An unmanned experimental spacecraft has flown near the nucleus of a comet to examine its environment.
The Deep Space 1 probe passed within 2,000km of Comet Borrelly.
It is expected to take more than 30 black-and-white images of Borrelly's heart, which is a ball of ice and dust. The first pictures may not be released to the media until tomorrow.
It is rare for probes to get so close to comets and take detailed measurements.
A Nasa spokesman said DS1 was performing well and had already sent back pictures of the comet, according to reports.
"I can't believe how cool this is,'' said Dr Marc Rayman, the mission director on the DS1 project, as the first data from the probe came through.
"The images are coming along fantastically. We're very, very excited," he added.
DS1 was launched in October 1998, to test a range of new technologies in space.
It finished its main mission two years ago, and will end its usefulness in November when all its fuel is consumed.