LOS ANGELES -- Scientists got only the second glimpse ever of the core of a comet as a NASA spacecraft flew past one of the icy, glowing bodies.
The Deep Space 1 probe flew within 1,360 miles of the comet Borrelly over the weekend, capturing as many as 50 images of its nucleus. Scientists expected to receive the final images from the spacecraft by Monday.
"This data set will make a significant contribution to the body of knowledge we have about comets," Robert Nelson, the mission's project scientist at NASA's Jet Propulsion Laboratory, said Sunday.
National Aeronautics and Space Administration officials said they wouldn't release any data until Tuesday, but scientists gave hints of what the spacecraft saw and recorded, including dust and ice boiling off the comet's surface.
Scientists are interested in comets because they are thought to contain pristine examples of the building blocks of our solar system from its birth 4.5 billion years ago.
The glowing veil of dust and gas that envelops Borrelly is perhaps as big as the Earth, but the comet's nucleus appears in the images to be just 2.5 miles wide by 5 miles long, Nelson said.
Borrelly was at its most active during Saturday's flyby, kicking off material that may give scientists clues about the comet's composition. The encounter, about 137 million miles from Earth, came about a week after the comet's closest approach to the sun on its seven-year orbital path.
Deep Space 1's instruments also measured ions, electrons, gases and Borrelly's magnetic and electrical fields.
"We collected a large amount of data on this previously completely mysterious body," said Marc Rayman, the mission's project manager. "It's going to take some time to understand all the secrets this body may be hiding."
Engineers had feared comet particles traveling at 36,900 mph would batter or destroy the aging probe. As of Sunday, preliminary data indicated the spacecraft remained in good health, but it is nearly out of fuel and will be turned off by NASA later this year.
The European Space Agency's Giotto was the first and only other spacecraft to ever spy a comet nucleus. It flew past Halley's comet in 1986.
In those images, the comet spewed fountains of ice and dust as the sun's rays warmed the comet's surface. Nelson said the Borrelly images show some features similar to those seen on Halley's comet, as well as others that have "their own unique qualities."
Another four American and European missions are scheduled to visit comets over the next decade.
On the Net:
Deep Space 1: http://nmp.jpl.nasa.gov/ds1/