After scarcely a month in orbit around asteroid Eros, NASA's Near Earth Asteroid Rendezvous spacecraft is astounding scientists with ever more detailed views of geologic features and with technical scientific accomplishments.
NEAR team members have found evidence of geologic phenomena that could have originated on a much larger parent body from which Eros was derived. In their search to decipher the mysteries of Eros, they have obtained the first ever laser range returns from an asteroid and the first ever X-ray detection of an asteroid. High-resolution images are surprising scientists by the abundance of ridges, chains of craters and boulders.
"Eros in our first month of observations has proven to be a marvelous and fascinating object," says Andrew F. Cheng, NEAR project scientist from APL, which manages the mission for NASA.
NEAR's first X-ray detection of Eros demonstrated the presence of magnesium, iron and silicon and possibly aluminum and calcium. Their detection was the result of a brilliant solar flare on March 2, when NEAR was 131 miles from Eros. That solar explosion made it possible for the spacecraft's X-ray spectrometer to view the asteroid from four times farther away than it was designed to do. "The solar X-ray burst caused elements on the asteroid to react and emit fluorescent X-rays that were measured by the spectrometer," says Jacob I. Trombka of NASA's Goddard Space Flight Center, who heads the X-ray/gamma ray instrument team. "It was only a 600-second window of opportunity, but it is a huge bonus for the mission," he says. "This detection at the higher orbit gives us confidence in our ability to develop elemental maps when we're at our operational orbit of 50 kilometers."
In what is the first detection of a laser return from an asteroid, the spacecraft's laser rangefinder, operating 180 miles from Eros, measured topographic profiles of chains of pits or craters.
In the last two weeks, the NEAR multispectral imager has returned more than 2,400 images. The spacecraft has been in a nearly circular orbit around Eros, traveling approximately 124 miles from the asteroid's center and taking images closer to an asteroid than has ever been done before. The unprecedented images show chains of craters, numerous boulders as small as 55 yards across and long ridges that extend for several kilometers across the surface.
Conspicuous on many of the crater walls are bright markings that Peter C. Thomas of Cornell University says are part of the loose, fragmental material on the surface, called regolith. This material appears to vary in properties across the asteroid, perhaps in response to impact cratering events. "We have found that Eros is literally covered with craters smaller than about 1 mile in diameter," says Clark R. Chapman of Southwest Research Institute. Both Thomas and Chapman are members of the multispectral imager and near-infrared spectrometer science team.