make a daredevil dive on our neighboring world’s largest moon, called Phobos.

Flying past at only 28 miles (45 kilometers) above its craggy surface on December 29, this will be the closest encounter with the potato-shaped moon ever attempted.

“At just 45 km from the surface, our spacecraft is passing almost within touching distance of Phobos,” said Michel Denis, the Mars Express Operations Manager, on the agency’s website.

“We’ve been carrying out manoeuvres every few months to put the spacecraft on track and, together with the ground stations that will be monitoring it on its close approach, we are ready to make some extremely accurate measurements at Phobos.”

Because the flyby speed will be so high, no photos will be possible during this encounter. But European Space Agency (ESA) researchers hope that as the spacecraft swoops in, the gravitational tug of the 17-mile (27 kilometer) wide Phobos will slightly change its speed,  helping researchers better understand the moon’s internal makeup.

Previous flybys, including the last one back in March 2010, have shown that Phobos, along with its smaller, more distant sister moon Diemos, are just piles of rubble that are barely held together by gravity. According to hotly contested theories, both Martian moons are most likely captured asteroids, or debris from an ancient impact that was shot into space.

“By making close flybys of Phobos with Mars Express in this way, we can help to put constraints on the origin of these mysterious moons,” said Olivier Witasse, ESA’s Mars Express project scientist.

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Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.
  • straw walker

    It doesn’t look like a pile of rubble. but it definitely has had a large number, of asteroid crater..In fact comparing other moons, it would seem to me that these 2 moons have far more craters than any other moons in the solar system. Would not this indicate that the moons were closer to the epic centre.

  • Apollo17

    Great shot of phobos but I fail to see how they can consider it a pile of rubble held together by gravity,are we looking at the same thing?

  • Lorna Amamo

    This is great shot the phobos moon is compact you cannot say its a rubble.

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