Who among us has never gazed into a starry night sky and wondered "are we alone"? With the hundreds of billions of stars in just our own Milky Way galaxy — many like our own sun — is it not possible that, orbiting nearby, there are planets and, at least on some of them, life?
You may be surprised to learn that these are not questions conjured up by modern astronomers. In fact, they've been debated and studied for millennia. In a letter to Herodotus, the ancient Greek philosopher Epicurus wrote: "There are infinite worlds both like and unlike this world of ours. ... We must believe that in all world there are living creatures and plants and other living things we see in this world."
But not until 20 years ago — on Oct. 6, 1995 — did Swiss astronomers Michel Mayor and Didier Queloz make an announcement that rocked the astronomical community.
They reported that the sun-like star 51 Pegasi, some 50.9 light years away, appeared to be wobbling as if a planet were orbiting nearby and tugging gravitationally on it. Officially named 51 Pegasi b, this world received the unofficial name of "Bellerophon" after the Greek hero who tamed Pegasus, the mythological winged horse.
They calculated that this alien world must have about half the mass of Jupiter, that it orbits its parent star in only 4.2 days, and that it endures a temperature of some 2,200 F. While a few worlds had already been reported to be circling pulsars, astronomers often cite this as the first detection of an extrasolar planet of an ordinary star.
Since that historic day two decades ago, astronomers have found more than 1,900 such extrasolar planets — many in the nearly 500 multiple-planet systems — and the spaceborne Kepler Telescope has located nearly 4,700 additional candidates. But 51 Pegasi, more affectionately known to astronomers as 51 Peg, will always be special, since it was our first. Not only that, it's a star that backyard stargazers can see easily from Earth.
This week, go outdoors after dark and look very high in the eastern sky. There you should spot the four stars making up what astronomers know as the Great Square of Pegasus. Identify its shape and some of the stars that make it up.
If your sky is dark and relatively free from light pollution, try to spot 51 Peg. It's located almost midway between the two westernmost stars of the square, and slightly west of the line connecting them.
It's a faint star, barely visible to the naked eye, but you should have little trouble spotting it with binoculars. Don't expect to see actual planets though; that's a feat beyond even today's most sophisticated telescopes.
Whether the 51 Peg — or any other extrasolar world — supports life is anyone's guess. What is clear, though, is that the number of planets where life might exist is growing every day and the chemistry for life as we know it is found everywhere we look in the universe.
As profound as is the question "are we alone?" there are only two answers: yes or no.
And either is staggering in its implications.