The U.S. space program's deep space comet-hunting mission ended after nine years and the transmission of 500,000 images of celestial bodies, NASA said Friday.

The project team at NASA's Jet Propulsion Laboratory in Pasadena, Calif., announced the Deep Impact mission's end after being unable to communicate with the craft since Aug. 8.

Deep Impact was history's most traveled comet research mission, traveling about 4.7 billion miles, NASA said in a release.

"Deep Impact has been a fantastic, long-lasting spacecraft that has produced far more data than we had planned," said Mike A'Hearn, the Deep Impact principal investigator at the University of Maryland. "It has revolutionized our understanding of comets and their activity."

Deep Impact successfully completed its original mission to study comet Tempel 1 six months after its launch in January 2005. On July 3, 2005, the spacecraft deployed an impactor into the path of the comet, essentially allowing the spacecraft to be run over by the comet's nucleus, causing material from below the comet's surface to be blasted into space where it could be examined by the telescopes and instrumentation of the flyby spacecraft.

In November 2010, the Deep Impact craft conducted a similar flyby with comet Hartley 2.

"Six months after launch, this spacecraft had already completed its planned mission to study comet Tempel 1," said Tim Larson, project manager of Deep Impact at the California lab. "But the science team kept finding interesting things to do, and through the ingenuity of our mission team and navigators and support of NASA's Discovery Program, this spacecraft kept it up for more than eight years, producing amazing results all along the way."