One day the sun will die.
Our beautiful star cannot last forever. Eventually, the elements fueling its fusion will run out, and Sol will undergo the wild transformation into a white dwarf – ballooning into a red giant whose radius could reach as far as Mars before ejecting its outer material while its core collapses into a stellar remnant that glows only with the heat left over from its death.
We have a pretty good idea of how this will play out for the Sun itself, starting in about 5 billion years. But the planets – what about them? What about the earth? What about us?
Led by physicist Amornrat Aungwerojwit from Naresuan University in Thailand, a team of scientists analyzed long-term brightness changes for three white dwarfs and deduced what this means for the planetary systems surrounding them.
Fortunately, we can be sure that humanity (and whatever we evolve into) will be long gone by then, extinct unless it lives on elsewhere in the cosmos. But this beautiful blue marble that we and other planets call home will not escape unscathed. According to white dwarf analysis, the sun’s death throes will trigger a bloodbath across the solar system.
In short, Mercury and Venus are dead, as is everything else in the innermost circle of the solar system. In the end they are torn apart by the sun and devoured like planetary spaghetti.
Earth may or may not survive, depending on how its orbit changes in light of the shrinking mass of the Sun and the changing interactions between planets. If it narrowly escapes, it will look very different from the lush, habitable world it is today.
“Whether the Earth can move away just fast enough before the sun can catch up and burn it is not clear,” says physicist Boris Gänsicke of the University of Warwick in the United Kingdom, “but [if it does] the earth would [still] It loses its atmosphere and the sea and is not a very nice place to live.”
How can we tell all this when we look at white dwarfs? By studying changes in their brightness.
Fluctuations in starlight can mean a few things, but if they occur regularly, the rise and fall in intensity may indicate that something is orbiting the star and periodically blocking some of its light.
The three stars analyzed by researchers in this latest study exhibit brightness changes that previous research suggests are caused by orbiting clouds of planetary debris.
“Previous studies had shown that when asteroids, moons and planets come close to white dwarfs,” says Aungwerojwit, “the enormous gravity of these stars tears these small planetary bodies into smaller and smaller pieces.”
By examining 17 years of data on their three very different white dwarfs, the researchers were able to paint a picture of how this process may unfold. All three stars showed signs of transits – dips in starlight – suggesting that huge, irregular clouds of debris were pulverized into smaller and smaller dust before disappearing, likely because the clumps of dust and rock were slurped up into the white dwarf.
One star showed signs of a catastrophic event in 2010, another in 2015. The third star experienced irregular dimming events and chaotic minute-scale fluctuations every few months. All three stars are now behaving completely normally and the transit events are no longer taking place.
This suggests that the dismemberment and devouring of the planet is occurring fairly quickly. But if Earth is doomed to destruction, it’s unlikely to be quite so violent.
“The sad news is that Earth will probably just be swallowed by an expanding sun before it becomes a white dwarf,” says Gänsicke.
“For the rest of the solar system, some of the asteroids between Mars and Jupiter, and possibly some of Jupiter’s moons, could break away and get close enough to the eventual white dwarf to undergo the crushing process we are studying.”
But no need to worry. Earth’s oceans will evaporate in about a billion years, long before the sun reaches that point.
The research was published in Monthly Notices of the Royal Astronomical Society.