Editing Habitable zone (section)

===Solar System estimates===
{{seealso|Water on terrestrial planets of the Solar System}}
[[File: Estimated extent of the Solar Systems habitable zone.png|thumb|The range of published estimates for the extent of the Sun's HZ. The conservative HZ<ref name=dole-1964 /> is indicated by a dark-green band crossing the inner edge of the [[Apsis#Perihelion and aphelion|aphelion]] of [[Venus]], whereas an extended HZ,<ref name=fogg-1992 /> extending to the orbit of the [[dwarf planet]] [[Ceres (dwarf planet)|Ceres]], is indicated by a light-green band.]]
[[File:Terrestrial planet size comp 2024.png|thumb|Solar System's [[Planetary-mass object]]s with partial or full orbits within the Extended Habitable Zone from left to right: Mercury, Venus, Earth & Moon, Mars, and Ceres. While many possess surface water in solid state, only Earth has liquid water on the surface. This is mainly due to a combination of low mass and an inability to mitigate evaporation and atmosphere loss against the [[solar wind]].]]
Estimates for the habitable zone within the Solar System range from 0.38 to 10.0 [[astronomical unit]]s,<ref name=zsom-2013 /><ref name= rayeric-2011 /><ref name= rk-2017 /><ref>{{cite web| url=http://depts.washington.edu/naivpl/sites/default/files/hz.shtml| title=Stellar habitable zone calculator| publisher=[[University of Washington]]| access-date=17 December 2015}}</ref> though arriving at these estimates has been challenging for a variety of reasons. Numerous planetary mass objects orbit within, or close to, this range and as such receive sufficient sunlight to raise temperatures above the freezing point of water. However, their atmospheric conditions vary substantially.

The aphelion of Venus, for example, touches the inner edge of the zone in most estimates and, while atmospheric pressure at the surface is sufficient for liquid water, a strong greenhouse effect raises surface temperatures to {{convert|462|C|F}} at which water can only exist as vapor.<ref name=venus-2006>{{cite web|url=http://burro.cwru.edu/stu/advanced/venus.html |title=Venus |publisher=Case Western Reserve University |date=13 September 2006 |access-date=2011-12-21 |archive-url=https://web.archive.org/web/20120426064658/http://burro.cwru.edu/stu/advanced/venus.html |archive-date=2012-04-26 }}</ref> The entire orbits of the [[Moon]],<ref name=sharp>{{cite web |url=http://www.space.com/18067-moon-atmosphere.html |title=Atmosphere of the Moon |publisher=TechMediaNetwork |work=Space.com |access-date=April 23, 2013 |author=Sharp, Tim}}</ref> [[Mars]],<ref name="bolonkin09">{{Cite book|first=Alexander A.|last=Bolonkin|date=2009|title=Artificial Environments on Mars|publisher=Springer |place=Berlin Heidelberg|pages=599–625|isbn=978-3-642-03629-3}}</ref> and numerous asteroids also lie within various estimates of the habitable zone. Only at Mars' lowest elevations (less than 30% of the planet's surface) is atmospheric pressure and temperature sufficient for water to, if present, exist in liquid form for short periods.<ref name="HaberleMcKay2001">{{cite journal|last1=Haberle|first1=Robert M.|last2=McKay|first2=Christopher P.|last3=Schaeffer|first3=James|last4=Cabrol|first4=Nathalie A.|last5=Grin|first5=Edmon A.|last6=Zent|first6=Aaron P.|last7=Quinn|first7=Richard|title=On the possibility of liquid water on present-day Mars|journal=Journal of Geophysical Research|volume=106|issue=E10|year=2001|pages=23317|issn=0148-0227|doi=10.1029/2000JE001360|bibcode = 2001JGR...10623317H |doi-access=free}}</ref> At [[Hellas Basin]], for example, atmospheric pressures can reach 1,115&nbsp;Pa and temperatures above zero Celsius (about the triple point for water) for 70 days in the Martian year.