This Dead Exoplanet Core Could Be a Preview of Earth’s Future

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Earth is currently enjoying the best eons of the sun’s life, but that friendly yellow globe in the sky won’t last forever. No matter what we do, the sun will one day destroy the world, leaving a fractured planetary corpse orbiting a dead star. Astronomers have spotted a distant star system that could offer a preview of Earth’s future. It’s a white dwarf star with a destroyed planetary core spinning around it.

Stars like our sun have life spans measured in the billions of years. At 4.6 billion years old, the sun is a middle-aged star. It hasn’t changed dramatically in about 4 billion years and will remain in its current state for another 4-5 billion years. However, energy output will increase over time, and in a billion years could make Earth inhospitable to humans. The real show starts in about five billion years when the sun exhausts its hydrogen fuel and expands into a red giant. This will destroy Earth, but maybe not in the way we expected.

This happened to the star known as SDSS J122859.93+104032.9 in the distant past. This system sits 410 light years away. This object is a white dwarf, an ultra-dense stellar core of “electron-degenerate matter” that remains after the outer layers of the star are blasted into space. Without normal electron orbital around atoms, gravity can squeeze the material in a white dwarf like J122859 down until it’s the size of Earth with 70 percent of the sun’s mass.

Earth, as seen propr to its eventual destruction.

Astronomers studied this star system using the 34.1-foot (10.4 meters) Gran Telescopio Canarias (GTC) in the Canary Islands. The team determined that the planetary core is about 370 miles (600 km) wide with a density of at least 7.7 grams per cubic centimeter. Any lower and it would have been torn apart by the star’s gravity as it orbits very close — just 123 minutes per revolution. Its properties are similar to the Earth’s iron core, which is why the team believes it’s the husk of an ancient shattered planet. It suggests dying stars might not completely annihilate their planets but break them into pieces leaving only the dense cores.

The team used a spectroscopic technique to detect the planetary core around J122859, which isn’t as accurate as the transit method employed by Kepler. It works on more objects, though. There are six other known white dwarf systems that might have detectable planetary cores.

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