Habitable zone for complex life

{{main|Exoplanets|Earth analog}}

The first confirmed exoplanets was discovered in 1992, several planets orbiting the pulsar PSR B1257+12.{{Cite journal | last1 = Wolszczan | first1 = A. |bibcode=1992Natur.355..145W| last2 = Frail | first2 = D. A. | doi = 10.1038/355145a0 | title = A planetary system around the millisecond pulsar PSR1257 + 12 | journal = Nature | volume = 355 | issue = 6356 | pages = 145–147 | year = 1992 | s2cid = 4260368 }} Since then the list of exoplanets has grown to the thousands.{{Cite web|url=https://exoplanetarchive.ipac.caltech.edu/docs/counts_detail.html|title=Exoplanet and Candidate Statistics|website=exoplanetarchive.ipac.caltech.edu}} Most exoplanets are hot Jupiter planets, that orbit very close the star.{{Cite web|url=http://users.auth.gr/~voyatzis/Exoplanets/voyatzis_Hipparchos.htm|title=Orbital Evolution of planets in Extra-solar systems|website=users.auth.gr|date=5 February 2024 }} Many exoplanets are super-Earths, that could be a gas dwarf or large rocky planet, like Kepler-442b at a mass 2.36 times Earths.{{cite journal |last1=Valencia |first1=V. |last2=Sasselov |first2=D. D. |last3=O'Connell |first3=R. J. |date=2007 |title=Radius and structure models of the first super-earth planet |journal=The Astrophysical Journal |volume=656 |issue=1 |pages=545–551 |arxiv=astro-ph/0610122 |bibcode=2007ApJ...656..545V |doi=10.1086/509800|s2cid=17656317 }}

{{main|Star|Solar twin}}

Unstable stars are young and old stars, or very large or small stars. Unstable stars have changing solar luminosity that changes the size of the life habitable zones. Unstable stars also produce extreme solar flares and coronal mass ejections. Solar flares and coronal mass ejections can strip away a planet's atmosphere that is not replaceable. Thus life habitable zones require and very stable star like the Sun, at ±0.1% solar luminosity change.{{Cite journal|title=Magnetospheres of Terrestrial Exoplanets and Exomoons: Implications for Habitability and Detection|first1=James|last1=Green|first2=Scott|last2=Boardsen|first3=Chuanfei|last3=Dong|date=February 20, 2021|journal=The Astrophysical Journal Letters|volume=907|issue=2|pages=L45|doi=10.3847/2041-8213/abd93a|doi-access=free |arxiv=2012.11694 |bibcode=2021ApJ...907L..45G }}{{Cite web|url=https://www.astronomy.com/science/is-earth-the-only-goldilocks-planet/|title=Is Earth the only Goldilocks planet? | Astronomy.com|first=Klaus R.|last=Brasch|date=July 7, 2023}} Finding a stable star, like the Sun, is the search for a solar twin, with solar analogs that have been found.{{Cite web|url=https://science.nasa.gov/science-research/planetary-science/08jan_sunclimate/|title=Solar Variability and Terrestrial Climate – NASA Science|website=science.nasa.gov}} Star metallicity, mass, age, color, and temperature all effect luminosity variations.{{Cite web|url=http://astro.unl.edu/classaction/animations/stellarprops/stellarlum.html|title=Stellar Luminosity Calculator|website=astro.unl.edu}}{{Cite book|url=http://www.nap.edu/catalog/13519|title=The Effects of Solar Variability on Earth's Climate: A Workshop Report|date=November 12, 2012|publisher=National Academies Press|doi=10.17226/13519 |isbn=978-0-309-26564-5 }}{{Cite web|url=https://scienceblogs.com/startswithabang/2013/06/05/most-of-earths-twins-arent-identical-or-even-close|title=Most of Earth's twins aren't identical, or even close! | ScienceBlogs|website=scienceblogs.com}} The Sun, a G2V star, has a mid-range metallicity optimal for the formation of rocky planets.{{Cite web|url=https://astrobiology.nasa.gov/news/galactic-habitable-zones/|title=NASA Astrobiology|website=astrobiology.nasa.gov}} Dwarf stars (red dwarf/orange dwarf/brown dwarf/subdwarf) are not only unstable, but also emit low energy, so the habitable zone is very close to the star and planets become tidally locked on the timescales needed for the development of life.{{cite book | title=Formation and Evolution of Exoplanets | editor1-first=Rory | editor1-last=Barnes | publisher=John Wiley & Sons | year=2010 | isbn=978-3527408962 | page=248 | url=https://books.google.com/books?id=-7KimFtJnIAC&pg=PA248 | access-date=2016-08-16 | archive-date=2023-08-06 | archive-url=https://web.archive.org/web/20230806163538/https://books.google.com/books?id=-7KimFtJnIAC&pg=PA248 | url-status=live }} Giant stars (subgiant/giant star/red giant/red supergiant) are unstable and emit high energy, so the habitable zone is very far from the star.{{Cite web|url=https://www.universetoday.com/83248/plausibility-check-habitable-planet-around-red-giants/|title=Plausibility Check - Habitable Planets around Red Giants|first=Jon|last=Voisey|date=February 23, 2011}} Multiple-star systems are also very common and are not suitable for complex life, as the planet orbit would be unstable due to multiple gravitational forces and solar radiation. Liquid water is possible in Multiple-star systems.{{Cite web|url=https://science.nasa.gov/universe/stars/multiple-star-systems/|title=Multiple Star Systems - NASA Science|website=science.nasa.gov}}{{cite journal |last1=Busetti |first1=F. |last2=Beust |first2=H. |last3=Harley |first3=C. |title=Stability of planets in triple star systems |journal=Astronomy & Astrophysics |date=November 2018 |volume=619 |pages=A91 |doi=10.1051/0004-6361/201833097 |arxiv=1811.08221 |bibcode=2018A&A...619A..91B }}{{cite book |doi=10.1007/978-3-319-30648-3_156-1 |chapter=Populations of Planets in Multiple Star Systems |title=Handbook of Exoplanets |date=2018 |last1=Martin |first1=David V. |pages=1–26 |isbn=978-3-319-30648-3 }}{{cite journal |last1=Cuntz |first1=M. |last2=Eberle |first2=J. |last3=Musielak |first3=Z. E. |title=Stringent Criteria for Stable and Unstable Planetary Orbits in Stellar Binary Systems |journal=The Astrophysical Journal |date=10 November 2007 |volume=669 |issue=2 |pages=L105–L108 |doi=10.1086/523873 |bibcode=2007ApJ...669L.105C }}

{{main | Habitable zone}}

A conventional habitable zone is defined by liquid water.

