NASA hopes asteroid landing will solve riddles

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

By Richard Stenger
CNN.com Writer

(CNN) -- NASA's yearlong asteroid orbiter mission is scheduled for a grand finale on Monday. The NEAR-Shoemaker spacecraft will descend to the surface of the asteroid in a controlled crash, beaming back pictures until the very last moments.

NEAR-Shoemaker will attempt the touchdown just two days shy of its first anniversary in orbit around Eros, an asteroid whose shape has been likened to everything from a peanut to a kidney bean.

However the probe was designed to study the asteroid, not land on it. That means it's unlikely the probe will survive the descent, according to NASA scientists.

"The thing could survive and get a signal saying it landed. But the chances are less than 1 percent. Too many things have to go right," NEAR mission director Bob Farquhar told CNN.

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NEAR (Near Earth Asteroid Rendezvous) scientists planned the deadly dive to gain the best-ever close-up views of the asteroid. The probe could take pictures from as close as 220 yards (200 meters) with resolutions smaller than 4 inches (10 centimeters) before smacking into a sunlit site between the South Pole and a distinctive saddle-shaped depression.

The automobile-sized craft will use its thrusters to brake several times during the four-hour descent, reducing its speed to that of an average human walking pace before impact. Along the way it will point its camera and snap a photo at least once every minute, NASA scientists said.

The space agency plans to broadcast the images live on the Internet as soon as they receive them. First, they must travel the 196 million mile (316 million km) distance from Eros, a trip that takes 17 or 18 minutes.

NEAR-Shoemaker has traveled 2 billion miles since it left Earth five years ago. Over the past year it conducted an unprecedented deep space geological study. The first asteroid orbiter has taken 160,000 pictures of Eros and zapped the Manhattan-sized rock with 11 million laser pulses.

Puzzles remain

Illustration of the NEAR-Shoemaker probe

The mountain of data has shed light on the gravity, mineral content and geological history of Eros, which scientists now speculate is made of material older than Earth.

The haunting images reveal boulder fields, impact craters and strange grooves and ridges. Some could keep space scientists busy for years, revealing geologic features seen nowhere else in the solar system.

"On the tiny fraction of the surface we've seen at high resolution, we noticed strange processes we haven't seen on the moon or anywhere else," said NEAR scientist and Cornell University astronomer Joseph Veverka.

For example, some boulders seem to have just disintegrated. And fine material on the surface has moved downhill and created flat surfaces in craters, despite the weakness of Eros' gravity. An average human would weigh only an ounce or two.

"These are big puzzles and we need to get a better look," Veverka said.

Space probe swoops within 3 miles of asteroid
October 26, 2000
Asteroid orbiter marks halfway point in historic flight
August 16, 2000
Summer lets orbiter see asteroid Eros in new light
June 27, 2000
Asteroid Eros resembles 'building blocks' of Earth
May 31, 2000
NASA unveils quartet of asteroid movies
April 28, 2000
NASA releases first 'flyover movie' of asteroid
March 24, 2000
'Stunning' images hint asteroid broke from a planet
February 17, 2000

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

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