Editing Tidal locking (section)

===Planets===
It was thought for some time that [[Mercury (planet)|Mercury]] was in synchronous rotation with the Sun. This was because whenever Mercury was best placed for observation, the same side faced inward. Radar observations in 1965 demonstrated instead that Mercury has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun, which results in the same positioning at those observation points. Modeling has demonstrated that Mercury was captured into the 3:2 spin–orbit state very early in its history, probably within 10–20 million years after its formation.<ref name=Noyelles2012>{{Cite journal | bibcode=2014Icar..241...26N | last1=Noyelles | first1=Benoit | last2=Frouard | first2=Julien | last3=Makarov | first3=Valeri V. | last4=Efroimsky | first4=Michael | name-list-style=amp | title=Spin–orbit evolution of Mercury revisited | journal=Icarus | date=2014 | volume=241 | doi=10.1016/j.icarus.2014.05.045 | pages=26–44 | arxiv = 1307.0136 | s2cid=53690707 }}</ref>

The 583.92-day interval between successive close approaches of [[Venus]] to Earth is equal to 5.001444 Venusian solar days, making approximately the same face visible from Earth at each close approach. Whether this relationship arose by chance or is the result of some kind of tidal locking with Earth is unknown.<ref>{{cite journal |last1=Gold |first1=T. |last2=Soter |first2=S. |date=1969 |title=Atmospheric tides and the resonant rotation of Venus |journal=Icarus |volume=11 |issue=3 |pages=356–366|bibcode=1969Icar...11..356G |doi=10.1016/0019-1035(69)90068-2 }}</ref>

The [[exoplanet]] [[Proxima Centauri b]] discovered in 2016 which orbits around [[Proxima Centauri]], is almost certainly tidally locked, expressing either synchronized rotation or a 3:2 spin–orbit resonance like that of Mercury.<ref>{{cite journal|title=Tidal locking of habitable exoplanets|url=https://link.springer.com/article/10.1007/s10569-017-9783-7|publisher=Springer|year=2017|doi=10.1007/s10569-017-9783-7|last1=Barnes|first1=Rory|journal=Celestial Mechanics and Dynamical Astronomy|volume=129|issue=4|pages=509–536|s2cid=119384474|arxiv=1708.02981|bibcode=2017CeMDA.129..509B|access-date=2021-03-29|archive-date=2021-02-26|archive-url=https://web.archive.org/web/20210226135913/https://link.springer.com/article/10.1007/s10569-017-9783-7|url-status=live}}</ref>

One form of hypothetical tidally locked [[exoplanet]]s are [[eyeball planet]]s, which in turn are divided into "hot" and "cold" eyeball planets.<ref>{{cite web|url=http://nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets|title=Forget "Earth-Like"—We'll First Find Aliens on Eyeball Planets|publisher=Nautilus|language=en|author=Sean Raymond|date=20 February 2015|access-date=5 June 2017|archive-date=23 June 2017|archive-url=https://web.archive.org/web/20170623082602/http://nautil.us/blog/forget-earth_likewell-first-find-aliens-on-eyeball-planets|url-status=dead}}</ref><ref name="SA-20200105">{{cite news |last=Starr |first=Michelle |title=Eyeball Planets Might Exist, And They're as Creepy as They Sound |url=https://www.sciencealert.com/eyeball-planets-might-exist-yep-they-re-exactly-as-creepy-as-they-sound |date=5 January 2020 |work=ScienceAlert.com |access-date=6 January 2020 |archive-date=6 January 2020 |archive-url=https://web.archive.org/web/20200106014046/https://www.sciencealert.com/eyeball-planets-might-exist-yep-they-re-exactly-as-creepy-as-they-sound |url-status=live }}</ref>