Where is the closest known exoplanet in a habitable zone to its star?

At only four light-years away, Proxima Centauri b is our closest known exoplanet neighbor.

Proxima b is a super Earth exoplanet that orbits a M-type star. Its mass is 1.27 Earths, it takes 11.2 days to complete one orbit of its star, and is 0.0485 AU from its star. Its discovery was announced in 2016.

In the habitable zone of its star, Proxima Centauri, Proxima b encounters bouts of extreme ultraviolet radiation hundreds of times greater than Earth does from the Sun. That radiation generates enough energy to strip away not just the lightest molecules — hydrogen — but also, over time, heavier elements such as oxygen and nitrogen.

Just because Proxima b’s orbit is in the habitable zone, which is the distance from its host star where liquid water could pool on a planet’s surface, doesn’t mean it’s habitable.