The last data from the overachieving Near Earth Asteroid Rendezvous (NEAR Shoemaker) mission to asteroid Eros will be received today via NASA's Deep Space Network telecommunications system.

A group of engineers at NASA's Jet Propulsion Laboratory stands by, monitoring final telemetry from this successful extended mission to map and understand the asteroid. NEAR Shoemaker was directed to a successful landing on the asteroid on Feb. 12. Today, the Deep Space Network, Earth's phone line to Eros, will hang up, marking the probable conclusion to the historic mission, which is managed by the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md, for NASA.

The Deep Space Network, managed by JPL for NASA, consists of large antennas at three complexes located in Goldstone, Calif., near Canberra, Australia, and near Madrid, Spain. Each complex houses several radio antennas of different sizes, including giant 70-meter (230-foot) telescopes, used to communicate with interplanetary.

Antennas at Goldstone today received science data from the last NEAR experiment, spectrometry from the spacecraft's gamma ray instrument. This data will tell scientists about the surface and subsurface composition of asteroid Eros. NEAR's position on the asteroid precludes it from using its largest communications antenna, called the high-gain antenna. To receive the weaker signal from the low-gain antenna, the Deep Space Network is using its own largest antenna, the 70-meter dish.

"The pass is going fine, we're locked on to the spacecraft's signal and we're getting good data back." said JPL's Allen Berman, the telecommunications and mission systems manager for NEAR. Telecommunications support of the mission were scheduled to end at 4 p.m Pacific Standard Time today, he said.

Throughout NEAR's five-year mission, controllers at the Deep Space Network have provided every link between the spacecraft and Earth. The Deep Space Network has transferred information about the size, shape and gravity of the asteroid from the spacecraft to Earth, sent commands to make changes in the spacecraft's course, and maintained the contact for the exciting landing on Feb. 12.

"We're the vehicle of getting those commands from the mission controllers at Applied Physics Lab to the spacecraft," said Berman. "Then we receive the science and engineering data from the spacecraft to Earth. We also generate navigational data -- the Deep Space Network continuously measures the velocity of the spacecraft through the Doppler shift imprinted in the signal. We extract that data, and send it to the JPL navigation team so that they can determine the orbit and develop maneuvers."

The antennas rotate toward certain portions of the sky where engineers predict the signal will come from the spacecraft. Data, in the form of radio signals, is intercepted by the antennas, and sent via data processing equipment at the facility to the Jet Propulsion Laboratory, where navigators determine the exact position of the spacecraft.

The Deep Space Network also provided all the ground communications for the NEAR mission between the Applied Physics Lab, JPL and worldwide Deep Space Network stations via voice and data networks.

The NEAR spacecraft spent the last year in a low-altitude orbit of asteroid 433 Eros, a near-Earth asteroid that is currently 316 million kilometers (196 million miles) from Earth. During that time it collected 10 times more data than originally planned and completed all its science goals before attempting its descent to the asteroid.

When NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft left for asteroid 433 Eros five years ago, scientists weren't certain what they would find when the probe arrived. Was Eros a 30-km fragment from a planet that broke apart billions of years ago? Or perhaps a jumble of space boulders barely held together by gravity? Was Eros young or old, tough or fragile ... no one knew for sure.

But now, after a year in orbit and a daring landing on the asteroid itself, NEAR Shoemaker is beaming back data that could confirm what many scientists have lately come to believe: Asteroid Eros is not a piece of some long-dead planet or a loose collection of space debris. Instead, it's a relic from the dawn of our solar system, one of the original building blocks of planets that astronomers call "planetesimals."

As NEAR Shoemaker was heading for its historic landing on Feb. 12, 2001, team members hoped the spacecraft - which was designed to orbit, not land - would simply survive. When it did survive, they set their sights a little higher. From its perch on the surface of the asteroid, NEAR's gamma-ray spectrometer (GRS) can detect key chemical signatures of a planetesimal - data that scientists are anxious to retrieve.

"The gamma-ray instrument is more sensitive on the ground than it was in orbit," says Goddard's Jack Trombka, team leader for the GRS. "And the longer we can accumulate data the better." NASA recently gave the go-ahead for NEAR's mission to continue through Feb. 28th, tacking four days onto an extension granted just after the spacecraft landed.

