Editing Habitable zone (section)

===Early findings===
{{Category see also|Giant planets in the habitable zone}}
The first discoveries of extrasolar planets in the HZ occurred just a few years after the first extrasolar planets were discovered. However, these early detections were all gas giant-sized, and many were in eccentric orbits. Despite this, studies indicate the possibility of large, Earth-like moons around these planets supporting liquid water.<ref>{{cite journal|author1=Williams, D. |author2=Pollard, D. | title=Earth-like worlds on eccentric orbits: excursions beyond the habitable zone| journal=International Journal of Astrobiology| volume=1|issue=1|pages=61–69|date=2002| doi=10.1017/S1473550402001064|bibcode = 2002IJAsB...1...61W |s2cid=37593615 }}</ref>
One of the first discoveries was [[70 Virginis b]], a gas giant initially nicknamed "Goldilocks" due to it being neither "too hot" nor "too cold". Later study revealed temperatures analogous to Venus, ruling out any potential for liquid water.<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 |access-date = 2009-04-02 |archive-url=https://web.archive.org/web/20120619015814/http://www.extrasolar.net/planettour.asp?PlanetID=22 |archive-date=2012-06-19}}</ref> [[16 Cygni Bb]], also discovered in 1996, has an extremely eccentric orbit that spends only part of its time in the HZ, such an orbit would causes extreme [[season]]al effects. In spite of this, simulations have suggested that a sufficiently large companion could support surface water year-round.<ref>{{cite journal|author1=Williams, D. |author2=Pollard, D. | title=Earth-like worlds on eccentric orbits: excursions beyond the habitable zone| journal=International Journal of Astrobiology| volume=1|issue=1|pages=61–69|date=2002|doi=10.1017/S1473550402001064|bibcode = 2002IJAsB...1...61W |s2cid=37593615 }}</ref>

[[Gliese 876 b]], discovered in 1998, and [[Gliese 876 c]], discovered in 2001, are both gas giants discovered in the habitable zone around [[Gliese 876]] that may also have large moons.<ref name="Sudarsky2003">{{cite journal |title=Theoretical Spectra and Atmospheres of Extrasolar Giant Planets |last1=Sudarsky |first1=David |last2=Burrows |first2=Adam |last3=Hubeny |first3=Ivan |display-authors=1 |journal=The Astrophysical Journal |volume=588 |issue=2 |pages=1121–1148 |date=2003 |doi=10.1086/374331 |bibcode=2003ApJ...588.1121S |arxiv=astro-ph/0210216 |s2cid=16004653 }}</ref> Another gas giant, [[Upsilon Andromedae d]] was discovered in 1999 orbiting Upsilon Andromidae's habitable zone.

Announced on April 4, 2001, [[HD 28185 b]] is a gas giant found to orbit entirely within its star's circumstellar habitable zone<ref>{{Cite journal | doi = 10.1086/506557| last1 = Jones | first1 = B. W. | last2 = Sleep | first2 = P. N. | last3 = Underwood | first3 = D. R. | title = Habitability of Known Exoplanetary Systems Based on Measured Stellar Properties | journal = The Astrophysical Journal | volume = 649 | issue = 2 | pages = 1010–1019 | year = 2006 | bibcode=2006ApJ...649.1010J|arxiv = astro-ph/0603200 | s2cid = 119078585 }}</ref> and has a low orbital eccentricity, comparable to that of Mars in the Solar System.<ref>{{Cite journal | last1 = Butler | first1 = R. P. | last2 = Wright | first2 = J. T. | last3 = Marcy | first3 = G. W. | last4 = Fischer | first4 = D. A. | last5 = Vogt | first5 = S. S. | last6 = Tinney | first6 = C. G. | last7 = Jones | first7 = H. R. A. | last8 = Carter | first8 = B. D. | last9 = Johnson | first9 = J. A. | last10 = McCarthy | first10 = C. | last11 = Penny | first11 = A. J. | title = Catalog of Nearby Exoplanets | doi = 10.1086/504701 | journal = The Astrophysical Journal | volume = 646 | issue = 1 | pages = 505–522 | year = 2006 |arxiv = astro-ph/0607493 |bibcode = 2006ApJ...646..505B | s2cid = 119067572 }}</ref> Tidal interactions suggest it could harbor habitable Earth-mass satellites in orbit around it for many billions of years,<ref>{{Cite journal | doi = 10.1086/341477 | last1 = Barnes | first1 = J. W. | last2 = O'Brien | first2 = D. P. | title = Stability of Satellites around Close-in Extrasolar Giant Planets | journal = The Astrophysical Journal | volume = 575 | issue = 2 | pages = 1087–1093 | year = 2002 | bibcode=2002ApJ...575.1087B|arxiv = astro-ph/0205035 | s2cid = 14508244 }}</ref> though it is unclear whether such satellites could form in the first place.<ref>{{Cite journal | last1 = Canup | first1 = R. M. | author-link = Robin Canup | last2 = Ward | first2 = W. R. | doi = 10.1038/nature04860 | title = A common mass scaling for satellite systems of gaseous planets | journal = Nature | volume = 441 | issue = 7095 | pages = 834–839 | year = 2006 | pmid =  16778883|bibcode = 2006Natur.441..834C | s2cid = 4327454 }}</ref>

