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Dying White Dwarf Stars Consume Rocky Earth-Like Planets

Planetary Nebula NGC 2371 - the glowing remains of a sun-like star

Astronomers say they have discovered two dying white dwarf stars encircled by debris fields containing a mixture of elements that suggest a rocky Earth-like planet, asteroid or other body may have orbited the stars much earlier in their history.

The University of California at Los Angeles astronomers made their observations with the Keck One telescope in the U.S. Pacific island state of Hawaii.

A white dwarf star is only about the size of the Earth, but about one million times denser with the approximate mass of our Sun. The hallmark of a white dwarf is a pollution-free atmosphere of either hydrogen or helium.

Previously, it was widely believed that random dust collecting around one of these pristine objects was the result of the star's travels. However, the UCLA scientists found each of the stars they observed is orbited by a disk of dust and gas containing some of the same raw materials believed to have formed the Earth 4.5 billion years ago.

Some of the elements found circling the white dwarfs include calcium, magnesium, iron, nickel, silicon and oxygen. The astronomers say the mix of some of the elements are in ratios similar in overall content to the Earth. The planet-like rocky material also orbits at an Earth-like distance from each white dwarf star. The scientists say it is not clear if the material is from a planet, asteroid or another rocky celestial body.

A dying star that transforms into a white dwarf can disrupt the orbits of the objects in its system. It can put some objects on a collision course with a star. Some small rocky objects meet their doom when they bounce off larger surviving worlds into the white dwarf. The UCLA scientists believe that likely was the fate of rocky bodies that are the source of the debris they observed.

Only certain types of stars end their evolutionary lives as white dwarfs. Our own Sun will become a white dwarf in about 5 billion years.