If we don’t dwell too much on the idea of death for most of our lives, from a spatio-temporal perspective, it might seem like an act of faith to imagine that everything will go to hell in a few billion years. However, scientists are here to calculate what might happen.When the Sun expands into a red giant, the Earth will likely not survive. But a recent discovery suggests that there may be hope after all.
The discovery. Researchers at the University of California at Berkeley recently discovered a rocky world 4,000 light-years from Earth. Yes, “far away.” But the important thing is that it orbits another star that has already passed through its red giant phase. This planet now orbits a white dwarf, the smallest stellar body left after a star dies.
As the research team describes in a paper published in Nature, evidence suggests that this planet once orbited the star in the same position that Earth orbits the Sun today. It did so until it was pushed into a more distant orbit, twice the Earth-Sun distance, sometime before the giant could devour it. As such, it’s the first rocky world astronomers have observed orbiting a white dwarf. And that’s good news.
The fate of the Earth? Scientists believe that the distant planetary system looks very similar to the expectations for the Sun and the Earth. If so, it would be an unusual mirror of the Earth’s future, a probable fate with a “happy ending.” As study leader Keming Zhang, an astrophysicist at the University of California, explained, “We don’t know if the Earth can survive. If it does, it will end up somewhere like this system.”
What do experts know about Earth’s future twin? In fact, another group of scientists discovered this planet in 2020 with a Korean network of telescopes using a process called microlensing. The team observed how the planet’s star passed in front of another star, magnifying the amount of light coming into the telescope 1,000 times from the background.
This unusual, unique event limited the possibility of detailed follow-up observations until researchers had more powerful telescopes to view the planet’s star in the future. Here’s where Zhang and his team come in, who were able to do additional work at the W. M. Keck Observatory in Hawaii last year. They identified the star as a white dwarf.
A companion white dwarf. Researchers observed at least two objects orbiting the white dwarf. One was a presumed brown dwarf, a failed star never ignited by nuclear fusion at a great distance from the star.
The other object caused more excitement. It was a planet, about 1.9 times the mass of Earth. Perhaps more importantly, it was orbiting much closer to the star, suggesting that it was a possible rocky planet. Using a program to model the evolution of the star system, Zhang and his team estimated that it might once have had the same habitable orbit as Earth, even a similar size.
The good news. In the research, experts describe an unexpected event. When the star ran out of fuel, it lost some mass, unexpectedly lengthening the rocky planet’s orbit. This allowed it to escape the expanding red giant phase of the star. It survived the white dwarf phase, which could happen to the Earth.
If the study data is correct, this would be the first known rocky planet orbiting such a star. “This is definitely the smallest, neatest little rockiest thing we’ve ever found around a white dwarf,” Susan Mullally, an astronomer at the Space Telescope Science Institute in Maryland, told The New York Times.
Image | Adam Makarenko | Keck Observatory
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