Satellite nearing historic rendezvous and orbit of asteroid

October 13, 1998
Web posted at: 2:00 PM EDT

MADISON, Wisconsin (AP) -- In the week before Christmas, some 163 million miles from Earth, a small satellite will fire rockets and become the first manmade object to be placed into an orbit around an asteroid.

Researchers said Monday that the satellite, called the Near Earth Asteroid Rendezvous, or NEAR, spacecraft was working well and was on target for its meeting in space with the asteroid called Eros.

Andy Cheng, a Johns Hopkins University researcher and the project scientist for NEAR, said the craft would begin orbiting Eros on Jan. 10, 1999, and that in the following months it would be lowered slowly until the craft was speeding just 21 miles above the asteroid.Cheng reported on NEAR at the annual meeting of the planetary division of the American Astronomical Society.

Six instruments aboard NEAR will analyze the composition, magnetic field and mass of the asteroid, sending the data back to Earth by radio.

Eros is something of a mystery. The rock is about the size of a mountain, 24 miles by 8 miles. It is a near-Earth asteroid, one whose orbit routinely carries it close to the orbit of Earth. Scientists don't know if the rock is solid or if it is a highly porous body with empty cavities or chunks of ice.

But it's similar to the asteroids that pounded Earth early in the planet's history. One such asteroid smashed into Earth 65 million years ago and is thought to have caused the extinction of the dinosaurs.

Like most asteroids, said Cheng, Eros probably formed early in the history of the solar system. What isn't known is whether Eros was once part of a bigger planet or if it formed independently. "There were many collisions in the early solar system," Cheng said.

Sometimes huge chunks of a planet are knocked into space by such celestial smashups and become independent bodies. The Earth's moon is thought to have come from such a collision.

Asteroids also could form from the leftover debris of planet-building. Bits of stray rock and dust slowly clump together until they form one object.

The process may not be finished, said Cheng. He said there is some concern that wandering space rocks or gravel that imperil the NEAR.

As NEAR approaches Eros, researchers will use cameras and instruments on board to search for any stray bits of rock or gravel that are still orbiting the asteroid.

After months in orbit of Eros, researchers may attempt to put the craft onto the surface of the asteroid. Cheng said the spacecraft was not designed to land, but that is one option the researchers are considering.

The density of Eros is unknown, but the asteroid is so small that its gravity force will be only a fraction of Earth's, making landing there less violent.

But it would still be tricky steering the craft to a touchdown because Eros is so far away that it takes 45 minutes for a radio signal to make a round trip journey between the Earth and NEAR.

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