IT'S HARD TO IMAGINE TWO more undesirable pieces of extraterrestrial real estate. The first, a planet orbiting a star known as 47 Ursae Majoris, 200 trillion miles from Earth in the Big Dipper, is about twice the size of Jupiter. Like our own largest planet, it probably consists mostly of such noxious gases as hydrogen sulfide, ammonia and methane. Fierce jet streams blow unceasingly at hundreds of miles per hour, sometimes spiraling into mammoth hurricanes that last for centuries and are big enough to swallow the Earth. And if this harsh world has any solid surface at all, it's buried under an atmosphere thousands of miles deep, crushed by pressures a thousandfold greater than those at the bottom of the deepest terrestrial sea. A second planet, circling the star 70 Virginis, in the constellation Virgo, is probably even less inviting: because it has more than six times the mass of Jupiter, weather conditions there could be even more extreme.
Yet inhospitable as both these worlds seem, their discovery, announced two weeks ago by San Francisco State University astronomers Geoffrey Marcy and Paul Butler, has thrown an almost wholly speculative area of study solidly into the realm of tangible fact. Despite years of searching with the most powerful telescopes, despite decades of listening for the faint crackle of radio signals from distant civilizations, despite endless theorizing about how life might or might not arise, nobody had ever found concrete evidence to suggest that our planet, our civilization, our life-forms were anything but unique in the cosmos.
Now, suddenly, everything has changed. Not only do these still unnamed planets triple the number of worlds known to orbit stars like the sun--the only other example having been found just four months ago--but they have an even more profound significance. Both of them are temperate enough to allow water to exist in liquid form. And whatever else is necessary for life as we know it, say biologists, liquid water is an absolute prerequisite.
It isn't that life necessarily exists on either of the new planets. The question is impossible to settle with today's technology, and if organisms do inhabit these distant worlds they would be a bizarre sort of life, proceeding from birth to death, generation after generation, without ever touching solid ground.
Even if the new planets are sterile, though, their very existence is a powerful piece of astronomical news. If our solar system is any indication, giant, unpleasant planets are likely to be accompanied by small, friendly ones. Giant planets also tend to be attended by giant moons, small worlds in their own right, and these too could be hospitable to life. Perhaps most important, the discovery of planets around three relatively nearby sunlike stars implies that the Milky Way, 100 billion stars strong, must be bursting with other worlds. Unless the chances are literally 100 billion to one against the emergence of life--and recent advances in biology suggest that the chances are considerably better--there is life out there, somewhere.