Don Savage

Headquarters, Washington, DC

(Phone: 202/358-1547)

Mike Buckley

Johns Hopkins University Applied Physics Laboratory, Laurel, MD
(Phone: 240/228-7536)

RELEASE: 00-28

Only a few days into the first close-up study of an asteroid,
data from NASA’s Near Earth Asteroid Rendezvous (NEAR) mission
indicate 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 in Laurel, MD, 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 bulk 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 radio science team leader Dr. Donald Yeomans of
NASA’s Jet Propulsion Laboratory in Pasadena, CA. “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’ age and
geography. The large number and concentration of craters points
to an older asteroid, uniform grooves across its craters and
ridges hint at a global fabric and, perhaps, underground layers.
In addition to numerous boulders, the digital camera has also
captured brighter spots on the surface that NEAR scientists are
anxious to study.

NEAR’s Near-Infrared Spectrometer has picked up variations in
the asteroid’s mineral composition, possibly the proportions of
pyroxene and olivine, iron-bearing minerals commonly found in

A low-phase flyby during last weekend’s final approach put
NEAR directly between the sun and Eros, allowing the 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 potato-shaped asteroid’s chemistry, geology, and
evolutionary history. The mission also includes a radio science
experiment to 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.

– end –

Images and information about the NEAR mission are available