Four dead planetary systems, each lit by the burned-out core of a star that once resembled the sun, provide a harrowing forecast for Earth's eventual demise.
Astronomers used the space-based Hubble telescope to probe the chemical signatures of dusty disks encircling the four star systems. In each they found a surprising abundance of elements that make up about 93 percent of Earth's mass.
“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 Boris Gänsicke, an astrophysicist at the University of Warwick, in a press release.
Gänsicke and his team's research on the white dwarfs, released May 1 on arXiv, suggests that the stars' death throes pulverized the nearest planets, leaving only chunks of their cores. The team's study is accepted for publication in the Monthly Notices of the Royal Astronomical Society.
The sun is about 4.57 billion years old and should survive another 5 billion years or so in its current state. After that it will run low on its hydrogen fuel, the fusion of which presently pushes away gas that would otherwise gather at its core. As the gas accumulates, rising pressure will fuse heavier helium atoms into carbon, drastically increasing the star's core temperature.
That final blaze that will push away its outer gas shells, turning it into a red giant star. Its surface will extend roughly to the orbit of Earth.
“When this happens in our own solar system, billions of years from now, the Sun will engulf the inner planets Mercury and Venus," Gänsicke said in the release. “It’s unclear whether the Earth will also be swallowed up by the Sun in its red giant phase -- but even if it survives, its surface will be roasted."
After that the sun will become a planetary nebula, or a vast, low-density cloud of gas. As its substance drifts away it will lose mass, and the gravitational shift will push planets out of their once-cozy orbits.
Material falling into the white dwarfs allowed Gänsicke and his team to study the stars' dusty halos. The results suggest that planets surviving the red giant phase will eventually crash into each other, crush into dust and form asteroid-like chunks.
While asteroids and comets might conceivably have formed the halos, the cloud around one star, PG0843+516, revealed a surprising amount of nickel, iron, sulfur and other elements found in abundance in Earth's core.
“It is entirely feasible that in PG0843+516 we see the accretion of such fragments made from the core material of what was once a terrestrial exoplanet," Gänsicke said.
*Images: Three panels illustrate the death sequence of a planetary system. Four terrestrial planets orbit a sun-like star (top); the host star turns into a red giant and mixes up planetary orbits, causing them to collide (middle); dusty debris and asteroid-like objects are all that remains around the star, now a white dwarf (bottom). (Copyright of Mark A. Garlick/University of Warwick) [high resolution]
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