First Light from Eros Orbit
February 14, 2000 -- This morning NASA's Near Earth
Asteroid Rendezvous (NEAR) spacecraft became the first space
probe to orbit an asteroid and quickly
began sending close-up pictures of 433 Eros back to Earth.
"This is what we are in this business for", enthused NASA associate administrator Carl Pincher. "This is a grand day."
"It's like Christmas for us," agreed Cornell University's Prof. Joe Veverka, the leader of NEAR's imaging team. Veverka was clearly anxious to return to the incoming data as he gamely answered questions throughout an hour-long press conference at Johns Hopkins University.
Above: Just over an hour after entering orbit around Eros, NEAR pointed its camera at the asteroid and took this picture from a range of 210 miles (330 km) above the surface. This view shows the 3-mile (5-kilometer) impact crater which the spacecraft has spied for over a week during its approach. The two smaller craters superimposed on its rim are each about 1.2 miles (2 kilometers) across. This crater doesn't yet have a name, but eventually it will be given one by the International Astronomical Union. The theme for naming craters on Eros will be love and lovers, according to NEAR project scientist Andrew Cheng.
"The picture shows evidence of layering and other structures, like grooves and rims. There's a lot of geologic complexity. Global structures like grooves suggest severe collisions. It looks like Eros will turn out to be an extremely interesting object!" said Prof. Veverka.
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The image also shows where a boulder has slid to the bottom
of the bowl-shaped depression under the influence of the asteroid's
feeble gravity. Gravity on Eros is 1000 times weaker than on
Earth. A human could easily leap out of the crater.
"We planned for this crater to be at the center of the camera's field of view after we entered orbit," Veverka continued. "We pointed the camera and there it was! That shows we're doing pretty well."
Indeed, mission scientists estimate that the orbital parameters are very close to their target values. Periapsis (closest approach to the asteroid) is 327 +- 49 km; apapsis (the farthest distance from Eros) is 450 +- 57 km.
"These uncertainties are not navigation errors," said NEAR mission director Robert Farquhar. "They represent uncertainties in the mass of the asteroid, which we expect to refine to within 1% in less than a week."
Farquhar said that the orbit around the irregularly-shaped asteroid is stable, but that corrections might be necessary. If so, they would be made on February 29.
A lingering danger to NEAR are moons of Eros, if they exist.
"We looked for moons of Eros during the December 1998 flyby," said Veverka. "And last month we had 3 sequences looking for moons. If there is an object bigger than 20 meters we would have seen it. The search is not yet complete [but it looks like there's nothing to worry about]."
Right: The robotic spacecraft Galileo, whose primary mission is to explore the Jupiter system, snapped this photo of asteroid Ida in 1995 during its long journey to Jupiter. Scientists were surprised to learn that Ida has a moon, which appears as a small dot to the right of Ida in this picture. The tiny moon, named Dactyl, is about one mile across, while the potato shaped Ida measures about 36 miles long and 14 miles wide. Eros doesn't have moons this large, but scientists are still concerned about satellites smaller than 20 meters across that could collide with NEAR.
More to Come
Another science briefing will be help on February 17 when
more images and data will be released. According to Prof. Veverka,
a critical science experiment with
the Near-Infrared Spectrometer was successfully completed just
before NEAR entered orbit around Eros.
"Key data for the spectrometer were obtained yesterday," said Veverka. "They are on the ground now and they look absolutely fantastic. We're in the process of putting these spectra together. It would be premature to state the results now. Hopefully we'll know more by [the briefing] on Thursday."
For more information about the NEAR mission, see the recent SpaceScience.com headline "Eros or Bust" and the NEAR Mission Home Page from Johns Hopkins University.
The NEAR (Near Earth Asteroid Rendezvous) mission, a NASA Discovery Program being conducted by the Johns Hopkins University Applied Physics Laboratory, Laurel, MD, is the first mission to orbit an asteroid.
Eros or Bust - February 8, 2000. NASA Science News. NASA's Near-Earth Asteroid Rendezvous Mission is nearing 433 Eros. It is scheduled to go into orbit around the space rock on Valentines Day, 2000. University
Guess Who's Coming to Breakfast? - February 13, 2000. NASA Science News. Critical science observations of Eros are scheduled to begin 11 hours before NEAR's orbit insertion on Valentines Day, 2000.
First Orbit Around an Asteroid - February 14, 2000. NASA Science News. NEAR successfully entered orbit around 433 Eros on Valentines Day, 2000
Near Earth Asteroid Rendezvous mission - NEAR home page from Johns Hopkins University