Volcanic and ferric surprises on Mercury

Volcanic activity more recent than expected, MESSENGER flyby shows

New images from the MESSENGER spacecraft’s third trip past Mercury reveal some of the most recent volcanic activity on the planet’s surface, scientists reported during a press teleconference November 3.

RECENT ACTIVITY An enhanced-color image generated from the MESSENGER spacecraft suggests relatively recent volcanic activity (yellow) on Mercury. NASA
DOUBLE BASIN Another close-up image from MESSENGER shows a double-ring basin 290 kilometers in diameter that appears to be only a billion years old. NASA
VOLCANIC VENT The crooked-edged bowl in this close-up image of Mercury is likely the volcanic vent itself. NASA

The images are evidence of activity recent enough that planetary scientists may need to rethink the planet’s history. “It was thought that the internal geological activity on Mercury ended much earlier than on any other planet,” said Brett Denevi of Arizona State University. “We’re seeing that might not be the case.”

On September 29, the spacecraft made its third and final flyby before it will settle into orbit around the innermost planet in 2011. The craft’s images fill in a 360-mile-wide swath of surface that had never been observed before.

This swath contains two features suggesting the most recent volcanic activity yet observed for Mercury, Denevi said. Both features are so new they haven’t been named yet. The first feature shows up as a bright yellow spot in enhanced color images, which is probably a blanket of material ejected from an explosive volcano. The crooked-edged bowl in the close-up image is likely the volcanic vent itself. “This is one of the best examples we’ve seen,” Denevi said. “We’ve seen other areas like this but I think this is the most spectacular.”

Another close-up image shows a double-ring basin 290 kilometers in diameter that appears to be only a billion years old, less than one-third the age of most other basins on Mercury. It could host some of the youngest volcanic material on the planet.

The flyby revealed another surprise: Mercury’s surface is composed of much more iron than scientist previously thought. The planet is well known for its dense iron core, so scientists were puzzled that earlier data suggested a surface lacking in iron. New measurements from the recent flyby show that the surface is actually rich in both iron and titanium, more like the moon’s surface. But the original puzzle gave way to a new one. Instead of being wrapped up in silicates the way iron is on the moon, Mercury’s iron seems to come in oxides.

“It’s not that we’ve necessarily made the problem any easier,” said David Lawrence of the Johns Hopkins University Applied Physics Lab. “Now we’ll have to see how iron and titanium got sequestered into these oxides to get the surface of the planet that we have today.”

Lisa Grossman

Lisa Grossman is the astronomy writer. She has a degree in astronomy from Cornell University and a graduate certificate in science writing from University of California, Santa Cruz. She lives near Boston.

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