Will the Sun Ultimately Destroy Earth?

 In six billion years, the sun is expected to expand into a red giant, potentially consuming Mercury and possibly Venus. For a long time, it was believed that Earth might face a similar fate. However, there may be hope for our planet, albeit in a far-off future when it has long ceased to be habitable.

Scientists have discovered a rocky planet orbiting a star that has already gone through its red giant phase. This planet now circles a white dwarf—the remnant of a star that has burned out. Remarkably, it appears that this planet once orbited its original star in a position similar to Earth’s current orbit, but was later pushed to a more distant orbit, roughly twice the distance between Earth and the sun, before the red giant could consume it. This makes it the first rocky planet observed around a white dwarf.

“We don’t know if Earth can survive,” said Keming Zhang, an astrophysicist at the University of California, San Diego, and the lead author of a study published in *Nature Astronomy*. “If it does, it could end up in a system like this.”

The planet is located about 4,000 light-years away and was identified in 2020 using a Korean telescope network through a method called microlensing. The team observed a moment when the planet's star passed in front of another star, amplifying the light observed by the telescope by 1,000 times.

This event was a unique occurrence, limiting opportunities for detailed follow-up observations until more advanced telescopes can study the planet’s star. However, Dr. Zhang and his team were able to conduct additional research at the Keck Observatory in Hawaii, identifying the star as a white dwarf.

From the data collected, researchers determined that at least two objects orbit the white dwarf: one suspected brown dwarf, a failed star that never ignited nuclear fusion, and a planet about 1.9 times Earth’s mass, indicating it could be rocky.

Modeling the evolution of this star system, the team theorized that the planet might have once occupied a habitable zone similar to Earth's. They believe the original star was comparable in size to our sun. As it exhausted its fuel, it lost some mass, which allowed the rocky planet’s orbit to expand, enabling it to escape the destructive red giant phase and survive into the white dwarf phase.

While some gaseous planets have been found around white dwarfs, they either orbit at greater distances or migrated inward after the red giant phase. If Dr. Zhang's findings are confirmed, this would be the first rocky planet identified orbiting such a star, according to Susan Mullally, an astronomer at the Space Telescope Science Institute. “This is definitely the smallest, neatest little rockiest thing we’ve ever found around a white dwarf,” Dr. Mullally noted.

Stephen Kane, an astronomer at the University of California, Riverside, expressed excitement over the discovery. However, he cautioned that the presence of the brown dwarf could complicate the system's dynamics. “If the brown dwarf was closer and then moved outward, it changes the whole environment of the system,” he said. “Other planets may have been ejected, and we might only see the survivors.”

NASA plans to launch the Nancy Grace Roman Space Telescope no earlier than 2027, which is expected to discover many more planets through microlensing, potentially including additional rocky worlds around white dwarfs. “Some of them might be close enough for further investigation,” Dr. Zhang added.