• Habitable zone (HZ) (also called the circumstellar habitable zone), the orbit around a star that would allow liquid water to remain for a short period of time (a given period of time) on at least a small part of the planet's surface. Thus within the HZ, water, (H₂O) is between {{convert|0|C|F K}} and {{convert|100|C|F K}} temperature.{{Cite web|url=https://science.nasa.gov/learn/heat/big-ideas/big-idea-2-1/|title=Big Idea 2.1 – NASA Science|website=science.nasa.gov}}{{Cite web|url=https://exoplanets.nasa.gov/resources/2255/what-is-the-habitable-zone|title=What Is the Habitable Zone?|website=Exoplanet Exploration: Planets Beyond our Solar System}}{{Cite web|url=https://www.esa.int/Science_Exploration/Space_Science/Plato/Planets_in_the_habitable_zone|title=Planets in the habitable zone|website=www.esa.int}} This zone is a temperature zone, set by the star's radiation and distance from the star. In the Solar System the planet Mars is just at the outer boundary of the habitable zone. The planet Venus is at the inner edge of the habitable zone, but due to its thick atmosphere it has no water. The HZ includes planets with elliptic orbits; such planets might orbit into and out of the HZ. When a planet moves out of the HZ, all its water would freeze to ice on the outside of the HZ, and/or all water would become steam on the inner side. The HZ could be defined as the region where bacteria, a form of life, could possibly survive for a short period of time. The HZ is also sometimes called the "Goldilocks" zone.
• Optimistic habitable zone (OHZ): a zone where liquid surface water could have been on a planet at some time in its past history. This zone would be larger than the HZ. Mars is an example of a planet in the OHZ.: it is just beyond the HZ today, but had liquid water for a short time span before the Mars carbonate catastrophe, some 4 billion years ago.{{Cite web|url=https://astrobites.org/2022/03/21/continuous-habitable-zone-2/|title=Which habitable zone planets are the best candidates for detecting life? | astrobites|date=21 March 2022 }}{{Cite web|url=https://exoplanets.nasa.gov/news/1720/second-earth-sized-world-found-in-systems-habitable-zone/|title=Second Earth-sized World Found in System's Habitable Zone|website=Exoplanet Exploration: Planets Beyond our Solar System|date=10 January 2023 }}
• Continuously habitable zone (CHZ): a zone where liquid water persists on the surface of a planet for years. This requires a near-circular planetary orbit and a stable star. The zone may be much smaller than the habitable zone.{{Cite web|url=https://www.e-education.psu.edu/astro801/content/l12_p4.html|title=The Habitable Zone | Astronomy 801: Planets, Stars, Galaxies, and the Universe|website=www.e-education.psu.edu}}
• Conservative habitable zone: a zone where liquid surface water remains on a planet over a long time span, as on Earth. This might also need a greenhouse effect provided by gases such as CO₂ and water vapor to maintain the correct temperature. Rayleigh scattering would also be needed.

Over time and with more research, astronomers, cosmologists and astrobiologist have discovered more parameters needed for life. Each parameter could have a corresponding zone. Some of the named zones include:{{cite journal|last= Taylor|first=Stuart Ross|date=29 July 2004|title=Why can't planets be like stars? |journal=Nature|pmid=15282586|volume=430|issue=6999|pages=509|doi=10.1038/430509a|bibcode = 2004Natur.430..509T |s2cid=12316875|doi-access=free}}{{cite web|url=http://www.planetary.org/articles/1956/|title=Ten Things I Wish We Really Knew In Planetary Science|last=Stern|first=Alan|access-date=2009-05-22}}

