From the standpoint of solar irradiation, the recently announced Proxima b planet seemed to be in the “life zone.” Small problem: while the total amount of sunlight falling on the planet approximates the amount Earth gets, it also gets other stuff far more abundantly than Earth does. In particular… nasty stuff. Stuff that would trash an Earthly atmosphere in a geological blink of an eye. In short: every two hours Proxima would send a storm of X-Rays and ultraviolet from superflares blasting into the atmosphere of Proxima b, ionizing the oxygen and accelerating its escape into space. It’s estimated that the oxygen atmosphere would last about 10 million years.
NASA Redefines Life Zones for Alien Planets –“Nixes Earth-Sized Planet of Our Closest Neighbor Red Dwarf Star Proxima Centauri”
Bummer.
Seems red dwarfs, the most common stars out there, are likely not going to be terribly good places to find Earthlike worlds. It *may* be that roughly Earthlike worlds might be found further out from the stars, Of course they would be frozen iceballs… unless they were in close enough orbit to massive companions, gas giants perhaps, that tidal forcing would pump enough energy into their cores to keep them warm. This would present its own set of troubles, such as being tidally locked to the gas giant, and common and likely astonishing earthquakes.