[[HD 69830 d]], a gas giant with 17 times the mass of Earth, was found in 2006 orbiting within the circumstellar habitable zone of [[HD 69830]], 41 light years away from Earth.<ref name=lovis-2006>{{cite journal |author=Lovis| title=An extrasolar planetary system with three Neptune-mass planets |journal=[[Nature (journal)|Nature]] |volume=441 |date=2006 |pages=305–309| doi=10.1038/nature04828 |pmid=16710412 |last2=Mayor |first2=M |last3=Pepe |first3=F |last4=Alibert |first4=Y |last5=Benz |first5=W |last6=Bouchy |first6=F |last7=Correia |first7=AC |last8=Laskar |first8=J |last9=Mordasini |first9=C |issue=7091 |arxiv = astro-ph/0703024 |bibcode = 2006Natur.441..305L | s2cid=4343578 |display-authors=1 }}</ref> The following year, [[55 Cancri f]] was discovered within the HZ of its host star [[55 Cancri|55 Cancri A]].<ref name="ScienceDaily">{{cite web |url = https://www.sciencedaily.com/releases/2007/11/071106133058.htm |title = Astronomers Discover Record Fifth Planet Around Nearby Star 55 Cancri |publisher = Sciencedaily.com |date = November 6, 2007 |access-date = 2008-09-14| archive-url = https://web.archive.org/web/20080926142319/https://www.sciencedaily.com/releases/2007/11/071106133058.htm| archive-date = 26 September 2008 | url-status = live}}</ref><ref name="Fischer2008">{{Cite journal |title=Five Planets Orbiting 55 Cancri |last1=Fischer |first1=Debra A. |last2=Marcy |first2=Geoffrey W. |last3=Butler |first3=R. Paul |last4=Vogt |first4=Steven S. |last5=Laughlin |first5=Greg |last6=Henry |first6=Gregory W. |last7=Abouav |first7=David |last8=Peek |first8=Kathryn M. G. |last9=Wright |first9=Jason T. |display-authors=1 |journal=The Astrophysical Journal |date=2008 |volume=675 |issue=1 |pages=790–801 |arxiv=0712.3917 |bibcode=2008ApJ...675..790F |doi=10.1086/525512 |s2cid=55779685 }}</ref> Hypothetical satellites with sufficient mass and composition are thought to be able to support liquid water at their surfaces.<ref name="guardian">{{cite news| url=https://www.theguardian.com/science/2007/nov/07/spaceexploration |title=Could this be Earth's near twin? Introducing planet 55 Cancri f |newspaper=[[The Guardian]] |author=Ian Sample |date= 7 November 2007|access-date=17 October 2008 |location=London| archive-url= https://web.archive.org/web/20081002080911/http://www.guardian.co.uk/science/2007/nov/07/spaceexploration| archive-date= 2 October 2008 | url-status= live}}</ref>

Though, in theory, such giant planets could possess moons, the technology did not exist to detect moons around them, and no extrasolar moons had been discovered. Planets within the zone with the potential for solid surfaces were therefore of much higher interest.