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Monday, January 22, 2001

University of Hawaii

UH scientist
may help lead
asteroid mission

By Helen Altonn

University of Hawaii planetary scientist Thomas McCord is one of the key investigators in a proposed mission to explore two of the first bodies in the solar system: asteroids Ceres and Vesta.

The mission is called Dawn because the two most massive asteroids have preserved a record of the earliest moments of formation of terrestrial planets at the dawn of the solar system.

The University of California-Los Angeles proposed the mission, which NASA selected for further study. Orbital Sciences Corp. and the Jet Propulsion Laboratory are partners in the venture, and various universities are participating.

McCord, with the Hawaii Institute of Geophysics and Planetology, said other asteroids have been studied in fly-by missions, but they were very small.

"These are the largest asteroids, and they are evolved to some extent. That is, they're not just inert rocks. They're big enough that there has been thermal evolution."

Vesta is the brightest asteroid and the only one ever seen with the naked eye. It has lava on the surface, which McCord discovered in 1972.

The basalts indicate the asteroid is hot enough inside to melt the rock and volcanism has occurred -- most likely much earlier in time, he said.

Ceres, the largest known asteroid, was the first discovered in the solar system 200 years ago with a small telescope atop the royal palace in Palermo, Italy.

McCord said Ceres appears to have water in minerals on the surface, evolving from materials inside the asteroid. But so far, no basalt, lavas or evidence of volcanism or melting of rocks have been found, he said.

"It is extremely interesting, to say the least," he said, because the two asteroids are so different.

Meteorites believed to be from Vesta indicate it was formed in only 5 million to 15 million years, while it took Mars about 30 million years and the Earth, 50 million.

No meteorites have been identified from Ceres, but it also is expected to have formed in the first 10 million years.

Scientists are interested in determining Vesta's volcanic history and how extensive the volcanism was, McCord said, "so we can apply that knowledge to understanding how bodies in general of that size evolved."

The asteroids are smaller than Earth's moon but larger than most or all of the asteroids, he said. "They're in an in-between size range, and we don't know how those small bodies evolved thermally very well.

"Here we have two examples, both thermally evolved, but both different ways -- one with release of water and hydrated minerals, the other with volcanism."

Perhaps the objects were made of different materials when they were formed, one with very wet material and the other not, McCord suggested.

"But we don't know. That takes some special creation itself. It's not too logical. At the moment there is no explanation for different evolution."

McCord will lead work with two spectrometers being built by Germans for the spacecraft. He has worked with them for years on development of instruments for space missions.

Another unique aspect of the Dawn mission will be use of ion engines to power the spacecraft to the asteroid belt, McCord noted.

It will orbit Vesta in an ever-tightening circle, then spiral outward and head to Ceres for a rendezvous.

"This would be the first full science mission using that propulsion system," McCord said. The thrust is weaker but lasts longer, so the spacecraft can go farther, he said.

If it performs well, he said, a number of science exploration and engineering missions could be done that are now impractical to do.

Scientists are preparing a detailed plan for NASA approval and funding of the Dawn mission, scheduled in July 2005.

UCLA lead investigator Christopher Russell said, "The data returned by the Dawn mission will open up a treasure trove of information" in meteorites and asteroid samples.

Hawaii Institute of Geophysics and Planetology

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