• Ultraviolet habitable zone: a zone where the ultraviolet (UV) radiation from a star is neither too weak nor too strong for life to exist.{{Cite web|url=https://astrobiology.com/2023/03/the-ultraviolet-habitable-zone-of-exoplanets.html|title=The Ultraviolet Habitable Zone Of Exoplanets|first=Keith|last=Cowing|date=March 30, 2023|website=Astrobiology}} Life needs the correct amount of ultraviolet for synthesis of biochemicals. The extent of the zone depends on the amount of ultraviolet radiation from the star, the range of UV wavelengths, the age of the star, and the atmosphere of the planet. In humans UV is used to produce vitamin D.{{Cite journal|title=The ultraviolet habitable zone of exoplanets|first1=Riccardo|last1=Spinelli|first2=Francesco|last2=Borsa|first3=Giancarlo|last3=Ghirlanda|first4=Gabriele|last4=Ghisellini|first5=Francesco|last5=Haardt|date=April 13, 2023|journal=Monthly Notices of the Royal Astronomical Society|volume=522|issue=1|pages=1411–1418|doi=10.1093/mnras/stad928|doi-access=free |arxiv=2303.16229}}{{Cite web|url=https://veradobos.webnode.page/research/habitable-zones/|title=Habitable zones :: Vera Dobos|website=veradobos.webnode.page}} Extreme ultraviolet (EUV) can cause atmospheric loss.
• Photosynthetic habitable zone: a zone where both long-term liquid water and oxygenic photosynthesis can occur.{{Cite journal|title=A New Definition of Exoplanet Habitability: Introducing the Photosynthetic Habitable Zone|first1=C.|last1=Hall|first2=P. C.|last2=Stancil|first3=J. P.|last3=Terry|first4=C. K.|last4=Ellison|date=May 1, 2023|journal=The Astrophysical Journal Letters|volume=948|issue=2|pages=L26|doi=10.3847/2041-8213/acccfb|doi-access=free |arxiv=2301.13836 |bibcode=2023ApJ...948L..26H }}
• Tropospheric habitable zone, or ozone habitable zone: a zone where the planet would have the correct amount of ozone needed for life. Inhaling too much ozone causes inflammation and irritation,{{Cite web|url=https://www.lung.org/clean-air/outdoors/what-makes-air-unhealthy/ozone|title=Ozone|first=American Lung|last=Association|website=www.lung.org}} whereas too little troposphere ozone would produce biochemical smog. On Earth, the troposphere ozone is part of the ground-level ozone protection. Tropospheric ozone is formed by the interaction of ultraviolet light with hydrocarbons and nitrogen oxides.{{Cite journal|title=A Limited Habitable Zone for Complex Life|first1=Edward W.|last1=Schwieterman|first2=Christopher T.|last2=Reinhard|first3=Stephanie L.|last3=Olson|first4=Chester E.|last4=Harman|first5=Timothy W.|last5=Lyons|date=June 10, 2019|journal=The Astrophysical Journal|volume=878|issue=1|pages=19|doi=10.3847/1538-4357/ab1d52|doi-access=free |arxiv=1902.04720 |bibcode=2019ApJ...878...19S }}{{Cite journal|title=Characterising the three-dimensional ozone distribution of a tidally locked Earth-like planet|first1=Elisavet|last1=Proedrou|first2=Klemens|last2=Hocke|date=June 1, 2016|journal=Earth, Planets and Space|volume=68|issue=1|pages=96|doi=10.1186/s40623-016-0461-x|doi-access=free |bibcode=2016EP&S...68...96P }}{{cite book |doi=10.1016/B978-0-12-823411-2.00003-7 |chapter=Methods of evaluation of the environmental impact on the life cycle |title=Sustainability Metrics and Indicators of Environmental Impact |date=2021 |last1=Jacob-Lopes |first1=Eduardo |last2=Zepka |first2=Leila Queiroz |last3=Deprá |first3=Mariany Costa |pages=29–70 |isbn=978-0-12-823411-2 }}
• Planet rotation rate habitable zone: the zone where a planet's rotation rate is best for life. If rotation is too slow, the day/night temperature difference is too great. The rotation rate also changes the planet's reflectivity{{clarify|date=February 2024}} and thus temperature. A fast rotation rate increases wind speed on the planet. The rotation rate affects the planet's clouds and their reflectivity. Slowing the rotation rate changes cloud distributions, cloud altitudes, and cloud opacities. These changes in the clouds changes the temperature of the planet. A high rotation rate also can cause continuous, very fast winds{{quantify|date=May 2024}} on the surface.{{cite journal |last1=Yang |first1=Jun |last2=Boué |first2=Gwenaël |last3=Fabrycky |first3=Daniel C. |last4=Abbot |first4=Dorian S. |title=Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate |journal=The Astrophysical Journal |date=25 April 2014 |volume=787 |issue=1 |pages=L2 |doi=10.1088/2041-8205/787/1/L2 |arxiv=1404.4992 |bibcode=2014ApJ...787L...2Y }}{{Cite web|url=https://phys.org/news/2014-08-rotation-planets-habitability.html|title=Rotation of planets influences habitability|website=phys.org}}{{cite conference |last1=Jansen |first1=T |date=March 2021 |title=Effects of Rotation Rate on the Habitability of Earth-like Planets using NASA's ROCKE-3D GCM |conference=AASTCS8, Habitable Worlds 2021 |bibcode=2021BAAS...53c0603J }}
• Planet rotation axis tilt habitable zone, or obliquity habitable zone: the region where a stable axial tilt for a planet's rotation is maintained.[http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/moonhab.html#c1 The Moon's Role in the Habitability of the Earth, Georgia State University Research] Earth's axis is tilted 23.5°; this gives seasons, providing snow and ice that can melt to provide water run off in the summer.[http://hyperphysics.phy-astr.gsu.edu/hbase/Solar/seasons.html#c1 Seasons, Georgia State University Research][http://hyperphysics.phy-astr.gsu.edu/hbase/eclip.html#c1 Ecliptic Plane, Georgia State University Research] Obliquity has a major impact on a planet's temperature, thus its habitable zone.[http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/orbtilt.html Axis Tilt is Critical for Life, Georgia State, astr.gsu.edu ]{{Cite web|url=https://www.sciencealert.com/an-axial-tilt-may-be-crucial-to-the-emergence-of-complex-life-in-the-universe|title=This One Planetary Feature May Be Crucial For The Rise of Complex Life in The Universe|first=Michelle|last=Starr|date=July 8, 2021|website=ScienceAlert}}{{Cite web|url=https://phys.org/news/2021-07-goldilocks-planets-tilt-complex-life.html|title=Goldilocks planets 'with a tilt' may develop more complex life|first=Goldschmidt|last=Conference|website=phys.org}}{{cite journal |last1=Jenkins |first1=Gregory S. |title=Global climate model high-obliquity solutions to the ancient climate puzzles of the Faint-Young Sun Paradox and low-altitude Proterozoic glaciation |journal=Journal of Geophysical Research: Atmospheres |date=27 March 2000 |volume=105 |issue=D6 |pages=7357–7370 |doi=10.1029/1999JD901125 |bibcode=2000JGR...105.7357J }}