To do its work the GRS relies partly on cosmic rays, high-energy particles accelerated by distant supernova explosions. When cosmic rays hit Eros, they make the asteroid glow, although it's not a glow you can see with your eyes; the asteroid shines with gamma-rays.

"Cosmic rays shatter atomic nuclei in the asteroid's soil," explains Trombka. Neutrons that fly away from the cosmic ray impact sites hit other atoms in turn. "These secondary neutrons can excite atomic nuclei (by inelastic scattering) without breaking them apart." Such excited atoms emit gamma-rays that the GRS can decipher to reveal which elements are present.

"We can detect cosmic-ray excited oxygen, iron and silicon, along with the naturally radioactive elements potassium, thorium and uranium," says Trombka. Measuring the abundances of these substances is an important test of the planetesimal hypothesis.

Planetesimals came to be when the solar system was just a swirling interstellar cloud, slowly collapsing to form the Sun and planets. Dust grains condensed within that primeval gas. The grains were small, but by hitting and sticking together they formed pebble-sized objects that fell into the plane of the rotating nebula. The pebbles accumulated into boulders, which in turn became larger bodies, 1 to 100 km wide. These were planetesimals -- the fundamental building blocks of the planets.

For reasons unknown Eros was never captured by a growing protoplanet. It remained a planetesimal even as other worlds in the solar system grew and matured.

Fully-developed planets like Earth are chemically segregated -- that is, they have heavier elements near their cores and lighter ones at the surface. Planetary scientists call this "differentiation." If Eros were a chip from a planet that broke apart, perhaps in the asteroid belt, it would exhibit chemical signatures corresponding to some layer from a differentiated world.

For example, Eros might be iron-rich if it came from the core of such a planet or silicon-rich if it came from the crust.

Instead, "orbital data from the x-ray spectrometer (a low-energy cousin of the GRS) showed Eros is very much like a type of undifferentiated meteorite we find on Earth called ordinary chondrites," says Andrew Cheng, the NEAR project scientist at Johns Hopkins University Applied Physics Laboratory (APL), which manages the mission for NASA.

Eros seems to harbor a mixture of elements that you would only find in a solar system body unaltered by melting (an unavoidable step in the process of forming rocky planets). But, says Cheng, there is a possible discrepancy.

"The abundance of the element sulfur on Eros is less than we would expect from an ordinary chondrite. However, the x-ray spectra tell us only about the uppermost hundred microns of the surface, and we do not know if the sulfur depletion occurs only in a thin surface layer or throughout the bulk of the asteroid."

The GRS can go deeper, as much as 10 cm below the surface. Although the instrument can't detect sulfur, it is sensitive to gamma-ray emissions from other elements such as radioactive potassium that are indicators of melting. Like sulfur, potassium is a volatile element -- it easily evaporates when a rock is heated. Finding plenty of potassium would strengthen the conclusion that Eros is an unmelted and primitive body.

On the other hand, a widespread dearth of "volatiles" would hint that Eros isn't so primitive after all.

It might sound like an ivory-tower question, but knowing the makeup of this asteroid -- both its internal structure and its chemical composition-- has a practical application. The solar system is littered with space rocks more or less like Eros, and many come uncomfortably close to Earth. One day we may need to blow one apart (or deflect one without blowing it apart) to avoid an unpleasant collision. Near-Earth asteroids are also potential mining resources as humans expand into space. In either case, knowing more about them is a good idea!

"Our first four data sets are here and they look great," says Jack Trombka. "John Goldsten, the lead engineer for the gamma-ray spectrometer at the Johns Hopkins Applied Physics Laboratory, has done a fabulous job making the instrument work on the surface, which is a different environment than orbit.

"We're just hoping to get as much data as we can before the mission ends."

Earth's most severe mass extinction -- an event 250 million years ago that wiped out 90 percent of all marine species and 70 percent of land vertebrates -- was triggered by a collision with a comet or asteroid, according to new findings by a team led by a University of Washington scientist.

The collision wasn't directly responsible for the extinction but rather triggered a series of events, such as massive volcanism and changes in ocean oxygen, sea level and climate. Those in turn led to species extinction on a wholesale level, said Luann Becker, UW acting assistant professor of Earth and Space Sciences.

"If the species cannot adjust, they perish. It's a survival-of-the-fittest sort of thing," Becker said. "To knock out 90 percent of organisms, you've got to attack them on more than one front."

