Mercury amazes scientists

The Baltimore Sun

Scientists poring over their first close-up data from Mercury in almost 33 years say they're delighted by some new discoveries and astonished by the remarkably sharp view of the planet captured by the Maryland-built Messenger spacecraft during its flyby Monday.

"We're just jumping up and down as each new image gets examined and new data comes down," said Messenger's principal investigator, Sean Solomon of the Carnegie Institution in Washington.

"One experimenter after another has been coming into the bullpen and showing us brand-new stuff," he said. "Even on the side of Mercury Mariner 10 was able to view 30 years ago, we're seeing things for the first time."

As Messenger flew within 124 miles of Mercury, its computers spat out preprogrammed commands for more than 1,200 photographs and observations by the spacecraft's cameras, spectrometers and other instruments.

It all went perfectly, and the data arrived Tuesday at the mission's Science Operations Center, at the Johns Hopkins University's Applied Physics Lab near Laurel.

"I was shocked at the quality ... much better than Mariner 10," said Robert G. Strom, a University of Arizona expert on craters and a Mariner 10 veteran who has written two books on Mercury. "We're ... going to have to go back and look at the entire planet all over again."

A close-up image released yesterday displayed a 300-mile-wide swath of Mercury's crater-scarred surface.

To the layman it looked like the moon. But Solomon said Mercury's brightness, colors and topography are actually quite different. There have been surprises.

"Mariner 10 saw these big, big cliff-shaped faults that have been interpreted as indicating the planet contracted - shrank" as it cooled, Solomon said. That theory predicted similar faults would be found on the opposite side, which Mariner missed. "We are seeing them, but there's a greater diversity of tectonic features than expected," he said.

Scientists are also seeing craters with mysterious dark halos around them, he said, "as if the craters had excavated through superficial material and brought up materials of some different composition."

Data from Messenger's spectrometers should identify the minerals and map them. Other instruments have reported on the planet's magnetic field, thin atmosphere and other features as scientists seek answers to larger questions about Mercury's origins and evolution.

"We expect ... to make some real progress on some of these basic questions about the planet that have been with us for three decades," Solomon said.

The gusher of data was a long time coming.

"I was a young scientist when Mariner 10 flew by Mercury. I got very excited by those results," Solomon said. But in the 1970s scientists didn't know how to get into an orbit around Mercury, and the 1980s at NASA was "a desert" for planetary missions, he said.

"We conceived this mission design, and spacecraft design, in 1996 and ... were selected in 1999. And here it is 2008 and we're finally seeing Mercury close up. This is not a business for the impatient," Solomon said.

"And we still have a long way to go," he added. Messenger has another 2 billion miles to go before it orbits Mercury in 2011.

But the first objective of the flyby has been accomplished - slipping Messenger through the tiny "keyhole" in space that keeps it on the trajectory needed to get back to the planet.

"We're on it," Solomon said. "We're getting good at flying this spacecraft."

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