near_end_000616 WASHINGTON -- The Near Earth Asteroid Rendezvous (NEAR) spacecraft will power dive toward asteroid Eros in a few weeks, giving scientists more data to help decipher the physical makeup and history of the huge potato-shaped body. Scientists and engineers will soon decide the probe's ultimate fate, perhaps carrying out a "hit-and-run" maneuver before crash landing on Eros early next year.
Watch the video of NEAR's approach to asteroid Eros.
NASA's NEAR space probe -- now renamed NEAR-Shoemaker after the late space geologist, Gene Shoemaker -- will fire its thrusters on July 7, nudging itself out of a 31-mile (50-kilometer) orbit around Eros. A week later, the spacecraft will reach its closest point to Eros yet: just 22 miles (35 kilometers) from the giant rock of ages that tumbles head-over-heel. The craft is slated to take a 10-day, once-around look-see. It then boosts itself back up to the earlier, pre-July altitude.
This image of Eros was taken by NEAR-Shoemaker on April 5, 2000.
"NEAR is just truckin' along," said Andrew Cheng, project scientist for the mission at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. The lab built and manages the mission for NASA.
But NEAR has not been free of
glitches. One of six scientific instruments aboard the probe, an infrared spectrometer, inexplicably stopped sending data in mid May. Efforts to bring the device back to life have been to no avail. "We can actually live with this," Cheng told SPACE.com. "That instrument had already measured about 70 percent of Eros' surface. By relying on the other instruments, we hope we will be able to measure the whole asteroid," he said.
By using NEAR's array of working sensors, Cheng said, it is thought that the missing data from the infrared spectrometer can be filled in.
Moratorium on science
Once NEAR reaches its new low orbit above Eros, science operations will be held off for the first four to five days, Cheng said. Putting the spacecraft into a quiet mode gives ground controllers the ability to better chart the asteroid's gravity field. "To do that, were going to have a moratorium on pointing the instruments, which means not moving the spacecraft around," he said.
Mapping the modest tug and pull of Eros' gravity will make it possible for NEAR to step down even closer to the mini-world. It reaches the end of its yearlong mission in February 2001.
"Each time we step down, we get more data. Then we need more time to mine that information," said Lucy McFadden, a science-team member from the University of Maryland in College Park. "We're all in a stage of discovery."
Signatures from the past
McFadden said that NEAR data suggest several things about the
cratered and rock-strewn denizen of the deep."It's a uniformly dense object. It has a uniform composition that lands it in the low iron, chondrite field, based on comparison with meteorites," McFadden said. A chondrite is the most primitive form of meteorite recovered on Earth.
There is growing belief that Eros is likely a fragment of a lot bigger object, McFadden said.
NEAR-Shoemaker recently imaged these side-by-side impact sites on Eros.
Cheng also said that Eros appears to be a chip off a bigger block. There are telltale signs such is the case.
"Parts of the asteroid mapped so far show patterns that run globally around Eros, from end to end. They don't seem to be associated with any particular crater on the asteroid. That's the kind of thing that is hard to understand unless Eros was part of a much larger body," Cheng said.
Digging up dirt
The entire NEAR science team is gathering at the Applied Physics Lab on June 26. At that time, decisions are to be made about carrying out the rest of NEAR's mission. In particular, about what future maneuvers are to be slated for the on-duty spacecraft.
"There are all kinds of things being talked about," Cheng said.
Actually plopping NEAR down on top of Eros at mission's end is still one option. "It would be a good thing if we could do it," Cheng said.
"We have not been cleared to land," said Robert Farquhar, mission manager for NEAR at APL. The last five weeks of the mission have not been scripted.
McFadden said that one scientifically valuable option that's been suggested is for NEAR to use its solar arrays to scrape the surface of Eros. The probe would then back off and take a look at the trough it made. "We'd be able to test our assumption that the surface layer exposed to solar wind over billions of years, or even over tens of millions of years, makes it a different color than material below the surface," she said.
"It would be a fun thing to try. And we would get some valuable information too," McFadden said.
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