2024-09-30 22:30:00
A group of astronomers has discovered a possible rocky world the size of Earth orbiting a white dwarf, suggesting a future where our planet survives its star.
In about six billion years, the Sun will become a red giant. This process would consume Mercury, and possibly Venus. For a long time, we’ve thought it might also incinerate Earth.
But perhaps not everything is doomed for the planet Earth (although it may well be an uninhabitable world by then).
Scientists have discovered a rocky world orbiting another star that has already passed through its red giant phase. This planet now orbits a white dwarf, the smallest stellar remnant left after a star’s combustion. The planet seems to have orbited the star in the same position that Earth does around our Sun, before being pushed into a more distant orbit, at twice the distance between Earth and the Sun, before the dying giant could devour it. This makes it the first potentially rocky world observed orbiting a white dwarf.
“We don’t know if Earth can survive,” said Keming Zhang, an astrophysicist at the University of California in San Diego, who led the work published on Thursday in the journal Nature Astronomy. “If it does, it will end up in a place like this system.”
The planet is about 4000 light-years away from us. It was discovered in 2020 with a network of Korean telescopes through a process called microlensing. The Korean team had observed the planet’s star passing in front of another star, which from the background magnified 1000 times the amount of light directed toward the telescope.
This specific event was an isolated occurrence, which limited the possibility of detailed follow-up observations until new and powerful telescopes could better observe the planet’s star in the future. However, Zhang and his team were able to conduct additional work at the Keck Observatory in Hawaii last year and identify the star as a white dwarf.
The data that the researchers managed to gather allowed them to calculate that there were at least two objects orbiting around the white dwarf.
One was a supposed brown dwarf, a failed star that never ignited with nuclear fusion, situated at a very great distance from the star. But the other object was a planet about 1.9 times the mass of Earth that orbited much closer to the star, suggesting it was a possible rocky planet.
By modeling the evolution of the stellar system, the team calculated that the planet could have once had the same habitable orbit as Earth. The star likely also had a size similar to our own. “We believe it had a mass similar to that of the Sun,” said Zhang.
However, when the star ran out of fuel, it lost some of its mass, which caused the orbit of the rocky planet to elongate. This allowed it to escape from the expanding red giant phase of the star and survive into the white dwarf phase.
A handful of gas planets have been found orbiting white dwarfs, but they either had more distant orbits or had migrated inward after the red giant phase. But if Zhang‘s detection is correct, this would be the first known rocky planet to orbit such a star, said Susan Mullally, an astronomer at the Space Telescope Science Institute in Maryland. “It is certainly the smallest and rockiest thing we’ve found around a white dwarf,” said Mullally.
Stephen Kane, an astronomer at the University of California in Riverside, said he was “really excited” when he saw the paper. However, having already researched whether planets can survive a star’s red giant phase, he noted that the presence of the brown dwarf posed complications. “If the brown dwarf was closer and then moved away, that changes the entire dynamic environment of the system,” he said. “Perhaps there were other planets that were ejected, and what we see is what survived.”
NASA plans to launch the Nancy Grace Roman Space Telescope no earlier than 2027, and it is expected to find many more planets through microlensing, including some around white dwarfs. “Some of them might be close enough to study further,” Zhang said.
For now, Zhang‘s system remains a possible crystal ball for our future that, for a fleeting moment, we managed to glimpse.