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Near-Earth Asteroid Rendezvous (NEAR): Launched on Feb. 17, 1996 the NEAR spacecraft made
successful flybys of asteroid 243 Mathilde on June 27, 1997 and asteroid 433 Eros on December
23, 1998.
The spacecraft then returned to asteroid Eros and on February 14, 2000 the spacecraft went int
o orbit around
Eros. Beginning with an orbit of about 320 x 366 km above Eros, a series of maneuvers put the
spacecraft
in lower and lower orbits and during the summer of 2000, the spacecraft spent several weeks in
a near
circular orbit of only 35 km from the center of Eros.
Although the NEAR spacecraft was originally scheduled to rendezvous and orbit
asteroid Eros in mid-January 1999, a scheduled main engine firing on
December 20, 1998 failed to take place. As a result, the spacecraft flew
past Eros at 4,100 km on December 23, 1998 at a relative velocity of
about one kilometer per second (2230 mph). However, a successful
main engine firing on January 3, 1999 allowed the spacecraft to catch
up with Eros in mid-February 2000. The spacecraft was built by the
Johns Hopkins University's Applied Physics Laboratory. The images of
asteroid Mathilde taken by the NEAR spacecraft show 4-5 very large
craters that were formed when other asteroids slammed into it long ago.
Mathilde may have survived these collisions intact only because it seems
to be a collection of rocky fragments (a rubble pile) rather than one
monolithic rock. A rubble pile asteroid can more easily absorb the
impact energy during a collision without breaking apart. By analogy, a
bag of sand (rubble pile) can withstand a blow by a hammer but a solid,
monolithic brick could not survive a blow of this type without shattering.
From the measurement taken while the spacecraft was in orbit about Eros, the asteroid's surface
has been
mapped, and determinations made for its size, shape, rotation rate, mass, density and composit
ion. These
Eros results have been presented in a series of four papers published in the weekly journal, S
cience
Magazine (dated September 22, 2000, volume 289, pp. 2085-2105). The earlier scientific result
s for
asteroid Mathilde were also published in Science magazine (volume 278, pp. 2106 Ð 2114, 1997).
NEAR Science Instruments:
Imager, IR spectrometer, x-ray/gamma ray spectrometer, magnetometer, lidar
Johns Hopkins University's Applied Physics Laboratory built the spacecraft and
provides the project management.
Look here for additional information on the NEAR mission:
http://near.jhuapl.edu/
[Image of 243 Mathilde]
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