A second planet might orbit the closest star to the sun, and astronomers think it's a super-Earth
- Proxima Centauri, the closest star to the sun, might have a second planet in its orbit, according to a new study.
- Astronomers think the planet, called Proxima c, is a super-Earth that formed far from the icy region where scientists think such worlds are born.
- But Proxima c might not exist at all. The researchers are looking for more clues in photos and waiting for additional data from space telescopes.
- Visit Business Insider's homepage for more stories.
The closest star to the sun might have a second planet in its orbit.Proxima Centauri is our nearest neighboring star at just 4.2 light-years away. It has one planet that astronomers know of, a potentially habitable world called Proxima b.Advertisement
But in a new study, researchers from Italy's National Institute for Astrophysics report that they have observed changes in the star's activity that indicate it could have another planet. They dubbed the world Proxima c in their paper, which was published Wednesday in the journal Science Advances.
The potential new planet seems to be a super-Earth - the term for a planet with a mass larger than Earth but significantly smaller than the ice giant Neptune."Proxima Centauri is the nearest star to the sun, and this detection would make it the closest planetary system to us," astronomer Mario Damasso, the paper's lead author, told Business Insider in an email.
Proxima c (if it exists) is probably not habitable - given its distance from its star, the planet is probably freezing or shrouded in a suffocating hydrogen-helium atmosphere. But its proximity to us could offer a unique opportunity to study another star system.
Proxima c could be a super-Earth in an unexpected placeAdvertisement
Astronomers think super-Earths form around the "snowline": the closest distance to a star where water can become ice. That's because icy solids accumulate in that region when a star system is in its infancy, helping to form planets.
Proxima c is far beyond that snowline, though, so its existence could challenge that theory.Advertisement
Then again, researchers still aren't sure whether planet exists at all.
The team discovered Proxima c using a technique called radial velocity. It works like this: Planets tug slightly on their stars as they orbit. When the star's position moves, even in this small way, it changes the colors of its light. If those changes are cyclical, that suggests the cause is an orbiting planet.Advertisement
Damasso's team identified this type of cyclical change in Proxima Centauri's light, and determined that it is unrelated to the movements of the planet Proxima b.
That suggested the presence of another planet, though Damasso said the researchers still "cannot discard the possibility that the signal is actually due to the activity of the star."So the team hopes to find more clues in data from the Gaia space telescope.Advertisement
Help from Gaia and James WebbAdvertisement
The next release of Gaia's data is planned for this summer, followed by another in 2021. The timeline for the full data release has not yet been announced.
While Damasso and Del Sordo wait for that, they're working with another team to scan photos of Proxima Centauri in search of signs of a second orbiting planet."Direct imaging may give results in a shorter time, but it cannot give a definitive answer," Del Sordo said. "In other words, if we will not see anything in the image, it doesn't necessarily mean Proxima c does not exist."Advertisement
Another telescope, NASA's upcoming James Webb Space Telescope (JWST), could help researchers answer these questions, too.Advertisement
That could help astronomers study nearby stars and, specifically, Proxima c, in great detail.
"It will surely be a target for JWST, but since the planet is likely very cold, we do not know if JWST will be able to detect it," Del Sordo said.Even if James Webb can't spot Proxima c, its neighboring planet, Proxima b, will be a prime target.Advertisement
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