Retrograde and prograde motion

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Retrograde motion is motion in the direction opposite to the movement of something else and the contrary of direct or prograde motion. This motion can be the orbit of one body about another body or about some other point, or the rotation of a single body about its axis, or other phenomena such as precession or nutation of the axis. In reference to celestial systems, retrograde motion usually means motion which is contrary to the rotation of the primary, that is, the object which forms the system's hub.


Formation of celestial systems[edit]


Orbital parameters[edit]



Axial tilt[edit]




It is unlikely that Venus was formed with its present slow retrograde rotation which takes 243 days to rotate. Venus probably began with a fast prograde rotation with a period of several hours much like most of the planets in the solar system. Venus is close enough to the Sun to experience significant gravitational tidal dissipation, and also has a thick enough atmosphere to create thermally driven atmospheric tides which create a retrograde torque. Venus' present slow retrograde rotation is in equilibrium balance between gravitational tides trying to tidally lock Venus to the Sun and atmospheric tides trying to spin-up Venus in a retrograde direction. In addition to maintaining this present day equilibrium, tides are also sufficient to account for evolution of Venus's rotation from a primordial fast prograde direction to its present-day slow retrograde rotation.[7] In the past various other alternative hypotheses have been proposed to explain Venus' retrograde rotation, such as collisions or it having originally formed that way. Mercury is closer to the Sun than Venus but Mercury is not tidally locked because it has entered a spin-orbit resonance due to the eccentricity of its orbit. The rotation of Earth and Mars is also affected by tidal forces with the Sun but they haven't reached an equilibrium state like Mercury and Venus because they are further out from the Sun where tidal forces are weaker. The gas giants of the solar system are too massive and too far from the Sun to have their rotations slowed down by tidal forces.[7]

Dwarf planets[edit]

All known dwarf planets and dwarf planet candidates have prograde orbits around the Sun, but some have retrograde rotation. Pluto has retrograde rotation; its axial tilt is approximately 120 degrees.[8] Pluto and its moon Charon are both tidally locked to each other. It is suspected that the Plutonian satellite system was created by a massive collision.[9][10]

Earth's atmosphere[edit]

Retrograde motion, or retrogression, within the Earth's atmosphere refers to weather systems which move from east to west through the Westerlies or from west to east through the Trade wind easterlies.

Moons and rings[edit]

The orange moon is orbiting in the opposite direction.


In the Solar System, many of the asteroid-sized moons have retrograde orbits, whereas all the large moons except Triton (the largest of Neptune's moons) have prograde orbits.[12] The particles in Saturn's Phoebe ring are thought to have a retrograde orbit because they originate from the irregular moon Phoebe.



With the exception of Hyperion all the known regular planetary natural satellites in the Solar System are tidally locked to their host planet, so they have zero rotation relative to their host planet, but have prograde rotation relative to the Sun because they have prograde orbits around their host planet.

If there is a collision, material could be ejected in any direction and coalesce into either prograde or retrograde moons which may be the case for the moons of dwarf planet Haumea although Haumea's rotation direction is not known.[14]

Small solar system bodies[edit]



Some asteroids with retrograde orbits may be burnt-out comets, [15] but some may acquire their retrograde orbit due to gravitational interactions with Jupiter.[16]

Due to their small size and their large distance from Earth it is difficult to telescopically analyse the rotation of most asteroids. As of 2012, data is available for less than 200 asteroids and the different methods of determining the orientation of poles often result in large discrepancies.[17] The asteroid spin vector catalog at Poznan Observatory[18] avoids use of the phrases "retrograde rotation" or "prograde rotation" as it depends which reference plane is meant and asteroid coordinates are usually given with respect to the ecliptic plane rather than the asteroid's orbital plane.[19]

Asteroids with satellites, also known as binary asteroids, make up about 15% of all asteroids less than 10km in diameter in the main belt and near-Earth population and most are thought to be formed by the YORP effect causing an asteroid to spin so fast that it breaks up.[20] As of 2012, and where the rotation is known, all satellites of asteroids orbit the asteroid in the same direction as the asteroid is rotating.[21]



