Cosmic-ray hit puts Cassini probe in safe mode

By Alicia Chang

updated 9:50 p.m. ET Sept. 12, 2007

LOS ANGELES - The international Cassini spacecraft went into safe mode this week after successfully passing over a Saturn moon that was the mysterious destination of a deep-space faring astronaut in Arthur C. Clarke's novel "2001: A Space Odyssey."

Cassini flew within 1,000 miles (1609 kilometers) of Iapetus on Monday and took images of its rugged, two-toned surface. As it was sending data back to Earth, it was hit by a cosmic ray that caused a power trip. The spacecraft was not damaged, but had to turn off its instruments and relay only limited information.

Mission controllers have since sent commands for Cassini to resume normal transmission, and scientists recovered all the data from the moon flyby despite a nearly 12-hour delay. The spacecraft was expected to be fully functional by week's end.

Iapetus, the third-largest Saturnian moon, gained science fiction fame in Clarke's mind-bending novel "2001: A Space Odyssey," that was developed in concert with Stanley Kubrick's 1968 movie by the same name.

Clarke, who lives in Sri Lanka, surprised the Cassini team with a five-minute video played Tuesday during an internal meeting at NASA's Jet Propulsion Laboratory. In it, Clarke told scientists he looked forward to viewing photos from the flyby.

Even before Clarke's taped greeting, scientists waxed poetic about Cassini's encounter with Iapetus and the fictional Discovery spaceship's rendezvous with Japetus, as the Saturn moon is known in Clarke's book.

It is the second time Cassini has flown by the walnut-shaped Iapetus, but the latest images are the crispest yet. The spacecraft focused on a jagged ridge surrounded by mountains near the equator that look geologically old. Scientists hope to find out what forces caused the ridge to form and how long it has been in existence.

"Iapetus is really a time machine. We're looking back at a really old surface," said Cassini scientist Torrance Johnson of JPL.

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