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.2020 Dec;20(12):1394-1404.
doi: 10.1089/ast.2019.2161. Epub 2020 Sep 18.

In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World

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In Search for a Planet Better than Earth: Top Contenders for a Superhabitable World

Dirk Schulze-Makuch et al. Astrobiology.2020 Dec.

Abstract

The fact that Earth is teeming with life makes it appear odd to ask whether there could be other planets in our galaxy that may be even more suitable for life. Neglecting this possible class of "superhabitable" planets, however, could be considered anthropocentric and geocentric biases. Most important from the perspective of an observer searching for extrasolar life is that such a search might be executed most effectively with a focus on superhabitable planets instead of Earth-like planets. We argue that there could be regions of astrophysical parameter space of star-planet systems that could allow for planets to be even better for life than our Earth. We aim to identify those parameters and their optimal ranges, some of which are astrophysically motivated, whereas others are based on the varying habitability of the natural history of our planet. Some of these conditions are far from being observationally testable on planets outside the solar system. Still, we can distill a short list of 24 top contenders among the >4000 exoplanets known today that could be candidates for a superhabitable planet. In fact, we argue that, with regard to the search for extrasolar life, potentially superhabitable planets may deserve higher priority for follow-up observations than most Earth-like planets.

Keywords: Extrasolar terrestrial planets; Habitability; Planetary environments.

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Conflict of interest statement

No competing financial interests exist.

Figures

FIG. 1.
FIG. 1.
Star-planet distances (along the abscissa) and mass of the host star (along the ordinate) of roughly 4500 extrasolar planet and extrasolar planet candidates. The temperatures of the stars are indicated with symbol colors (see color bar). Planetary radii are encoded in the symbol sizes (see size scale at the bottom). The conservative habitable zone, defined by the moist-greenhouse and the maximum greenhouse limits (Kopparapuet al., 2013) is outlined with black solid lines. Stellar luminosities required for the parameterization of these limits were taken from Baraffeet al. (2015) as a function of mass as shown along the ordinate of the diagram. The dashed box refers to the region shown in Fig. 2. Data fromexoplanets.org as of May 20, 2019. Color images are available online.
FIG. 2.
FIG. 2.
Same as Fig. 1, but here with a zoom into the habitable zone around K dwarf stars, the potential site for superhabitable planets. Twenty-four planets and planet candidates that are smaller than 2 Earth radii are labeled with name tags. Uncertainties in the observed stellar, planetary, and orbital parameters propagate into the planetary radius measurements, which is why we include planets as large as 2 Earth radii, although truly superhabitable planets might be restricted to radii<1.1 Earth radii. Color images are available online.
See this image and copyright information in PMC

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