Third planet discovered orbiting Proxima Centauri

In October 2012, I shared how astronomers had announced the discovery of an Earth-sized planet orbiting Proxima Centauri, the star closest to our Sun. Now a decade later, the planet count in Proxima Centauri system potentially has been raised to three with the discovery of what appears to be another smaller planet.

The discovery was published on February 10, 2022 in the journal Astronomy & Astrophysics.1 An international team of astronomers led by João Faria, a researcher at the Instituto de Astrofísica e Ciências do Espaço of Portugal, found the planetary candidate using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) in Chile. The potential planet — known as Proxima d — is estimated to have a mass of about twice the mass of Mars. Proxima d was detected using the radial-velocity method and orbits Proxima Centauri at a distance of about four million kilometers,2 which unfortunately puts it well outside the habitable zone.3

“The discovery shows that our closest stellar neighbor seems to be packed with interesting new worlds, within reach of further study and future exploration,” said lead researcher Faria.

It is worth noting that Proxima Centauri — and the larger Alpha Centauri star system where it resides — frequently has been used as a setting in science fiction. Given its status as the closest star to our Sun, the Proxima Centauri system seems a likely destination once humans begin traveling to other stars. Works as diverse as the Robert Heinlein novel Orphans of the Sky (1963) and the television series Babylon 5 (1993–1998) have set stories around Proxima Centauri. Discovering a third planet orbiting Proxima Centauri adds more fuel to the speculation of what we may discover once humans venture outside our own solar system.

1. Faria, J. P. et al. Astron. Astrophys. 658, A115 (2022). [↩]
2. For comparison, Earth orbits the Sun at a distance of about 150 million kilometers. [↩]
3. The “habitable zone” is the distance from a star at which a planet could have liquid water, and thus potentially support life similar to what exists on Earth. [↩]