NEAR Begins Looking Closely at Eros
17 Feb 2000
(Source: NASA Headquarters)
Headquarters, Washington, DC
Johns Hopkins University Applied Physics Laboratory, Laurel, MD
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 meteorites.
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.
Images and information about the NEAR mission are available at: