Astronomers have discovered a planet 35 percent more massive than Earth in orbit around a red dwarf star just 11 light years from the Sun. The planet, Ross 128 b, likely exists at the edge of the small, relatively faint star's habitable zone even though it is 20 times closer to its star than the Earth is to the Sun. The study in the journal Astronomy & Astrophysics finds the best estimate for its surface temperature is between -60 degrees Celsius and 20 degrees Celsius.

This is not the closest Earth-size world that could potentially harbor liquid water on its surface—that title is held by Proxima Centauri b, which is less than 4.3 light years away from Earth and located in the star system closest to the Sun. Even so, due to a variety of factors, Ross 128 b is tied for fourth on a list of potentially most habitable exoplanets, with an Earth Similarity Index value of 0.86.

In the new research, astronomers discuss another reason to believe that life might be more likely to exist on Ross 128 b. That's because its parent star, Ross 128, is a relatively quiet red dwarf star, producing fewer stellar flares than most other, similar-sized stars such as Proxima Centauri. Such flares may well sterilize any life that might develop on such a world.

Ultimately, the question of habitability on these worlds will have to wait for more powerful telescopes to come online. For worlds that transit in front of their star, such as the promising exoplanet TRAPPIST-1 d , the James Webb Space Telescope should have the capability to characterize the composition of their atmospheres with just a few hours of observation.

For other worlds that don't make such a transit, such as Ross 128 b, other methods will have to be employed. The next generation of large ground-based telescopes, including the European Extremely Large Telescope, should be able to resolve features such as oxygen in the atmosphere of these nearby exoplanets. And if one of them has oxygen, our confidence that life is probably there will increase dramatically.