SAN FRANCISCO -- Authorities were scouring the waters off Northern California on Monday, looking for a man who embarked alone on a day sailing trip to the Farallon Islands to scatter his mother's ashes and never returned.

Jim Gray, 63, a noted computer scientist who founded Microsoft's Bay Area Research Center, last spoke to a family member at 10:30 a.m. Sunday, when he called from his 40-foot yacht called Tenacious to say he was sailing out of cell phone range, according to the U.S. Coast Guard. He had left for the Farallons, about 27 miles west of the Golden Gate Bridge, that morning and planned to return by evening.

Coast Guard spokeswoman Lt. Amy Marrs called Gray's disappearance a mystery because the weather was good, he was in good health and the boat was equipped with radios and flares. There have been no distress signals.

A C-130 cargo plane was called in Monday evening to help search 4,000 square miles of the Pacific, from Point Ano Nuevo in the south to Tomales Bay in the north.

Well-known in Silicon Valley, Gray won the A.M. Turing Award -- the so-called "Nobel Prize of computer science" -- in 1998 for his body of work, which helped paved the way for automatic-teller machines, computerized airline reservations and e-commerce. He earned the first Ph.D from the University of California, Berkeley's computer-science department in 1969.