The Sun Will Destroy Earth One Day, Right? Maybe Not (PDF)

https://www.nytimes.com/2024/09/26/science/planet-white-dwarf.html The Sun Will Destroy the Earth One Day, Right? Maybe Not. Astronomers spotted a potential Earth-size rocky world orbiting a white dwarf, suggesting a future in which our planet outlives its star....

https://www.nytimes.com/2024/09/26/science/planet-white-dwarf.html The Sun Will Destroy the Earth One Day, Right? Maybe Not. Astronomers spotted a potential Earth-size rocky world orbiting a white dwarf, suggesting a future in which our planet outlives its star. Listen to this article · 4:00 min Learn more By Jonathan O’Callaghan Sept. 26, 2024 In six billion years the sun will expand into a red giant. That process should consume Mercury, and maybe Venus. For a long time we have thought it might incinerate Earth, too. But perhaps all is not doomed for planet Earth (although it may be a world that will have long since become uninhabitable). Scientists have discovered a rocky world orbiting another star that already went through its red giant phase. This planet now orbits a white dwarf, the smaller stellar body that remains after a star burns out. Crucially, the planet looks like it once orbited the star in the same position Earth currently travels around our sun, and did so until it was pushed to a more distant orbit, twice the Earth-sun distance, sometime before the dying giant could eat it. This makes it the first potential rocky world to be observed orbiting a white dwarf. “We don’t know if Earth can survive,” said Keming Zhang, an astrophysicist at the University of California, San Diego, who led the work published on Thursday in the journal Nature Astronomy. “If it does, it’ll end up somewhere like this system.” The planet is about 4,000 light-years away from us. It was discovered in 2020 with a Korean telescope network using a process called microlensing. The Korean team had watched as the planet’s star passed in front of another star, which from the background magnified the amount of light heading toward the telescope by 1,000 times. This specific occurrence was a one-off event, limiting the chance for detailed follow-up observations until powerful new telescopes can better view the planet’s star in the future. But Dr. Zhang and his team were able to do additional work at the Keck Observatory in Hawaii last year and identify the star as a white dwarf. The data the researchers managed to gather allowed them to calculate that there were at least two objects orbiting the white dwarf. One was a suspected brown dwarf, a failed star that never ignited with nuclear fusion, situated at a very great distance away from the star. But the other object was a planet about 1.9 times the mass of Earth orbiting much closer to the star, suggesting it was a possible rocky planet.  The microlensing event showing the white dwarf, as indicated by the perpendicular white lines. Researchers captured images of the star years before the event (a), shortly after peak magnification of the background star in 2020 (b) and after its disappearance, in 2023 (c). OGLE, CFHT, Keck Observatory Modeling the star system’s evolution, the team calculated that the planet might once have been the same habitable orbit like Earth’s. The star was also probably a similar size to our own. “We expect it was around the sun’s mass,” Dr. Zhang said. However, as the star ran out of fuel, it lost some of its mass, which caused the rocky planet’s orbit to lengthen. This allowed it to escape the star’s expanding red giant phase and survive to the white dwarf phase. A handful of gaseous 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 Dr. Zhang’s detection is correct, this would be the first rocky planet known to orbit such a star, said Susan Mullally, an astronomer at the Space Telescope Science Institute in Maryland. “This is definitely the smallest, neatest little rockiest thing we’ve ever found around a white dwarf,” Dr. Mullally said. Stephen Kane, an astronomer at the University of California, Riverside, said he was “really excited” when he saw the paper. However, Dr. Kane, who has previously investigated whether planets can survive a star’s red giant phase, said the presence of the brown dwarf posed complications. “If the brown dwarf was closer and then moved out, that changes the whole dynamical environment of the system,” he said. “Maybe there were other planets that were thrown out, and what we see is what survived.” NASA is set 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 for further investigation,” Dr. Zhang said. For now, Dr. Zhang’s system remains a potential crystal ball into our future that, for a fleeting moment, we managed to glimpse. A version of this article appears in print on , Section D, Page 2 of the New York edition with the headline: Cosmic Burnout: If the Sun Refused to Shine, Earth May Still Tag Along