• Tidal habitable zone. Planets too close to the star become tidally locked. The mass of the star and the distance from the star set the tidal habitable zone. A planet tidally locked has one side of the planet facing the star, this side would be very hot. The face away from the star would be well below freezing. A planet too close to the star will also have tidal heating from the star. Tidal heating can vary the planet's orbital eccentricity. Too far from the star and the planet will not receive enough solar heat.{{Cite journal|title=The Influence of Tidal Heating on the Habitability of Planets Orbiting White Dwarfs|first1=Juliette|last1=Becker|first2=Darryl Z.|last2=Seligman|first3=Fred C.|last3=Adams|first4=Marshall J.|last4=Styczinski|date=March 1, 2023|journal=The Astrophysical Journal Letters|volume=945|issue=2|pages=L24|doi=10.3847/2041-8213/acbe44|doi-access=free |arxiv=2303.02217 |bibcode=2023ApJ...945L..24B }}{{Cite web|url=http://eos.org/features/tidally-locked-and-loaded-with-questions|title=Tidally Locked and Loaded with Questions|first=Caroline|last=Hasler|date=February 17, 2022|website=Eos}}{{Cite web|url=https://www.sciencedaily.com/releases/2011/02/110224091735.htm|title=New conditions for life on other planets: Tidal effects change 'habitable zone' concept|website=ScienceDaily}}
• Astrosphere habitable zone: the zone in which a planet's astrosphere will be strong enough to protect the planet from the solar wind and cosmic rays. The astrosphere must be long lasting to protect the planet. Mars lost its water and most of its atmosphere after the losing its magnetic field and Mars carbonate catastrophe event.{{cite conference |last1=Airapetian |first1=Vladimir S. |date=May 2017 |title=Space Weather Affected Habitable Zones Around Active Stars |conference=AASTCS5 Radio Exploration of Planetary Habitability |bibcode=2017reph.conf10105A }}{{cite journal |last1=Smith |first1=David S. |last2=Scalo |first2=John M. |title=Habitable Zones Exposed: Astrosphere Collapse Frequency as a Function of Stellar Mass |journal=Astrobiology |date=September 2009 |volume=9 |issue=7 |pages=673–681 |doi=10.1089/ast.2009.0337 |pmid=19778278 |bibcode=2009AsBio...9..673S }} Star-Sun's solar wind is made of charged particles, including plasma, electrons, protons and alpha particles. The solar wind is different for each star. Earth's magnetic field is very large and has protected Earth since its formation.{{cite journal |last1=Lillis |first1=Robert J. |last2=Robbins |first2=Stuart |last3=Manga |first3=Michael |last4=Halekas |first4=Jasper S. |last5=Frey |first5=Herbert V. |title=Time history of the Martian dynamo from crater magnetic field analysis |journal=Journal of Geophysical Research: Planets |date=July 2013 |volume=118 |issue=7 |pages=1488–1511 |doi=10.1002/jgre.20105 |bibcode=2013JGRE..118.1488L }}{{cite journal |last1=Schubert |first1=G. |last2=Russell |first2=C. T. |last3=Moore |first3=W. B. |title=Timing of the Martian dynamo |journal=Nature |date=December 2000 |volume=408 |issue=6813 |pages=666–667 |doi=10.1038/35047163 |pmid=11130059 }}{{Cite journal |last1=Langlais |first1=Benoit |last2=Thébault |first2=Erwan |last3=Houliez |first3=Aymeric |last4=Purucker |first4=Michael E. |last5=Lillis |first5=Robert J. |date=2019 |title=A New Model of the Crustal Magnetic Field of Mars Using MGS and MAVEN |journal=Journal of Geophysical Research: Planets |language=en |volume=124 |issue=6 |pages=1542–1569 |doi=10.1029/2018JE005854 |issn=2169-9100 |pmc=8793354 |pmid=35096494|bibcode=2019JGRE..124.1542L }}
• Atmosphere electric field habitable zone: the place in which the ambipolar electric field is correct for the planet's electric field to help ions overcome gravity.{{Cite web|url=https://www.nasa.gov/humans-in-space/space-radiation-is-risky-business-for-the-human-body/|title=Space Radiation is Risky Business for the Human Body – NASA|date=September 19, 2017}}{{failed verification|date=August 2024}} The planet's ionosphere must be correct to protect against the loss of the atmosphere. This is addition to a strong magnetic field to protect against the solar wind stripping away the atmosphere and water into outer space.{{cite journal |last1=Collinson |first1=Glyn A. |last2=Frahm |first2=Rudy A. |last3=Glocer |first3=Alex |last4=Coates |first4=Andrew J. |last5=Grebowsky |first5=Joseph M. |last6=Barabash |first6=Stas |last7=Domagal-Goldman |first7=Shawn D. |last8=Fedorov |first8=Andrei |last9=Futaana |first9=Yoshifumi |last10=Gilbert |first10=Lin K. |last11=Khazanov |first11=George |last12=Nordheim |first12=Tom A. |last13=Mitchell |first13=David |last14=Moore |first14=Thomas E. |last15=Peterson |first15=William K. |last16=Winningham |first16=John D. |last17=Zhang |first17=Tielong L. |title=The electric wind of Venus: A global and persistent 'polar wind'-like ambipolar electric field sufficient for the direct escape of heavy ionospheric ions |journal=Geophysical Research Letters |date=28 June 2016 |volume=43 |issue=12 |pages=5926–5934 |doi=10.1002/2016GL068327 |bibcode=2016GeoRL..43.5926C |url=https://insu.hal.science/insu-03669491/file/Geophysical%20Research%20Letters%20-%202016%20-%20Collinson%20-%20The%20electric%20wind%20of%20Venus%20A%20global%20and%20persistent%20polar%20wind%20%25u2010like.pdf }}{{cite journal |last1=Collinson |first1=Glyn |last2=Mitchell |first2=David |last3=Glocer |first3=Alex |last4=Grebowsky |first4=Joseph |last5=Peterson |first5=W. K. |last6=Connerney |first6=Jack |last7=Andersson |first7=Laila |last8=Espley |first8=Jared |last9=Mazelle |first9=Christian |last10=Sauvaud |first10=Jean-André |last11=Fedorov |first11=Andrei |last12=Ma |first12=Yingjuan |last13=Bougher |first13=Steven |last14=Lillis |first14=Robert |last15=Ergun |first15=Robert |last16=Jakosky |first16=Bruce |title=Electric Mars: The first direct measurement of an upper limit for the Martian 'polar wind' electric potential |journal=Geophysical Research Letters |date=16 November 2015 |volume=42 |issue=21 |pages=9128–9134 |doi=10.1002/2015GL065084 |bibcode=2015GeoRL..42.9128C }}{{Cite web|url=https://www.ucl.ac.uk/news/2016/jun/strong-electric-wind-strips-planets-oceans-and-atmospheres|title=Strong 'electric wind' strips planets of oceans and atmospheres|date=June 20, 2016|website=UCL News}}
• Orbital eccentricity habitable zone: the zone in which planets maintain a nearly circular orbit. As orbits with eccentricity have the planets move in and out of the habitable zones.{{Cite web|url=https://exoplanets.nasa.gov/resources/99/eccentric-habitable-zones|title=Eccentric Habitable Zones|website=Exoplanet Exploration: Planets Beyond our Solar System}} In the solar system, the grand tack hypothesis proposes the theory of the unique placement of the gas giants, the solar system belts and the planets near circular orbits.{{cite web| last1=Zubritsky| first1=Elizabeth| title=Jupiter's Youthful Travels Redefined Solar System| url=https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html| publisher=NASA| accessdate=4 November 2015| archive-date=1 March 2017| archive-url=https://web.archive.org/web/20170301170530/https://www.nasa.gov/topics/solarsystem/features/young-jupiter.html| url-status=dead}}{{cite web| last1=Beatty| first1=Kelly| title=Our "New, Improved" Solar System| url=http://www.skyandtelescope.com/astronomy-news/our-new-improved-solar-system/| work=Sky & Telescope| date=16 October 2010| accessdate=4 November 2015}}{{cite web| last1=Sanders| first1=Ray| title=How Did Jupiter Shape Our Solar System?| url=http://www.universetoday.com/88374/how-did-jupiter-shape-our-solar-system/| work=Universe Today| date=23 August 2011| accessdate=4 November 2015}}
