Circumstellar habitable zones for deep terrestrial biospheres

Sean Hendry McMahon, Jack O'Malley-James, John Parnell

Research output: Contribution to journalArticlepeer-review

17 Citations (Scopus)
9 Downloads (Pure)


The habitable zone (HZ) is conventionally the thin shell of space around a star within which liquid water is thermally stable on the surface of an Earth-like planet (Kasting et al., 1993). However, life on Earth is not restricted to the surface and includes a "deep biosphere" reaching several km in depth. Similarly, subsurface liquid water maintained by internal planetary heat could potentially support life well outside conventional HZs. We introduce a new term, subsurface-habitability zone (SSHZ) to denote the range of distances from a star within which rocky planets are habitable at any depth below their surfaces up to a stipulated maximum, and show how SSHZs can be estimated from a model relating temperature, depth and orbital distance. We present results for Earth-like, Mars-like and selected extrasolar terrestrial planets, and conclude that SSHZs are several times wider and include many more planets than conventional surface-based habitable zones. (C) 2013 Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)312-318
Number of pages7
JournalPlanetary and space science
Early online date18 Jul 2013
Publication statusPublished - 1 Sep 2013


  • habitable zones
  • deep biosphere
  • subsurface
  • astrobiology
  • exobiology
  • extrasolar planets
  • main-sequence stars
  • Mars
  • planets
  • energy
  • clouds
  • earths
  • life


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