Becker; Robert Poreda and Andrew Hunt from the University of Rochester, N.Y.; Ted Bunch of the National Aeronautics and Space Administration's Ames Research Center at Moffett Field, Calif.; and Michael Rampino of New York University and the Goddard Institute of Space Sciences, present their findings in the Feb. 23 edition of the journal Science.Funding for the research came from NASA's Astrobiology and Cosmochemistry programs and the National Science Foundation.

The scientists do not know the site of the impact 250 million years ago, when all Earth's land formed a supercontinent called Pangea. However, the space body left a calling card -- a much higher level of complex carbon molecules called buckminsterfullerenes, or Buckyballs, with the noble (or chemically nonreactive) gases helium and argon trapped inside their cage structures. Fullerenes, which contain at least 60 carbon atoms and have a structure resembling a soccer ball or a geodesic dome, are named for Buckminster Fuller, who invented the geodesic dome.

The researchers know these particular Buckyballs are extraterrestrial because the noble gases trapped inside have an unusual ratio of isotopes. For instance, terrestrial helium is mostly helium-4 and contains only a small amount of helium-3, while extraterrestrial helium -- the kind found in these fullerenes -- is mostly helium-3.

"These things form in carbon stars. That's what's exciting about finding fullerenes as a tracer," Becker said. The extreme temperatures and gas pressures in carbon stars are perhaps the only way extraterrestrial noble gases could be forced inside a fullerene, she said. These gas-laden fullerenes were formed outside the Solar System, and their concentration at the Permian- Triassic boundary means they were delivered by a comet or asteroid.

The researchers estimate the comet or asteroid was 6 to 12 kilometers across, or about the size of the asteroid that left the huge Chicxulub crater near what is now the town of Progresso on Mexico's Yucatan Peninsula 65 million years ago. That impact is believed responsible for the extinction of the dinosaurs. The scientists determined the size based on two factors -- if the body were smaller than 6 kilometers the effects wouldn't be seen globally, as they appear to have been; if it were larger than 12 kilometers there would have to be more gas-laden fullerenes distributed globally.

The telltale fullerenes containing helium and argon were extracted from sites in Japan, China and Hungary, where the sedimentary layer at the boundary between the Permian and Triassic periods had been exposed. The evidence was not as strong from the Hungary site, possibly because the sample came from slightly above or below the boundary layer, but the China and Japan samples bear strong evidence, Becker said. Fullerenes are found at very low concentrations above and below the boundary layer, but they are found in unusually high concentrations at the time of the extinction.

Scientists have long known of the mass extinction 250 million years ago, since many fossils below the boundary -- such as trilobites, which once numbered more than 15,000 species -- diminish sharply close to the boundary and are not found above it. There also is strong evidence suggesting the extinction happened very rapidly, in as few as 8,000 to 100,000 years, which the latest research supports. "That's a microsecond in geologic time," Becker said.

Previously it was thought that any asteroid or comet collision would leave strong evidence of the element iridium, the signal found in the sedimentary layer from the time of the dinosaur extinction. Iridium was found at the Permian-Triassic boundary, but not nearly at the concentration found in sediments from the time of the dinosaur extinction. Becker believes that difference might be because the two space bodies that slammed into Earth had different compositions.

While the findings illustrate that impact with large space bodies can be detrimental to life on Earth, Becker noted that there also is evidence they might have been key to life starting here in the first place. Some scientists believe the first life-forming chemicals were deposited on Earth in collisions with comets or asteroids, and some believe comets carried virtually all of the water that exists on the planet today.

Becker also noted that her group's work was made more difficult because there are few 250 million-year-old rocks left on Earth. Most rocks of that age have been recycled through the planet's tectonic processes.

"It took us two years to do this research, to try to narrow it down enough so that we could see this fullerene signature," she said.

Flight controllers at the Applied Physics Laboratory in Maryland report that NASA's Near Earth Asteroid Rendezvous spacecraft continues to function well on the surface of asteroid 433 Eros. Moreover, it is still collecting useful scientific data from two instruments. As fate would have it, the one experiment that stood to lose the most by NEAR Shoemaker's early retirement, the X-ray and gamma-ray spectrometer, benefited the most from the craft's newfound role as a lander. The gamma-ray spectrometer has suffered from poor sensitivity -- it had failed to detect anything even when the spacecraft was close to Eros. More time in orbit would have improved the spectrometer's meager counting statistics, so team leader Jacob I. Trombka (NASA/Goddard Space Flight Center) was not happy about the decision to attempt a landing.