• Coupled planet-moon - Magnetosphere habitable zone: the zone that planet's moon and the planet's core produce a strong magnetosphere, magnetic field to protect against the solar wind stripping away the planet's atmosphere and water into outer space. Just as Mars had a magnetic field for a short time. Earth's Moon had a large magnetosphere for several hundred million years after its formation, as proposed in a 2020 study by Saied Mighani. The Moon's magnetosphere would have given added protection of Earth's atmosphere as the early Sun was not as stable as it today. In 2020, James Green modeled the coupled planet-moon-magnetosphere habitable zone. The modeling showed a coupled planet–moon magnetosphere that would give planet the protection from stellar wind in the early Solar System. In the case of Earth, the Moon was closer to Earth in the early formation of the solar system, giving added protection. This protection was needed then as the Sun was less stable.{{cite journal |last1=See |first1=V. |last2=Jardine |first2=M. |last3=Vidotto |first3=A. A. |last4=Petit |first4=P. |last5=Marsden |first5=S. C. |last6=Jeffers |first6=S. V. |last7=do Nascimento |first7=J. D. |title=The effects of stellar winds on the magnetospheres and potential habitability of exoplanets |journal=Astronomy & Astrophysics |date=October 2014 |volume=570 |pages=A99 |doi=10.1051/0004-6361/201424323 |arxiv=1409.1237 |bibcode=2014A&A...570A..99S }}
• Pressure-dependent habitable zone: the zone in which planets may have the correct atmospheric pressure to have liquid surface water. With a low atmospheric pressure, the temperature at which water boils is much lower, and at pressures below that of the triple point, liquid water cannot exist.{{Cite web|url=https://wwwuser.oats.inaf.it/astrobiology/planhab/|title=Planetary Habitability page of the Trieste Astrobiology Group|website=wwwuser.oats.inaf.it}}{{cite journal |last1=Vladilo |first1=Giovanni |last2=Murante |first2=Giuseppe |last3=Silva |first3=Laura |last4=Provenzale |first4=Antonello |last5=Ferri |first5=Gaia |last6=Ragazzini |first6=Gregorio |title=The Habitable Zone of Earth-Like Planets with Different Levels of Atmospheric Pressure |journal=The Astrophysical Journal |date=25 March 2013 |volume=767 |issue=1 |pages=65 |doi=10.1088/0004-637x/767/1/65 |arxiv=1302.4566 |bibcode=2013ApJ...767...65V }} The average surface pressure on Mars today is close to that of the triple point of water; thus, liquid water cannot exist there.{{Cite web|url=https://mars.nasa.gov/comets/|title=Mars & Comets – NASA|website=mars.nasa.gov}}{{Cite journal|title=Stability of the Liquid Water Phase on Mars: A Thermodynamic Analysis Considering Martian Atmospheric Conditions and Perchlorate Brine Solutions|first1=C. P. Reghunadhan|last1=Nair|first2=Vibhu|last2=Unnikrishnan|date=April 18, 2020|journal=ACS Omega|volume=5|issue=16|pages=9391–9397|doi=10.1021/acsomega.0c00444|pmid=32363291|pmc=7191838}} Planets with high-pressure atmospheres may have liquid surface water, but life forms would have difficulty with respiratory systems at high-pressure{{quantify|date=May 2024}} atmospheres.{{Cite web|url=https://www.medicinenet.com/how_does_barometric_pressure_affect_humans/article.htm|title=How Does Barometric Pressure Affect Humans?|website=MedicineNet}}{{cite book |last1=Tarver |first1=William J. |last2=Volner |first2=Keith |last3=Cooper |first3=Jeffrey S. |title=StatPearls |date=2024 |publisher=StatPearls Publishing |chapter-url=http://www.ncbi.nlm.nih.gov/books/NBK470190/ |chapter=Aerospace Pressure Effects |pmid=29262037 }}
• Galactic habitable zone (GHZ): The GHZ, also called the Galactic Goldilocks zone, is the place in a galaxy in which heavy elements needed for a rocky planet and life are present, but also a place where strong cosmic rays will not kill life and strip the atmosphere off the planet. The term Goldilocks zone is used, as it is a fine balance between the two sites (heavy element and strong cosmic rays). Galactic habitable zone is the place a planet will have the needed parameters to support life. Not all galaxies are able to support life.{{cite news |last1=Cho |first1=Adrian |title=Complex life may be possible in only 10% of all galaxies |url=https://www.science.org/content/article/complex-life-may-be-possible-only-10-all-galaxies |work=Science News |date=24 November 2014 }} In many galaxies, life-killing events such as gamma-ray bursts can occur. About 90% of galaxies have long and frequent gamma ray bursts, thus no life. Cosmic rays pose a threat to life. Galaxies with many stars too close together or without any dust protection also are not hospitable for life. Irregular galaxies and other small galaxies do not have enough heavy elements. Elliptical galaxies are full of lethal radiation and lack heavy elements. Large spiral galaxies, like the Milky Way, have the heavy element needs for life at its center and out to about half distance from center bar.{{Cite web|url=https://www.discovermagazine.com/the-sciences/which-galaxies-are-best-suited-for-the-evolution-of-alien-life|title=Which Galaxies are Best Suited for the Evolution of Alien Life?|website=Discover Magazine}} Not all large spiral galaxies are the same, spiral galaxies with too much active star formation can kill the galaxy and life.{{Cite web|url=https://brighterworld.mcmaster.ca/articles/whats-killing-galaxies-large-survey-reveals-how-star-formation-is-shut-down-in-extreme-regions-of-the-universe/|title=What's killing galaxies? Large survey reveals how star formation is shut down in extreme regions of the Universe}}{{Cite web|url=https://nrc.canada.ca/en/stories/whats-killing-galaxies-large-survey-reveals-how-star-formation-shut-down-extreme-regions-universe|title=What's killing galaxies? Large survey reveals how star formation is shut down in extreme regions of the Universe|first=National Research Council|last=Canada|date=November 2, 2021|website=nrc.canada.ca}} Too little star formation and the spiral arms will collapse.