Editing Terrestrial planet (section)

===Frequency===
In 2013, astronomers reported, based on [[Kepler (spacecraft)|Kepler space mission]] data, that there could be as many as 40 billion Earth- and super-Earth-sized [[extrasolar planets|planets]] orbiting in the [[habitable zone]]s of [[Solar analog|Sun-like stars]] and [[red dwarf]]s within the [[Milky Way]].<ref name="NYT-20131104">{{cite news |last=Overbye |first=Dennis |title=Far-Off Planets Like the Earth Dot the Galaxy |url=https://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |date=4 November 2013 |work=[[The New York Times]] |access-date=5 November 2013 |url-status=live |archive-url=https://web.archive.org/web/20131105023653/http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |archive-date=5 November 2013  }}</ref><ref name="PNAS-20131031">{{cite journal |last1=Petigura |first1=Eric A. |last2=Howard |first2=Andrew W. |last3=Marcy |first3=Geoffrey W. |title=Prevalence of Earth-size planets orbiting Sun-like stars |date=31 October 2013 |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |doi=10.1073/pnas.1319909110 |arxiv=1311.6806 |bibcode=2013PNAS..11019273P |volume=110 |issue=48 |pages=19273–19278 |pmid=24191033 |pmc=3845182 |doi-access=free }}</ref><ref name="Space-20130107">{{cite web |author=Staff |title=17 Billion Earth-Size Alien Planets Inhabit Milky Way |url=http://www.space.com/19157-billions-earth-size-alien-planets-aas221.html |date=7 January 2013 |publisher=[[Space.com]] |access-date=8 January 2013 |url-status=live |archive-url=https://web.archive.org/web/20141006095334/http://www.space.com/19157-billions-earth-size-alien-planets-aas221.html |archive-date=6 October 2014  }}</ref> Eleven billion of these estimated planets may be orbiting Sun-like stars.<ref name="LATimes-20131104">{{cite news |last=Khan |first=Amina |title=Milky Way may host billions of Earth-size planets |url=https://www.latimes.com/science/la-sci-earth-like-planets-20131105,0,2673237.story |date=4 November 2013 |work=[[Los Angeles Times]] |access-date=5 November 2013 |url-status=live |archive-url=https://web.archive.org/web/20131106030558/http://www.latimes.com/science/la-sci-earth-like-planets-20131105%2C0%2C2673237.story |archive-date=6 November 2013  }}</ref> The nearest such planet may be 12 light-years away, according to the scientists.<ref name="NYT-20131104" /><ref name="PNAS-20131031" /> However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see [[Kepler-138]]d).<ref>{{cite web|url=http://www.cfa.harvard.edu/news/2014-01|title=Newfound Planet is Earth-mass But Gassy|date=3 January 2014|website=harvard.edu|access-date=2 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171028063815/https://www.cfa.harvard.edu/news/2014-01|archive-date=28 October 2017}}</ref>

Estimates show that about 80% of potentially habitable worlds are covered by land, and about 20% are ocean planets. Planets with rations more like those of Earth, which was 30% land and 70% ocean, only make up 1% of these worlds.<ref>[https://www.space.com/habitable-rocky-planets-dominated-by-land 'Pale blue dots' like Earth may be rare among habitable worlds]</ref>