A second planet may orbit Proxima Centauri

The planet orbiting the star closest to the sun may have a neighbor.

Proxima Centauri, a dim red star just 4.2 light-years away, is already known to host one potentially habitable planet, Proxima b, that’s a bit more massive than Earth (SN: 8/24/16). Now, astronomers see hints of a second planet, this one much larger and farther from the star.

If it exists, Proxima c appears to be at least 5.8 times as massive as Earth and orbits its star about once every five Earth years, researchers report January 15 in Science Advances. Given its distance from Proxima Centauri, the planet is also much too cold to have liquid water, a key test for habitability.

Clues to the planet’s existence showed up in spectroscopic data of Proxima Centauri from two telescopes in Chile, Mario Damasso, an astrophysicist at the Astrophysical Observatory of Turin in Italy, and colleagues report. The data, which span 17 years, record the star’s back-and-forth motion relative to Earth. After accounting for the known planet, the researchers found hints of an additional unexplained wobble, likely caused by a second planet gravitationally tugging on the star.

Damasso’s team emphasizes that additional data are needed to confirm the planet’s existence. Given its proximity to Earth, Proxima c could be a prime candidate for direct imaging with next-generation supersized telescopes, the scientists say.