{{Cite web|url=https://www.sciencedaily.com/releases/2020/05/200501120104.htm|title=New study examines which galaxies are best for intelligent life|website=ScienceDaily}} Not all spiral galaxies have the correct galactic ram pressure stripping parameters; too much ram pressure can deplete the galaxy of gas and thus end star formation. The Milky Way is a barred spiral galaxy, the bar is important to star formation and metallicity of the galaxy's stars and planets. Barred spiral galaxy, must have stable arms with the just right star formation. Bars galaxies are in about 65% of spiral galaxies, but most have too much star formation.{{cite journal |last1=Vera |first1=Matias |last2=Alonso |first2=Sol |last3=Coldwell |first3=Georgina |title=Effect of bars on the galaxy properties |journal=Astronomy & Astrophysics |date=November 2016 |volume=595 |pages=A63 |doi=10.1051/0004-6361/201628750 |arxiv=1607.08643 |bibcode=2016A&A...595A..63V }} Peculiar galaxies lack stable spiral arms,{{cite journal |last1=Nairn |first1=A. |last2=Lahav |first2=O. |title=What is a peculiar galaxy? |journal=Monthly Notices of the Royal Astronomical Society |date=21 April 1997 |volume=286 |issue=4 |pages=969–978 |doi=10.1093/mnras/286.4.969 |doi-access=free |arxiv=astro-ph/9607113 }} while irregular galaxies contain too many new stars and lack heavy elements.{{Cite web|url=https://ned.ipac.caltech.edu/level5/Hunter/Hunter1.html|title=Star Formation in Irregular Galaxies|website=ned.ipac.caltech.edu}}{{Cite web|url=https://www.letstalkstars.com/irregular-galaxy-a-unique-collections-of-stars/|title=Irregular Galaxy: A Unique Collections of Stars – Let's Talk Stars|date=February 17, 2023|website=www.letstalkstars.com}} Unbarred spiral galaxy, do not correct star formation and metallicity for a galactic goldilocks zone.{{cite journal |last1=Martel |first1=Hugo |last2=Kawata |first2=Daisuke |last3=Ellison |first3=Sara L. |title=The connection between star formation and metallicity evolution in barred spiral galaxies |journal=Monthly Notices of the Royal Astronomical Society |date=21 May 2013 |volume=431 |issue=3 |pages=2560–2575 |doi=10.1093/mnras/stt354 |doi-access=free |arxiv=1302.6211 }} For long term life on a planet, the spiral arms must be stable for a long period of time, as in the Milky Way. The spiral arms must not be too close to each other, or there will be too much ultraviolet radiation. If the planet moves into or across a spiral arm the orbits of the planets could change, from gravitational disturbances. Movement across a spiral arms also would cause deadly asteroid impacts and high radiation.{{Cite journal|title=On the Connection between Spiral Arm Pitch Angle and Galaxy Properties|first1=Si-Yue|last1=Yu|first2=Luis C.|last2=Ho|date=January 31, 2019|journal=The Astrophysical Journal|volume=871|issue=2|pages=194|doi=10.3847/1538-4357/aaf895|doi-access=free |arxiv=1812.06010 |bibcode=2019ApJ...871..194Y }}{{Cite web|url=https://www.scientificamerican.com/article/what-process-creates-and/|title=What process creates and maintains the beautiful spiral arms around spiral galaxies? I've been told that density waves are responsible—so where do the density waves come from?|website=Scientific American}}{{Cite web|url=https://www.scientificamerican.com/article/the-milky-ways-spiral-arms-may-have-carved-earths-continents/|title=The Milky Way's Spiral Arms May Have Carved Earth's Continents|first=Shannon|last=Hall|website=Scientific American}} The planet must be in the correct place in the spiral galaxy: near the galactic center, radiation and gravitational forces are too great for life, whereas the outskirts of a spiral galaxy are metal-poor. The Sun in 28,000 light years from the center bar, in the galactic Goldilocks zone. At this distance, the Sun revolves in the galaxy at the same rate as the spiral-arm rotation, thus minimizing arm crossings.{{Cite web|url=https://www.astro.umd.edu/~miller/teaching/honr/suppl02.pdf|title=The origin of elements, by Miller, astro.umd.edu}}{{Cite web|url=https://medium.com/predict/why-different-types-of-galaxies-may-affect-the-development-of-life-32d705e0023b|title=Why Different Types of Galaxies May Affect the Development of Life|first=Trevor|last=Mahoney|date=July 13, 2020}}
• Supergalactic habitable zone: a place in a supercluster of galaxies that can provide for habitability of planets. The supergalactic habitable zone takes into account events in galaxies that can end habitability not only in a galaxy, but all galaxies nearby, such as galaxies merging, active galactic nucleus, starburst galaxy, supermassive black holes and merging black holes, all which output intense radiation. The supergalactic habitable zone also takes into account the abundance of various chemical elements in the galaxy, as not all galaxies or regions within have all the needed elements for life.{{cite conference |last1=Mason |first1=Paul |date=January 2018 |title=The Supergalactic Habitable Zone |publisher=American Astronomical Society |conference=AAS Meeting #231, id. 401.04 |bibcode=2018AAS...23140104M }}{{cite conference |last1=Mason |first1=P. A. |last2=Biermann |first2=P. L. |date=November 2017 |title=The Large-Scale Structure of Habitability in the Universe |conference=Habitable Worlds 2017: A System Science Workshop |bibcode=2017LPICo2042.4149M }}{{cite conference |last1=Mason |first1=Paul |date=January 2019 |title=The dawn of habitable conditions for complex life in the Universe |publisher=American Astronomical Society |conference=AAS Meeting #233, id.432.06 |bibcode=2019AAS...23343206M }}{{Cite web|url=https://cosmos.asu.edu/publication/cosmic-blueprint|title=The Cosmic Blueprint | Paul Davies|website=cosmos.asu.edu}}
• Habitable zone for complex life (HZCL): the place that all the life habitable zones overlap for a long period of time, as in the Solar System.{{Cite web|url=https://news.ucr.edu/articles/2019/06/10/new-study-dramatically-narrows-search-advanced-life-universe|title=New study dramatically narrows the search for advanced life in the universe | UCR News | UC Riverside|website=news.ucr.edu}} The list of habitable zones for complex life has grown longer with increasing understanding of the Universe, galaxies, and the Solar System.Gribbin, John (2011). Alone in the Universe: Why our planet is unique. Wiley.{{pn|date=January 2025}}{{cite book |doi=10.1007/b97646 |title=Rare Earth |date=2000 |last1=Ward |first1=Peter D. |last2=Brownlee |first2=Donald |isbn=978-0-387-95289-5 }}{{pn|date=January 2025}}Gonzales, Guillermo; Richards, Jay W (2004). The Privileged Planet. Regnery Publishing, Inc.{{Cite web|url=https://davidwaltham.com/lucky-planet/|title=Lucky Planet - Why Earth is Exceptional & Life In The Universe}} Complex life is normally defined as eukaryote life forms, including all animals, plants, fungi, and most unicellular organisms. Simple life forms are normally defined as prokaryotes.{{Cite web|url=https://royalsociety.org/blog/2020/06/the-origin-and-rise-of-complex-life/|title=The origin and rise of complex life | Royal Society|website=royalsociety.org|date=7 December 2022 }}

