Read out Almost three dozen Jupiter-like planets discovered. The bloated gas giants come dangerously close to their stars and have exotic properties. The discovery of life-friendly worlds is only a matter of time. Before David Latham talks about other worlds, he goes shopping first. And plenty of it. "I spent 28 dollars and 83 cents earlier, " the astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, begins a lecture at a science congress in Washington, DC, and removes his grocery bag in front of the audience.

"That's the sun, " he says and blows up a bright red giant balloon, "1.4 meters in diameter, one billion times smaller. On this scale, our earth does not make a big impression. "Latham holds up a pea:" 1.2 centimeters, I've measured it. Our moon and the planet Mercury, on the other hand, are three millimeters of peppercorns. "The astronomer places two of them on the overhead projector. "Jupiter and Saturn are oranges or apples."

But Latham did not come to play with fruit, but to talk about questions that human fantasy has been dealing with for millennia: are there planets in other stars as well? Could they harbor life? Is there a second earth somewhere in the immensity of space?

"The good news is that there is now compelling evidence for the existence of planets in other stars, " Latham explains, projecting a chart onto the canvas with nearly three dozen discoveries. "The bad news: none of the worlds resembles our earth. None has a solid surface and water necessary for life as we know it. "Ad

Almost all known extrasolar planets have been discovered by the subtle traces they leave in the spectrum of their star. With this method succeeded Michel Mayor and Didier Queloz of the Observatory of Geneva in 1995 for the first time the detection of another planet in a sun-like star - at 50 light years away 51 Pegasi (bild der wissenschaft 5/1996, "Departure to foreign planet").

The astronomers are now in regularity always new discoveries known. "So far, we have only tracked down a few percent of the observed stars, " says Latham. "But the selection effect is huge: Our methods currently only allow the detection of very heavy bodies in close proximity to their home star, while others are systematically escaping."

Exactly exotic are the newly discovered planets: Most of the celestial bodies weigh more than Jupiter and are very hot: temperatures above 1000 degrees Celsius are the rule. Astronomers have already established a terminus technicus for these hellish worlds: Hot Jupiter. The discovery of an Earth-like planet will take a while to come.

But the search for a second earth has just begun. It will be several years before the technical possibilities have been developed. With the next and next but one generation of space telescopes, the planet hunters want to detect and even photograph earth-sized celestial bodies at other stars. "The discoveries of recent years have opened a new window to the universe, " says Stephen Lubow of the Space Telescope Science Institute in Baltimore. Now it's important to look out for what's out there. "We will probably have many surprises that will force us to rethink, " says Alan P. Boss of the Carnegie Institution in Washington.

=== Rüdiger Vaas

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