MESSENGER’s Third Flyby of Mercury

The MESSENGER spacecraft has recently made its third flyby of Mercury, taking pictures of parts of that planet that no spacecraft had earlier been able to photograph. So about 90% of the planet has now been photographed from spacecraft, leaving only some regions near the poles.

MESSENGER was launched on August 3, 2004, it flew by the Earth on August 2, 2005, by Venus on October 24, 2006 and June 5, 2007, and by Mercury on January 14, 2008, October 6, 2008, and September 29 this year. It is expected to arrive in orbit around Mercury on March 18, 2011.

It has been sent on all these flybys so it can slow down relative to the Sun by flying by those planets, making it get closer to the Sun and saving on rocket fuel.

Only one spacecraft has been sent to Mercury before it, the Mariner 10 spacecraft, which flew by 3 times in 1974 and 1975.

Mercury looks much like the Moon, with lots and lots and lots of impact craters and some lava plains. Its biggest one is the Caloris Basin, about 1550 km / 960 mi across, bigger than most of the Moon’s ones. At its antipode is some chaotic or “weird” terrain, likely produced by focusing of tremors from the Caloris impact. When MESSENGER arrives in orbit, it will have a lot to look at in the months that it will be there. Like the Moon’s surface features, many of Mercury’s likely date back to the first few hundred million years of the Solar System’s history, giving us some clues as to what had happened back then.

Mercury from MESSENGER's third flyby

Mercury from MESSENGER's third flyby

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

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