Goldilocks planet: Difference between revisions - Wikipedia
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#REDIRECT [[Habitable zone]]
{{About||the planet initially nicknamed "Goldilocks"|70 Virginis b|other uses|Goldilocks (disambiguation)}}
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A "'''Goldilocks planet'''" is a planet that falls within a [[star]]'s [[habitable zone]], and the name is often specifically used for planets close to the size of [[Earth]].<ref name="Muir">{{cite news | first = Hazel | last = Muir | url = http://www.newscientist.com/article/dn11710 | title = 'Goldilocks' planet may be just right for life| work = New Scientist | date = 25 April 2007 | accessdate = 2009-04-02}}</ref><ref name="BBC-R4">{{cite web | date = 31 August 2005 | url = http://www.bbc.co.uk/radio4/science/goldilocksplanet.shtml | title = The Goldilocks Planet | publisher = [[BBC Radio 4]] | accessdate = 2009-04-02}}</ref> The name comes from the children's [[fairy tale]] of ''[[Goldilocks and the Three Bears]]'', in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is "just right". Likewise, a planet following this [[Goldilocks Principle]] is one that is neither too close nor too far from a star to rule out liquid water on its surface and thus [[life]] (as humans understand it) on the planet. However, planets within a habitable zone that are unlikely to host life (e.g., [[gas giant]]s) may also be called Goldilocks planets. The best example of a Goldilocks planet is the Earth itself.
Goldilocks planets are of key interest to researchers looking either for existing (and possibly intelligent) life or for future homes for the [[human race]]. The [[Drake equation]], which attempts to estimate the likelihood of non-terrestrial intelligent life, incorporates a factor (''n<sub>e</sub>'') for the average number of life-supporting planets in a star system with planets. The discovery of [[Extrasolar planet|extrasolar]] Goldilocks planets helps to refine estimates for this figure. Very low estimates would contribute to the [[Rare Earth hypothesis]], which posits that a series of extremely unlikely events and conditions led to the rise of life on Earth. High estimates would reinforce the [[Nicolaus Copernicus|Copernican]] [[mediocrity principle]], in that large numbers of Goldilocks planets would imply that Earth is not especially exceptional.
Finding Earth-sized Goldilocks planets is a key part of the [[Kepler Mission]], which uses a [[space telescope]] (launched on 7 March 2009 UTC) to survey and compile the characteristics of habitable-zone planets.<ref name="Koch-Gould">{{cite web | author = David Koch; Alan Gould | title = Overview of the Kepler Mission | url = http://www.kepler.arc.nasa.gov/about | publisher = NASA |date = March 2009| accessdate = 2009-04-02}} {{Dead link|date=October 2010|bot=H3llBot}}</ref>
==Potential examples==
Although the extrasolar planet [[70 Virginis b]] was initially nicknamed "Goldilocks" because it was thought to be within the star's [[habitable zone]], it is now believed to be closer to its sun making it far too warm to be "just right" for life, thus it is not a Goldilocks planet.<ref name="Extrasolar.net">{{cite web | url = http://www.extrasolar.net/planettour.asp?PlanetID=22 | title = 70 Virginis b | work = Extrasolar Planet Guide | publisher = Extrasolar.net | accessdate = 2009-04-02}}</ref>
The [[Gliese 581]] system has a set of slightly oversized [[terrestrial planets]] mirroring our own solar system's. It is currently believed that the third planet, [[Gliese 581 c|planet c]], is analogous to Venus's position (slightly too close), the fourth [[Gliese 581 g|planet g]] (unconfirmed as of Oct. 2010) to the Earth/Goldilocks position, and the fifth [[Gliese 581 d|planet d]] to the Mars position. Planet d may be too cold, but unlike Mars, it is several times more massive than Earth and may have a dense atmosphere to retain heat. One caveat with this system is that it orbits a [[red dwarf]], probably resulting in most of the issues regarding [[habitability of red dwarf systems]], such as all the planets likely being [[tidally locked]] to the star.
More recently, on February 2, 2011, the [[Kepler_(spacecraft)|Kepler Space Observatory Mission team]] released a list of 1,235 extrasolar planet candidates, including 54 that may be in the "[[habitable zone]]."<ref>{{cite web |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=98 |title=NASA Finds Earth-size Planet Candidates in Habitable Zone, Six Planet System |date=2011-02-02 |publisher=[http://www.nasa.gov/ NASA] |accessdate=2011-02-02 }}</ref><ref Name="Borenstein">{{cite news |first=Seth |last=Borenstein |title=NASA spots scores of potentially livable worlds |work=MSNBC News |date=2 February 2011 |url=http://msnbc.msn.com/id/41387915/ns/technology_and_science-space |accessdate=2011-02-02 }}</ref><ref name="Overbye">{{cite news |first=Dennis |last=Overbye |title=Kepler Planet Hunter Finds 1,200 Possibilities |work=New York Times |date=2 February 2011 |url=http://www.nytimes.com/2011/02/03/science/03planet.html |accessdate=2011-02-02 }}</ref> Based on these latest Kepler findings, astronomer [[Seth Shostak]] estimates that "within a thousand light-years of Earth" there are "at least 30,000 of these habitable worlds."<ref name="Shostak">{{cite news |first=Seth |last=Shostak |title=A Bucketful of Worlds |work=[[Huffington Post]] |date=3 February 2011 |url=http://www.huffingtonpost.com/seth-shostak/a-bucketful-of-worlds_b_817921.html |accessdate=2011-02-03 }}</ref>
{| class="wikitable"
|-
! Exoplanet
! Year of discovery
! Notes
|-
| [[70 Virginis b]]
| style="text-align: center;" | 1996
| Later confirmed '''not''' to be a Goldilocks planet.
|-
| [[Gliese 581 d]]
| style="text-align: center;" | 2007
| Found to be in its sun's habitable zone in 2009.
|-
| [[Gliese 581 g]] (unconfirmed)
| style="text-align: center;" | 2010
| Most Earth-like Goldilocks planet found to date; probably tidally locked.
|-
|}
== References ==
{{reflist}}
==External links==
* {{cite web |url=http://arxiv.org/abs/astro-ph/0212551 |title=Characterizing Earth-like planets with Terrestrial Planet Finder |last=Seager |first=Sara |work=arXiv |accessdate=2010-03-31}}
* {{cite web |url=http://science.nasa.gov/headlines/y2009/20feb_kepler.htm |title=Kepler Mission to Hunt for Earth-like Planets |date=February 20, 2009 |work=Science@NASA |accessdate=2010-03-31}}
* {{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=Simmonsa et al |work=New Worlds |accessdate=2010-03-31}}
* {{cite web |url=http://www.springerlink.com/content/c18m4q1487204x85/fulltext.pdf |title=Darwin—an experimental astronomy mission to search for extrasolar planets |author=Cockell et al. |work=Springerlink |year=2009 | volume=23 |pages=435–461 |doi=10.1007/s10686-008-9121-x}}
* {{cite web |url=http://www.universetoday.com/2009/03/19/jwst-will-provide-capability-to-search-for-biomarkers-on-earth-like-worlds/ |title=JWST Will Provide Capability to Search for Biomarkers on Earth-like Worlds |work=Universe Today |last=Atkinson |first=Nancy |date=March 19, 2009 |accessdate=2010-03-31}} {{Dead link|date=October 2010|bot=H3llBot}}
* {{cite web |url=http://planetquest.jpl.nasa.gov/missions/simPQMission.cfm |title=PlanetQuest: Mission |work=SIM PlanetQuest |accessdate=2010-03-31}}
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