CLOSER, CLOSER, and still closer, the NEAR spacecraft snapped a series of revealing photos of the surface of Eros as it gracefully came in for a landing.
Much to the surprise and delight of mission controllers here on Earth, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft glided in for a soft landing last Monday on the surface of 433 Eros, an asteroid 196 million miles away. As the tiny car-size craft neared its final destination, it took 69 detailed photographs of the space rock, revealing features as small as one centimeter across (right).
These pictures join a gallery of roughly 160,000 images taken during NEAR's two billion miles of travel over the past five years. Not only has NEAR now made what may be one of the slowest descents in history¿cruising in to a touchdown at speeds of less than four miles an hour¿but is has also provided scientists with an unprecedented close encounter.
"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 Lab. "This could not have worked out better."
As a result of the successful landing¿and the fact that the spacecraft is still in contact¿the scientists have extended the mission, which was supposed to end when NEAR hit Eros. They were concerned at first that NEAR might land in such a way as to interfere with communications and had therefore planned on possibly refiring one of its engines for repositioning.
LANDING SITE, marked by the white arrow, was in fact only 650 feet away from the planned site. Fortunately, the spacecraft landed such that it could still communicate with controllers back on Earth.
After the landing at 3:01:52 p.m. Eastern Standard Time on February 12th, however, scientists discovered that the probe's signal came through loud and clear. They will now try to use an instrument on board to collect information about the asteroid's surface and subsurface composition.
Regardless of whether or not they get any additional information, the landing itself was a remarkable feat. The scientists had to plan and orchestrate a set of five breaking maneuvers to move the NEAR spacecraft out of its orbit around Eros¿a path it had faithfully taken since February 14th of last year. In fact, they put NEAR down within 650 feet of the planned 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 is real happy about that."
They are also really happy about what they see in the pictures NEAR took during the last three miles of its descent. Indeed, the photographs¿snapped from as close as 394 feet away¿display several curious features that may tell scientists more of Eros' life story. For instance, the surface is strewn with several fractured boulders. Also, it appears to have collapsed in one region. Elsewhere a football-field-size crater, filled with dust, scars the terrain. "These spectacular images have started to answer the many questions we had about Eros," says Jospeh Veverka, NEAR imaging team leader from Cornell University, "but they also revealed new mysteries that we will explore for years to come."
Also in the years to come, NASA will launch more missions like NEAR, the first in its Discovery Program of low-cost, scientifically focused planetary missions. "NEAR has raised the bar," says Stamatios Krimigis, head of the Applied Physics Laboratory's Space Department. "This team had no weak links¿not only did we deliver a spacecraft in 26 months, we were ready to launch a month early, and that efficiency continued through five years of operations. This is what the Discovery Program is designed to do." NEAR will be a tough act to follow.