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Scientists begin study as Mercury images pour in

The Baltimore Sun

LAUREL - Like Columbus' crew reconnoitering the coast of the New World with spyglasses, scientists with NASA's Messenger mission gathered in an unremarkable office park yesterday to take in mankind's first glimpse of broad swaths of the planet Mercury.

Hunched over computer monitors, they pointed out bright young craters and marveled at the energy of a meteor impact that threw debris halfway around the planet. With fingers, they traced fault lines for hundreds of miles and speculated about the forces that cracked and wrinkled the planet's crust.

Even more photos and data were still being downloaded from Messenger yesterday by a team based at the Johns Hopkins University's Applied Physics Lab here - the same group that worked Messenger's first Mercury flyby 10 months ago.

"Everybody here is having a great time. It's like the candy store has been locked for 10 months, and we've all just been let in with $10 in our pockets," said Sean C. Solomon of the Carnegie Institute of Washington, the principal investigator for the Messenger team at APL.

Messenger flew within 124 miles of Mercury on Monday morning, and Solomon and his crew were all smiles yesterday as the $446 million mission's scientific payoff continued.

Until this year, the only close-up pictures scientists had of Mercury were video images taken by Mariner 10 during three flybys in 1974 and 1975. Less than half the planet was photographed then. Monday's flyby has brought 30 percent more into view.

"Now we have 95 percent of the planet imaged, and it's going to allow us for the very first time to have a global view of our neighbor," Solomon said.

One of the first to see the new territory on Mercury was Brett Denevi, 28, a postdoctoral student from Arizona State University and a member of the mission's science team. She was seated at one of four computers in APL's Messenger Science Operations Center, a bedroom-size space in a low-rise office building off U.S. 29.

Dozens more scientists, their students and post-docs were scattered elsewhere in the building with their laptops, poring over the scientific bonanza.

Denevi's task was to assemble a color photo mosaic of a heavily cratered swath near the planet's equator. It was the most finely detailed picture of Mercury ever, with details as small as 300 yards across. When matched to Messenger data on the region's chemical composition and elevation, Solomon said, "it will be a very heavily studied piece of terrain."

Already, planetary scientists could point out huge impact craters billions of years old. Their basins are filled with layers of lava and debris.

The colors on Denevi's monitor were dominated by grays and exaggerated reds and blues. The brighter and bluer colors betray the craters' relative youth. "Space weathering," she explained. Hundreds of millions of years of pounding by metallic micro-meteorites adds a lot of iron. "The longer the exposure, the darker and redder things get."

One of the most striking newly discovered features on Mercury are bright lines or "rays" that appear to radiate in all directions from an unnamed crater like lines of longitude on a globe. They're trails of debris, launched from the crater by the meteor impact, that dropped back to the surface along paths hundreds to thousands of miles long.

Some of the rays were visible on old Mariner 10 images. The crater was detected in radar images obtained in the 1990s by an observatory in Puerto Rico. But only now, with Messenger's latest photos, is the connection between the crater and the rays obvious.

The long-distance debris scattering also reveals something about the high velocities of space rocks that accelerate toward the sun, only to smash into Mercury, Solomon said: "These are very high-energy impacts compared to what we're used to."

"You're seeing science on the hoof here," said APL's Messenger project scientist Ralph L. McNutt.

To see more photos, go to http://messenger.


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