Mercury Ho!

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

So prosaic and anonymous an image, I almost didn't bother posting it, but this thin monochrome crescent is our first close-up view of Mercury since the last (and first) robot to visit it over twenty years ago. On Monday, MESSENGER will fly right by the closest planet to the sun, snapping pictures as it goes. This gravity assist will help it to enter orbit around Mercury some time in 2011.

This is a good excuse for me to finally get around to brushing up my orbital mechanics, firstly because of the much-bandied factoid that it takes more effort to get closer to the sun than to leave the solar system, but also because, so close to the sun and taking such a long time to rotate on its axis (about 58 times longer than the Earth) the solar day on Mercury is seriously weird.

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

As you can see, MESSENGER's journey has been pretty convoluted. More shockingly, although it's approaching Mercury right now, it's actually just over halfway through its journey to orbit insertion.

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Credit: NASA/JPL/Northwestern University

This image of Mercury is courtesy of Mariner 10, the last robot to stop by. It's a monochrome image, since Mercury is actually a kind of bronze-y brown, I believe. Now that Titan (which is larger than Mercury, btw) and Iapetus have been illuminated by Cassini's curious eye, Mercury is perhaps the most obvious world of great mystery out there. If all goes well, the veils should begin to drop starting next week...