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NASA's Messenger probe beams back amazing images of Mercury

NASA's Messenger probe, the first spacecraft ever to orbit Mercury, has already taken more than 20,000 images.

By Mike WallSPACE.com Senior Writer / June 17, 2011

This image provided by NASA Thursday shows the impact melt coating the floor of the crater Degas on the planet Mercury. After nearly three months in orbit about Mercury, Messenger's payload is providing a wealth of new information about the planet closest to the Sun, as well as a few surprises.

NASA/AP

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A NASA spacecraft circling Mercury is returning spectacular photos of the planet — and delivering some tantalizing surprises about the tiny, scorched world.

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On March 17, NASA's Messenger probe became the first spacecraft ever to orbit Mercury. Since then, Messenger has already snapped more than 20,000 pictures and made observations that could help unlock long-standing mysteries of the solar system's innermost planet, researchers announced at a press conference today (June 16).

"We had many ideas about Mercury that were incomplete, ill-formed," said Messenger principal investigator Sean Solomon of the Carnegie Institution of Washington. "Many of those ideas are now having to be cast aside as we see orbital data for the first time." [Latest Messenger Photos of Mercury]

IN PICTURES: Planets

Mercury has 'personality'

Messenger is photographing every inch of Mercury's surface from orbit, and some of its early pictures have revealed huge expanses of volcanic deposits near the planet's north pole. These features were detected by Messenger and NASA's Mariner 10 probe on previous Mercury flybys, but the new observations map them out in greater detail. [Infographic: The Messenger Mission]

"Now we're seeing their full extent for the first time," said Messenger scientist Brett Denevi of Johns Hopkins University's Applied Physics Laboratory (APL). And that extent is impressive; the northern volcanic plains cover 1.54 million square miles (4 million square kilometers) — nearly half the size of the continental United States.

These new observations help confirm that volcanism has substantially shaped Mercury's crust and surface for much of its history, researchers said.

Messenger has been scrutinizing Mercury with more than just its camera gear. The probe's X-ray spectrometer, for example, has already discovered that the planet's surface is made of different stuff than the moon, which is dominated by feldspar-rich rock.

The spectrometer has also detected surprisingly high levels of sulfur at the planet's surface, which could help scientists understand the nature of Mercury's origin and volcanism, researchers said.

So far, the spacecraft's observations are putting the lie to the notion that Mercury is similar to the moon. In fact, the early returns indicate that it's also very different than the other terrestrial planets, in ways that are only just beginning to come clear.

"Mercury really is a world in and of its own," said Messenger project scientist Ralph McNutt of APL. "Just like the Earth, it's got its own personality."

Water ice on Mercury?

Messenger is using another one of its seven instruments, a laser altimeter, to map out Mercury's topography. The spacecraft has already taken more than 2 million laser-ranging readings, revealing the planet's geological features in great detail.

"We're seeing the broad shape of the planet for the first time," Solomon said.

One of the many questions Messenger hopes to answer is whether or not Mercury harbors water ice on its surface. That might not seem very likely, since average surface temperatures on the planet can top 842 degrees Fahrenheit (450 degrees Celsius). However, Earth-based radar observations from 20 years ago suggest large amounts of ice may lurk in permanently shadowed craters at its poles.

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