Difference between revisions 796678400 and 797251635 on enwiki

{{redirect|Goldilocks Zone|the more general principle|Goldilocks principle|the planet first called "Goldilocks"|70 Virginis b}}
{{redirect|Habitable zone|the galactic zone|Galactic habitable zone}}
{{redirect|Comfort zone (astronomy)|other uses|Comfort zone (disambiguation)}}
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In red dwarf systems, gigantic [[stellar flare]]s which could double a star's brightness in minutes<ref>{{cite web |first=Ken| last=Croswell| url=http
s://www.newscientist.com/article/mg16922754.200-red-willing-and-able.html |title=Red, willing and able |accessdate=August 5, 2007|date=January 27, 2001 |format= [http://www.kencroswell.com/reddwarflife.html Full reprint] |magazine=[[New Scientist]]}}</ref> and huge [[starspot]]s which can cover 20% of the star's surface area,<ref name=alekseev-2002>{{Cite journal | last1 = Alekseev | first1 = I. Y.| last2 = Kozlova | first2 = O. V.| title = Starspots and active regions on the emission red dw(contracted; show full)e=November 7, 2005 |accessdate=January 19, 2013}}</ref><ref>{{cite web|title=AstronomyCast episode 40: American Astronomical Society Meeting, May 2007 |work=Universe Today |last1=Cain |first1=Fraser |last2=Gay |first2=Pamela |authorlink2=Pamela L. Gay |url=http://media-c02m01.libsyn.com/podcasts/c50d001e8872db18d96cd44a73adccdc/46762eec/astronomycast/AstroCast-070611.mp3 |date=2007 |accessdate=2007-06-17 }}{{dead link|date=November 2016 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>


Once a star has evolved sufficiently to become a red giant, its circumstellar habitable zone will change dramatically from its main-sequence size.<ref>{{cite web| url=http://www.astrobio.net/topic/solar-system/sun/living-in-a-dying-solar-system-part-1/ |title=Living in a Dying Solar System, Part 1| publisher=Astrobiology| language=English|author=Ray Villard|date=27 July 2009|accessdate=8 April 2016}}</ref> For example, the Sun is expected to engulf the previously-habitable Earth as a red giant.(contracted; show full)t;/ref><ref name="planetmodels">{{cite journal |last1= Kuchner |first1= Seager |first2=M.|last2=Hier-Majumder | first3=C. A.|last3=Militzer |date=2007 |title=Mass–radius relationships for solid exoplanets |journal=The Astrophysical Journal |volume=669 |issue= 2|pages=1279–1297 |url=http://www.iop.org/EJ/abstract/0004-637X/669/2/1279/ |doi=10.1086/521346 |bibcode=2007ApJ...669.1279S|arxiv = 0707.2895 }}</ref> or [[Kepler-22b]] may be.<ref name=vastag-2011>{{cite news |url=http
s://www.washingtonpost.com/national/health-science/newest-alien-planet-is-just-the-right-temperature-for-life/2011/12/05/gIQAPk1vWO_story.html |title=Newest alien planet is just the right temperature for life |work=The Washington Post |date=December 5, 2011 |accessdate=April 27, 2013 |author=Vastag, Brian}}</ref>

(contracted; show full)nd its [[red dwarf]] star. Among [[List of nearest terrestrial exoplanet candidates|nearest terrestrial exoplanet candidates]], [[Tau Ceti e]] is 11.9 light-years away. It is in the inner edge of its solar system's habitable zone, giving it an estimated average surface temperature of {{convert|68|C}}.<ref>{{cite book| title=The Mystery of the Seven Spheres: How Homo sapiens will Conquer Space| author=Giovanni F. Bignami| publisher=Springer| year=2015| ISBN=9783319170046}}, [https://books.google.
secom/books?id=crvpCQAAQBAJ&pg=PA110 Page 110]</ref>

Studies that have attempted to estimate the number of terrestrial planets within the circumstellar habitable zone tend to reflect the availability of scientific data. A 2013 study by Ravi Kumar Kopparapu put ''η<sub>e</sub>'', the fraction of stars with planets in the CHZ, at 0.48,<ref name="kopparapu-2013" /> meaning that there may be roughly 95–180 billion habitable planets in the Milky Way.<ref n(contracted; show full)Enrico |author4= Jones, Hugh R. R. |author5= Reiners, Ansgar |author6= Rivera, Eugenio J. |author7= Vogt, Steven S. |author8= Butler, Paul |journal=Astronomy and Astrophysics |arxiv=1211.1617|doi = 10.1051/0004-6361/201220268 |date= 2012 |volume= 549 |pages= A48 |bibcode = 2013A&A...549A..48T }}</ref> In December 2012, [[Tau Ceti e]] and [[Tau Ceti f]] were found in the circumstellar habitable zone of [[Tau Ceti]], a Sun-like star 12 light years away.<ref name=aron-2012>{{cite web |url=http
s://www.newscientist.com/article/dn23021-nearby-tau-ceti-may-host-two-planets-suited-to-life.html |title=Nearby Tau Ceti may host two planets suited to life |publisher=Reed Business Information |work=New Scientist |date=December 19, 2012 |accessdate=April 1, 2013 |author=Aron, Jacob}}</ref> Although more massive than Earth, they are among the least massive planets found to date orbiting in the habitable zone;<ref name="tuomi-2013">{{Cite journal | last1 = Tuomi | first1 = M. | last2 = J(contracted; show full) 2012 |publisher=Skymania News |accessdate=27 April 2012 }}</ref><ref name="EGU-20120426">{{cite web |last1=de Vera |first1=J.-P. |last2=Kohler |first2=Ulrich |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |date=26 April 2012 |publisher=[[European Geosciences Union]] |accessdate=27 April 2012 |deadurl=yes |archiveurl=http
s://www.webcitation.org/68GROCilv?url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |archivedate=8 June 2012 |df= }}</ref><ref name="Onofride Vera2015">{{cite journal|last1=Onofri|first1=Silvano|last2=de Vera|first2=Jean-Pierre|last3=Zucconi|first3=Laura|last4=Selbmann|first4=Laura|last5=Scalzi|first5=Giuliano|last6=Venkateswaran|first6=Kasthuri J.|last7=Rabbow|first7=Elke|last8=de la Torre|first8=Rosa|last9=Horneck|first9=Gerda|title=Survival of Antarc(contracted; show full)
*{{cite web |url=http://www.planetarybiology.com/exoexplorer_planets/| title=Exoplanets in relation to host star's current habitable zone |work=www.planetarybiology.com}}
*{{cite web |url=http://www.planetarybiology.com/exoexplorer/|title=exoExplorer: a free Windows application for visualizing exoplanet environments in 3D |work=www.planetarybiology.com}}

*{{cite web |url=https://www.newscientist.com/article/mg20026831.600-why-the-universe-may-be-teeming-with-aliens.html?full=true |title=Why the universe may be teeming with aliens |date=November 19, 2009 |last=Shiga |first=David |magazine=NewScientist}}
*{{cite web |url=http://newworlds.colorado.edu/info/documents/NewWorldsObserver2004.pdf |title=The New Worlds Observer: a mission for high-resolution spectroscopy of extra-solar terrestrial planets |author=Simmons |work=New Worlds|display-authors=etal}}
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