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6 minute read
Michael D. Lemonick

DEEP IN INTERPLANETARY SPACE, AN irregularly shaped chunk of rock about twice as long as the island of Manhattan is silently speeding along the orbit it has traced for billions of years. It is an asteroid known as 433 Eros, and it is just one of thousands that have been discovered since the first was spotted in 1801. Astronomers believe these mysterious objects are rubble left over from the formation of the solar system and that they’ve occasionally smashed into Earth; it may well have been a wayward asteroid, for example, that wiped out the dinosaurs 65 million years ago. But nobody has ever got a close enough look to say anything definitive about what the asteroids are or where they came from.

That should soon change. Two weeks ago, a space probe called NEAR was launched from the Kennedy Space Center on a trajectory that will carry it to within 20 miles of Eros, where it will remain in orbit for a year of intensive study. The mission should give astronomers important clues to the formation of the planets and the origin of asteroids. Just as significant, however, it should demonstrate that NASA has started to change its bloated, bureaucratic ways. Although this is one of the trickiest space missions ever, it’s also one of the cheapest. The Galileo probe, now in orbit around Jupiter, cost $1.6 billion and took nearly a decade, while NEAR (Near Earth Asteroid Rendezvous) came in at $118 million and was built in two years. Says Wesley Huntress, NASA’s associate administrator for space science: “This really is a revolution in the way we do business.” NEAR is just the first of the agency’s Discovery series–space missions that nasa chief Daniel Goldin has decreed must be “faster, better, cheaper.”

One way NASA saved money was by farming the job out to an independent lab, the Applied Physics Laboratory at Johns Hopkins University. The agency agreed that it wouldn’t dictate APL’s procedures, just its results. “That,” says Johns Hopkins engineer Thomas Coughlin, who managed the project, “saved us from having to do a lot of expensive and unnecessary paperwork.” Thanks to the rapid advance of microelectronics in recent years, NEAR’s designers were able to put a lot of instruments into a smaller and less costly package. Result: the probe came in an unprecedented nine months early and about $32 million under budget.

Despite its low cost, NEAR is bristling with sensors. It carries not only a camera but also a laser-based radar system to map Eros’ surface in detail, three different spectrometers to analyze the asteroid’s chemical composition, and a magnetometer to gauge its magnetic field. The ship itself is an instrument of sorts. On its first approach, NEAR will deliberately overshoot Eros to see how much the asteroid’s gravity slows it down and thus how massive Eros really is.

With so many instruments, NEAR is almost certain to transform scientists’ understanding of the asteroids. According to prevailing theory, asteroids are remnants of the very earliest days of the solar system, when chunks of rock clumped together to form hundreds of small planets known as planetesimals. These objects–hundreds but not thousands of miles across–would frequently smash into one another; then the fragments would reassemble under gravity only to smash again. Eventually, a few grew large enough to resist breaking up, and they swallowed up the smaller pieces and became the planets. The asteroids are believed to be the few pieces that escaped being swallowed–some of them presumably the debris from cosmic smashups and the rest pieces of rock that never were part of planetesimals in the first place.

No one is sure which category Eros belongs to, but NEAR should be able to solve that mystery. Says M.I.T. planetary scientist Maria Zuber, who is working on the laser-mapping experiment: “The topography of Eros reflects the object’s whole history–it will tell us a lot about how it formed. And combined with the gravity measurements, it will tell us what the density is.” That’s important because in a large object like a planetesimal, iron and other metals sink to the core under gravity, while lighter rock stays closer to the surface. A very dense or a relatively light Eros would suggest that it was once part of a larger body that was later destroyed, a well-preserved relic of the solar system’s violent youth. Says Zuber: “An asteroid is essentially a snapshot of the planetary-formation process.”

Ideally, scientists would love to get closer than 20 miles away from an exotic object like Eros. And by the time the mission is over, they may get their chance. If there’s enough propellant left in NEAR’s tanks at the end of the year, ground controllers will have the option of sending the probe into a slow-motion, controlled crash. That would give NEAR’s sensors one last, very detailed look at Eros’ surface and perhaps reveal even more scientific information. Will they do it? Says APL’s Coughlin: “We aren’t even going to consider that question until we’ve successfully gotten there and gone into orbit. But we certainly aren’t ruling it out.”

By that time NASA will have plenty of other missions to manage. The next project in the Discovery series is the Mars Pathfinder, scheduled for launch next December, which will land on the Red Planet and send a robot rover off to explore. Then comes Lunar Prospector in 1997, designed to chart the mineral composition of Earth’s nearest neighbor, and after that a mission to bring a chunk of comet back to Earth, slated for 1999. Each is supposed to cost a few hundred million dollars at most, and thanks to NEAR that goal, considered highly improbable when it was first proposed five years ago, doesn’t seem so absurd. “We’ve now proved we can get it built and out to the launch pad on time and on budget,” says Huntress. “Until it reaches Eros, we can’t call it a complete success. But it’s looking very good so far.”

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