Fate of the Earth: Remains of a planet following violent death of its parent star

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http://theconversation.com/the-fate-of-t...tar-114848

EXCERPT: If it weren’t for the sun constantly showering us with energy, there would be no life on Earth. But eventually stars like it run out of fuel, expand into red giants and finally collapse into small, faint objects called white dwarfs. Now my colleagues and I have spotted the possible core remnant of a planet orbiting the white dwarf SDSSJ122859.93+104032.9, residing some 410 light years away. Our results, published in Science, offer important clues about the fate of the planets in our own solar system.

[...] The discovery is surprising, as we didn’t think anything could survive so close to a white dwarf. A white dwarf is only about the size of the Earth but it contains around 60-70% of the sun’s mass – making it extremely dense. If a body orbits too close to a white dwarf, its immense gravity will tear it apart. This was the fate of the material that formed the disc around it.

So how did it survive without getting ripped apart? It would have to be very dense or have some amount of internal strength holding it together. We calculated that it would have a maximum diameter of 720km, which is the size of a small minor planet. To compare, the dwarf planet Ceres in our own solar system has a diameter of 946km.

The origin of this body remains a mystery. One possibility is that this is the core of a minor planet that was pushed close to the white dwarf by a larger planet further out in the remnant planetary system – like a Jupiter. As the minor planet passed close to the white dwarf, its crust and mantle layers would have been ripped apart. All that would be left of the body would be its dense, iron-dominated core. This kind of object is quite common, with one famous resident in our own solar system: the asteroid 16-Psyche.... (MORE - details)
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