Kepler 22-b

The recent announcement of the discovery of planet Kepler 22-b has been met with great excitement. Google search returns over 12 million results for the term ‘Kepler 22-b’ and the discovery has been extensively covered by the mainstream media, an usual situation and one that has not been afforded to many other exoplanet announcements. It’s clear that the possibility that this distant world may be suitable for life (as we understand it) has spurred the imagination of scientists and the public alike. Kepler 22-b has been calculated to be orbiting well within the habitable zone (a term used often in astrobiology, and one that I have discussed in some depth here) of its Sun-like G5 star Kepler 22, but this is not the only factor controlling the habitability of a planet.

Yesterday I covered the launch of the new Habitable Exoplanet Catalogue (HEC), which provided an excellent resource and standardisation tool for assessing the possible habitability of newly discovered planets. In the last few hours, the HEC team has released a provisional assessment of Kepler-22b, based on their habitability metrics, and their findings are summarised by the graphic below:

Habitability analysis of Kepler 22-b by the team at the Habitable Exoplanet Catalogue

So whilst Kepler-22b is comfortably within the habitable zone, it’s huge mass and crushing gravity effectively rules out the possibility of terrestrial life. The planetary temperature given here (313 °K or 40 °C)  seems more realistic than that reported in the press (295 °K or 22 °C)  but I am yet to find the official figure. Accordingly, it is classified as a non-habitable warm neptunian exoplanet.

Below is a table listing some of the characteristics of Kepler 22-b. At the top of the table is the information that has been garnered on the planet and star from photometry to a reasonable degree of accuracy. At the bottom however, are comparisons of Kepler 22-b based on the two likely composition and mass outcomes, which can only be confirmed with more information. I use the terms ‘best’ case and ‘worst’ case relative to terrestrial habitability. I’ve discussed these figures in more detail here.

Kepler 22-b characteristics table. ‘Best’ and ‘worst’ case scenarios are in reference to terrestrial habitability

It’s wonderful to see that exoplanet science is featuring so prominently in the media and is being discussed outside the dusty confines of academia. The Kepler team deserves high praise and recognition for their exciting and relevant work. However, with hundreds more Kepler candidate planets due to be announced, we should be careful not to hype planets like Kepler-22b too much. It would be a travesty if the public (our funding source, remember) loses interest after repeated ‘nearly Earth’ stories (akin to Gliese 581 g) and misses the significance of a truly wonderful, unique and decisively habitable Earth-like planet discovered in the near future.

#EDIT (17/12): Inserted characteristics table into post.

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5 comments on “Kepler 22-b

  1. it’s to the point now that when I *do* find an article in Yahoo news, or some such (before finding it in a more scientific-targeted article) that mentions a new exoplanet with possibility of life I quickly dismiss it (although curiosity always gets the better of me).

    Great article though Andrew. I can’t wait to actually read about the time we find an exoplanet IN the habitable zone that’s of a size more conducive to supporting terrestrial life.

  2. The NASA interview I saw had the temperature at 72 degrees. Luminosity was 75% of our Sun / star and the distance at 85% resulting in a habitable zone position near the same as the Earth. Diameter was estimated at 2.5 times that of Earth, and mass could not be found until this summer. Your figures are not even in the neighborhood.

    • With respect, they aren’t my figures. They are estimates from the Planetary Habitability Laboratory, and my next post illustrated the huge uncertainty in the mass estimate as Kepler 22b’s composition could not yet be verified. However, the Earth and Planetary Astrophysics paper outlining the discovery gives the upper mass limit as 36 Earth masses, a radius of 2.4 Earth radii, a semi-major axis of 0.840 AU and an equilibrium temperature of 262 degrees Kelvin. All that sounds well within ‘the neighbourhood’ to me. Not sure where 72 degrees (Celsius, I’m assuming?) came from, I haven’t heard that myself but if a strong H20 or CO2 greenhouse is present (which may be very likely in my opinion) then I guess it’s possible. Often the excitement proves too much for NASA and they churn out any old back of the envelope model to accompany the press release – their estimates are usually revised in the coming days and weeks.

  3. Pingback: Gliese 667Cc: A new ‘Super-Earth’ basking in the light of three Suns « the II-I- blog

  4. Pingback: Enough Time for Life: Part II | the II-I- blog

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