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The Sciences

Mercury Close-Ups Reveal the Planet's Ancient Volcanic Eruptions

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On October 6, NASA's Messenger space probe swooped down to within 125 miles of the surface of Mercury, and the just-released images from that flyby are shaking up astronomers' ideas about the planet's geologic history. The remarkable pictures reveal a vast patch of lava, indicating that the planet was shaped by a long age of volcanic eruptions.

Astronomers used to dismiss Mercury, the planet closest to the sun, as mere "dead rock," little more than a target for cosmic collisions that shaped it, said MIT planetary scientist Maria Zuber. "Now, it's looking a lot more interesting," said Zuber [AP].

Messenger's cameras spotted a crater of about 60 miles in diameter that was not as deep as other nearby craters, and determined that it had been filled in with a huge amount of solidified lava.

To get an idea of how much, Zuber explains, you could imagine the entire Baltimore-Washington region covered with a layer of solidified lava about 12 times the height of the Washington monument. "So it's a great, great deal of vulcanism," she says. "That's an awful lot of volcanic material in one place for such a little planet" [NPR News].

Researchers think the eruption happened between 3.8 and 4 billion years ago.

The October 6 flyby was the second in a planned series of three close sweeps past Mercury that will ultimately put MESSENGER in orbit around the planet in 2011.... "The main purpose of this flyby was to have a trajectory correction to help us to get into orbit later," said [NASA scientist] Marilyn Lindstrom.... But astronomers have been using the close approaches as opportunities to collect more data about an otherwise largely neglected planet [National Geographic News].

The previous flyby revealed swaths of the eastern hemisphere never before seen, while the latest images reveal features of the planet's western hemisphere for the first time. Messenger's images are shown in exaggerated false color, which helps researchers study the chemical composition and age of the terrain.

Younger, rougher ground, such as the ejecta from a meteorite impact, shows up yellow. Over time, smaller impacts and the solar wind will wear it down and turn it more red. Orange areas are likely from volcanic eruptions, and the blue areas are still somewhat of a mystery [Wired News].

When the probe settles into orbit around Mercury in 2011, it will be able to study the planet's surface in still greater detail. Related Content: Bad Astronomy: The colors of Mercury 80beats: Brand New Postcards From Mercury, Courtesy of Messenger Space Probe 80beats: Mercury Is Shrinking and Cooling, Space Probe Reveals

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

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