(CN) — Astronomers have finally discovered a planet that resembles Earth — only it shows what our planet might look like eight billion years in the future.
Scientists estimate that in around five billion years, Earth’s sun will begin to expand outward into a red giant, eventually becoming larger than Earth’s current orbit. In around eight billion years, the sun will reach the end of its life. Its outer layers will have dispersed, leaving behind a white dwarf star — a dense glowing ball smaller in size than the Earth but still with half the sun’s original mass. Before this point, Earth will most likely have been consumed by the expanding sun.
However, the recent discovery of an Earth-sized planet orbiting a white dwarf star shows another possible future for our world. There’s a slim chance that, as the sun’s gravity decreases, Earth will move into a more distant orbit, allowing it to survive the sun’s expansion.
In a study published Thursday in the journal Nature Astronomy, researchers detail how this planetary system, located around four thousand light years from our solar system, illustrates what such a future for Earth would look like, with the Earth-sized planet orbiting its tiny star at a distance twice that of Earth’s current orbit.
“This 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,” one of the study’s authors, Jessica Lu, said in a statement.
Even if Earth is able to achieve a similar fate, however, it will have long ceased to be habitable.
“We do not currently have a consensus whether Earth could avoid being engulfed by the red giant sun in 6 billion years,” study leader Keming Zhang said in a statement. “In any case, planet Earth will only be habitable for around another billion years, at which point Earth’s oceans would be vaporized by runaway greenhouse effect — long before the risk of getting swallowed by the red giant.”
Luckily for us, Zhang says humans could possibly survive by moving further out into the solar system, as several moons of Jupiter and Saturn appear to have large amounts of frozen water that will likely thaw as the sun expands.
“As the sun becomes a red giant, the habitable zone will move to around Jupiter and Saturn’s orbit, and many of these moons will become ocean planets,” Zhang said. “I think, in that case, humanity could migrate out there.”
The system Zhang and his team analyzed was first discovered in 2020 due to a phenomenon called “microlensing.” When it passed in front of a more distant star, the system’s gravity acted like a lens to focus and magnify the other star’s light by a factor of a thousand.
This microlensing event was first detected by the Korea Microlensing Telescope Network, which consists of three identical telescopes at observatories in Chile, South Africa and Australia. The team that discovered it estimated that the system includes a star with about half the mass of Earth’s sun, a planet about the mass of Earth and another, much larger planet about 17 times the mass of Jupiter.
Zhang’s team analyzed the system in 2023 using the Keck telescope in Hawaii. Because it was three years after the microlensing event, the light from the background star had become faint enough that the system’s star should have been visible if it was a main-sequence star like Earth’s sun.
Instead, however, the researchers were not able to detect anything, leading them to conclude the star is a white dwarf.
“This is a case of where seeing nothing is actually more interesting than seeing something,” Lu said.