<ref name = "HaberleMcKay2001"/> Despite indirect evidence in the form of [[seasonal flows on warm Martian slopes]],<ref name="WRD-20140218">{{cite magazine |last=Mann |first=Adam  |title=Strange Dark Streaks on Mars Get More and More Mysterious|url=https://www.wired.com/wiredscience/2014/02/flowing-lineae-water-mars/ |date=February 18, 2014 |magazine=[[Wired (magazine)|Wired]]  |access-date=February 18, 2014 }}</ref><ref name=voanews>{{cite web|url=https://www.voanews.com/a/nasa-finds-possible-signs-of-flowing-water-on-mars-126807133/143341.html|title=NASA Finds Possible Signs of Flowing Water on Mars|date=3 August 2011 |publisher=Voice of America|access-date=August 5, 2011|url-status=live|archive-url=https://web.archive.org/web/20110917071451/http://www.voanews.com/english/news/science-technology/NASA-Finds-Possible-Signs-of-Flowing-Water-on-Mars-126807133.html|archive-date=September 17, 2011}}</ref><ref name=mag>{{cite web|url=http://news.sciencemag.org/sciencenow/2011/08/is-mars-weeping-salty-tears.html|title=Is Mars Weeping Salty Tears?|publisher=news.sciencemag.org|access-date=August 5, 2011|archive-url=https://web.archive.org/web/20110814065220/http://news.sciencemag.org/sciencenow/2011/08/is-mars-weeping-salty-tears.html|archive-date=August 14, 2011}}</ref><ref name="NASA-20131210">{{cite web |last1=Webster |first1=Guy |last2=Brown |first2=Dwayne |title=NASA Mars Spacecraft Reveals a More Dynamic Red Planet |url=http://www.jpl.nasa.gov/news/news.php?release=2013-361&1#1 |date=December 10, 2013 |work=[[NASA]] |access-date=December 10, 2013 }}</ref> no confirmation has been made of the presence of liquid water at the surface. While other objects orbit partly within this zone, including comets, [[Ceres (dwarf planet)|Ceres]]<ref name=ahearn-1992>{{cite journal|last=A'Hearn|first=Michael F.|author2=Feldman, Paul D.|title=Water vaporization on Ceres|journal=Icarus|volume=98|issue=1|pages=54–60|date=1992|doi=10.1016/0019-1035(92)90206-M|bibcode= 1992Icar...98...54A}}</ref> is the only one of planetary mass. 

Despite this, studies indicate the strong possibility of past liquid water on the surface of [[Water on Venus|Venus]],<ref name="SalvadorMassol2017">{{cite journal|last1=Salvador|first1=A.|last2=Massol|first2=H.|last3=Davaille|first3=A.|last4=Marcq|first4=E.|last5=Sarda|first5=P.|last6=Chassefière|first6=E.|title=The relative influence of H2 O and CO2 on the primitive surface conditions and evolution of rocky planets|journal=Journal of Geophysical Research: Planets|volume=122|issue=7|year=2017|pages=1458–1486|issn=2169-9097|doi=10.1002/2017JE005286|bibcode=2017JGRE..122.1458S|s2cid=135136696 |url=https://hal-insu.archives-ouvertes.fr/insu-01540209/file/2017JE005286.pdf}}</ref> [[Lunar water|the Moon]],<ref>{{cite web |url=https://news.wsu.edu/2018/07/23/possibility-of-moon-life/ |title=Mysteries from the moon's past |date=23 July 2018 |publisher=[[Washington State University]] |access-date=22 August 2020}}</ref><ref>{{Cite journal|doi=10.1089/ast.2018.1844|title=Was There an Early Habitability Window for Earth's Moon?|year=2018|last1=Schulze-Makuch|first1=Dirk|last2=Crawford|first2=Ian A.