Tiny new planet discovered around Sun's nearest neighbor

Astronomers may have detected a new exoplanet around Proxima Centauri, the star closest to our solar system. This tiny new world is one of the lightest ever discovered, which is even more impressive given the technique the team used to find it.

Proxima Centauri is a red dwarf star just four light-years away from us, in the constellation Centaurus. In 2016 the first exoplanet in the system was discovered – Proxima b, an Earth-sized world that orbits the star every 11 days. A few years later, hints of a second planet arose, with a mass of about six Earths and a five-year orbit. Both of these planets orbit within the star's habitable zone, where temperatures are just right for liquid water to potentially gather on the surface.

And now astronomers have detected signs of a third planet in the system. Proxima d, as it’s known, is actually closer to the star than its siblings, orbiting every five days at a distance about one-tenth of Mercury’s distance from the Sun. That makes it a bit too close to be in the habitable zone.

Proxima d was discovered using the radial velocity technique, which involves watching for slight wobbles of a star produced by the gravitational pull of orbiting planets. In this case, that wobble was tiny, moving Proxima Centauri back and forth at about 1.44 km/h (0.89 mph), meaning it took follow-up observations to confirm it wasn’t just the star itself changing. With a mass just one quarter that of Earth, Proxima d is now the lightest exoplanet ever discovered using this method.

“This achievement is extremely important,” said Pedro Figueira, an author of the study. “It shows that the radial velocity technique has the potential to unveil a population of light planets, like our own, that are expected to be the most abundant in our galaxy and that can potentially host life as we know it.”

As exciting as it is to find new planets so close, we might need to look further afield to find signs of life. Red dwarfs are known to be more active, throwing off flares and radiation that would strip away the atmospheres of orbiting exoplanets. Proxima Centauri itself has even shown that rowdy side, with a huge flare detected in 2017 far surpassing anything our Sun is capable of. Billions of years under this kind of space weather would likely sterilize any planet of its atmosphere and oceans long before life could take hold, even it were located within the habitable zone.

Still, it’s a fascinating star system, and its proximity to us makes it a worthwhile target for further study.

The research was published in the journal Astronomy & Astrophysics.

Source: ESO