most “earthlike” planets in habitable zones around sunlike stars are on average 1.8 Billion years older than the Earth.
That would push many of them over into Venus mode seeing as all stars increase in brightness slowly as they age and Earth will fall over into positive greenhouse feedback mode within 2 gigayears (possibly within 500 megayears).
However, seeing as star brightness increases with the 3.5th power of mass, and therefore lifetime decreases with the 2.5th power of mass, stars not much smaller than the sun can be pretty ‘sunlike’ while brightening much slower and having much longer stable regimes. This is where it gets confusing; are we an outlier in having such a large star (larger than 90% of stars in fact), or do these longer-lived smaller stars have something about them that makes it less likely that observers will find themselves there?
That would push many of them over into Venus mode seeing as all stars increase in brightness slowly as they age and Earth will fall over into positive greenhouse feedback mode within 2 gigayears (possibly within 500 megayears).
However, seeing as star brightness increases with the 3.5th power of mass, and therefore lifetime decreases with the 2.5th power of mass, stars not much smaller than the sun can be pretty ‘sunlike’ while brightening much slower and having much longer stable regimes. This is where it gets confusing; are we an outlier in having such a large star (larger than 90% of stars in fact), or do these longer-lived smaller stars have something about them that makes it less likely that observers will find themselves there?