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.