Los ANGELES Correspondent John Wilhelm first seriously considered the possibility of extraterrestrial life four years ago while visiting the mam moth radio telescope at Arecibo, Puerto Rico. Pulsars -- radio signals now thought to emanate from rapidly rotating neutron stars in the far reaches of space -- had just been discovered. Arecibo Director Frank Drake let Wilhelm listen a audio signals originating light-years away. Recalls Wilhelm: "It was a little like putting a stethoscope to the heart of the universe. Drake did not dismiss the possibility, however slight, that pulsars might in fact be navigation beacons used by an advanced civilization. I was hooked."

Doing the principal reporting for this week's cover story has given Wilhelm his best opportunity so far to indulge his addiction. As a science correspondent, he has covered several Gemini and Apollo flights for TIME as well as the death of three astronauts during a 1967 training exercise. Wilhelm found the scientists and the atmosphere at Pasadena's Jet Propulsion Laboratory, home of the Mariner program, different from the men and mood at Houston and Cape Kennedy.

"The J.P.L. crowd," he says, "is looser, more relaxed, without those worries of having a man up there. Also there is more of a sense of true exploration, more a feeling of touching the 2001 slab. Because of the scarcity of facts about Mars, there is more scientific speculation, a broader spectrum of scenarios upon which hinge some mighty scientific reputations."

To Wilhelm, the assignment was almost like researching a Jules Verne sequel. In addition to interviewing many of the Mariner 9 "investigators" at J.P.L., he talked with Cornell University's Carl Sagan and other experts. Wilhelm's files, together with those of Correspondents Horace Judson and Jerry Hannifin, went to Associate Editor Fred Golden, who wrote the cover story, his third on space.

Has being so close to the subject made Wilhelma believer in extra terrestrial life? "It is simply too arrogant a presumption to say flat out that kind humans are alone in the universe," he says. "Sometimes this kind of mystical belief rings truer than the cleanest scientific logic. That's why I dig Shelley's poetic leap of faith: Life, like a dome of many-coloured glass, Stains the white radiance of Eternity."

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