Editing Planet (section)

==== Rotation ====
{{See also|Exoplanetology#Rotation and axial tilt}}
The planets rotate around invisible axes through their centres. A planet's [[rotation period]] is known as a [[day|stellar day]]. Most of the planets in the Solar System rotate in the same direction as they orbit the Sun, which is counter-clockwise as seen from above the Sun's [[Poles of astronomical bodies#Geographic poles|north pole]]. The exceptions are Venus<ref>{{cite journal |title=Rotation of Venus: Period Estimated from Radar Measurements | last1=Goldstein | first1=R. M. | last2=Carpenter | first2=R. L. |date=1963 |journal =Science |volume=139 |doi=10.1126/science.139.3558.910 |pmid=17743054 |issue=3558 |bibcode=1963Sci...139..910G |pages=910–911|s2cid=21133097 }}</ref> and Uranus,<ref name="Belton-1984">{{cite conference |title=Rotational properties of Uranus and Neptune |first1=M. J. S. |last1=Belton | last2=Terrile | first2=R. J. |date=1984 |conference=Voyager "Uranus-Neptune" Workshop Pasadena 6–8 February 1984 |pages=327–347|bibcode=1984NASCP2330..327B |editor=Bergstralh, J. T.}}</ref> which rotate clockwise, though Uranus's extreme axial tilt means there are differing conventions on which of its poles is "north", and therefore whether it is rotating clockwise or anti-clockwise.<ref>{{cite book |title=The Outer Worlds; Uranus, Neptune, Pluto, and Beyond |pages=195–206 |date=2006 |first=Michael P. |last=Borgia |publisher=Springer New York}}</ref> Regardless of which convention is used, Uranus has a [[retrograde rotation]] relative to its orbit.<ref name="Belton-1984" />

{{solar_system_bodies_rotation_animation.svg|upright}}

The rotation of a planet can be induced by several factors during formation. A net [[angular momentum]] can be induced by the individual angular momentum contributions of accreted objects. The accretion of gas by the giant planets contributes to the angular momentum. Finally, during the last stages of planet building, a [[stochastic process]] of protoplanetary accretion can randomly alter the spin axis of the planet.<ref name="araa31">{{cite journal | title=Planet formation |last=Lissauer |first=Jack J. |journal=Annual Review of Astronomy and Astrophysics |volume=31 |pages=129–174 |date=September 1993 |doi=10.1146/annurev.aa.31.090193.001021 |bibcode=1993ARA&A..31..129L}}</ref> There is great variation in the length of day between the planets, with Venus taking 243&nbsp;[[Julian day|days]] to rotate, and the giant planets only a few hours.<ref name="planetcompare">{{cite web |title=Planet Compare |url=https://solarsystem.nasa.gov/planet-compare/ |url-status=live |archive-url=https://web.archive.org/web/20180309204400/https://solarsystem.nasa.gov/planet-compare/ |archive-date=9 March 2018 |access-date=12 July 2022 |website=Solar System Exploration |publisher=NASA}}</ref> The rotational periods of exoplanets are not known, but for [[hot Jupiter]]s, their proximity to their stars means that they are [[Tidal locking|tidally locked]] (that is, their orbits are in sync with their rotations). This means, they always show one face to their stars, with one side in perpetual day, the other in perpetual night.<ref>{{cite journal |title=Magnetically-Driven Planetary Radio Emissions and Application to Extrasolar Planets | last1=Zarka |first1=Philippe | last2=Treumann | first2=Rudolf A. | last3=Ryabov | first3=Boris P. | last4=Ryabov | first4=Vladimir B. |date=2001 |journal=Astrophysics and Space Science |volume=277 |issue=1/2 |pages=293–300 |doi = 10.1023/A:1012221527425|bibcode = 2001Ap&SS.277..293Z | s2cid=16842429 }}</ref> Mercury and Venus, the closest planets to the Sun, similarly exhibit very slow rotation: Mercury is tidally locked into a 3:2 spin–orbit resonance (rotating three times for every two revolutions around the Sun),<ref>{{cite journal |last1=Liu |first1=Han-Shou |last2=O'Keefe |first2=John A. |title=Theory of Rotation for the Planet Mercury |journal=Science |year=1965 |volume=150 |issue=3704 |page=1717 |doi=10.1126/science.150.3704.1717 |pmid=17768871 |bibcode=1965Sci...150.1717L|s2cid=45608770 }}</ref> and Venus's rotation may be in equilibrium between [[tidal force]]s slowing it down and [[atmospheric tide]]s created by solar heating speeding it up.<ref>{{cite journal |last1=Correia |first1=Alexandre C. M. |last2=Laskar |first2=Jacques |last3=De Surgy |first3=Olivier Néron |title=Long-Term Evolution of the Spin of Venus, Part I: Theory |journal=Icarus |volume=163 |issue=1 |pages=1–23 |date=May 2003 |url=http://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus1.2002.pdf |doi=10.1016/S0019-1035(03)00042-3 |bibcode=2003Icar..163....1C |access-date=9 September 2006 |archive-date=27 September 2019 |archive-url=https://web.archive.org/web/20190927122047/https://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus1.2002.pdf |url-status=live }}</ref><ref>{{cite journal |last1=Laskar |first1=Jacques |last2=De Surgy |first2=Olivier Néron |title=Long-Term Evolution of the Spin of Venus, Part II: Numerical Simulations |journal=Icarus |volume=163 |issue=1 |pages=24–45 |url=http://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus2.2002.pdf |doi=10.1016/S0019-1035(03)00043-5 |bibcode=2003Icar..163...24C |year=2003 |access-date=9 September 2006 |archive-date=2 May 2019 |archive-url=https://web.archive.org/web/20190502225637/https://www.imcce.fr/Equipes/ASD/preprints/prep.2002/venus2.2002.pdf |url-status=live }}</ref>

