Deep Space 1 flew within 16 miles of Braille, a peanut-shaped object about 1.3 miles long. The July 26 flyby was the closest ever by a spacecraft. Its camera failed to take close-up pictures during the encounter, but a spectrometer was able to capture data on the surface composition.
"It's often said a picture is worth a thousand words, but today under this circumstance a spectrum is worth a thousand pictures," said Robert Nelson, a mission scientist at NASA's Jet Propulsion Laboratory in Pasadena.
Braille is remarkably similar to Vesta, a much bigger asteroid that orbits millions of miles away between Mars and Jupiter, mission scientists said Tuesday. Both contain rock that was once molten - something rarely found in other asteroids.
The simple explanation is that "Vesta was a victim of a collision of some sort and that it spewed off chips of the old rock," said Bonnie Buratti, a member of the mission's science team. Pictures from the Hubble Space Telescope also show Vesta, which is about 325 miles across, has a large impact crater on its surface.
Scientists will continue to run computer models to find out how Braille could have traveled so far. Braille has an irregular orbit between Earth and Mars while Vesta is in a belt of asteroids between Mars and Jupiter.
Such studies could help scientists figure out ways of redirecting asteroids that may one day threaten Earth, said Eileen Ryan, an assistant professor of physics at New Mexico Highlands University in Las Vegas, N.M. "We can prepare for a possible asteroid hazard situation as we learn more about how they break up," she said.
Such information might be useful in about 4,000 years when Braille's orbit could put it on a collision course with Earth, but more number crunching is necessary to better assess the danger, Buratti said.
Despite the misdirected camera, controllers said they were pleased with both Deep Space 1's science results and its successful testing of a dozen new technologies for future missions - including autonomous navigation, ion propulsion and a combination camera-spectrometer.
Deep Space 1's mission is scheduled to end Sept. 18. If NASA extends its assignment, the barrel-shape probe will encounter two comets in 2001.