Trombka's instrument not only survived the February 12th touchdown, but in doing so it gets to assess the surface from a closer range than ever imagined. (The detector may even be immersed in dusty rubble.) NASA managers had expected to silence NEAR Shoemaker for good on February 14th, but because of the gamma-ray instrument's fortuitous survival they granted the mission a two-week extension. "The detector system is working well," Trombka reports. A set of calibration data, trickled to Earth at 10 bits per second on February 16th, has paved the way for relaying abundance measurements for iron, potassium, and silicon over the next week. "Things are looking very good," he told Sky & Telescope. "Had I known this was going to happen, I wouldn't have been upset about landing at all!"

The other operating instrument, the magnetometer, was initially to remain off. But project scientists changed their minds and sent commands to activate it late on February 14th. So far the instrument has found no trace of a magnetic field from its surface outpost, a finding consistent with earlier measurements from orbit. Of the five asteroids seen at close range by spacecraft to date, none show any evidence of either an intrinsic or induced magnetic field.

NASA's NEAR Shoemaker spacecraft, the first spacecraft to touch down and operate on the surface of an asteroid, will not be immediately shut down after all, NASA officials announced yesterday.

Brought to a successful landing on Feb. 12 with guidance from the NEAR Shoemaker navigation team at NASA's Jet Propulsion Laboratory, Pasadena, Calif., the spacecraft's mission will be extended for up to 10 days to gather data from a scientific instrument that could provide unprecedented information about the surface and subsurface composition of the asteroid Eros.

Three days after touchdown, NEAR Shoemaker is still in communication with the NEAR team at Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, MD. Earlier this week, the team sent commands to NEAR Shoemaker and guided the robotic researcher to a gentle touchdown on a rock-strewn plain on the asteroid. The spacecraft gently hit the surface at 12:02 p.m. Pacific Standard Time (3:02 p.m. EST). It had slowed to a gentle speed of between 1.5 and 1.8 meters per second (less than 4 miles per hour) just before finally coming to rest after a journey of 3.2 billion kilometers (2 billion miles).

Mission operators say the touchdown may have been one of the slowest planetary landings in history. They also have a better picture of what happened in the moments after the landing. What they originally thought was the spacecraft bouncing may have been little more than short hop or "jiggle" on the surface; the thrusters were still firing when the craft hit the surface, but cut off on impact; and NEAR Shoemaker came down only about 200 meters (650 feet) from the projected landing site.

"It essentially confirmed that all the mathematical models we proposed for a controlled descent would work," said Dr. Bobby Williams, NEAR navigation team leader at the Jet Propulsion Laboratory. "You never know if they'll work until you test them, and this was like our laboratory. The spacecraft did what we expected it to do, and everyone's real happy about that."

On Tuesday, Feb. 13, the NEAR mission operations team decided against another engine firing that could have lifted the space probe off the asteroid's surface. There were initial concerns that it might be necessary to adjust the spacecraft's orientation in order to receive telemetry from the ground. However, NEAR Shoemaker landed with a favorable orientation, and there is no problem with receiving information. Mission managers have decided it is not necessary to move the spacecraft from its resting place on the surface of Eros.

The spacecraft spent the last year in a close-orbit study of asteroid 433 Eros, a near-Earth asteroid that is currently 196 million miles from Earth. During that time it collected 10 times more data than originally planned and completed all its science goals before its descent to the asteroid.

Funding for the mission extension will come from the NEAR Project.

The NEAR Shoemaker spacecraft's historic soft landing on asteroid 433 Eros Feb. 12 turned out to be a mission planner's dream -- providing NEAR team members with more scientific and engineering information than they ever expected from the carefully designed series of descent maneuvers.

"We put the first priority on getting high-resolution images of the surface and the second on putting the spacecraft down safely -- and we got both," says NEAR Mission Director Dr. Robert Farquhar of the Applied Physics Laboratory, which manages the Near Earth Asteroid Rendezvous (NEAR) mission for NASA. "This could not have worked out better."

NEAR Shoemaker snapped 69 detailed pictures during the final 5 kilometers (3 miles) of its descent, the highest resolution images ever obtained of an asteroid. The camera delivered clear pictures from as close as 120 meters (about 400 feet) showing features as small as one centimeter (one-third inch) across. The images also included several things that piqued the curiosity of NEAR scientists, such as fractured boulders, a football-field sized crater filled with dust, and a mysterious area where the surface appears to have collapsed.

