Recent views of Eros. Click each image for a larger version and caption

Spacecraft descends toward asteroid for landing

Scientists hope the landing will yield some extreme close-ups of Eros' surface. This image was obtained last February at a range of 1,100 miles (1,800 kilometers)   VIDEO Check out NASA's movie simulation of NEAR-Shoemaker's risky descent to Eros 2.2 MB / 48.11 sec. / 320X240 QuickTime movie Please enable Javascript

In this story: High-risk maneuver NASA puzzled by images of asteroid RELATED STORIES, SITES

(CNN) -- The NEAR-Shoemaker spacecraft executed a 20-second deorbit manuever at 10:31 a.m. ET, beginning the first in a series of steps as it descends toward a historic landing on asteroid Eros.

"We are on a flight path that will take us to the surface," NEAR mission director Robert Farquhar said after receiving a signal back from the spacecraft.

Scientists said there is a high risk the craft will be damaged in the landing process, but they hope to collect invaluable pictures of the 21-mile-long asteroid's surface as the craft descends. (Image of landing site)

The NEAR -- Near Earth Asteroid Rendezvous -- Shoemaker spacecraft has been circling around the Eros asteroid since February 14, 2000. NASA is hoping the spacecraft's camera will capture surface details as small as a 4-inch rock in the final minutes before the craft touches down, helping scientists answer questions about the asteroid's geology.

Mission controllers at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, will command the craft to initiate a series of engine burns designed to bring it down to the asteroid's surface. Touchdown was expected to occur at 3:04 p.m. EST.

High-risk maneuver

The controlled descent is a high-risk maneuver, NASA said, and is intended to slow the rate of descent from 20 mph to 5 mph. The camera will begin snapping pictures about every 30 seconds during the final 45 minutes of descent.

RESOURCES Web sites and recent CNN coverage of the mission     GALLERY View the best of Eros     MESSAGE BOARD Stargazing

The camera will cease taking pictures at about 200 meters above the surface, said Helen Worth, spokeswoman for the Johns Hopkins laboratory.

"The purpose of the camera was to take pictures at a much greater distance," she told CNN. "It comes out of focus between 500 and 200 meters."

The spacecraft was never meant to land, she added, and may not make it in one piece. "Chances are less than one per cent for it to land intact," she said. "Plus, all the instruments are on the bottom." Once the craft lands, it will stay there and NASA has no plans to retrieve it.

NASA puzzled by images of asteroid

NASA said NEAR imaging team members have been puzzling over strange surface features first spotted in images in October. They hope the close-ups taken by the spacecraft will help to answer their questions about the geology of the asteroid more than 196 million miles from Earth.

Illustration of the NEAR-Shoemaker probe

"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," Cornell University astronomer Joseph Veverka, who heads the imaging team, said in a statement. "That's why we are so excited about getting close to the surface."

The Johns Hopkins laboratory built the spacecraft and manages the NEAR mission for NASA.

Cornell researchers say the biggest surprise is the discovery that some small craters have flat, smooth floors, indicating fine-grain material has pooled at the bottom. Although gravity on Eros is only one one-thousandth of that on Earth, the researchers say it is strong enough to collect material in the asteroid's depressions.

Another surprise, Veverka said, is 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. But it seems to be very common," he said.

Pictures of the asteroid landing attempt will be shown live on NASA's Web site, www.nasa.gov.

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Near Earth Asteroid Rendezvous Mission
Johns Hopkins University Applied Physics Laboratory
Near Earth Object Program

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