After you’ve been getting messages for about nine years, and they suddenly stop, you don’t just shrug and give up, even if the distances involved were great. So efforts were made to get back in touch.

But the silence went on, and last week, the long mission of the spacecraft sent out years ago to study a comet, with a University of Maryland professor as principal investigator, was formally declared by NASA to be over.

The mission was regarded as hugely successful, for its length and for its findings about comets, the small, icy bodies that are regarded as remnants of the creation of the Earth and other planets.

The College Park campus said its scientists helped conceive the Deep Impact mission, to convert the idea into reality and then to continue it for years beyond original hopes. The scientists described the descent of the spacecraft into silence as “a big loss.”

It “really is like losing an old friend,” said Maryland astronomy professor Jessica Sunshine.

Mike A’Hearn, the Maryland professor of astronomy who was the principal investigator, said in a statement that he was “saddened” by the apparent end of the spacecraft’s functional lifetime. He noted that it had been a main focus of his astronomy work for more than 10 years.

However, he said, he was “very proud of the many contributions” that it made to the way science understands comets.

The formal end of the mission was announced Friday by NASA in Pasadena, Calif., at its Jet Propulsion Laboratory.

In one of its most memorable achievements, the mission launched a small probe to smash into the comet named Tempel 1. That crash — as well as the main spacecraft’s flyby of comet Hartley 2 and its sensing from a distance of a third comet — made important contributions, A’Hearn said.

The “surprising results” that stemmed from those achievements, he said, produced “a complete rethinking of our understanding of how comets form and how they work.”

It turned out, he said, that comets show much greater variety than scientists had anticipated.

Distinctions appear between the parts of individual comets, as well as between one entire comet and another, he said.

On Friday, NASA said its last communication with the space probe was Aug. 8. It said it had tried for several weeks to reactivate its onboard systems.

It said it had “reluctantly pronounced the mission at an end.”

In spelling out the surprises provided by the mission, Sunshine, the Maryland astronomy professor, cited “views of beautiful landscapes including flows, cliffs, and spires that we could never have imagined.”

She was deputy principal investigator for the part of the mission in which the spacecraft was sent to Hartley 2.

Describing herself as “very grateful for the opportunity” with the spacecraft, Sunshine said she was also “deeply saddened” that she couldn’t do more with it.