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The brilliant planet Jupiter is slowly pulling away from the face of Taurus, the bull. The bull’s orange eye, the star Aldebaran, is to the lower left of Jupiter at nightfall. The other stars of the bull’s V-shaped face are members of a stellar family known as the Hyades cluster. It’s closer than any other cluster, so it’s a popular target for study.
Among other things, astronomers have looked for planets orbiting the stars of the Hyades. They haven’t found any, but they have found evidence of a planetary system around a dead star known as a white dwarf.
A white dwarf is the collapsed core of a once-normal star. Its surface and atmosphere consist of hydrogen and helium. But a white dwarf in the Hyades shows evidence of calcium in its atmosphere. The calcium can’t come from the star itself, so it must come from outside.
The most likely source is asteroids - large boulders that are some of the building blocks of planets. Encounters with other objects may fling some of the asteroids toward the white dwarf. When they get close enough, they’re pulverized by the star’s gravity. They form a ring of debris, which eventually settles on the surface of the white dwarf.
In fact, about one in five white dwarfs shows evidence of “pollution” from asteroids. Most of this debris matches the composition of Earth - suggesting that worlds that are made much like our own are common throughout the galaxy.
We’ll have more about exoplanets tomorrow.
Script by Damond Benningfield, Copyright 2013
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