New Images Show Volcanic Activity on Mercury

New images from NASA’s MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft are yielding a wealth of new information on the smallest planet in our solar system.

Earlier this year, a fly by of the planet  took hundreds of high-resolution pictures covering 30 percent of the planet’s eastern hemisphere that had never been seen before including discovering volcanoes on the planet’s surface.   The second fly by took place on October 6 on the western side, revealing another 30 percent of Mercury’s surface never seen before by spacecraft and allowing scientists to compare the two sides of the planet for the first time.

The latest fly by took images of two craters that are side-by-side on the planet’s surface.  What makes them unusual is that craters next to each other are usually about the same depth.  In the case of the craters on Mercury, one is four times as deep as the other.

The shallow crater basin, which is about the size of the greater Washington, D.C. and Baltimore metropolitan area, has been filled in with a massive amount of lava, according to Maria Zuber of MIT, one of the leaders of the Messenger mission. The 3,600 cubic miles of lava would be enough to cover the cities in a 1.5-miles thick layer.  The lava flow comes from the volcanoes discovered earlier this year.

“The surprise is that it appears to be more volcanic than the moon,” Zuber said at a press conference. “Very few people would have thought that before the first Messenger flyby.”

Mercury has a large iron core that makes up the majority of the planet’s width, Zuber said, so “volcanic processes could have continued much further into time, but the preponderance of activity probably occurred early.”

Planetary bodies tend to heat up slowly and cool off pretty quickly. Earth, which is the largest terrestrial planet in the solar system, is still active volcanically, Zuber noted, suggesting size may help slow the cooling process.

But smaller rocky bodies such as Mercury and our moon are believed to have seen most of their volcanism in their earliest history.

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 Marilyn Lindstrom, a program scientist at NASA headquarters in Washington, D.C.

But astronomers have been using the close approaches as opportunities to collect more data about an otherwise largely neglected planet.

Until recently humans had seen just 45 percent of Mercury’s surface, based on images taken during the Mariner mission in the 1970s.

Still, the new data show that Mercury had even more eruptions than the moon, “which has always been the planetary body we’ve compared Mercury to,” Zuber said.

MESSENGER’s third and final flyby is scheduled for September 29, 2009.

Below is video footage of the fly by, released by NASA.