|journal=Astrobiology|volume=18|issue=8|pages=985–988|pmid=30035616|pmc=6225594|bibcode=2018AsBio..18..985S}}</ref> [[Water on Mars|Mars]],<ref>{{cite web |url=http://www.space.com/scienceastronomy/flashback-water-on-mars-announced-10-years-ago-100622.html |title=Flashback: Water on Mars Announced 10 Years Ago| publisher=SPACE.com| date=June 22, 2000| access-date=December 19, 2010}}</ref><ref name='Willson 2018'>{{cite web|url=https://www.space.com/8642-flashback-water-mars-announced-10-years.html |title=Flashback: Water on Mars Announced 10 Years Ago| publisher=SPACE.com| date=June 22, 2010| access-date=May 13, 2018}}</ref><ref>{{cite web| url=https://science.nasa.gov/headlines/y2001/ast05jan_1.htm| title=Science@NASA, The Case of the Missing Mars Water| access-date=March 7, 2009| archive-url=https://web.archive.org/web/20090327234049/https://science.nasa.gov/headlines/y2001/ast05jan_1.htm| archive-date=March 27, 2009}}</ref> [[4 Vesta|Vesta]]<ref name="ScullyRussell2015">{{cite journal|last1=Scully|first1=Jennifer E.C.|last2=Russell|first2=Christopher T.|last3=Yin|first3=An|last4=Jaumann|first4=Ralf|last5=Carey|first5=Elizabeth|last6=Castillo-Rogez|first6=Julie|last7=McSween|first7=Harry Y.|last8=Raymond|first8=Carol A.|last9=Reddy|first9=Vishnu|last10=Le Corre|first10=Lucille|title=Geomorphological evidence for transient water flow on Vesta|journal=Earth and Planetary Science Letters|volume=411|year=2015|pages=151–163|issn=0012-821X|doi=10.1016/j.epsl.2014.12.004|bibcode=2015E&PSL.411..151S}}</ref> and Ceres,<ref name="RaponiDe Sanctis2018">{{cite journal|last1=Raponi|first1=Andrea|last2=De Sanctis|first2=Maria Cristina|last3=Frigeri|first3=Alessandro|last4=Ammannito|first4=Eleonora|last5=Ciarniello|first5=Mauro|last6=Formisano|first6=Michelangelo|last7=Combe|first7=Jean-Philippe|last8=Magni|first8=Gianfranco|last9=Tosi|first9=Federico|last10=Carrozzo|first10=Filippo Giacomo|last11=Fonte|first11=Sergio|last12=Giardino|first12=Marco|last13=Joy|first13=Steven P.|last14=Polanskey|first14=Carol A.|last15=Rayman|first15=Marc D.|last16=Capaccioni|first16=Fabrizio|last17=Capria|first17=Maria Teresa|last18=Longobardo|first18=Andrea|last19=Palomba|first19=Ernesto|last20=Zambon|first20=Francesca|last21=Raymond|first21=Carol A.|last22=Russell|first22=Christopher T.|title=Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle|journal=Science Advances|volume=4|issue=3|year=2018|pages=eaao3757|issn=2375-2548|doi=10.1126/sciadv.aao3757|pmid=29546238|pmc=5851659|bibcode=2018SciA....4.3757R }}</ref><ref>[https://photojournal.jpl.nasa.gov/catalog/PIA21471 NASA.gov] PIA21471: Landslides on Ceres</ref> suggesting a more common phenomenon than previously thought. Since sustainable liquid water is thought to be essential to support complex life, most estimates, therefore, are inferred from the effect that a repositioned orbit would have on the habitability of Earth or Venus as their surface gravity allows sufficient atmosphere to be retained for several billion years.

According to the extended habitable zone concept, planetary-mass objects with atmospheres capable of inducing sufficient radiative forcing could possess liquid water farther out from the Sun. Such objects could include those whose atmospheres contain a high component of greenhouse gas and terrestrial planets much more massive than Earth ([[super-Earth]] class planets), that have retained atmospheres with surface pressures of up to 100&nbsp;kbar. There are no examples of such objects in the Solar System to study; not enough is known about the nature of atmospheres of these kinds of extrasolar objects, and their position in the habitable zone cannot determine the net temperature effect of such atmospheres including induced [[albedo]], anti-greenhouse or other possible heat sources.

