Happy landing: Craft descends onto Eros

What could be better than landing a spacecraft for the first time on an asteroid?

The ability to do research once the craft has landed.

On Feb. 12, the unmanned spacecraft NEAR (Near Earth Asteroid Rendezvous) Shoemaker touched down on the asteroid 433 Eros, the twirling, elongated space rock that the craft had orbited for nearly a year (SN: 11/4/00, p. 293). During its descent, the craft’s camera recorded close-ups of an asteroid that were 10 times as sharp as any previously taken.

NEAR’s camera remained in focus even as the craft came within 120 meters of Eros, showing details just 10 centimeters wide. That image was probably NEAR’s last, since the camera is on the craft’s landing side.

Indeed, the craft was never designed to land on Eros, and researchers expected it to be crippled by the impact when it hit just outside a saddle-shaped crater called Himeros. But to the team’s amazement, NEAR broadcast a strong signal after landing, indicating that its solar panels and other key equipment were still functioning.

The landing proved so gentle that researchers initially considered another history-making maneuver: Using NEAR’s remaining fuel to lift the craft briefly a few hundred meters off the asteroid and take the first image showing the impact of a spacecraft on the surface of a space rock.

The researchers soon determined, however, that any liftoff attempt would be risky because of uncertainties about the amount of fuel remaining and its capability to achieve sufficient altitude. Moreover, the camera is likely to be covered with dirt. The team then decided that NEAR should stay put, so that the craft’s gamma-ray spectrometer could gather precise data about the asteroid’s composition.

“We’re on cloud nine, and now we’re trying to get to cloud 18,” says NEAR scientist Joseph Veverka of Cornell University.

The close-up images show a transition between a region with a small number of angular boulders and one with a larger population, more rounded in appearance, he notes. The close-ups explain why scientists had seen lots of large craters on Eros but few small ones, adds Mark Robinson of Northwestern University in Evanston, Ill. The plentiful, small craters near the landing site are ghostlike, all but buried by a layer of rubble.