Earth-like planets may in fact be common in the galaxy, increasing the likelihood of extraterrestrial life.

By observing the remains of smashed up asteroids around dead stars, astronomers were able to deduce their chemical composition. They found that the dust of many chewed-up asteroids resembles the materials inside Earth and the other small, rocky inner planets of our solar system.

"We found evidence that this asteroid dust is similar to rocks on

Earth," said UCLA astronomer Michael Jura in a press conference today at the American Astronomical Society meeting in Long Beach, California. "This strengthens suspicions that Earth-like planets are common."

Asteroids and planets are made from the same stuff: the dusty material that circles around

young stars in disks. Eventually some of the dust clumps together and grows into planets, while asteroids represent the detritus left over. Because asteroids are formed from the same material as planets, observing asteroids around other stars can tell us crucial information about what ingredients are available to form planets around those stars.

"Asteroids are leftover building blocks that didn’t get incorporated into the planets," Jura said. "What we have now is a tool to measure the bulk composition of planets."

Jura and his team used NASA's Spitzer Space Telescope to observe six dead white-dwarf stars that were coated with the debris of shredded asteroids that had collided into them. By viewing the stars through a spectrograph, which separates out light from different wavelengths, the scientists were able to observe the telltale signatures of certain chemicals in the light. Since that starlight is passing through the film of the asteroid debris, the light picked up signatures of the asteroids’ composition, too.

The team found that the asteroid dust contains a glassy silicate mineral similar to minerals commonly found on Earth. They also detected a lack of carbon in the dust, which again echoes the solar system’s rocky planets and asteroids, which also have no carbon.

Finding planets similar to our own is a priority for scientists yearning for a hint that we are not alone, because Earth-like worlds may be the likeliest place for extraterrestrial life.

Jura said observing asteroid debris around dead stars represents a wealth of opportunity for learning about how planets are formed. The team hopes to find more stars with this asteroid film around them, and observe the current ones in further detail.

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*Image: NASA/JPL-Caltech *