title: Tidal Venuses: triggering a climate catastrophe via tidal heating.
abstract: Traditionally, stellar radiation has been the only heat source considered capable of determining global climate on long timescales. Here, we show that terrestrial exoplanets orbiting low-mass stars may be tidally heated at high-enough levels to induce a runaway greenhouse for a long-enough duration for all the hydrogen to escape. Without hydrogen, the planet no longer has water and cannot support life. We call these planets "Tidal Venuses" and the phenomenon a "tidal greenhouse." Tidal effects also circularize the orbit, which decreases tidal heating. Hence, some planets may form with large eccentricity, with its accompanying large tidal heating, and lose their water, but eventually settle into nearly circular orbits (i.e., with negligible tidal heating) in the habitable zone (HZ). However, these planets are not habitable, as past tidal heating desiccated them, and hence should not be ranked highly for detailed follow-up observations aimed at detecting biosignatures. We simulated the evolution of hypothetical planetary systems in a quasi-continuous parameter distribution and found that we could constrain the history of the system by statistical arguments. Planets orbiting stars with masses<0.3 MSun may be in danger of desiccation via tidal heating. We have applied these concepts to Gl 667C c, a ∼4.5 MEarth planet orbiting a 0.3 MSun star at 0.12 AU. We found that it probably did not lose its water via tidal heating, as orbital stability is unlikely for the high eccentricities required for the tidal greenhouse. As the inner edge of the HZ is defined by the onset of a runaway or moist greenhouse powered by radiation, our results represent a fundamental revision to the HZ for noncircular orbits. In the appendices we review (a) the moist and runaway greenhouses, (b) hydrogen escape, (c) stellar mass-radius and mass-luminosity relations, (d) terrestrial planet mass-radius relations, and (e) linear tidal theories.
authors.affiliation: Astronomy Department, University of Washington, Seattle, Washington 98195, USA. rory@astro.washington.edu
authors.forename: Rory
authors.initials: R
authors.lastname: Barnes
authors.forename: Kristina
authors.initials: K
authors.lastname: Mullins
authors.forename: Colin
authors.initials: C
authors.lastname: Goldblatt
authors.forename: Victoria S
authors.initials: VS
authors.lastname: Meadows
authors.forename: James F
authors.initials: JF
authors.lastname: Kasting
authors.forename: René
authors.initials: R
authors.lastname: Heller
mesh_terms: D002980:Climate; D004190:Disasters; D005118:Extraterrestrial Environment; D017752:Greenhouse Effect; D006358:Hot Temperature; D016083:Planets; D055871:Tidal Waves
references.citation: Icarus. 1993 Jan;101(1):108-28
references.pmid: 11536936
references.citation: Astrobiology. 2010 Sep;10(7):751-71
references.pmid: 20879863
references.citation: Philos Trans A Math Phys Eng Sci. 2012 Sep 13;370(1974):4197-216
references.pmid: 22869797
references.citation: Science. 1979 Mar 2;203(4383):892-4
references.pmid: 17771724
references.citation: Nature. 2009 Dec 17;462(7275):891-4
references.pmid: 20016595
references.citation: Science. 2006 Sep 8;313(5792):1413-6
references.pmid: 16960000
references.citation: Science. 1992 Mar 13;255(5050):1391-7
references.pmid: 17801227
references.citation: Science. 1982 May 7;216(4546):630-3
references.pmid: 17783310
references.citation: Nature. 2001 Jun 14;411(6839):767-70
references.pmid: 11459048
references.citation: Nature. 2008 Dec 11;456(7223):770-2
references.pmid: 19079055
references.citation: Astrobiology. 2010 Jan-Feb;10(1):45-68
references.pmid: 20307182
references.citation: Astrobiology. 2003 Summer;3(2):415-27
references.pmid: 14577888
references.citation: Nature. 2007 May 17;447(7142):292-4
references.pmid: 17507977
references.citation: Nature. 1996 Dec 19-26;384(6610):619-21
references.pmid: 8967949
references.citation: Astrobiology. 2007 Feb;7(1):185-207
references.pmid: 17407407
references.citation: Icarus. 1988;74:472-94
references.pmid: 11538226
references.citation: Astrobiology. 2007 Feb;7(1):167-84
references.pmid: 17407406
references.citation: Science. 2002 Mar 8;295(5561):1885-7
references.pmid: 11884752
references.citation: Science. 2000 May 19;288(5469):1198-201
references.pmid: 10817987
references.citation: Astrobiology. 2008 Oct;8(5):875-81
references.pmid: 18800860
references.citation: Science. 2007 Oct 12;318(5848):244
references.pmid: 17932291
references.citation: Astrobiology. 2007 Feb;7(1):30-65
references.pmid: 17407403
references.citation: Nature. 2009 Jun 18;459(7249):957-9
references.pmid: 19536258
references.citation: Astrobiology. 2007 Feb;7(1):85-166
references.pmid: 17407405
references.citation: Astrobiology. 2011 Jun;11(5):443-60
references.pmid: 21707386
references.citation: Science. 2006 Mar 10;311(5766):1393-401
references.pmid: 16527964
references.citation: Nature. 2000 Jun 15;405(6788):775-8
references.pmid: 10866194
references.citation: Astrobiology. 2008 Jun;8(3):557-68
references.pmid: 18598142
references.citation: Science. 1994 Jul 22;265(5171):482-90
references.pmid: 17781305
references.citation: Science. 2006 Mar 10;311(5766):1422-5
references.pmid: 16527971
references.citation: Nature. 2005 May 26;435(7041):459-61
references.pmid: 15917800
references.citation: Orig Life Evol Biosph. 1993 Feb;23(1):11-21
references.pmid: 11536522