Has Messenger revealed lava flows on Mercury?
来源：未知 作者：红渝缌 时间：2019-02-26 02:07:00
By Stuart Clark (Image: NASA/JHU APL/CIW) (Image: NASA/JHU APL/CIW) Images from NASA’s Messenger spacecraft hint at the presence of solidified lava flows on the surface of Mercury. If confirmed, they should provide crucial clues to unlocking the planet’s history. The first image released after the spacecraft’s flyby on 14 January 2008, taken from a distance of 27,000 kilometres, shows dark areas near the top of the globe. “Those dark splotchy regions look like lava flows to me,” says David Rothery, a planetary scientist at the Open University in the UK. The suspected flows appear to lie on top of the original crust, he says, implying that they formed after the end of the cratering that scarred Mercury’s surface during the planet’s first half-billion years of existence. If so, then when Messenger gets a closer look at the planet’s surface, scientists will be able to compare the composition of the lava flows with the surrounding, older crust. That should provide a window onto the processes that took place in the interior of the planet after the crust formed. Planetary scientists have used a similar method to help understand the Moon’s history, comparing the older lunar highlands with the dark areas – called maria – formed by lava flows. No equivalent lava flows were visible on Mercury in the Mariner images from 1970s. “The big question we had before going back to Mercury is whether we can identify two crustal regions,” says Rothery, “This is very encouraging that we are actually going to see lava flows.” It is not the only sighting that has planetary scientists excited. Messenger team member Jeffrey Gillis-Davis of the Hawaii Institute of Geophysics and Planetology has drawn attention to the sharp cliffs and escarpments visible on the close-up images. These features indicate that the whole planet shrank as it cooled, he told New Scientist. During the flyby, Messenger recorded 1000 images, as well as other scientific data. “The increased resolution makes Mercury look like a whole new planet to discover,” says Gillis-Davis. Messenger returns for another fly-by of Mercury on 6 October this year, before finally going into orbit in March 2011. After that, Europe and Japan plan to send a combined mission to Mercury called BepiColombo. On 18 January, the European Space Agency signed a contract with Astrium in Friedrichshafen, Germany, to build the Mercury Planetary Orbiter spacecraft. Along with Japan’s Mercury Magnetospheric Orbiter, it should launch in 2013,