| 17 February 2000
For Immediate Release
NEAR Team Digs into Data from Eros
Only a few days into the first close-up study of an asteroid, data from NASA's Near Earth Asteroid Rendezvous (NEAR) mission indicates that 433 Eros is no ordinary space rock.
Since the NEAR spacecraft met up with and began its historic orbit of Eros on Feb. 14, NEAR team members at The Johns Hopkins University Applied Physics Laboratory, which manages the mission for NASA, have pored over images and other early scientific returns. It will take months to unravel the deeper mysteries of Eros, but data from NEAR's final approach and first days of orbit offer tantalizing glimpses of an ancient surface covered with craters, grooves, layers, house-sized boulders and other complex features.
"Work is just starting, but it's already clear that Eros is much more exciting and geologically diverse than we had expected," says Dr. Andrew Cheng, of the Applied Physics Laboratory, who serves as the NEAR mission's lead scientist.
Scientists now know that Eros' mass is 2.4 grams per cubic centimeter - about the same density of Earth's crust and a near match of the estimates derived from NEAR's flyby of Eros in December 1998.
"With this new data, it now looks like we have a fairly solid object," says NEAR radio science team leader Dr. Donald Yeomans of NASA's Jet Propulsion Laboratory in Pasadena, Calif. "There is no strong evidence that it's a rubble pile like Mathilde," the large asteroid NEAR passed and photographed in 1997.
Even without in-depth analysis, pictures snapped with NEAR's Multispectral Imager offer several clues about Eros' origin, age and geography. The large number and concentration of craters point to an older asteroid. Uniform grooves across its craters and ridges hint at a global fabric of underground layers, which Cheng says could indicate Eros was once part of a larger body.
The digital camera has also captured brighter spots on the surface that NEAR scientists are anxious to study.
"One patch is about 25 percent brighter than the rest of the asteroid, and that's a very large difference from the materials you expect to find on the surface," says Dr. Mark Robinson, a NEAR imaging team member from Northwestern University. "That's a really neat feature to keep our eyes on."
The spacecraft's Near Infrared Spectrometer has picked up variations in the asteroid's mineral composition, possibly proportions of pyroxene and olivine, iron-bearing minerals commonly found on Earth, the moon, Mars and in meteorites.
A low-phase flyby during last weekend's final approach put NEAR directly between the sun and Eros, allowing the infrared instrument to gather unique data on the asteroid's mineral makeup under optimal lighting. Combined with multispectral images, this information will help form the first mineral map ever made of an asteroid.
"We want to correlate the changes in color with the geologic features," says Dr. Scott Murchie, a science team member from the Applied Physics Laboratory. "If we see a crater, for example, is it different on the outside than on the inside? Is the face of a cliff different than the ridge? This data will eventually tell us about the asteroid's history."
For the next year, NEAR's instruments will continue to examine the 21-mile-long, potato-shaped asteroid's chemistry, geology, and evolutionary history. The mission's radio science experiment will more precisely calculate Eros' density and mass distribution - clues critical to determining the asteroid's gravity and refining NEAR's orbit.
NEAR's scientific capabilities expand soon, when its X-ray/Gamma-Ray Spectrometer and Laser Rangefinder are turned on within the next two weeks. The spectrometer will measure important chemical elements such as silicon, magnesium, iron, uranium, thorium and potassium; the laser scans will determine Eros' precise shape.
Visit the NEAR Web site at http://near.jhuapl.edu for the latest images and mission news.