Astronomers have for the first time detected the chemical composition of the atmosphere of a planet orbiting a distant star, it was announced in the United States last night.
They believe it is an important step in the search for extraterrestrial life. Scientists focused the Hubble Space Telescope on a star 150 light-years away and found that a planet there contained sodium in its atmosphere.
Experts said the achievement demonstrates that it might be possible to search for the chemical signature of life on planets beyond the solar system.
"Suddenly, discussing searches for Earth-like planets seems quite reasonable," said Mr David Charbonneau, an astronomer at the California Institute of Technology.
"This opens up an exciting new phase of extrasolar planet exploration, where we can begin to compare and contrast the atmospheres of planets around other stars." The planet orbits a sun-like star called HD 209458 in the constellation Pegasus, some 150 light-years from Earth.
Known as HD209458b the planet is one of about 80 discovered in the last decade outside Earth's solar system.
Most of these are giant planets made of gas, like Jupiter in our own system. About 15, including this one, are "hot Jupiters", giant planets about 100 times closer to their star than Jupiter is to the sun.
That makes them far too hot for life as we know it. Not only would any hypothetical human traveller to this planet die but the planet's intense heat would quickly melt any coins in the person's pockets, the scientists said. The planet's hospitality is not the issue, however. What is important is the notion that Hubble, an orbiting telescope, managed to detect an atmosphere outside our immediate neighborhood.