What makes a planet habitable?

• Published in: The Astronomy and astrophysics review Vol. 17; no. 2; pp. 181 - 249
• Main Authors: Lammer, H., Bredehöft, J. H., Coustenis, A., Khodachenko, M. L., Kaltenegger, L., Grasset, O., Prieur, D., Raulin, F., Ehrenfreund, P., Yamauchi, M., Wahlund, J.-E., Grießmeier, J.-M., Stangl, G., Cockell, C. S., Kulikov, Yu. N., Grenfell, J. L., Rauer, H.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01-06-2009; Springer Nature B.V; Springer Verlag
• Subjects: Astrobiology; Astronomi och astrofysik; Astronomy; Astronomy and astrophysics; Astrophysics and Astroparticles; Astrophysics and Cosmology; Atmosphere evolution; Earth; Earth Sciences; Earth-like exoplanets; Ethane; Extrasolar planets; Extraterrestrial life; Fysik; Geological time; Habitability; Habitats; NATURAL SCIENCES; NATURVETENSKAP; Observations and Techniques; Oceans; Origin of life; Physics; Physics and Astronomy; Planetology; Planets; Review Article; Sciences of the Universe; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Space weather; Subsurface oceans; Subsurface water; Terrestrial planets; Terrestrial planets; Earth-like exoplanets; Habitability; Origin of life; Astrobiology; Subsurface oceans; Atmosphere evolution; Space weather
• ISSN: 0935-4956; 1432-0754; 1432-0754
• DOI: 10.1007/s00159-009-0019-z

This work reviews factors which are important for the evolution of habitable Earth-like planets such as the effects of the host star dependent radiation and particle fluxes on the evolution of atmospheres and initial water inventories. We discuss the geodynamical and geophysical environments which are necessary for planets where plate tectonics remain active over geological time scales and for planets which evolve to one-plate planets. The discoveries of methane–ethane surface lakes on Saturn’s large moon Titan, subsurface water oceans or reservoirs inside the moons of Solar System gas giants such as Europa, Ganymede, Titan and Enceladus and more than 335 exoplanets, indicate that the classical definition of the habitable zone concept neglects more exotic habitats and may fail to be adequate for stars which are different from our Sun. A classification of four habitat types is proposed. Class I habitats represent bodies on which stellar and geophysical conditions allow Earth-analog planets to evolve so that complex multi-cellular life forms may originate. Class II habitats includes bodies on which life may evolve but due to stellar and geophysical conditions that are different from the class I habitats, the planets rather evolve toward Venus- or Mars-type worlds where complex life-forms may not develop. Class III habitats are planetary bodies where subsurface water oceans exist which interact directly with a silicate-rich core, while class IV habitats have liquid water layers between two ice layers, or liquids above ice. Furthermore, we discuss from the present viewpoint how life may have originated on early Earth, the possibilities that life may evolve on such Earth-like bodies and how future space missions may discover manifestations of extraterrestrial life.