Weird "Spider," Volcanism Discovered on Mercury

January 30, 2008

The solar system's smallest planet created a huge buzz today as NASA unveiled preliminary photos and findings from the first Mercury flyby in 30 years.

The photos reveal widespread volcanic activity, asteroid assaults, and a spider-shaped formation the likes of which have never before been seen in the solar system.

The MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft cruised past the innermost planet on January 14.

The approach was the first of three planned flybys that will eventually position the probe to settle into orbit around Mercury in March 2011.

Until MESSENGER, Mariner 10 had been the only spacecraft to scope out the planet. The craft had swung by in 1974 and 1975, but it left more than half the planet unseen by human eyes.

During the MESSENGER flyby, cameras captured 1,213 images, revealing another 30 percent of the tiny planet. (Related photo: "First View of Mercury's 'Other Face'" [January 16, 2008].)

"We were continually surprised," Sean Solomon, MESSENGER's principal investigator at the Carnegie Institution of Washington, D.C., said during a press briefing.

"It was not the planet we expected. It was not [like] the moon. It's a very dynamic planet with an awful lot going on."

Volcanic Oozing

With Pluto's demotion to "dwarf planet" last year, Mercury became the smallest planet in our solar system. The rocky world is 3,031 miles (4,879 kilometers) across, hardly bigger then Earth's moon.

But its petite stature has not spared it from massive bombardment, the MESSENGER photos revealed.

The surface is pockmarked by craters—some reaching 100 feet (30 meters) across or bigger—from asteroid impacts.

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