NASA’s Messenger spacecraft took this parting shot of the planet Mercury after its close flyby in September 2009. When it passes Mercury again this Thursday, it will slow down and drop into orbit. From there, it will completely map the surface of this mysterious planet.

NASA/Courtesy

NASA’s Messenger spacecraft took this parting shot of the planet Mercury after its close flyby in September 2009. When it passes Mercury again this Thursday, it will slow down and drop into orbit. From there, it will completely map the surface of this mysterious planet.

Jimmy Westlake: Messenger arrives at Mercury

Spacecraft could solve long-standing mysteries about planet

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Jimmy Westlake

Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.

Find more columns by Westlake here.

— The Messenger spacecraft is about to become the first craft ever to orbit Mercury, the solar system’s innermost planet. Launched from Earth Aug. 3, 2004, Messenger has been looping around Earth and Venus in an epic game of celestial billiards for the past six years in order to nudge Messenger toward its target. Messenger has zoomed past Mercury three times during the years since its launch, but on its next pass, on Thursday, Messenger will fire its braking engine and drop into a polar orbit around the hot little planet.

Mercury has been largely unexplored territory for decades, since the only previous spacecraft to zoom past it, NASA’s Mariner 10, was way back in the mid-1970s.

Someone at NASA had to really stretch their imagination to come up with an acronym for their Mercury-bound spacecraft, Messenger. The letters stand for MErcury Surface, Space Environment, GEochemistry and Ranging. The name is apparently a play on the identity of Mercury as the swift Messenger god from Roman mythology.

Throughout a period of months, Messenger will map the entire surface of Mercury and hopefully answer some nagging questions about our neighboring world.

For example, why is Mercury so dense? It appears to be a planet made of nearly pure iron, toped off with a thin, rocky crust. Such a planet should not exist, according to our present understanding of planet formation.

Another mystery: Does Mercury really have deposits of ice in the shadowed craters near its north and south poles? Some observations from Earth have suggested that it might, but it would be a very startling discovery on such a hot, foreboding world.

Yet another mystery: What caused the long, meandering faults, called scarps, that cover Mercury’s surface? No other world we’ve studied has such a global network of faults.

As fate would have it, you can spot the illusive planet Mercury for yourself this week without optical aid, low in the western sky after sunset. It looks like a bright, yellowish star very close to the slightly brighter planet Jupiter. Catch these planets early, though, because they set by 8:30 p.m., only an hour and a half behind the sun.

Stay tuned to the news media in the coming days for spectacular photos and science from our Mercury Messenger. For more information, check out NASA’s Messenger Mission home page at http://messenger.jhuapl.edu/.

Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all around the world. Visit Westlake’s website at www.jwestlake.com.

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