Astronomers Confirm Earth-Like Exoplanet Orbiting Nearest Star

This artist’s impression shows the planet Proxima b orbiting in the Goldilocks zone around the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image between the planet and Proxima itself. Image: ESO

Scientists used to wonder if planets were common throughout the universe, and now we know: they are. Observations with ground-based and space telescopes like Kepler and TESS have proven planets are extremely common. There’s even a small, Earth-like planet right next door orbiting Proxima Centauri. We can say that with confidence now that a team from the University of Geneva has confirmed and refined the initial observations. While Proxima Centauri b is similar in size to Earth, it might not be a great place to vacation. 

Scientists discovered Proxima b in 2016, but it took longer to confirm because of how it was detected. Most exoplanet identifications over the past decade come from the Kepler Space Telescope, which used the transit method of detection. When an exoplanet orbits its star, it can block out the star’s light for brief periods. By tracking these dips in brightness, we can infer the properties of the planet. This is a reliable way to spot planets, but it only works when the plane of the other solar system is aligned with ours. That is not the case for Proxima Centauri, the closest star to Earth at just 4.2 light-years distant. 

A team from the European Southern Observatory discovered Proxima b with the aid of HARPS (High Accuracy Radial Velocity Planet Searcher), a sophisticated spectrograph at the La Silla Observatory in Chile. A spectrograph can measure the small wobbles in a star’s motion that can indicate the presence of an exoplanet. Now, the University of Geneva team has fired up ESPRESSO, a more powerful spectrograph in the same observatory to confirm Proxima b. 

This is what we think it looks like on the surface of Proxima b, a temperate exoplanet orbiting in the habitable zone around a red dwarf in our nearest neighboring star system, Alpha Centauri. Image: ESO

The ESPRESSO data confirms Proxima b is there and that it’s just 1.17 times Earth mass. It also completes a full solar orbit in 11.2 Earth days. Despite being so close to the star, Proxima b is inside the habitable zone because Proxima Centauri is a small, cool red dwarf. With its presence confirmed, the team can also say with certainty that Proxima b gets about 400 times more X-ray radiation than Earth. 

Because Proxima b doesn’t transit the star, it’s harder to gather data about its composition. We know it’s only slightly more massive than Earth, so it’s probably a rocky world. However, no one knows if it might have an atmosphere that could protect it from all that radiation. There’s a lot more to learn about Proxima b, but we might need to wait for future instruments like the James Webb Space Telescope to help us get there.

Now read:

• There’s an Earthlike planet orbiting our nearest neighbor, Proxima Centauri – but how might we actually get there?
• Closest exoplanet Proxima b remains mysterious, in the absence of direct observation
• Nearby exoplanet Proxima b could be a habitable ocean world