MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE (818) 354-5011
Contact: Martha J. Heil (818) 354-0850
FOR IMMEDIATE RELEASESeptember 21, 2000
REVEALING EROS' SECRETS, ONE BY ONE
Eros, the chunky asteroid named after the god of love, is
slowly revealing to scientists the mysteries of its size,
rotation and other properties.
Eros has been studied by the Near Earth Asteroid Rendezvous
(NEAR)-Shoemaker spacecraft since last Valentine's day when a
careful maneuver put the spacecraft in orbit around the asteroid
to determine its properties. Some of those findings, such as
Eros' mass and bulk density, appear in the Sept. 22, 2000 edition
of the journal Science in a paper by principal author Dr. Don
Yeomans of NASA's Jet Propulsion Laboratory. Yeomans is the radio
science team chief for NEAR-Shoemaker. The journal also features
three other research reports on Eros.
Scientists have learned that Eros is most likely made of
rocky material with a uniform density throughout. The asteroid's
bulk density is similar to that of Earth's crust. Like Earth, the
surface of Eros is covered with a layer of looser rock and soil.
Though it is about 6,700 trillion kilograms (14,700 trillion
pounds) in mass, Eros is a fragment from the breakup of a once
larger asteroid. "It's a chip off a larger block from millions of
years ago," said Yeomans.
Eros is rotating around its shortest axis, making one
revolution every 5 hours and 16 minutes. As though thrown in a
tight spiral pass by some cosmic quarterback, Eros' rotation axis
appears to remain steady on its journey through space. Because
the asteroid is so much smaller with much less gravity than
Earth, it wouldn't take an Olympic athlete to jump entirely off
the surface into space.
Scientists were able to study Eros' rotation, mass
distribution and structure based on a series of observations
taken onboard the spacecraft. By photographing the asteroid and
measuring infrared light reflected from it, scientists could
determine its mass, detect minerals and record its motion. As the
craft edged into closer and closer orbits around the asteroid, it
took fresh data that helped determine the asteroid's size, shape
and mass distribution. These activities were critical for
navigating the spacecraft in to tighter orbits about Eros so that
close-up images could be taken.
"If we didn't know the precise size, shape and mass
distribution of the asteroid ahead of time, it would not have
been safe to send the spacecraft to within a few kilometers of
the asteroid's surface," said Yeomans.
By the mission's end in February 2001, the total surface of
the asteroid will have been imaged and measured.
Johns Hopkins University manages the NEAR mission for NASA,
and JPL is performing navigation support. Bobby G. Williams, also
an author on the paper, is the navigation team leader. For the
latest images and announcements of mission progress and
discoveries visit the NEAR web site at http://near.jhuapl.edu .