After the sun finally dies, billions of years in the future, Earth too will meet a grisly end.
There are several ways that our home planet may be destroyed after the sun dies, possibly being swallowed up by the sun as it expands outwards, or simply being torn apart by gravity.
The sun is expected to fade into a white dwarf after its death, so studying white dwarfs out in space allows astronomers to get an idea of how planets and moons in the rest of the solar system fare after the death of a star.
According to a new paper in the journal Monthly Notices of the Royal Astronomical Society, planets and moons orbiting close to a white dwarf that survive the star's expansion may get ripped to shreds.
White dwarfs are the remains of stars that have died after using up all their hydrogen fuel. Initially, a star like our sun will start to burn helium instead, expanding out to an immense size and becoming a red giant. Eventually, the outer layers of the red giant are expelled into space, leaving behind a hot core, which contracts under gravity and becomes a white dwarf.
"Previous research had shown that when asteroids, moons and planets get close to white dwarfs, the huge gravity of these stars rips these small planetary bodies into smaller and smaller pieces," study author Amornrat Aungwerojwit, a researcher at Naresuan University in Thailand, said in a statement.
The researchers studied the changes in brightness of several white dwarves over 17 years, which allowed them to get some idea of how objects orbiting the stars were behaving. They found that the white dwarves were being orbited by strange-shaped bodies with chaotic movements, indicating that many of them had been torn apart or destroyed.
"The simple fact that we can detect the debris of asteroids, maybe moons or even planets whizzing around a white dwarf every couple of hours is quite mind-blowing, but our study shows that the behavior of these systems can evolve rapidly, in a matter of a few years," study author Boris Gänsicke, a physics professor at the University of Warwick in the U.K., said in the statement. "While we think we are on the right path in our studies, the fate of these systems is far more complex than we could have ever imagined."
One of the white dwarves, ZTF J0328−1219, was seen to have a stable solar system for several years, but possibly having had a catastrophic event in 2010. Another white dwarf, ZTF J0923+4236, dimmed irregularly every couple of months, while a third named WD 1145+017 was seen in 2015 to have variations in transits of orbiting objects, which have since disappeared.
"The system is, overall, very gently getting brighter, as the dust produced by catastrophic collisions around 2015 disperses", Gänsicke said. "The unpredictable nature of these transits can drive astronomers crazy—one minute they are there, the next they are gone. And this points to the chaotic environment they are in."
As for the future of our own solar system, the Earth might not even live long enough to meet this chaotic fate, likely being swallowed up by the sun as it expands.
"The sad news is that the Earth will probably just be swallowed up by an expanding Sun, before it becomes a white dwarf," Gänsicke said.
Even if the Earth were to survive the sun's expansion into a red giant, and avoid being torn apart, it would not be habitable by any means.
"Whether or not the Earth can just move out fast enough before the Sun can catch up and burn it is not clear, but [if it does] the Earth would [still] lose its atmosphere and ocean and not be a very nice place to live," Gänsicke said.
The inner planets Mercury and Venus will almost certainly be crushed and engulfed by the sun, the researchers said.
This would leave the only remaining planets in the solar system as Mars and the four gas giants, as well as their moons.
"For the rest of the solar system, some of the asteroids located between Mars and Jupiter, and maybe some of the moons of Jupiter may get dislodged and travel close enough to the eventual white dwarf to undergo the shredding process we have investigated," Gänsicke explained.
Thankfully, we don't have to worry about this happening any time soon: the sun is expected to carry on burning as usual for the next 5 billion years, and take another billion years to become a white dwarf.
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