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Mercury Rising

by Bruno Van de Casteele

April 7, 2013

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Donate There were two interesting news stories last month about Mercury. Closest to our Sun, it's a bit bigger as our Moon. Due to its proximity to the Sun, it's one of the hotter places in our solar system (although Venus is hotter due to the green house effect), and also one of the coldest. That may sound odd, but there is no atmosphere on Mercury to dampen temperature differences, so the night side is very cold.

The first news item was about a meteorite found in Morocco. After investigation, Irving (professor at the University of Washington), identified it as likely coming from Mercury. Or, in a description reminiscent of the first announcement of the Higgs boson discovery, it's a rock created on a body that resembles Mercury and its magnetic field.

How did NWA 7325 (the name of this meteorite) get here? It's already known that a big impact on a planetary body can eject some material at such a high speed that it reaches escape velocity and leaves the planet. After a (very) long travel through space, some of it ends up on other planets, like Earth. We know this happens with Mars meteorites, but it's a first for Mercury. Indeed, it is very exceptional that such a rock would survive being in the vicinity of the sun, and slowly make it into the neighborhood of Earth, and impact with it. Oh, and that it lands on solid ground (about 30% chance) and gets found. Very slim odds indeed.

But that is exactly what we suspect happened to this green meteorite. If confirmed (and it seems rather solid evidence), that is a very rare find indeed.

The second news item is a bit related to the first. We currently have a probe around Mercury, called Messenger. Because of its detailed analysis of Mercury, we know more about the structure of its rocks and its magnetic field. This helped show that there is a possible link between the meteorite and Mars.

But there is more. As odd as it may sound after 50 years of spaceflight, we never had a complete, detailed view of this planet. Mariner 10 passed three times in 1975 before it ran out of fuel. It was only able to photograph about half of the planet, the rest remained unknown. Oddly enough, there was no more interest in getting to Mercury until we launched the Messenger probe in 2004. And only last month, a complete and detailed map of Mercury, created by combining thousands and thousands of pictures, was finally published by NASA (the last 1% took a long time). If you like this sort of stuff, you should download the full image, and enjoy the awesome resolution - each pixel is only 1 km across!

In short, March was a very good month for Mercury news. Humbling news, that a piece of rock made it all the way, and amazing news, that we can map a planet in such detail. And a bit disconcerting too, that it took us so long to get back to it. Oh, and do you think it's a coincidence these news items pop up now? Maybe, but do keep in mind that the first mission extension is expiring, and that NASA is considering a second prolongation. So popping up in the news is probably a good idea...

by Bruno Van de Casteele

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