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White-Dwarf Planets II

October 17, 2012

The life of a planet is never easy. When it’s young, it’s bombarded by the leftover building blocks from the process that gave it birth. In middle age, the energy from its star varies, changing the planet’s temperature and allowing it to be zapped by cosmic radiation. And at the end, it may be done in by the star’s own demise.

Astronomers from England have found evidence of that final stage in the outer layers of white dwarfs — the hot, dense corpses of stars that were once like the Sun.

The surface of a white dwarf usually consists of just hydrogen and helium. But using Hubble Space Telescope, the British astronomers detected oxygen, magnesium, iron, and silicon at the surfaces of four white dwarfs — the materials that make up almost all of Earth and the other rocky planets in our own solar system. These elements must have come from outside the star. Yet such heavy materials would quickly sink into the white dwarf’s center, so the supply must be renewed. The astronomers say that means there’s a “rain” of residue from one or more Earth-like planets — up to a thousand tons a second.

As a Sun-like star ends its life, it puffs up, then ejects its outer layers into space. This process may knock some of the planets out of their orbits and cause them to ram together. That could pulverize the planets, leaving a ring of debris. The debris then rains onto the surface of the white dwarf — ending a planet’s life in the embrace of its parent star.


Script by Damond Benningfield, Copyright 2012

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