White Dwarfs Are Eating 'Earth-like' Planets for Dinner

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There is one doomsday scenario that will, without a doubt, come true.

In 4-5 billion years time, when the sun runs out of fuel, it will become a bloated red giant star. During this violent phase, it will blowtorch the Earth before shedding huge quantities of mass and disintegrating into a planetary nebula. A tiny white dwarf star will remain — the remnant of our sun's core — with the dust cloud of pulverized inner solar system planets raining down onto it.

Now, using data from the Hubble Space Telescope, astronomers from the University of Warwick have discovered four white dwarf stars containing dust in their atmospheres, giving us a rare glimpse into the future death of our own solar system.

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Although dusty white dwarfs are a well-known astronomical phenomenon — the extreme tidal shear and dynamical instability produced by a white dwarf will pulverize planetary bodies in orbit through a demolition derby of epic proportions — these four new examples may be what our solar system will look like in a few billion years time.

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In each case, the researchers have detected oxygen, magnesium, iron and silicon hanging in their stellar atmospheres. The presence of these elements are a telltale sign that rocky worlds used to exist in orbit. Interestingly, these four elements make up the composition of approximately 93 percent of the Earth.

In addition to these key elements is the detection of small quantities of carbon in proportions that closely match the proportion of carbon found inside the solar system's rocky planets. This is the first time such a proportion of carbon has been detected in the dusty debris surrounding white dwarfs.

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Although the term "Earth-like" is often misrepresented in the field of exoplanetary studies, the Warwick astronomers are acutely aware of the implications of spotting these elements around distant stars. "What we are seeing today in these white dwarfs several hundred light-years away could well be a snapshot of the very distant future of the Earth," said lead researcher Boris Gänsicke.

Although we have little clue about the physical characteristics of the exoplanets before they were pulverized, all the components that make up the terrestrial planets — Mercury, Venus, Earth, Mars and the asteroids — are present in the white dwarfs' dust. The proportions of these elements are about as "Earth-like" as it gets.

There is one white dwarf, called PG0843+516, that stands out from the other three; it has an overabundance of iron, nickel and sulfur in its atmosphere. These particular elements are found in the cores of rocky planets. During planetary evolution, gravity pulls these elements into the core — a process known as "differentiation." Differentiation will occur in large rocky worlds like Earth, forming a core, mantle, crust and, probably, tectonic activity.

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Also, as the white dwarfs' gravity should consume these elements very quickly, the fact that they have been spotted in the star's atmosphere indicates a rocky planetary body is being ripped to shreds right now.

In all four white dwarfs, the researchers estimate 1 million kilograms of planetary material must be raining down into the stars every second. This is significant as they are witnessing the final stages of these star systems' death throes.

One can't help but wonder, if true "Earth-like" worlds are being pulverized and eaten by white dwarf stars, are the remnants of ancient extraterrestrial civilizations also being consumed?

This research has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

Source: University of Warwick

Image: This is the future of our solar system. Credit: © Mark A. Garlick/space-art.co.uk/University of Warwick. Used with permission.

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