NASA Lands Probe on Asteroid

Feb. 12, 2001 -- After an apparently gentle descent, the first spacecraft ever to land on an asteroid touched down today shortly after 3 p.m. ET.

The 1,100-pound craft settled on a saddle-shaped depression of the asteroid, Eros, and then continued transmitting signals to Earth, suggesting it was not damaged as it struck the asteroid's rock-strewn surface.

Asteriod Landing Animation"I am happy to report that the NEAR has touched down," saidRobert Farquhar, the NEAR mission director, just after the craft transmitted its zero altitude location. "We are still getting signals!"

Not only was the dicey landing the first successful touchdown on an asteroid, it was also the most faraway landing ever attempted — at a distance of 196 million miles from Earth. The NEAR Shoemaker robot craft has no legs or landing gear and was never designed to land. To ensure a successful landing, controllers managed to slow the craft from about 20 to about 3 miles per hour.

First, controllers at The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., triggered the craft to thrust its engines so the compact car-sized probe was knocked from its orbit and aimed for the asteroid. Then the team used a series of four rocket firings to slow the craft as it drifted toward the asteroid.

"We're right on the money," said NEAR Mission Operations Manager Robert Nelson as the NEAR probe drifted toward Eros. By just before 3 p.m. ET, the probe was less than a mile from the asteroid and approaching slowly. During its final descent scientists snapped about two photos of the asteroid every minute.

At one point controllers believed the craft had landed and then bounced away from the asteroid, but soon they received data suggesting it was resting on the rocky celestial outpost. The craft landed nearly on time, touching down on a 6-mile-wide, saddle-shaped depression at Eros' side at 3:07 p.m.

Risky Landing

"It's an exciting area geologically because we're on the edge of this large depression — which is probably a very large impact crater — and we'll be getting images of its interior as well as of the heavily cratered terrain on the outside," says NEAR imaging team member Mark Robinson of Northwestern University.

The NEAR craft was launched into space on board a rocket in 1996 and has traveled 2 billion miles since then. The first long-term study of an asteroid relayed more than 160,000 images of Eros back to Earth and was a relatively cheap mission, costing $223 million. Now that funds have run out and the ship's fuel tank is nearly empty, controllers decided to hazard a landing on the celestial hunk of rock.

Many things could have gone wrong. Scientists were worried the craft would strike a boulder on the asteroid's surface and glance off into space. It could also have landed on its head and effectively blocked any visibility of its cameras.

Asteroid Up Close

Now that it has managed a gentle landing, the tin-can shaped probe is expected to provide unprecedented up-close images and data from the asteroid for up to three months.

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

Some of the questions scientists hope to learn from the craft's focused snapshots are the nature and depth of the bits of rock and dirt that coat the asteroid and the materials' possible origins. That information could prove useful if the need ever arises to deflect an asteroid from a path toward Earth.

The probe could also provide clues about the history of the solar system since scientists believe Eros formed during the solar system's earliest beginnings 4.5 billion years ago.

As Farquhar says, "We have an opportunity here to do unprecedented science."

ABCNEWS' Ned Potter contributed to this report.

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