Many new potentially habitable worlds waiting to be confirmed
Last week NASA’s Kepler mission added 1,924 new objects of interest to its list of 2,713 exoplanet candidates. The new data has not been completely analyzed yet and many of these objects might be attributed to non-planetary processes (false-positives). However, this new batch gives a general idea of what new types of planets could be announced in the future.
The Planetary Habitability Laboratory (PHL) did a basic analysis of this new Kepler data compared to the existing exoplanets data. The new data suggests the addition of up to 83 new potentially habitable exoplanet candidates, a big increase from the current 18 listed in the Habitable Exoplanets Catalog. Only four of these have been confirmed so far: Kepler-22b, Kepler-62e, Kepler-62f, and Kepler-61b.
Two types of potential exoplanets are particularly notable in this new Kepler data. There is a big increase of the number of warm and cold super-Earths. This is somewhat expected since the new data includes objects with longer periods. However, other larger objects did not increase as well but it might be too early to attribute this to the abundance of low mass planets.
The most interesting additions are the first potential Earth-like planets. All currently known potentially habitable exoplanets are quite larger than Earth and therefore not very Earth-like by definition. The new Kepler data suggests six new objects with the right size and distance from their star to be considered Earth-like worlds. Since Kepler is no longer operating, it will be very hard to confirm any of these objects with additional data in the near future.
The recent study by Everett et al. (2013) suggests that one fourth of the Kepler exoplanets candidates are 35% larger than expected, which could also affect the number of those considered potentially habitable. The new Kepler data is being used by the PHL and other groups to prioritize targets of interest for analyses and future observations.
About the Habitable Exoplanets Catalog
The PHL’s Habitable Exoplanets Catalog (HEC) uses a wide definition for potentially habitable exoplanets that includes planets with 0.1 to 10 Earth masses (or 0.4 to 2.6 Earth radii) orbiting the habitable zone of their parent star within the Venus-Mars empirical limits. Other research groups use narrower or wider definitions. A much wider definition that includes ‘dry planets’ and ‘hydrogen-rich planets’ will be implemented in the future.
Figure 1. New 1,924 NASA Kepler objects of interest added to the NASA Exoplanet Archive. These are objects that are still being considered for inclusion as exoplanets candidates. Notable additions are many 'warm and cold superterrans' (super-Earths) and six 'warm terrans' (potential Earth-like worlds). Check the Periodic Table of Exoplanets for confirmed and current Kepler exoplanets candidates for comparison. CREDIT: PHL @ UPR Arecibo
Figure 2. Planetary radius versus habitable zone location for the current 890 confirmed exoplanets. All known potentially habitable exoplanets are superterrans (labeled) and there are no terrans yet. Solar System planets in dark blue. Note that most of these radii are estimates based on mass-radius relationship since only their mass was available. CREDIT: PHL @ UPR Arecibo.
FIgure 3. Planetary radius versus habitable zone location for the current 2,713 NASA Kepler exoplanet candidates. All potentially habitable exoplanet candidates are superterrans and there are no terrans yet. Light blue dots are candidates, red dots confirmed, and Solar System planets in dark blue. CREDIT: PHL @ UPR Arecibo.
FIgure 4. Planetary radius versus habitable zone location for the new 1,924 NASA Kepler objects of interest. All potentially habitable objects include many superterrans and now, for the first time, six terrans. Solar System planets in dark blue. CREDIT: PHL @ UPR Arecibo.
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