For the first 15 years of DISCOVER’s existence, if you wanted to hear about planets orbiting other stars, you had your choice of sources: Star Wars and Star Trek. That all changed in 1995 with the discovery of a planet orbiting 51 Pegasi, a near-twin of the sun located about 50 light-years away. Swiss astronomers Michel Mayor and Didier Queloz found the distant world by watching its gravity tug its parent star. Over the following year, American scientists Geoffrey Marcy and Paul Butler confirmed the observation and soon found several more planets on their own.
The first exoplanet discoveries upended the world of astronomy. Scientists had always assumed that other solar systems (if they existed) would look pretty much like ours. Not these: The new planets were giants, like Jupiter, but more than half lay closer to their stars than Mercury does to our sun, whipping around in just a few days and baking at temperatures close to 2,000 degrees Fahrenheit. Our theories about how planets form and evolve had to be ripped up and rewritten. Since then, planet searchers have found more than 400 new worlds, and it has been one surprise after another. Some planets follow wildly oval orbits. Others orbit their stars backwards, have strange and unexpected compositions, are puffed up like marshmallows, or shed tails like comets. Collectively, they prove that the universe is far stranger and more creative than anyone imagined.
By next spring, the planet-hunting space telescope known as Kepler—rejected by NASA three times but then approved after those initial detections of exoplanets in the 1990s—will most likely report the discovery of the first known Earth-like planet in an Earth-like orbit. This milestone will inevitably spark another revolution, as observers redouble their efforts to see Earth-like worlds directly and probe their atmospheres for the telltale chemical signatures of life. It’s a good bet that these planets, too, will not be what we expected.
Simply studying the light from Earth-like planets—much less getting direct pictures of them—will be wildly difficult. But then, 15 years ago nobody thought we could find any exoplanets at all. (The James Webb Space Telescope, launching in 2014, might be able to find hints of biology on an alien world.) Even if the next space telescope only comes close, the one after that will very likely do the trick. So here is a bold prediction: By the time discover celebrates its 50th anniversary, the mystery of whether life exists elsewhere in the universe will finally be solved.
Michael Lemonick, senior science writer at Climate Central, has written for DISCOVER for more that two decades.