PASADENA, Calif. (AP) — A close flyby of Saturn's big moon Titan by the international Cassini spacecraft revealed an upper atmosphere brimming with complex organic material, a finding that could hold clues to how life arose on Earth, scientists said Monday.

Cassini flew within 638 miles of Titan's surface April 16 and discovered a hydrocarbon-laced upper atmosphere.

Titan's atmosphere is made up mainly of nitrogen and methane, the simplest type of hydrocarbon. But scientists were surprised to find complex organic material in the latest flyby. Because Titan is extremely cold — about minus 290 degrees — scientists expected the organic material to condense and rain down to the surface.

"We are beginning to appreciate the role of the upper atmosphere in the complex carbon cycle that occurs on Titan," said Hunter Waite, a professor at the University of Michigan.

Scientists believe Titan's atmosphere may be similar to that of the primordial Earth. They believe studying it could provide clues to how life began.

The $3.3 billion Cassini mission, funded by NASA and the European and Italian space agencies, was launched in 1997 and took seven years to reach Saturn. The European Huygens probe carried aboard Cassini was released Dec. 24 and plunged to the surface of Titan in January.

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