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Mercury: Unusual insides and active history

New information collected by NASA's Messenger shows that Mercury was more geologically active than scientists previously thought.

By Mike / March 21, 2012

Mercury appears to have had a more exciting geologic history than was previously understood, according to data gathered by NASA's Messenger.



The small, sun-scorched planet Mercury has an interior unlike that of any other rocky planet in our solar system and a surprisingly dynamic history, two new studies suggest.

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Using observations from NASA's Messenger spacecraft in orbit around Mercury, researchers have found that the planet's huge iron core is even larger than they had thought, and it's likely overlain with a solid shell of iron and sulfur — a layered structure not known to exist on Earth, Venus or Mars. And there's more: Mercury appears to have remained geologically active for a surprisingly large chunk of its evolutionary history, researchers said.

"Many scientists expected Mercury, being a small planet only slightly larger than the moon, to have cooled off not long after it formed and to be essentially 'dead' for most of its evolution," said Maria Zuber of the Massachusetts Institute of Technology, lead author of one of the new studies and a co-author on the other. "But it appears that Mercury had an exciting and active middle age."

Mercury from above

The $446 million Messenger (MErcury Surface, Space ENvironment, GEochemistry and Ranging) spacecraft launched in 2004. It then took a circuitous route to the solar system's innermost planet, becoming the first probe ever to orbit Mercury in March 2011. [Latest Mercury Photos from Messenger]

Since then, Messenger has been zipping around the baking-hot planet — which orbits the sun from just 36 million miles (58 million kilometers) away, compared to 93 million miles (150 million km) for Earth — once every 12 hours.

The probe is mapping Mercury's surface and gathering data on the planet's composition, magnetic environment and tenuous atmosphere, among other features. To date, Messenger has taken nearly 100,000 images and made more than 4 million measurements of the planet's surface, researchers said.

Messenger's original science campaign was designed to last one Earth year, but NASA announced in November that it had granted the spacecraft a one-year mission extension. Messenger officially began its extended mission earlier this week.

Surprising findings

The two new studies, which both appear in the March 23 issue of the journal Science, detail findings that should help scientists better understand Mercury's murky past.

In one study, researchers used observations made by Messenger's laser altimeter to map the topography of Mercury's northern hemisphere. They found that the range of elevations was smaller than that found on either Mars or the moon.

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