Dynamical Habitability of Extrasolar Planetary Systems

Siegfried Franck Christine Bounama Werner von Bloh Potsdam Institute for Climate Impact Research GERMANY [email protected]

We apply computer models to investigate known exoplanetary systems to determine whether they could host Earth-like planets with surface conditions sufficient for the emergence and maintenance of life on a stable orbit. Such a configuration is described as dynamic habitable. Our definition of habitability is linked to the photosynthetic activity of the planet. This leads to additional spatial and temporal limitations of habitability, as the stellar habitable zone (HZ) becomes narrower with time due to the persistent decrease of the planetary atmospheric CO2 concentration. The stability of orbits of hypothetical Earth-like planets is based on a method derived from giant's orbital eccentricity. We calculate the dynamic habitability of 86 extrasolar planetary systems in dependence of the relative continental area of a putative Earth-like planet. The likelihood that an Earth-like planet is both on a stable orbit and also within the HZ can be quantitatively estimated from the width of the HZ excluding the interval of orbital instability.

Almost 60% of the investigated systems could harbour habitable Earth-like planets on stable orbits. There are remarkable differences for land worlds and for systems older than about 7 Gyr. In 18 extrasolar planetary systems we find even better prerequisites for dynamic habitability than in our own solar system. This is a manifestation of the mediocrity principle introduced by Copernicus: There is nothing special about Earth. The Earth is a relatively ordinary planet orbiting a relatively ordinary star in a relatively ordinary galaxy, which is one of the countless others in a giant universe.