"These spectacular images have started to answer the many questions we had about Eros," says Dr. Joseph Veverka, NEAR imaging team leader from Cornell University in Ithaca, N.Y., "but they also revealed new mysteries that we will explore for years to come."

NEAR Shoemaker launched on Feb. 17, 1996 -- the first in NASA's Discovery Program of low-cost, scientifically focused planetary missions -- and became the first spacecraft to orbit an asteroid on Feb. 14, 2000. The car-sized spacecraft gathered 10 times more data during its orbit than originally planned, and completed all the mission's science goals before Monday's controlled descent.

One year after NASA's NEAR Shoemaker spacecraft went into orbit around asteroid 433 Eros, and two days after it actually landed on the space rock, mission planners say they aren't ready to turn off the spacecraft just yet.

The mission will be extended for up to 10 days to gather data from a scientific instrument that could provide unprecedented information about the surface and subsurface composition of the asteroid.

NEAR Shoemaker's historic soft landing on Eros has turned out to be a mission planner's dream. "We put the first priority on getting high-resolution images of the surface and the second on putting the spacecraft down safely - and we got both," says NEAR Mission Director Robert Farquhar of the Johns Hopkins University Applied Physics Laboratory, which manages the Near Earth Asteroid Rendezvous (NEAR) mission for NASA. "This could not have worked out better," he said.

Two days after a set of maneuvers brought it to the surface of Eros, NEAR Shoemaker is still communicating with the team at the Applied Physics Lab. The spacecraft gently touched down just after 3:01 p.m. EST on Monday, February 12th, ending a full year in orbit around the large space rock.

Mission operators say the touchdown speed of less than 4 miles per hour (between 1.5 and 1.8 meters per second) may have been one of the slowest planetary landings in history. They also have a better picture of what happened in the moments after the landing: What they originally thought was the spacecraft bouncing may have been little more than a short hop or "jiggle" on the surface; the thrusters were still firing when the craft hit the surface, but cut off on impact. NEAR Shoemaker came down only about 650 feet (200 meters) from the projected landing site.

"It essentially confirmed that all the mathematical models we proposed for a controlled descent would work," says Bobby Williams, NEAR navigation team leader at NASA's Jet Propulsion Laboratory. "You never know if they'll work until you test them, and this was like our laboratory. The spacecraft did what we expected it to do, and everyone's real happy about that."

NEAR Shoemaker snapped 69 detailed pictures during the final three miles (five kilometers) of its descent, the highest resolution images ever obtained of an asteroid. The camera delivered clear pictures from as close as 394 feet (120 meters) showing features as small as one centimeter across. The images also included several things that piqued the curiosity of NEAR scientists, such as fractured boulders, a football-field sized crater filled with dust, and a mysterious area where the surface appears to have collapsed.

"These spectacular images have started to answer the many questions we had about Eros," says Joe Veverka, NEAR's imaging team leader from Cornell University, N.Y., "but they also revealed new mysteries that we will explore for years to come."

Yesterday, the NEAR mission operations team decided against another engine firing that could have lifted the space probe off the asteroid's surface again.

Funding for the mission's extension will come from the NEAR project.

What next for NEAR-Shoemaker? On the morning after the NASA robot ship made the first landing on an asteroid, mission scientists were trying to figure out how much more science they could squeeze from the small craft.

One of several options being debated: firing up the thrusters for a short encore flight. But NEAR (Near Earth Rendezvous Asteroid) managers said that would happen no earlier than Wednesday.

Instead, they planned to spend Tuesday looking at the data stream sent from their half-ton spacecraft, some 196 million miles (315 million km) away.

The information so far indicates NEAR-Shoemaker is alive, well and generating plenty of power from its solar panels. It is an astounding outcome no one predicted. The vessel was not designed to land.

The team is taking its time deciding on a possible liftoff from the asteroid Eros, an oddly shaped space rock 21 miles (34 km) in length.

Once they fire the rocket thrusters, there is a strong likelihood they will not hear from the probe again. A second landing might very well damage the craft or knock its antenna or solar arrays out of alignment.