For reference, the average distance from the Sun of some major bodies within the various estimates of the habitable zone is: Mercury, 0.39&nbsp;AU; Venus, 0.72&nbsp;AU; Earth, 1.00&nbsp;AU; Mars, 1.52&nbsp;AU; Vesta, 2.36&nbsp;AU; Ceres and Pallas, 2.77&nbsp;AU; Jupiter, 5.20&nbsp;AU; Saturn, 9.58&nbsp;AU. In the most conservative estimates, only Earth lies within the zone; in the most permissive estimates, even Saturn at perihelion, or Mercury at aphelion, might be included.

{| class="wikitable sortable"
|- style="text-align:center; align:center; background:#90b0f0;"
|+ Estimates of the circumstellar habitable zone boundaries of the Solar System
! Inner edge ([[Astronomical unit|AU]]) !! The outer edge (AU) !! Year !! Notes
|-
| 0.725 || 1.24 || 1964, Dole<ref name=dole-1964 />|| Used optically thin atmospheres and fixed albedos. Places the aphelion of Venus just inside the zone.
|-
| || 1.005–1.008 || 1969, Budyko<ref name=budyko-1969>{{Cite journal | last1 = Budyko | first1 = M. I. | title = The effect of solar radiation variations on the climate of the Earth | doi = 10.1111/j.2153-3490.1969.tb00466.x | journal = Tellus | volume = 21 | issue = 5 | pages = 611–619 | year = 1969 | bibcode = 1969Tell...21..611B| citeseerx = 10.1.1.696.824 }}</ref>|| Based on studies of ice-albedo feedback models to determine the point at which Earth would experience global glaciation. This estimate was supported in studies by Sellers 1969<ref>{{cite journal |title=A Global Climatic Model Based on the Energy Balance of the Earth-Atmosphere System |author=Sellers, William D. |journal=Journal of Applied Meteorology |date=June 1969 |volume=8 |issue=3 |pages=392–400 |doi=10.1175/1520-0450(1969)008<0392:AGCMBO>2.0.CO;2 |doi-access=free |bibcode=1969JApMe...8..392S}}</ref> and North 1975.<ref>{{cite journal
 |last1 = North
 |first1 = Gerald R.
 |date=November 1975
 |title = Theory of Energy-Balance Climate Models
 |journal = Journal of the Atmospheric Sciences
 |volume = 32
 |issue = 11
 |pages = 2033–2043
 |doi = 10.1175/1520-0469(1975)032<2033:TOEBCM>2.0.CO;2
|doi-access=free
 |bibcode = 1975JAtS...32.2033N
 }}</ref>
|-
| 0.92–0.96 || || 1970, Rasool and De Bergh<ref name=rasool-1970>{{cite journal | pages = 1037–1039 | issue = 5250 | volume = 226 | date = 13 Jun 1970 | doi = 10.1038/2261037a0 | pmid = 16057644 | issn = 0028-0836 | journal = Nature | first2 = C. | first1 = I. | title = The Runaway Greenhouse and the Accumulation of CO<sub>2</sub> in the Venus Atmosphere | url = https://pubs.giss.nasa.gov/docs/1970/1970_Rasool_ra00500s.pdf | archive-url = https://web.archive.org/web/20231114213658/https://pubs.giss.nasa.gov/docs/1970/1970_Rasool_ra00500s.pdf | archive-date = 14 November 2023 | url-status = live | last1 = Rasool | last2 = De Bergh | bibcode = 1970Natur.226.1037R | s2cid = 4201521 }}</ref>|| Based on studies of Venus's atmosphere, Rasool and De Bergh concluded that this is the minimum distance at which Earth would have formed stable oceans.
|-
| 0.958 || 1.004 || 1979, Hart<ref name=hart-1979>{{Cite journal | last1 = Hart | first1 = M. H. | doi = 10.1016/0019-1035(79)90141-6 | title = Habitable zones about main sequence stars | journal = Icarus | volume = 37 | issue = 1 | pages = 351–357 | year = 1979 |bibcode = 1979Icar...37..351H }}</ref>|| Based on computer modeling and simulations of the evolution of Earth's atmospheric composition and surface temperature. This estimate has often been cited by subsequent publications.
