The Little Probe That Could

NASA's NEAR Shoemaker spacecraft, which beat long odds to land softly on an asteroid called Eros, got a Valentine's Day reprieve Wednesday: a 10-day extension of its five-year mission.

The bus-sized craft was never meant to land on the lumpy 21-mile-long asteroid, so scientists were ecstatic Monday when the space probe came to rest at the rim of a crater and kept beaming information back to Earth, some 196 million miles away.

"The landing on Eros was so successful that not only did the spacecraft survive the impact, but we have remained in communications," said Jay Bergtralh, director of NASA's solar system exploration program. "This is beyond our highest expectations and NASA is taking advantage."

He said scientists will continue to collect data from a NEAR instrument that can analyze the chemistry of the barren space rock. NEAR rests on the surface of Eros like a tripod, leaning against the outer edges of two solar panels and on the edge of its base.

The craft's solar panels are pointing at the sun, gathering full power, officials said.

However, the craft's best antenna is not pointed at Earth, and mission controllers said they can receive only about 10 bits a second of data from a low-gain, backup antenna. From the high-gain antenna data is about 2,600 times faster.

But officials said the communication is good enough to gather data from NEAR's gamma ray spectrometer, an instrument that can evaluate the chemistry of the asteroid rock.

From its position on the side of the spacecraft, the spectrometer is only a few inches from the asteroid surface, providing an unprecedented opportunity, officials said.

NASA animation of asteroid Eros. For more animations go to NASA's NEAR-Shoemaker site.

Farquhar said it might be possible, when sunlight returns to the NEAR landing site, to send a message to the pacecraft, but that is only speculation. He said the craft's equipment may freeze and break in the intense cold of space while the landing site is in darkness.

Mission officials said an analysis of radar and other data from the landing on Monday shows that NEAR - Near Earth Asteroid Rendezvous - actually landed more smoothly than originally thought. Engineers at first believed that NEAR hit Eros and then bounced off - perhaps as high as 300 feet. But Bobby Williams, a Jet Propulsion Laboratory navigator, said the apparent bounce was actually a "jiggle" after landing caused by the spacecraft firing rocket thrusters in a vain and automatic effort to maintain high-gain antenna contact with Earth.

The jiggling stopped when the thrusters shut down.

"It's sitting stable now, like a tripod," said Williams.

Farquhar said NEAR's touchdown may have been the "softest landing ever," even though the 1,100-pound craft was never supposed to land. He said the landing speed was between 1.5 and 1.8 meters per second, around four miles per hour. Unmanned spacecraft landings on Mars and the moon were up to twice as fast, "but of course they were designed to land," he said.

Joseph Veverka, a Cornell University scientist who headed the NEAR imaging team, said photos taken by the spacecraft during its descent have uncovered a "mystery" about Eros.

He said the photos show "ghost craters." depressions gouged out by past impacts and then filled in by a process that is not understood by scientists.

"Some process appears to make flat areas in low places," he said, noting that geologists and other scientists are still trying to understand.

The pictures also picked up the edge of a depression caused when an overlying crust of the asteroid apparently collapsed. Veverka said if that feature was seen on Mars it would be attributed to water or the atmosphere. Eros has neither.

"We don't know what's happening here," said Veverka. "It's a mystery."

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