LAUREL, MARYLAND--Researchers are scratching their heads over the last pictures from a spacecraft now lying comfortably on the surface of asteroid Eros. At a press conference here today at The Johns Hopkins University's Applied Research Laboratory, team members suggested that something--no one knows quite what--is erasing small impact craters and shaping a bizarre landscape.
Never designed to land, the NEAR Shoemaker spacecraft gently touched down on the a 33-kilometer-long asteroid on Monday (ScienceNOW, 12 February). To the surprise of everyone on the team, the spacecraft continued to beam a radio beacon back to Earth. Signals are still being received, prompting plans to extend the mission for 10 days. With the spacecraft apparently propped on two solar panels, its gamma ray spectrometer may be in the right position to make the best measurements yet of Eros' surface composition, according to spectrometer team leader Jacob Trombka of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
The spacecraft's picture-taking days are over--it's telephoto camera has its lens practically in the dirt--but the last ones it sent back should keep planetary geologists busy for years. "I never would have imagined you'd see some of these things on an asteroid," says imaging team member Clark Chapman of the Southwest Research Institute in Boulder, Colorado. One mystery is the abundance of huge boulders, perhaps as many as a million. One idea is that large impacts might so shake Eros that the surface debris would settle like mixed nuts in a can, with the boulders rising to the top.
The other surprise was the near-absence of small craters--which may have been filled by debris. Some craters and low spots are only partially filled, apparently by dust, so as to look like ponds. One way to transport dust around a windless asteroid would be for sunlight to charge it up electrostatically, says imaging team leader Joseph Veverka of Cornell University in Ithaca. That could levitate the dust and allow it to move downhill. But right now it's all speculation. "We're facing processes we're not familiar with," says Veverka. "I truly don't know what's going on."