A newly discovered exoplanet could provide a window into Earth’s future, billions of years from now.
The planet, called KMT-2020-BLG-0414L b is 4,000 lightyears away in the constellation of Sagittarius and has around the same mass as Earth, but orbits its white dwarf star twice as far out.
Studies of KMT-2020-BLG-0414L b may suggest that Earth could survive being swallowed up by the Sun.
Our ageing Sun and the end of Earth
In around one billion years, our Sun will begin the long transition into becoming a white dwarf.
Initially, it will swell to a red giant, consuming Mercury and Venus during its expansion. There’s a chance, however, that Earth could be spared.
As it swells, the Sun will start losing mass, which will cause the planets to migrate outwards, meaning Earth could outrun the growing star.
If Earth survives, it will end up at double its current orbital distance, while the Sun will continue to lose gas until it becomes a white dwarf.
KMT-2020-BLG-0414L b, a window to the future?
"Whether life can survive on Earth through that red giant period is unknown," says Jessica Lu from the University of California, Berkeley, who took part in the study.
"But this [distant] system… is an example of a planet – probably an Earth-like planet originally on a similar orbit to Earth – that survived its host star’s red giant phase."
Planet KMT-2020-BLG-0414L b was found using a technique known as microlensing, where light from a distant star is bent and magnified by a closer ‘lens’ star, causing it to brighten.
By studying patterns in how the light brightens during such events, astronomers can uncover planets in orbit around the star.
When the lensing event occurred in 2020, it revealed the lens star was surrounded by both the rocky Earth-mass planet and a gas giant 17 times Jupiter’s mass.
Three years later, once the background star had moved away, the team returned to observe the lens star on its own, only to find the star was too dim to be seen.
"Our conclusions are based on ruling out the alternative scenarios, since a normal star would have been easily seen," says Keming Zhang, who led the study at UC Berkeley and is now at University of California, San Diego.
"Because the lens is both dark and low mass, we concluded that it can only be a white dwarf."
Is Earth safe?
We’re so used to thinking about our Solar System as stable – eight planets circling timelessly around the Sun – that it can come as a shock to realise things can change.
Never mind being engulfed by the swelling Sun, there’s a burgeoning astronomical industry in studying the debris left by planets splatted on the surface of white dwarfs.
One recent study of twin Sun-like stars showed that one in 12 pairs had differences in composition, the result, it seems, of consuming planets that had spiralled too close to their parents.
With such catastrophic endings possible, it might be foolish to take the stability of our own Solar System, and the future of Earth, for granted.