There is little time for debate. NASA will cut off NEAR- Shoemaker's access to the tracking system known as the Deep Space Network at on Wednesday at 7 p.m. EST, ending the five-year NEAR mission.

The NEAR team, located at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, conducted the asteroid landing to gain "bonus science" after an already successful mission.

During its yearlong orbit of Eros, NEAR-Shoemaker beamed a colossal amount of information about the asteroid, including 160,000 images of its surface. It was 10 times more data than scientists anticipated.

The automobile-sized craft sent back about 100 images during its descent on Monday, offering the closest look yet at an asteroid. The images are able to resolve objects as small as a centimeter.

A NASA robot ship ended a deep space odyssey by touching down on an asteroid on Monday, despite having no landing gear.

Shortly after the first landing on an asteroid, excited mission managers were considering an almost unthinkable encore: coaxing the craft from its resting spot for another flight.

NEAR engineers should decide within hours after landing whether to command the resilient robot to fire up its thrusters for a return to space, mission director Robert Farquhar said.

"I am happy to report that the NEAR has touched down. We are still getting signals. It is still transmitting from the surface," said Farquhar as NEAR engineers cheered and clapped their hands.

NEAR's landing was confirmed when mission control received a beacon signal from the craft resting on the surface of Eros, some 196 million miles from Earth.

Before colliding with the space rock, the NEAR-Shoemaker spacecraft beamed back pictures with unprecedented clarity of the asteroid. NASA scientists hope to see features as small as a human hand when they process the images in the coming hours and days.

Mission astronomers didn't expect the $225 million orbiter to survive the impact. It was designed to study, not land, on Eros, an oddly shaped rock whose appearance has been likened to everything from a potato to a kidney bean. But somehow against all odds it survived the landing and sent a radio message back home.

Mission engineers think NEAR-Shoemaker landed on its side on a sunlit landing site between the South Pole and a distinctive saddle-shaped depression.

NEAR-Shoemaker began descending toward the asteroid in the morning, drifting toward its rocky companion and using its thrusters to brake several times after closing to within 3 miles (5 km) of Eros.

The spacecraft snapped dozens of pictures in its final hour, the closest only several hundred yards away, NEAR scientists said. It likely smacked into the surface at about 5 mph (8 km/h), according to NEAR scientists, a speed similar to that of a parachutist hitting the ground.

Its yearlong mission over, its budget exhausted, its fuel spent, NEAR-Shoemaker was sent on the deadly dive to gain "bonus science," said Farquhar.

NEAR scientists have puzzled 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.

A NASA robot ship ended a deep space odyssey on Monday by succesfully touching down on an asteroid it had orbited for almost a year.

NEAR's landing was confirmed when mission control received a beacon signal from the craft resting on the surface of Eros, some 196 million miles from Earth.

Before colliding with the space rock, the NEAR-Shoemaker spacecraft beamed back pictures with unprecedented clarity of the asteroid. NASA scientists hope to see features as small as a human hand when they process the images in the coming hours and days.

Mission astronomers were scanning the skies Monday afternoon for a signal from the spacecraft, but didn't expect the $225 million orbiter to survive the impact. It was designed to study, not land, on Eros, an oddly shaped rock whose appearance has been likened to everything from a potato to a kidney bean.

NEAR-Shoemaker began descending toward the asteroid in the morning, drifting toward its rocky companion and using its thrusters to brake several times after closing to within 3 miles (5 km) of Eros.

The spacecraft snapped dozens of pictures in its final hour, the closest only several hundred yards away, NEAR scientists said. It smacked into the surface at about 1.5 metres per second, according to NEAR scientists.

Mission engineers think NEAR-Shoemaker could have landed on its side or bounced and turned over on a sunlit landing site between the South Pole and a distinctive saddle-shaped depression.

Weak signals were still being received after the time of impact showing that NEAR had survived at least partially intact.

Its yearlong mission over, its budget exhausted, its fuel spent, NEAR-Shoemaker was sent on the deadly dive to gain "bonus science," said NEAR mission director Bob Farquhar.

NEAR scientists have puzzled 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.

Some unexplained erosion processes seem to have taken place on Eros, according to team scientist Joseph Veverka.

"Suddenly we started seeing things we didn't expect and hadn't seen on other surfaces in the solar system," the Cornell University astronomer said. "It's like another door has opened."