|-
| || 3.0 || 1992, Fogg<ref name=fogg-1992>{{cite journal |title=An Estimate of the Prevalence of Biocompatible and Habitable Planets |author=Fogg, M. J. |journal=Journal of the British Interplanetary Society |date=1992 |volume=45 |pages=3–12 |bibcode=1992JBIS...45....3F |pmid=11539465 |issue=1}}</ref>|| Used the [[carbon cycle]] to estimate the outer edge of the circumstellar habitable zone.
|-
| 0.95 || 1.37 || 1993, Kasting et al.<ref name=kasting-1993 />|| Founded the most common working definition of the habitable zone used today. Assumes that CO<sub>2</sub> and H<sub>2</sub>O are the key greenhouse gases as they are for the Earth. Argued that the habitable zone is wide because of the [[carbonate–silicate cycle]]. Noted the cooling effect of cloud albedo. Table shows conservative limits. Optimistic limits were 0.84–1.67 AU.
|-
| || 2.0 || 2010, Spiegel et al.<ref name="speigel-2010">{{Cite journal | last1 = Spiegel | first1 = D. S. | last2 = Raymond | first2 = S. N. | last3 = Dressing | first3 = C. D. | last4 = Scharf | first4 = C. A. | last5 = Mitchell | first5 = J. L. | title = Generalized Milankovitch Cycles and Long-Term Climatic Habitability | doi = 10.1088/0004-637X/721/2/1308 | journal = The Astrophysical Journal | volume = 721 | issue = 2 | pages = 1308–1318 | year = 2010 |arxiv = 1002.4877 |bibcode = 2010ApJ...721.1308S | s2cid = 15899053 }}</ref>|| Proposed that seasonal liquid water is possible to this limit when combining high obliquity and orbital eccentricity.
|-
| 0.75 || || 2011, Abe et al.<ref name="abe-2011">{{Cite journal | last1 = Abe | first1 = Y. | last2 = Abe-Ouchi | first2 = A. | last3 = Sleep | first3 = N. H. | last4 = Zahnle | first4 = K. J. | title = Habitable Zone Limits for Dry Planets | doi = 10.1089/ast.2010.0545 | journal = Astrobiology | volume = 11 | issue = 5 | pages = 443–460 | year = 2011 | pmid =  21707386|bibcode = 2011AsBio..11..443A }}</ref>|| Found that land-dominated "desert planets" with water at the poles could exist closer to the Sun than watery planets like Earth.
|-
|  ||10  || 2011, Pierrehumbert and Gaidos<ref name= rayeric-2011 />||Terrestrial planets that accrete tens-to-thousands of bars of primordial hydrogen from the protoplanetary disc may be habitable at distances that extend as far out as 10 AU in the Solar System.
|-
| 0.77–0.87 || 1.02–1.18 || 2013, Vladilo et al.<ref name=vladilo-2013>{{cite journal |title=The habitable zone of Earth-like planets with different levels of atmospheric pressure |author1=Vladilo, Giovanni |author2=Murante, Giuseppe |author3=Silva, Laura |author4=Provenzale, Antonello |author5=Ferri, Gaia |author6=Ragazzini, Gregorio |journal=The Astrophysical Journal |date=March 2013 |volume=767 |issue=1 |pages=65–? |doi=10.1088/0004-637X/767/1/65 |arxiv=1302.4566|bibcode = 2013ApJ...767...65V |s2cid=49553651 }}</ref>|| Inner edge of the circumstellar habitable zone is closer and outer edge is farther for higher atmospheric pressures; determined minimum atmospheric pressure required to be 15 mbar.
