TOKYO--A Japanese mission to sample a small asteroid got a boost last week when NASA announced it would contribute a robotic rover and ground support. The spacecraft, scheduled for launch in January 2002, will give scientists the first hands-on contact with ancient rock from a known source that has remained relatively unchanged since the earliest days of the solar system.
Peeks at the 4-billion-year-old history of the rocky inner planets come mainly from meteorites--tiny pieces of asteroids--that have landed on Earth. But those materials generally have been transformed over time by thermal processes and lose much information. "It's not clear how well meteorites are representative of the material in the solar system," says Akira Fujiwara, a planetary scientist with Japan's Institute of Space and Astronautical Science (ISAS). The earliest days of planets like Earth and Mars could be clarified with a fresh chunk of asteroid: "These are the fossils of the solar system," he says.
The $104 million spacecraft, called MUSES-C, will take 20 months to reach Nereus, a near-Earth asteroid about 1 kilometer in diameter. The craft will drift along with the asteroid for 2 months, landing three times to deploy NASA's 1-kilogram rover, which will photograph the surface and analyze its composition with a near-infrared point spectrometer. NASA will also cooperate on the operational aspects of the mission, such as navigating and tracking the spacecraft. While details of the agreement must still be worked out, NASA expects its contribution to be worth about $20 million, 10% of the mission's total cost.
Along with the challenge of landing on such a small target, ISAS engineers face the problem of collecting samples without gravity. Unable to drill or pick at the surface, MUSES-C will fire a small metal projectile into the asteroid's surface, dislodging fragments with sufficient force to allow some of them to bounce up through a funnellike device and into the spacecraft. The mission will also permit ISAS to test several new technologies, including an ion-thruster propulsion system that promises to greatly reduce the weight of the fuel that rockets must carry.