Some factors that depend on planetary distance and may limit complex aerobic life have not been given zone names. These include:

• Milankovitch cycle The Milankovitch cycle and ice age have been key is shaping Earth.{{Cite web|url=https://www.usgs.gov/special-topics/water-science-school/science/ice-snow-and-glaciers-and-water-cycle|title=Ice, Snow, and Glaciers and the Water Cycle | U.S. Geological Survey|website=www.usgs.gov}}{{Cite journal|title=Exo-Milankovitch Cycles. I. Orbits and Rotation States|first1=Russell|last1=Deitrick|first2=Rory|last2=Barnes|first3=Thomas R.|last3=Quinn|first4=John|last4=Armstrong|first5=Benjamin|last5=Charnay|first6=Caitlyn|last6=Wilhelm|date=January 16, 2018|journal=The Astronomical Journal|volume=155|issue=2|pages=60|doi=10.3847/1538-3881/aaa301|doi-access=free |arxiv=1712.10060 |bibcode=2018AJ....155...60D }} Life on Earth today is using water melting from the last ice age. The ice ages cannot be too long or too cold for life to survive. Milankovitch cycle has an impact on the planet's obliquity also.{{Cite journal|title=Exo-Milankovitch Cycles. II. Climates of G-dwarf Planets in Dynamically Hot Systems|first1=Russell|last1=Deitrick|first2=Rory|last2=Barnes|first3=Cecilia|last3=Bitz|first4=David|last4=Fleming|first5=Benjamin|last5=Charnay|first6=Victoria|last6=Meadows|first7=Caitlyn|last7=Wilhelm|first8=John|last8=Armstrong|first9=Thomas R.|last9=Quinn|date=June 1, 2018|journal=The Astronomical Journal|volume=155|issue=6|pages=266|doi=10.3847/1538-3881/aac214|doi-access=free |arxiv=1805.00283 |bibcode=2018AJ....155..266D }}{{Cite web|url=https://www.space.com/milankovitch-cycles|title=Milankovitch cycles: What are they and how do they affect Earth?|author1=Tereza Pultarova|date=June 14, 2022|website=Space.com}}{{Cite web|url=https://climate.nasa.gov/news/2948/milankovitch-orbital-cycles-and-their-role-in-earths-climate|title=Milankovitch (Orbital) Cycles and Their Role in Earth's Climate|first=By Alan Buis, NASA's Jet Propulsion|last=Laboratory|website=Climate Change: Vital Signs of the Planet}}