All the large moons are tidally locked to their parent planets;<ref>{{cite book|last1=Schutz|first1=Bernard|title=Gravity from the Ground Up|publisher=Cambridge University Press|isbn=978-0521455060|page=43|url=https://books.google.com/books?id=P_T0xxhDcsIC&pg=PA43|access-date=24 April 2017|date=2003|archive-date=6 August 2023|archive-url=https://web.archive.org/web/20230806164032/https://books.google.com/books?id=P_T0xxhDcsIC&pg=PA43|url-status=live}}</ref> Pluto and Charon are tidally locked to each other,<ref name="Young1997">{{cite web
| title = The Once and Future Pluto
| first = Leslie A.
| last = Young
| work = Southwest Research Institute, Boulder, Colorado
| url = http://www.boulder.swri.edu/~layoung/projects/talks03/IfA-jan03v1.ppt
| date = 1997
| access-date = 26 March 2007
| archive-date = 30 March 2004
| archive-url = https://web.archive.org/web/20040330212503/http://www.boulder.swri.edu/~layoung/projects/talks03/IfA-jan03v1.ppt
| url-status = live
}}</ref> as are Eris and Dysnomia,<ref name="Szakats2022">{{cite journal
  |display-authors = etal
  |first1 = R. |last1 = Szakáts
  |first2 = Cs. |last2 = Kiss
  |first3 = J. L. |last3 = Ortiz
  |first4 = N. |last4 = Morales
  |first5 = A. |last5 = Pál
  |first6 = T. G. |last6 = Müller
  |title      = Tidally locked rotation of the dwarf planet (136199) Eris discovered via long-term ground-based and space photometry
  |journal = Astronomy & Astrophysics |year = 2023 |volume = 669 |page = L3 |doi = 10.1051/0004-6361/202245234 |arxiv      = 2211.07987
|bibcode = 2023A&A...669L...3S |s2cid = 253522934 }}</ref> and probably {{dp|Orcus}} and its moon [[Vanth (moon)|Vanth]].<ref name="Brown2023"/> The other dwarf planets with known rotation periods rotate faster than Earth; Haumea rotates so fast that it has been distorted into a [[triaxial ellipsoid]].<ref name="Rabinowitz2005">
{{cite journal
| author = Rabinowitz, D. L.
| date = 2006
| title = Photometric Observations Constraining the Size, Shape, and Albedo of 2003&nbsp;EL<sub>61</sub>, a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt
| journal = [[Astrophysical Journal]]
| volume = 639
| issue = 2
| pages = 1238–1251
| doi = 10.1086/499575
| bibcode = 2006ApJ...639.1238R
| arxiv = astro-ph/0509401
| last2 = Barkume | first2 = Kristina
| last3 = Brown | first3 = Michael E.
| last4 = Roe | first4 = Henry
| last5 = Schwartz | first5 = Michael
| last6 = Tourtellotte | first6 = Suzanne
| last7 = Trujillo | first7 = Chad
| s2cid = 11484750
}}
</ref> The exoplanet [[Tau Boötis b]] and its parent star [[Tau Boötis]] appear to be mutually tidally locked.<ref>{{cite journal | title=Life on a tidally-locked planet | last=Singal | first=Ashok K. | journal=Planex Newsletter | volume=4 | issue=2 | page=8 | date=May 2014 | bibcode=2014arXiv1405.1025S | arxiv=1405.1025 }}</ref><ref>{{cite journal | title=MOST detects variability on tau Bootis possibly induced by its planetary companion | url=http://www.aanda.org/articles/aa/full/2008/17/aa8952-07/aa8952-07.html | last1=Walker | first1=G. A. H. | last2=Croll | first2=B. | last3=Matthews | first3=J. M. | last4=Kuschnig | first4=R. | last5=Huber | first5=D. | last6=Weiss | first6=W. W. | last7=Shkolnik | first7=E. | last8=Rucinski | first8=S. M. | last9=Guenther | first9=D. B. | display-authors=1 | year=2008 | journal=Astronomy and Astrophysics | volume=482 | issue=2 | pages=691–697 | doi=10.1051/0004-6361:20078952 | arxiv=0802.2732 | bibcode=2008A&A...482..691W | s2cid=56317105 | access-date=6 August 2022 | archive-date=25 February 2021 | archive-url=https://web.archive.org/web/20210225212508/https://www.aanda.org/articles/aa/full/2008/17/aa8952-07/aa8952-07.html | url-status=live }}</ref>