Spacecraft watch comet flyby Mars

The three probes have monitored the effect of the dust trail on the planet

MRO took  these five images as it flew by the planet, revealing the comet's size.

Credit: NASA/JPL-Caltech/University of Arizona

Three spacecraft in orbit around the Red Planet have spent the last month carefully observing the effects of Comet Siding Spring that passed by Mars on 19 October 2013. This has been a fantastic opportunity to see the effect a comet’s debris trail has on a planet.

NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission and Mars Reconnaissance Orbiter (MRO) as well as ESA’s Mars Express all had to take refuge on the far side of Mars when the comet buzzed past the Red Planet at a distance on 140,000km, ten times closer than any known comet flyby of Earth.

“Observing the effects on Mars of the comet's dust slamming into the upper atmosphere makes me very happy that we decided to put our spacecraft on the other side of Mars at the peak of the dust tail passage and out of harm's way,” said Jim Green, director of NASA’s Planetary Science Division.

Since the close encounter, the three observatories have been taking measurements to find how the debris trail affected the planet. As the dust from the comet hit the thin Martian atmosphere, it was vapourised, and produced what is likely a very impressive meteor shower, though the only things around to see it were the handful of rovers on the surface. But this shower caused significant changes to the planet’s upper atmosphere.

The MAVEN spacecraft has already managed to directly sample the comet dust in Mars’s atmosphere, finding eight different metals in the grains including sodium, magnesium and iron. This is the first time that an Oort Cloud comet has been directly sampled in this way.

ESA’s Mars Express measured a huge increase in electrons following the comet’s approach, most likely caused by fine particles burning up in the atmosphere. Meanwhile MRO turned its attention to the comet itself, discovering that the nucleus was smaller than the expected 2km, and that it rotated once every eight hours.

While the rest of the world has turned its attention to another comet, 67P/Churyumov-Gerasimenko, and the Rosetta mission, these three probes have been keeping an eye on Mars’s close caller.

“This historic event allowed us to observe the details of this fast-moving Oort Cloud comet in a way never before possible using our existing Mars missions,” says Green.


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