A very interesting new article was just published (draft version) by scientists at Cornell University on September 12 regarding lower mass Kepler exoplanetary candidates. Specifically, dealing with six exoplanet candidates with sizes estimated to range from just larger than Earth (1.85 Earth radius) to a bit smaller than Earth (0.85 Earth radius), and residing within the habitable zones of their stars, with estimated equilibrium temperatures ranging from about 217 K (-56˚ C / -69˚ F) to 261 K (-12˚ C / 10˚ F). On the cool side, but within the accepted habitable zone temperature range. From the abstract of the article:
“Our results significantly reduce the sizes of the corresponding planet-candidates, with many less than 1 Earth radius. Recalculating the equilibrium temperatures of the planet-candidates from the implied stellar luminosities and masses, and assuming Earth’s albedo and re-radiation fraction, we find that six of the planet-candidates are terrestrial-sized with orbital semi-major axes that lie within the habitable zones of their low-mass host stars.”
These are still listed as candidates, but if confirmed, and the stated characteristics are confirmed (or at least close), this would be a very significant finding in the quest for Earth-like planets elsewhere.