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Watch an asteroid
twirl in space
NEAR heads for Feb. 14 rendezvous
By Alan Boyle
MSNBC
Feb. 3 ? The Near Earth Asteroid Rendezvous spacecraft has successfully executed a maneuver aimed at putting it on course for this month?s encounter with the asteroid Eros. Right now Eros looks like a rock slowly rolling in the blackness of space, but scientists expect it to grow to a screen-filling extravaganza.
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AFTER ALMOST exactly four years of space flight, NEAR is due to go into orbit around the micro-world Feb. 14. The Valentine?s Day arrival time is strangely fitting, since Eros is named after the Greek god of love (also known by his Roman sobriquet, Cupid).
In preparation for the rendezvous, the 18.3-foot-wide (5.6-meter-wide) spacecraft fired its engines for 90 seconds Thursday, slowing its speed to 18 mph (28.8 kilometers per hour) relative to Eros. The maneuver was originally scheduled for Wednesday, but it had to be reconfigured when the spacecraft went into ?safe mode? hours before the burn.
A second maneuver on Feb. 8 should put NEAR back on its original track, mission controllers said.
?We were able to come back right away and devise a turnaround burn,? NEAR?s mission director, Bob Farquhar, said in a written statement. ?It really shows the resiliency of the mission plans.?
As of Thursday, NEAR was about 5,000 miles (8,000 kilometers) away from Eros.
The spacecraft and the asteroid are both roughly 164 million miles (265 million kilometers) from Earth ? and experts emphasize that there?s absolutely no danger that Eros will collide with our planet, at least for the next few million years or so.
NEAR was originally scheduled to start swinging around the asteroid a year ago. Engine problems forced a course change, however, meaning that the spacecraft could come no closer than 2,375 miles (3,830 kilometers) to Eros during its December 1998 flyby.
Despite the disappointment, scientists learned a great deal about the rock from that earlier pass. They determined that the asteroid was slightly smaller than previously thought ? about 21 by 8 by 8 miles (33 by 13 by 13 kilometers). And they saw variations in surface color and reflectivity indicating that the asteroid has a diverse surface makeup.
Scientists said Eros appeared to be about as dense as Earth?s crust, and twice as dense as asteroid Mathilde, which NEAR flew past in June 1997. It also has two medium-size craters and a prominent ridge that extends as far as 12 miles (20 kilometers).
All this suggests that Eros is a rocky object rather than a floating rubble pile, as scientists believe Mathilde to be.
Images taken during an earlier flyby in December 1998 (top row) were used to develop computerized renditions of Eros' contorted shape (bottom row). Eros' shape has been compared to that of a shoe, a battered boat or a cosmic peanut.
This month?s encounter with Eros is sure to be more intimate, so to speak. That?s the reason why mission managers are interested in the approach pictures: They help confirm Eros? position and rate of rotation, and would also eventually show whether there were any mini-moons or other material floating around the asteroid. In the past, satellites have been detected orbiting other asteroids, such as Ida and Eugenia.
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?If Eros has a moon, we surely wish to know about it before we go into orbit,? NEAR mission managers explained in a status report.
Johns Hopkins University?s Applied Physics Laboratory is overseeing the $211 million NEAR mission on NASA?s behalf.
During its yearlong orbital mission, NEAR is expected to take images from as close as nine miles away ? and even attempt a landing. Eventually, data from NEAR could help scientists learn how to divert an asteroid from colliding with Earth if such a situation ever arose.
Earthlings won?t have to worry about Eros specifically for a long time, said project scientist Andy Cheng.
?Eros is in a chaotically changing orbit that will within the next few million years most likely become an Earth-crossing orbit,? he told MSNBC. He estimated that the asteroid might have a 5 percent chance of hitting Earth at some point in the next 100 million years or so.
But if such a collision ever occurred, it would pack a catastrophic wallop, Cheng said.
?Eros is actually bigger than the asteroid that ended the age of the dinosaurs,? he said.
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