A two-tiered approach to assessing the habitability of exoplanets

Dirk Schulze-Makuch, Abel Méndez, Alberto G. Fairén, Philip Von Paris, Carol Turse, Grayson Boyer, Alfonso F. Davila, Marina Walther-Antonio, David Catling, Louis N. Irwin

Research output: Contribution to journalArticle

44 Citations (Scopus)

Abstract

In the next few years, the number of catalogued exoplanets will be counted in the thousands. This will vastly expand the number of potentially habitable worlds and lead to a systematic assessment of their astrobiological potential. Here, we suggest a two-tiered classification scheme of exoplanet habitability. The first tier consists of an Earth Similarity Index (ESI), which allows worlds to be screened with regard to their similarity to Earth, the only known inhabited planet at this time. The ESI is based on data available or potentially available for most exoplanets such as mass, radius, and temperature. For the second tier of the classification scheme we propose a Planetary Habitability Index (PHI) based on the presence of a stable substrate, available energy, appropriate chemistry, and the potential for holding a liquid solvent. The PHI has been designed to minimize the biased search for life as we know it and to take into account life that might exist under more exotic conditions. As such, the PHI requires more detailed knowledge than is available for any exoplanet at this time. However, future missions such as the Terrestrial Planet Finder will collect this information and advance the PHI. Both indices are formulated in a way that enables their values to be updated as technology and our knowledge about habitable planets, moons, and life advances. Applying the proposed metrics to bodies within our Solar System for comparison reveals two planets in the Gliese 581 system, GJ 581 c and d, with an ESI comparable to that of Mars and a PHI between that of Europa and Enceladus.

Original languageEnglish (US)
Pages (from-to)1041-1052
Number of pages12
JournalAstrobiology
Volume11
Issue number10
DOIs
StatePublished - Dec 1 2011
Externally publishedYes

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habitability
Planets
extrasolar planets
similarity index
planet
chemistry
Mars
liquids
planets
energy
Solar System
temperature
Europa
Technology
Enceladus
solar system
Temperature
Moon
index
terrestrial planets

Keywords

  • Complexity
  • Earth similarity
  • Exoplanets
  • Habitability
  • Index
  • Life

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Schulze-Makuch, D., Méndez, A., Fairén, A. G., Von Paris, P., Turse, C., Boyer, G., ... Irwin, L. N. (2011). A two-tiered approach to assessing the habitability of exoplanets. Astrobiology, 11(10), 1041-1052. https://doi.org/10.1089/ast.2010.0592

A two-tiered approach to assessing the habitability of exoplanets. / Schulze-Makuch, Dirk; Méndez, Abel; Fairén, Alberto G.; Von Paris, Philip; Turse, Carol; Boyer, Grayson; Davila, Alfonso F.; Walther-Antonio, Marina; Catling, David; Irwin, Louis N.

In: Astrobiology, Vol. 11, No. 10, 01.12.2011, p. 1041-1052.

Research output: Contribution to journalArticle

Schulze-Makuch, D, Méndez, A, Fairén, AG, Von Paris, P, Turse, C, Boyer, G, Davila, AF, Walther-Antonio, M, Catling, D & Irwin, LN 2011, 'A two-tiered approach to assessing the habitability of exoplanets', Astrobiology, vol. 11, no. 10, pp. 1041-1052. https://doi.org/10.1089/ast.2010.0592
Schulze-Makuch D, Méndez A, Fairén AG, Von Paris P, Turse C, Boyer G et al. A two-tiered approach to assessing the habitability of exoplanets. Astrobiology. 2011 Dec 1;11(10):1041-1052. https://doi.org/10.1089/ast.2010.0592
Schulze-Makuch, Dirk ; Méndez, Abel ; Fairén, Alberto G. ; Von Paris, Philip ; Turse, Carol ; Boyer, Grayson ; Davila, Alfonso F. ; Walther-Antonio, Marina ; Catling, David ; Irwin, Louis N. / A two-tiered approach to assessing the habitability of exoplanets. In: Astrobiology. 2011 ; Vol. 11, No. 10. pp. 1041-1052.
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