Second planet could be orbiting neighbouring star just four light years away

By Nilima Marshall, PA Science Reporter

Astronomers have discovered what could be a second planet in another solar system just four light years from Earth.

Proxima c is approximately half the size of Neptune and orbits Proxima Centauri, the red dwarf star nearest star to the Sun.

This neighbouring star, which is about eight times smaller than the Sun, became famous in 2016 with the discovery of an “Earth-like” planet in orbit called Proxima b.

An international team of researchers, including scientists from the University of Hertfordshire, have found what they believe could be yet another exoplanet, describing the object as a “low-mass planet candidate”.

The team combed through 17 years’ worth of data, analysing the cyclical changes in the light spectrum emitted by Proxima Centauri.

They found evidence of the star “wiggling” back and forth, indicating another planet could be in orbit.

Findings suggest Proxima c orbits its host star every 5.2 years and may be a “super-Earth”, with “a mass higher than Earth’s but much lower than Uranus and Neptune”.

Measurements indicate Proxima c is orbiting at a distance that is 1.5 times farther than Earth is from the Sun, making it much colder than Proxima b, where temperatures are mild enough to permit liquid surface water.

If its existence is confirmed, the researchers say Proxima c may provide insights into how low-mass planets form around low-mass stars.

They believe it could also challenge models of how super-Earths are born, as planets such as these are believed to form near the “snowline” – the minimum distance from a star at which water can turn to solid ice.

Proxima Centauri taken by Nasa’s Hubble Telescope (Nasa)

According to the researchers, Proxima c’s orbit lies “far beyond this sweet spot”.

Hugh Jones, a professor of astrophysics at University of Hertfordshire, said: “The proximity of the planet and its orbit at a relatively great distance from its star, means it is one of the best possible chances for direct observations that will enable detailed understanding of another planet.

“Our continuing observations and improved data processing has allowed us to discern the signal of Proxima c.”

However, the authors say more evidence is needed to confirm their conclusion.

Mr Jones added: “We look forward to confirming the signal with new facilities and finding out how similar or different from our Solar System planets Proxima c really is.”

The research is published in the Journal of Science Advances.