Worlds with potential for life might be more common than thought

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Washington, Feb 18 : Astronomers have discovered that terrestrial planets might form around many of the nearby sun-like stars in the disk of our galaxy, which indicates that worlds with potential for life might be more common than thought.

A University of Arizona (UA) team made the finding with help from NASA's Spitzer Space telescope.

The astronomers surveyed six groups of stars with masses comparable to our sun using the Spitzer telescope, which includes an instrument built at UA's Steward Observatory.

The stars were grouped by age, ranging from three-to-10 million years, 10-to-30 million years, 30-to-100 million years, 100-to-300 million years, 300 million to one billion years and one-to-three billion years old.

Out of these stars, the researchers found that at least 20 percent, and possibly as many as 60 percent, are similar to the sun and are candidates for forming rocky planets.

The Spitzer telescope detects dust at a range of infrared wavelengths. The hottest dust, at temperatures more than 2,000 degrees Fahrenheit, is detected at the shortest wavelengths, between 3.6 microns and 8 microns.

Because dust closer to the star is hotter than dust farther from the star, the warm dust likely traces material orbiting the star at distances comparable to distances between Earth and Jupiter around our star, the sun.

"We found that about 10 to 20 percent of the stars in each of the four youngest age groups shows 24 micron emission due to dust," said Meyer.

In a separate study, Thayne Currie and Scott Kenyon of the Smithsonian Astrophysical Observatory in Cambridge, Mass., and their team including researchers from UA, also found evidence of dust from terrestrial planet formation around stars from 10-to-30 million years old.

"Our evidence suggests that similar processes could be occurring around stars between 3 million and 300 million years old," said Meyer.

Kenyon and Ben Bromley of the University of Utah have developed planet formation models that provide a plausible scenario. heir models predict warm dust would be detected at 24 micron wavelengths during planet formation, as small rocky bodies collide and merge, creating larger rocky bodies, eventually assembling the asteroids, moons and planets.

According to Kenyon, "Our work suggests that the warm dust Meyer and colleagues detect is a natural outcome of rocky planet formation. We predict a higher frequency of dust emission for the younger stars, just as Spitzer observes."

The next critical test for evidence that terrestrial planets could be common around stars like the sun will come next year with the launch of NASA's Kepler mission. Kepler will detect the tiny dips in the amount of light seen as planets pass in front of their stars.


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