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Scientists closing in on the asteroid Eros

UA scientists are planning a year-long rendezvous with the asteroid Eros, 240 million miles from Earth.

"This is the first time ever a spacecraft will orbit an asteroid," stated William Boynton, of the UA's Lunar and Planetary Laboratory, in a press release. "There have been flybys and snapshots of asteroids, but not much in the way of quantitative scientific data."

Asteroids are small bodies without atmospheres that orbit the sun but are too small to be classified as planets. Tens of thousands of asteroids are contained in the asteroid belt, a doughnut-shaped ring between the orbits of Mars and Jupiter.

Asteroids are thought to be primordial material that were prevented from accreting into a planet-sized body by Jupiter's strong gravitational pull when the solar system was forming 4.6 billion years ago.

Boynton, currently in Washington D.C., is a scientist for the Near Earth Asteroid Rendezvous spacecraft. Known as NEAR, the spacecraft is designed to operate at distances of 203 million miles from the sun, the longest distance ever for a solar-powered instrument.

"The role of the UA was to make a scientific database to allow more efficient data analysis," said Irina Mikheeva, a software specialist for the NEAR team.

Launched in 1996, NEAR is to spend almost a year orbiting as close as nine miles above Eros' surface. Eros was the first-discovered near-Earth asteroid and measures 21 miles in length, eight miles high and eight miles wide.

This mission was almost aborted when the spacecraft experienced communication problems in 1998 while trying to rendezvous with Eros.

The overall scientific goals of the NEAR mission include characterizing physical and geological properties of near-Earth asteroids, clarifying relationships among asteroids, comets and meteorites and further understanding the processes and conditions during the formation and early evolution of the planets, Mikheeva said.

The total mission cost is projected to be $211.5 million. The cost for development came to $124.9 million and launch support and tracking amounted to $44.6 million.

Boynton conducts research on the X-Ray/Gamma Ray Spectrometer, or XRGS, experiment. Its primary objective is to determine the composition of Eros.

Data will be taken several weeks after NEAR arrives at Eros when it descends to within 120 miles of the asteroid's surface, Mikheeva said. The best data will be collected at the end of April when the spacecraft is at its closest point to Eros, about 30 miles above the surface.

The XRGS was designed and built by the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., which manages the NEAR mission for NASA.

The researchers at the UA Lunar and Planetary Laboratory will process data and manage the data base, as well as work on the scientific interpretation of results. Samuel "Hop" Bailey, project manager, and software specialists Jasbir "Jesse" Bhangoo and Mikheeva work with Boynton in the research.

These results are crucial to understanding such mysteries as the source of meteorites and their relationship to asteroids, Mikheeva said.

Boynton stated this project will impact scientific knowledge about asteroids.

"Eros is a very important asteroid because it ... appears to be similar to a rare type of meteorite on Earth called 'stony-irons,' which have 50 percent metal and 50 percent silicate," Boynton stated. "Though the S-asteroids are very common in space, they do not seem to match many of the meteorites that fall to Earth."

"The other half of this problem is that the most common meteorites found on Earth ... appear to be rare in space. This mission should really answer this question," Boynton stated.

It's possible that the composition of Eros might turn out to be different from any of the known meteorites, Boynton stated.

It's also possible that Eros, a highly irregularly shaped object, is "possibly a chip off some larger, pre-existing asteroid that was smashed up," richer in silicates on one side and richer in metal on another, he stated. "This might allow us to learn something about the processes that go on in asteroids."

NEAR, launched Feb. 17, 1996, from Cape Canaveral, Fl., is the first in NASA's Discovery Program for "faster, better, cheaper" planetary missions.

It was launched nine months before it was scheduled to and $41.6 million under the $150 million budget. The other NEAR instruments are a multispectral imager, a laser range-finder, a near-infrared spectrometer, a magnetometer and a radio science package.

NEAR is the first spacecraft powered by solar cells to operate beyond the orbit of Mars. It returned 500 images of asteroid 253 Mathilde when it flew within 750 miles of that object on June 27, 1997.

In January 1998, NEAR returned to the Earth's vicinity for a "slingshot" gravity assist toward Eros' orbital plane.

On Thursday, exactly four years after NEAR was launched, NASA will hold a press conference at its headquarters in Washington, D.C. that will feature early science return information and images.