Already the spacecraft has sent home a bonanza of data about the composition, gravity and appearance of Eros, which it zapped with 11 million laser pulses and photographed almost 200,000 times.

The pictures reveal a haunting panorama with fields of craters, mysterious bright spots and boulders the size of soccer fields. Some have been turned into dramatic movies of NEAR's close-up view as it swooped near the surface of the revolving rock.

The data has given scientists clues about the history of the solar system. Eros is considered a geologic relic from the infancy of the solar system, which formed about 4.5 billion years ago.

It could also prevent a future catastrophe. Eros belongs to a group of large asteroids with orbits relatively close to Earth, like the one that scientists speculate slammed into Earth and killed off the dinosaurs 67 million years ago.

Scientists warn that there is a remote risk another such killer asteroid will someday hit Earth. Learning about Eros could offer them clues to prevent such a catastrophic collision.

Named after famed astronomer Eugene Shoemaker, a pioneer in lunar and asteroid studies, NEAR-Shoemaker traveled about 2 billion miles (3.2 billion km) during a trek that lasted five years.

It was supposed to reach Eros in 1998 but a software glitch sparked a costly engine misfire that pushed back its arrival time until February 14, 2000. Eros became only the fifth celestial body touched by a human spacecraft, following the Moon, Mars, Venus and Jupiter.

As NASA's Near Earth Asteroid Rendezvous spacecraft, known as NEAR Shoemaker, closes in on asteroid 433 Eros, Cornell University astronomers hope that surface details as small as a hand-size rock will be captured by the camera before the spacecraft bumps down on the boulder-strewn surface Feb. 12.

Since last October, the NEAR imaging team has been puzzling over strange surface features of Eros seen in new, high-resolution images. There is the hope that the close-up images taken in the final few minutes before the spacecraft drops onto the surface will help to answer their questions about the geology of the 22-mile-long asteroid more than 196 million miles (316 million kilometers) from Earth.

"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."

The landing -- what NASA is calling a "controlled descent" -- is a highly risky maneuver, involving four thruster firings over four hours intended to slow the rate of descent to 7 mph from 20 mph. In the final 45 minutes, when the spacecraft is about 3.5 to 4.5 miles (about 6 to 7.5 kilometers) from its landing site at the edge of the crater Himeros, the camera will begin taking a new image about every 30 seconds.

The final picture will be captured at just 550 yards (500 meters) from the surface, enough to capture details as small as perhaps 4 inches (10 centimeters) across. Mission leaders at the Applied Physics Laboratory at Johns Hopkins University, which built the spacecraft and manages the NEAR mission, do not expect images to be transmitted from the surface because Eros's spin and topography will almost certainly prevent communication between Earth and the craft.

Why does Veverka's team want to get such a close look at Eros' surface details? Because, says Veverka, who is professor of astronomy at Cornell, his team is frankly puzzled by what it has seen on Eros over the past few weeks. Last October, with much of NEAR's mission accomplished, the spacecraft was sent into orbit just 4 miles (about 6 kilometers) or so from the asteroid's surface. For the first time the imaging team was seeing details as small as a yard (.9 meter) across, compared with the approximately 5.5 yards (5 meters) resolution that had been captured by the camera since the spacecraft went into orbit around Eros on Feb. 14, 2000.

"Suddenly, we started seeing things we didn't expect and hadn't seen on other surfaces in the solar system," says Veverka. "It's like another door has opened."

The biggest surprise, says 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 says, 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, says 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 says. "But it seems to be very common."

It is just possible, says Veverka, that the final image will be taken almost at the surface itself. He explains that the camera will remain in focus until about 220 yards (200 meters) from the landing site. If the spacecraft is still on course, it is possible that the camera will take one final image and have time to send a partial image on its way to Earth before the spacecraft touches down. It takes 10 milliseconds for the exposure, 1 second to read the image into the spacecraft recorder and 30 seconds for the data to emerge from the recorder. The data then take 17 to 18 minutes to reach Earth tracking stations.

The imaging team now is getting even higher-resolution images of these features. On Jan. 24 the spacecraft entered a close flyby sequence, including a four-day orbit that produced images from as close as 2 miles (3.2 kilometers) above the surface. These new images are enabling the Cornell imaging team to accumulate data at a resolution of about 1.1 yards (1 meter). "The hope is that during the descent we can improve this resolution by perhaps a factor of 10 so that we can find out more about what is going on there," says Veverka.