... And Others ?

The discovery of extraterrestrial life, whether intelligent or not, remains for the future. The negative results from the Moon and the ambiguous results from Mars give no indication that we have company in the solar system, but the intense interest in this subject leads us to explore other possible habitats for life: Jupiter, Saturn's moon Titan, and certain as yet unexplored regions of Mars. Spacecraft observations or the return of samples to Earth may yield definite answers, even if they are negative.

Regardless of whether the solar system outside the Earth proves in hospitable and lifeless, there are billions of stars beyond it. Here we must deal both with speculation and with probabilities. A certain percentage of the stars are like the Sun, a fraction of those suns may have planets, a percentage of those planets may have life, on a percentage of those planets life may have evolved to the intelligent state, a percentage of those planets with intelligent beings may be the sites of technical civilizations.... The odds against each individual step may be tremendous, but there are so many billions upon billions of stars in our galaxy and so many galaxies in the universe that the odds in favor of life - even intelligent life - somewhere else in space seem overwhelming. Just as the radio and television signals broadcast on Earth a few years ago now are spreading out past the stars in our own neighborhood, so might signals from other life-forms be passing us at this very moment.

The stars are far away, and we can't go to them to look for life, not for a while anyway. Even so there are methods that we can adopt on Earth, at modest cost, to look for life else where in the universe. One thing we can do is look for planets around the nearer stars, to check our theory that the solar system is not unique, to verify at least one link in the chain of logic which suggests that intelligent life must be common in the universe.

We may not be able to see planets around the nearest stars, even with the Space Telescope. Planets are too small and dim, and the nearest stars are still too far. But we can detect other planets - possibly even from the ground - by making careful measurements of the motions of nearby stars. Planets orbiting around a star would cause tiny wiggles in its motion across the sky. With high-precision observations, we perhaps can determine that a star has planets, even though we could not see them. Proof that the solar system is not unique would be a major scientific discovery in any case. It would also be an important step toward the eventual discov ery of life elsewhere.

photo of one of NASA deep space radio telescopes

Listening to the stars.
Radio telescopes in NASA's5 Deep Space Network regularly trace interplanetary spacecraft. With minor modifications, some day they could also be used in search for signals from intelligent beings on the planets of distant stars.

Another way to discover extraterrestrial life is simpler: sit back and listen. The huge and highly developed radio telescopes now operating on Earth can be equipped to detect artificial signals amid the cacophony of natural radio sources in the sky. (Suitably instrumented antennas many light years away could likewise pick up and recognize the radio and video signals now escaping into space from the Earth.)

A few limited attempts to detect communications from other civilizations have already been made. We can begin now to listen more sensitively and systematically for such signals from other civilizations, and we could detect them whether they were addressed to us or not. Some ideas for doing this have already been developed, and most of the necessary equipment is already in place. With a modest investment for improvements in existing radio telescopes, and some shrewd guesses about where and how to listen, a systematic search for other life could be started now. The "First Contact", about which so many science fiction stories have been written, may yet come in our own lifetime, if we take the trouble to listen.