{{main|Life|Carbon-based life}}

Life on Earth is carbon-based. However, some theories suggest that life could be based on other elements in the periodic table.{{Cite web|url=http://www.fao.org/forestry/17111/en/|title=Knowledge reference for national forest assessments – modeling for estimation and monitoring|website=www.fao.org|access-date=Feb 20, 2019|archive-date=January 13, 2020|archive-url=https://web.archive.org/web/20200113113656/http://www.fao.org/forestry/17111/en/|url-status=dead}} Other elements proposed have been silicon, boron, arsenic, ammonia, methane and others. As more research has been done on life on Earth, it has been found that only carbon's organic molecules have the complexity and stability to form life.{{cite journal |last1=Allison |first1=Steven D. |last2=Vitousek |first2=Peter M. |title=Responses of extracellular enzymes to simple and complex nutrient inputs |journal=Soil Biology and Biochemistry |date=May 2005 |volume=37 |issue=5 |pages=937–944 |doi=10.1016/j.soilbio.2004.09.014 |bibcode=2005SBiBi..37..937A }}{{cite web | url = http://biocab.org/Astrobiology.html | title = Astrobiology | access-date = 2011-01-17 | date = September 26, 2006 | publisher = Biology Cabinet | archive-date = 2010-12-12 | archive-url = https://web.archive.org/web/20101212184044/http://biocab.org/Astrobiology.html | url-status = dead }}{{cite web |url=http://library.thinkquest.org/C003763/index.php?page=interview07 |title=Polycyclic Aromatic Hydrocarbons: An Interview With Dr. Farid Salama |access-date=2008-10-20 |year=2000 |work=Astrobiology magazine |url-status=dead |archive-url=https://web.archive.org/web/20080620075201/http://library.thinkquest.org/C003763/index.php?page=interview07 |archive-date=2008-06-20 }} Carbon properties allows for complex chemical bonding that produces covalent bonds needed for organic chemistry. Carbon molecules are lightweight and relatively small in size. Carbon's ability to bond to oxygen, hydrogen, nitrogen, phosphorus, and sulfur (called CHNOPS) is key to life.{{cite journal | last1=Lipkus | first1=Alan H. | last2=Yuan | first2=Qiong | last3=Lucas | first3=Karen A. | last4=Funk | first4=Susan A. | last5=Bartelt | first5=William F. | last6=Schenck | first6=Roger J. | last7=Trippe | first7=Anthony J. |display-authors=3 | title=Structural Diversity of Organic Chemistry. A Scaffold Analysis of the CAS Registry | journal=The Journal of Organic Chemistry | publisher=American Chemical Society (ACS) | volume=73 | issue=12 | date=2008 | doi=10.1021/jo8001276 | pages=4443–4451| pmid=18505297 | doi-access=free }}

{{Cite journal|url=https://opentextbc.ca/biology/chapter/2-3-biological-molecules/|title=2.3 Biological Molecules|first1=Charles|last1=Molnar|first2=Jane|last2=Gair|date=May 14, 2015|via=opentextbc.ca|journal=Introduction to the Chemistry of Life}}{{cite web |title=CHNOPS: The Six Most Abundant Elements of Life |url=http://www.phschool.com/science/biology_place/biocoach/biokit/chnops.html |last=Education |year=2010 |work=Pearson Education |publisher=Pearson BioCoach |access-date=2010-12-10 |quote=Most biological molecules are made from covalent combinations of six important elements, whose chemical symbols are CHNOPS. ... Although more than 25 types of elements can be found in biomolecules, six elements are most common. These are called the CHNOPS elements; the letters stand for the chemical abbreviations of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. |archive-date=27 July 2017 |archive-url=https://web.archive.org/web/20170727200948/http://www.phschool.com/science/biology_place/biocoach/biokit/chnops.html |url-status=live }}

Photosynthesis en.svg|Photosynthetic habitable zone has the need parameters for photosynthesis in plants. The carbohydrates produced are stored in or used by the plant. Photosynthesis is foundation of food on Earth

AtmosphCirc2.svg|Troposphere habitable (Ozone habitable) zone as the correct atmospheric circulation and ozone for life. The Three Cell Model of the circulation of the planetary atmosphere of the Earth, of which the troposphere is the lowest layer.

File:Animation of Orbital eccentricity.gif|Orbital eccentricity habitable zone is low enough orbital eccentricity to support life. Elliptic orbit by eccentricity
{{legend2| OrangeRed |0.0}}{{·}}{{legend2|Lime|0.2}}{{·}}{{legend2|Cyan|0.4}}{{·}}{{legend2|Gold|0.6}}{{·}}{{legend2|hotpink|0.8}}

{{Commons category|Habitable zone}}

• Exoplanet orbital and physical parameters
• Habitability of natural satellites – liquid water on a moon
• Habitability of yellow dwarf systems – liquid water on yellow dwarf star
• Habitability of red dwarf systems – liquid water on red dwarf star
• Planetary habitability in the Solar System – liquid water in our Solar System
• Habitability of binary star systems – liquid water on binary stars
• Habitability of F-type main-sequence star systems – liquid water on planets orbiting F-type stars
• Superhabitable planet – a hypothetical exoplanet

{{reflist}}

{{Exoplanet}}

{{Exoplanet search projects}}

{{Astrobiology}}

Category:Planetary habitability

Category:Astronomical hypotheses

Category:Extraterrestrial life

Category:Extraterrestrial water