Polluted Stars

StarDate: May 18, 2009

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Pollution can take many forms: smog, oil slicks, chemical leaks -- and the pulverized remains of planets and asteroids.

Astronomers have detected this "pollution" around several white dwarfs -- the hot, dense corpses of once-normal stars. The debris suggests that the materials that make up Earth-like planets are common.

A white dwarf forms when a star like the Sun reaches the end of its life. The star puffs up to many times its original size, gobbling up any nearby planets and asteroids.

Eventually, the star casts off its outer layers, leaving only its dead core -- a white dwarf. It's about half as massive as the original star, but only as big as Earth.

The white dwarf's gravity is extremely strong. So if a leftover planet or asteroid wanders too close, it's pulverized. The debris forms a ring of boulders and dust. It "pollutes" the light from the star with the signatures of many chemical compounds.

Astronomers recently found more than a half-dozen of these systems. They used Spitzer Space Telescope to analyze the debris, and found that much of it consists of minerals that are common on Earth.

These minerals are also found in the debris around very young stars, where planets are just taking shape. Together, they suggest that the materials for making planets like Earth are common. If so, then to find Earth-like planets around other stars, we just need to keep looking -- especially for stars with polluted environments.

Script by Damond Benningfield, Copyright 2009

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