Hopkins lab chosen to design asteroid watcher Craft would take close look at mysterious space object


A research arm of the Johns Hopkins University has been chosen to design a spacecraft intended to take the first close-up look at the kind of asteroid that could one day collide with Earth, officials said yesterday.

Hopkins' Applied Physics Laboratory in Laurel has been given a $450,000 contract by NASA for preliminary work on the Near Earth Asteroid Rendezvous satellite, called NEAR. If NASA and Congress approve construction of the compact $150 million spacecraft, it could begin orbiting an asteroid called "Nereus" in January 2000.

The unmanned spacecraft is expected to conduct the first long-term study of any asteroid.Robert W. Farquhar, the physics laboratory's head of mission planning for NEAR, said the asteroid was chosen because it's easy to get to -- it's orbit closely follows that of Earth and occasionally crosses it.

Nereus did not have a name until recently, when it was chosen as the target for the mission. "It was kind of a pun by some people, because you can also read it as near-us," he said.

It is precisely these near-Earth asteroids that may have collided with the planet in the past, and could do so again, said astronomer Donald K. Yeomans of the Jet Propulsion Laboratory in Pasadena, Calif.

Such a collision could be far more than a fender-bender. An asteroid the size of Nereus could explode with the force of 25,000 hydrogen bombs, creating a huge shock wave and throwing up enough debris to block out the sun.

Near-Earth asteroids are different from what are termed "main belt" asteroids, which orbit the sun in a vast doughnut-shaped ring between Jupiter and Mars.

Dr. Farquhar said that NEAR will spend a year either flying alongside Nereus or spinning around the asteroid, coming within a mile of its surface.

Dr. Yeomans said that should tell scientists what near-Earth asteroids are made of and help decide if they pose any threat to our planet.

"We really don't know what's typical of a near-earth asteroid," he said. "We've never seen one."

If, as some scientists theorize, they are extinct comets made mostly of icy material, "then they are fairly low-density objects and perhaps not a threat at all," Dr. Yeomans said.

"Or are they true asteroids?" similar to those in the main belt, he asked, "in which case they're made of rock or iron, in which case they're more of a threat."

Dr. Yeomans said he hopes NASA decides to send NEAR to other asteroids and perhaps a comet after its lengthy study of Nereus.

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