Six Earth-sized exoplanetary candidates in habitable zones?

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.

Paul Scott Anderson is a freelance space writer with a life-long passion for space exploration and astronomy. He started his blog The Meridiani Journal in 2005, which is a chronicle of planetary exploration. He also publishes The Exoplanet Report e-paper. In 2011, he started writing about space on a freelance basis, and now also currently write for AmericaSpace and He has also written for Universe Today and SpaceFlight Insider, has been published in The Mars Quarterly and has done supplementary writing for the well-known iOS app Exoplanet for iPhone and iPad.

1 Comment

  1. Also, they use Kasting, and he is dated. AGW and better observations have made his results on early CO2 requirements for keeping Earth ice free during the early weak sun period come down with an order of magnitude and be consistent with the mineral record. [“Warming the early earth – CO2 reconsidered”, Paris et al, Planetary and Space Science, 2008.]

    Presumably a similar reassessment of the HZ would move maximum distance out & minimum planetary mass down quite a bit. [Disclaimer: Just an interested layman, but this came up during an astrobiology course.]

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