UH professor
helps plan asteroid
landing mission

An unmanned craft will travel
to a nearby asteroid and bring
back samples

By Helen Altonn
Star-Bulletin

Hawaii astronomer David Tholen will be one of six American scientists participating in a space venture that he says is "sort of like the Wright brothers."

"You're doing something for the first time ... It's very exciting."

The University of Hawaii Institute for Astronomy scientist was selected by the National Aeronautics and Space Administration for the world's first expedition to put a robotic lander on an asteroid and return rocks to Earth.

NASA and Japan's Institute of Space and Astronautical Science are partners in the mission, called MUSES-C for Mu Space Engineering Spacecraft. The "C" indicates it's the third in a series.

Japan's MUSES-C spacecraft will be launched in January 2002 from Kagoshima Space Center -- headed to asteroid Nereus, about a half mile wide.

Donald K. Yeomans, NASA's MUSES-C mission project scientist, said, "Nereus is one of Earth's closest neighbors, easily accessible for a spacecraft rendezvous and an object of key scientific interest."

If the spacecraft can't make it to Nereus, asteroid 1989 ML was chosen as an alternate target. It's a little smaller but easier to get to, Tholen said.

Nereus is believed to have changed little since the Earth and other planets were formed in the inner solar system about 4.6 billion years ago.

Scientists hope the asteroid studies will reveal the Earth's initial chemical composition and conditions under which the planets were created.

Tholen, internationally recognized for his work in categorizing asteroids, was selected for the U.S. team in a highly competitive NASA process.

He will use data from the spacecraft's camera to determine Nereus' rotational cycle and estimate its age, shape, size, density and other properties.

He said he did some observations of Nereus in 1992 and 1993 to try to learn its surface composition.

He also studied it in 1997 to find out how fast it rotates. That will determine how long it will be exposed to sunlight at any one time and how hot or cold it's going to get, he said.

He said Nereus' rotation takes about 15 hours, more slowly than a typical asteroid, and its surface composition is somewhat uncertain.

It's difficult to determine from the UH observations what fraction of light is reflected by the surface, "the so-called albedo," he said. "Is it dark like asphalt or is it bright like snow?

"One possibility is it's a metallic asteroid, which means it could be the parent of some nickel-iron meteorites."

Tholen said the launch is timed "to take advantage of the geometric arrangement of the Earth and asteroid target." An alternate was chosen in case of technical problems or a slip in the launch date, he said.

He said 1989 ML, which he studied intensively in March, rotates a little more slowly then Nereus, about 18 hours, and might be tumbling. Indications are that it also could be a nickel-iron object, he said.

The MUSES-C spacecraft is expected to return asteroid samples to Earth in January 2006, leaving the rover behind.

NASA is developing the rover, which won't be much larger than a book, Tholen said. The Japanese are developing the orbiter, the main spacecraft. Both will carry an array of instruments.

Nereus' gravity field is believed to be about 100,000 times weaker than the Earth's, which NASA says is a challenge for its Jet Propulsion Laboratory engineers.

They're designing the small rover to take advantage of the low gravity field and hop more than 33 feet above the surface by drawing its wheel struts together, then springing them outward.

The instruments then would have "a bird's-eye view" of the terrain and the rover would be able to cover more ground, NASA said.

The weak gravity would pull it back to the surface. Solar panels on its back and belly will allow a constant flow of electricity no matter how it lands.

"Like an agile cat, the rover is also equipped to right itself if necessary," NASA said.

Small pellets will be fired into the asteroid's surface and material collected through an inverted funnel and stored in a capsule on the orbiter. The capsule will parachute to Earth when the orbiter returns in January 2006.

The MUSES-C mission, like NASA's current Deep Space One mission, is a technology demonstration, Tholen said. Both are attempts to try new technology, to see what works best, he said. "Whatever science we're able to accomplish will be frosting on the cake."

Tholen said he knows nearly all the members of the American science team. They include Beth Clark of Cornell University, a 1993 UH graduate student.

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Ka Leo O Hawaii