On August 24, 2016, astronomers announced the discovery of a rocky planet in the habitable zone of Proxima Centauri, the closest star to Earth (not counting the Sun).
[10] However, Proxima Centauri's classification as a red dwarf casts doubts on the habitability of any exoplanets in its orbit due to low stellar flux, high probability of tidal locking, small circumstellar habitable zones and high stellar variation.
Another likely candidate is Alpha Centauri, Earth's nearest Sun-like star system 4.37 light-years away.
It has similar characteristics to Proxima Centauri b and is one of the nearest discovered potentially habitable exoplanets to Earth.
Characterizing its atmosphere is more difficult than with a transiting exoplanet as transmission spectroscopy is inapplicable, and instruments for alternative techniques such as analysis of thermal emission and reflected light are not yet available.
[41][42] One of the planets, Gliese 163 c, about 6.9 times the mass of Earth and somewhat hotter, was considered to be within the habitable zone, but is probably not terrestrial.