A Search for the Chemicals of Alien Life

Scientists looking at a star 150 light-years away with the Hubble Space Telescope found that a planet there contains sodium in its atmosphere. This demonstrates that it may 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,? says 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. The planet is one of 76 that have been found to orbit distant stars. The 76 planets outside our solar system were found by carefully measuring the gravitational effect they have on their parent star, since each planetary orbit causes the star to wobble slightly.

This is the first planet in the group to have its atmosphere chemically analyzed. It?s about 70 percent the size of Jupiter, but it orbits just 4 million miles from its sun, meaning that the planet circles the star every 3 ? days. In contrast, the Earth is about 93 million miles from the sun and takes a year to complete one orbit.

The planet is unlikely to have life on it, however, because it is so close to its star. Scientists estimate the planet?s surface temperature to be around 2,000 degrees. But the same technique could be used to search for the chemicals of life in the atmospheres of other planets.

The Hubble spectrograph was tuned to detect only sodium. A new observation effort is being planned to search for more Earth-like chemicals such as methane, water vapor and potassium.

This data will help to determine whether planets with atmospheres conducive to life are common or rare. ?Is this planet?s chemical personality unique or is it typical of a certain class of extrasolar planets?? Brown says. ?We have no clue. We hope to find out.?

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