Habitable Planets Quotes

“How many habitable planets are there?
From Figure 12 it is evident that there are a handful of planets with instellation in the habitable zone range, and which are also of a size or mass small enough to have a potentially rocky composition. Most of these orbit M stars, but that is just because smallish planets with Earthlike instellation are easier to detect around low mass stars. Taking into account the effect of stellar type on the habitable zone instellation boundaries, at the time of writing there are eighteen known planets in the habitable zone, including Proxima Centauri b (orbiting our nearest stellar neighbour) and planets d, e, f, and g in the remarkable Trappist 1 system. There are an additional twenty-six near-misses which could perhaps be rendered habitable if cloud conditions or other uncertain bits of climate physics become more favourable than current best estimates. One would like to extrapolate from this number to an estimate of the proportion of all stars that have a planet in their habitable zone.”
― Raymond T. Pierrehumbert, Planetary Systems: A Very Short Introduction