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Discovering New Worlds

By Jeremy Caplan

Scientists have long wondered whether Earth is one of a kind. Could planets the size of our own exist anywhere outside our solar system? Last week, NASA officials announced that they are one step closer to an answer.

This summer, using telescopes in Hawaii and Texas, teams of veteran astronomers discovered two medium-size planets outside our solar system. Scientists call such planets exoplanets. A team of European scientists announced that they, too, had found a new exoplanet earlier this summer.

The recently discovered planets give researchers reason to believe that smaller, Earth-like planets may be found in distant solar systems.

To spot exoplanets, scientists use a technique that measures how much a distant star wobbles. The wobble measurement helps determine whether there are planets orbiting the star and, if so, how large they are.

A Decade of Discovery
Since 1995, scientists have found more than 110 exoplanets. Until now, however, all of those planets have been large. Most are about the size of Jupiter and around 300 times as heavy as Earth. And like Jupiter, they are giant balls of gas that lack a solid surface.

The newly discovered planets are closer in size to our solar system's icy Neptune or Uranus. They are only about 15 times as heavy as Earth. Scientists believe that these smaller exoplanets might be made of rock, ice and gas rather than gas alone.

"We can't quite see the Earth-like planets yet, but we are seeing their big brothers," says astronomer Geoffrey Marcy, who announced one of this week's discoveries. Marcy is a professional planet hunter. He and his colleagues helped find many of the exoplanets that have been discovered in the last 10 years.

Charles Beichman, the head of NASA's mission to find Earth-size planets, says scientists will continue to search for exoplanets for the next decade. By around 2014, an official space mission to find Earth-size exoplanets is scheduled to be launched. "One of the oldest questions people have asked is, Are we alone in the universe?" says Beichman. "Scientists may one day find some answers."

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