The spacecraft was launched in January 2005 for a close-up study of Comet Tempel-1.

It was not just a passive experiment. The probe released a 372-kilogram metal impactor that crashed into the comet's nucleus, triggering a shower of particles for analysis by the mother spacecraft and remote observatories.

Deep Impact continued its comet quest with a flyby of Hartley 2 in November 2010 and long-distance studies of other bodies, including the approaching Comet ISON. The spacecraft was also used to look for planets beyond the solar system.

NASA last heard from Deep Impact on 8 August. Engineers suspect a software problem caused the spacecraft to lose its orientation system, cutting off radio contact with Earth in the process.

After a month of fruitless attempts to find the probe, NASA announced it was formally ending the mission.

"Despite this unexpected final curtain call, Deep Impact already achieved much more than ever was envisioned," says Lindley Johnson, who oversees the program at NASA Headquarters in Washington.

University of Maryland astronomer Michael A'Hearn, who led the Deep Impact science team, says "I'm saddened by its functional loss. But, I am very proud of the many contributions to our evolving understanding of comets that it has made possible."

"These small, icy remnants of the formation of our solar system are much more varied, both one from another and even from one part to another of a single comet, than we had ever anticipated," says A'Hearn.

NASA had hoped Deep Impact would play a key role in observations of the approaching Comet ISON, a suspected first-time visitor to the inner solar system that was discovered in September 2012 by two Russian astronomers.

The comet is heading toward a close encounter with the Sun in November, a brush that it may not survive.

Later this month, NASA's Mars Curiosity rover and Mars Reconnaissance Orbiter will attempt to catch a glimpse of the comet as it flies by Mars.