As NASA's Near Earth Asteroid Rendezvous spacecraft, known as NEAR Shoemaker, closed in on asteroid 433 Eros Feb. 12, Cornell astronomers were busy making final calculations at the mission operations center at the Applied Physics Laboratory at Johns Hopkins University and being interviewed by CNN. Then, at 3:02 p.m. Eastern time, as the announcement came that the spacecraft had touched down on the asteroid's surface, they reacted with cheers and congratulations.
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| Cornell's NEAR Shoemaker computer team, clockwise from bottom left, Maureen Bell, Elaina McCartney, Jonathan Joseph, Colin Peterson, Brian Carcich and Ann Harch in the Space Sciences Building. Charles Harrington/University Photography |
For the Cornell teams, it was the end of years of tense, hard work and a year of enormous successes in producing more than 160,000 images from the multispectral imager (MSI), or camera, and masses of data from the NEAR X-ray/gamma-ray spectrometer (XGRS) -- 10 times more data than originally planned.
The final image was taken just 394 feet from the asteroid's surface as the spacecraft drifted down at a speed of 4 miles per hour, coming to rest in a saddle-shaped depression called Himeros after a 2-billion-mile journey. It was the first man-made instrument to land on an asteroid, and the maneuver went flawlessly despite the fact that NEAR Shoemaker was designed only to orbit Eros and not to land. Eros is a 22-mile-long asteroid more than 196 million miles (316 million kilometers) from Earth.
As NEAR Shoemaker touched down, it began sending a beacon, assuring the team that the small spacecraft had landed gently. The signal was identified by radar science data and about an hour later was locked onto by NASA's Deep Space Network antennas, which monitored the spacecraft until the $223 million mission officially ended on Wednesday.
Joseph Veverka, professor of astronomy, chair of the Cornell astronomy department and head of the MSI team, told The New York Times that the spacecraft took more than 80 pictures on its way to landing on Himeros. "We really got some remarkable pictures. In the last ones, we got resolutions down to a few inches, much better than we expected," he told the Times.
He told The Washington Post: "The pictures are absolutely fantastic. It is one of the greatest experiences to sit here and basically accompany the spacecraft on its trip to the surface."
Veverka's team hopes that these final close-up images will help to answer some of the questions about the geology of Eros. Since this past fall, Veverka's imaging team had been puzzling over strange surface features of Eros seen in new, high-resolution images.
"Since last October we have seen details of Eros at 1 meter resolution that we haven't seen anywhere else before and don't understand," said Veverka. "That's why we are so excited about getting close to the surface."
The spacecraft went into orbit around Eros on Feb. 14, 2000, and in October, with much of the NEAR mission accomplished, it was sent into orbit just 4 miles or so from the asteroid's surface. For the first time the imaging team was seeing details as small as a yard across, compared with the approximately 5.5 yards resolution that had been captured by the camera since the spacecraft first went into orbit.
"Suddenly, we started seeing things we didn't expect and hadn't seen on other surfaces in the solar system," said Veverka. "It's like another door has opened."
The biggest surprise, said Cornell researcher Peter Thomas, who has been interpreting the geology of the asteroid's surface, "is that some small craters and other small depressions have flat, smooth floors, unlike most craters you see on Eros and other objects. It looks as if fine-grain material has slid down the craters' sides and ponded in the bottoms." Apparently, he said, there is some mechanism "we hadn't anticipated" that moves fine-grain material around on the surface. Although gravity on Eros is only one one-thousandth of that on Earth -- an average person would weigh only an ounce or two -- it is still "very effective in gathering materials in very flat floors on the bottom of depressions."
Another surprise, said Veverka, is the discovery that some small boulders are surrounded by material that appears to have disintegrated from the boulders' surfaces. "There is some process that is very gentle that somehow disintegrates rock. We haven't seen this on the moon, and we haven't seen this before on Eros," he said. "But it seems to be very common."
Other Cornell members of the imaging team are Jim Bell, assistant professor of astronomy, and researchers Maureen Bell, Brian Carcich, Beth Clark, Ann Harch, Jonathan Joseph and Colin Peterson.
Much information about the chemical composition of asteroids also has been obtained by the X-ray/gamma-ray spectrometer. Steven Squyres, professor of astronomy at Cornell, is one of the four members of the instrument team, aided by researcher Elaina McCartney.
On Wednesday, Veverka was a member of a wrap-up press conference panel at APL, which built the spacecraft and managed the mission.
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