|-
| 0.99 || 1.67 || 2013, Kopparapu et al.<ref name=kopparapu-2013 /><ref name="Kopparapu2013b" />|| Revised estimates of the Kasting et al. (1993) formulation using updated moist greenhouse and water loss algorithms. According to this measure, Earth is at the inner edge of the HZ and close to, but just outside, the moist greenhouse limit. As with Kasting et al. (1993), this applies to an Earth-like planet where the "water loss" (moist greenhouse) limit, at the inner edge of the habitable zone, is where the temperature has reached around 60 Celsius and is high enough, right up into the troposphere, that the atmosphere has become fully saturated with water vapor. Once the stratosphere becomes wet, water vapor photolysis releases hydrogen into space. At this point cloud feedback cooling does not increase significantly with further warming. The "maximum greenhouse" limit, at the outer edge, is where a {{CO2}} dominated atmosphere, of around 8 bars, has produced the maximum amount of greenhouse warming, and further increases in {{CO2}} will not create enough warming to prevent {{CO2}} catastrophically freezing out of the atmosphere. Optimistic limits were 0.97–1.67 AU. This definition does not take into account possible radiative warming by {{CO2}} clouds.
|-
| 0.38 || || 2013, Zsom et al.<br /><ref name=zsom-2013>{{cite journal |title=Towards the Minimum Inner Edge Distance of the Habitable Zone |last1=Zsom |first1=Andras |date=2013 |arxiv=1304.3714 |last2=Seager |first2=Sara |last3=De Wit |first3=Julien |doi=10.1088/0004-637X/778/2/109 |volume=778 |issue=2 |journal=The Astrophysical Journal |page=109 |bibcode=2013ApJ...778..109Z|s2cid=27805994 }}</ref>|| Estimate based on various possible combinations of atmospheric composition, pressure and relative humidity of the planet's atmosphere.
|-
| 0.95  ||  || 2013, Leconte et al.<ref name= leconte-2013>{{cite journal |title=Increased insolation threshold for runaway greenhouse processes on Earth-like planets |last1=Leconte |first1=Jeremy |date=2013 |arxiv=1312.3337 |last2=Forget |first2=Francois |last3=Charnay |first3=Benjamin |last4=Wordsworth |first4=Robin |last5=Pottier |first5=Alizee |doi=10.1038/nature12827 |pmid=24336285 |volume=504 |issue=7479 |pages=268–71 |journal=Nature |bibcode=2013Natur.504..268L|s2cid=2115695 }}</ref>||Using 3-D models, these authors computed an inner edge of 0.95 AU for the Solar System.
|-
| 0.95 ||2.4 || 2017, Ramirez and Kaltenegger<br /><ref name=rk-2017>{{cite journal |title=A Volcanic Hydrogen Habitable Zone |last1=Ramirez |first1=Ramses |date=2017 |arxiv=1702.08618|last2=Kaltenegger |first2=Lisa |doi=10.3847/2041-8213/aa60c8 |volume=837 |issue=1 |pages=L4 |journal=The Astrophysical Journal Letters|bibcode=2017ApJ...837L...4R|s2cid=119333468 |doi-access=free }}</ref>|| An expansion of the classical carbon dioxide-water vapor habitable zone<ref name=kasting-1993 /> assuming a volcanic hydrogen atmospheric concentration of 50%.
|-
| 0.93–0.91|| || 2019, Gomez-Leal et al.<br /><ref name=gomez-2019>{{cite journal |title=Climate sensitivity to ozone and its relevance on the habitability of Earth-like planets|last1=Gomez-Leal |first1=Illeana |date=2019 |arxiv=1901.02897|last2=Kaltenegger |first2=Lisa |last3=Lucarini |first3=Valerio |last4=Lunkeit |first4=Frank |doi=10.1016/j.icarus.2018.11.019 |volume=321 |pages=608–618 |journal=Icarus|bibcode=2019Icar..321..608G|s2cid=119209241 }}</ref>|| Estimation of the moist greenhouse threshold by measuring the water mixing ratio in the lower stratosphere, the surface temperature, and the climate sensitivity on an Earth analog with and without ozone, using a global climate model (GCM). It shows the correlation of a water mixing ratio value of 7 g/kg, a surface temperature of about 320 K, and a peak of climate sensitivity in both cases. 
|-
! 0.99 !! 1.004 !! !! The tightest bounded estimate from above
|- 
! 0.38 !! 10 !! !! The most relaxed estimate from above
|-
|}