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 The space agency declared an end to the Deep Impact spacecraft after it unexpectedly fell silent. Engineers tried for a month to regain contact, but lost hope.
Mission scientist Jessica Sunshine of the University of Maryland said she was "saddened at the loss of an old friend."
Deep Impact put on a celestial fireworks display July 4, 2005, when it fired a projectile into comet Tempel 1. The high-speed impact carved a crater and hurled a plume of debris into space, giving scientists their first glimpse of the comet's frozen primordial ingredients.
Afterward, Deep Impact journeyed toward comet Hartley 2, flying through a blizzard of ice particles and escaping unharmed. It later flew by the distant comet Garradd and also observed stars in search of Earth-sized planets outside the solar system.
Before Deep Impact lost contact last month, it was studying another comet named Ison that could shine as bright as the moon when it makes a close swing by Earth in November.
The cause of the failure was unknown, but engineers suspect the spacecraft lost control, causing its antenna and solar panels to point in the wrong direction. Without power flowing to its onboard computer, Deep Impact likely froze to death.
Scientists were disappointed at the timing of the silence that cut short their observations of comet Ison and future plans.
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 "It is hard to say goodbye," said mission scientist Lori Feaga of the University of Maryland.
Deep Impact's comet adventures have changed scientists' views of comets, irregular bodies of ice and dust that orbit the sun and are leftovers from the formation of the solar system. Once thought to be similar, scientists said comets are more varied than initially realized. Comet Tempel 1, for example, turned out to be fluffier than scientists imagined.
The $372 million Deep Impact mission was managed by the NASA Jet Propulsion Laboratory. With communication lost, the spacecraft will continue traveling around the sun.
[Associated
Press; By ALICIA CHANG]
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