A second planet could orbit Proxima Centauri

The planet that orbits the closest star to the sun may have a neighbor. Proxima Centauri, a dim red star just 4.2 light-years away, is already known to host a potentially habitable planet, Proxima b, which is slightly more massive than Earth. 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 more massive than Earth and orbits its star about once every five Earth years, researchers report. Given its distance from Proxima Centauri, the planet is also too cold to support liquid water, a key test for habitability.

Clues to the planet’s existence appeared in Proxima Centauri spectroscopic data from two telescopes in Chile, astrophysicists report. The data, spanning 17 years, records 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 tugging gravitationally on the star.

The team of researchers emphasizes that additional data is needed to confirm the existence of the planet. Given its proximity to Earth, Proxima c could be a prime candidate for direct imaging with next-generation large telescopes, scientists say.