Comets from the Oort cloud are much more likely than asteroids to be retrograde.[15] Halley's Comet has a retrograde orbit around the Sun.[23]

Kuiper belt[edit]



Meteoroids in a retrograde orbit around the Sun hit the Earth with a faster relative speed than prograde meteoroids and tend to burn-up in the atmosphere and are more likely to hit the side of the Earth facing away from the Sun (i.e. at night-time) whereas the prograde meteoroids have slower closing speeds and more often land as meteorites and tend to hit the sun-facing side of the Earth. Most meteoroids are prograde.[25]

The Sun[edit]



Stars and planetary systems tend to be born in star clusters rather than forming in isolation, and protoplanetary disks can collide with or steal material from molecular clouds within the cluster and this can lead to disks and their resulting planets having inclined or retrograde orbits around their stars.[3][4] Retrograde motion may also result from gravitational interactions with other celestial bodies in the same system (See Kozai mechanism.) or a near-collision with another planet,[27] or it may be that the star itself flipped over early in their system's formation due to interactions between the star's magnetic field and the planet-forming disk.[28][29]

The accretion disk of the protostar IRAS 16293-2422 has parts rotating in opposite directions, the first time a counterrotating accretion disk has been found and means that when planets form, the inner planets will orbit in the opposite direction to the outer planets.[30]




The pattern of stars appears fixed in the sky, but that is only because they are so far away that their motion isn't visible to the naked eye; actually, they are orbiting the centre of the galaxy. Stars with a retrograde orbit are more likely to be found in the galactic halo than in the galactic disk. The Milky Way's outer halo has many globular clusters with a retrograde orbit[33] and with a retrograde or zero rotation.[34] The halo consists of two distinct components. The stars in the inner halo mostly have prograde orbits around the galaxy, whereas stars in the outer halo typically have retrograde orbits.[35]



Satellite galaxies[edit]


A galaxy called Complex H, which was orbiting the Milky Way in a retrograde direction relative to the Milky Way's rotation, is colliding with the Milky Way.[38][39]

Counter-rotating bulges[edit]

NGC 7331 is an example of a galaxy which has a bulge that is rotating in the opposite direction to the rest of the disk, probably as a result of infalling material.[40]

Central black holes[edit]

The center of a spiral galaxy contains at least one supermassive black hole.[41] A retrograde black hole – one whose spin is opposite to that of its disk – spews jets much more powerful than those of a prograde black hole, which may have no jet at all. Scientists have produced a theoretical framework for the formation and evolution of retrograde black holes based on the gap between the inner edge of an accretion disk and the black hole.[42][43]

See also[edit]


  1. ^ Grossman, Lisa (13 August 2008). "Planet found orbiting its star backwards for first time". NewScientist. Retrieved 10 October 2009. 
  2. ^ a b Turning planetary theory upside down
  4. ^ a b A natural formation scenario for misaligned and short-period eccentric extrasolar planets, Ingo Thies, Pavel Kroupa, Simon P. Goodwin, Dimitris Stamatellos, Anthony P. Whitworth, 11 Jul 2011
  8. ^
  10. ^ Stern, S. A.; Weaver, H. A.; Steff, A. J.; Mutchler, M. J.; Merline, W. J.; Buie, M. W.; Young, E. F.; Young, L. A.; Spencer, J. R. (2006-02-23). "A giant impact origin for Pluto's small moons and satellite multiplicity in the Kuiper belt". Nature 439 (7079): 946–948. Bibcode:2006Natur.439..946S. doi:10.1038/nature04548. PMID 16495992. Retrieved 2011-07-20. 
  11. ^ Encyclopedia of the solar system. Academic Press. 2007. 
  12. ^ Mason, John (22 July 1989). "Science: Neptune's new moon baffles the astronomers". NewScientist. Retrieved 10 October 2009. 
  13. ^ Chaos-assisted capture of irregular moons, Sergey A. Astakhov, Andrew D. Burbanks, Stephen Wiggins & David Farrelly, NATURE |VOL 423 | 15 MAY 2003
  14. ^ On the Dynamics and Origin of Haumea's Moons, Matija Ćuk, Darin Ragozzine, David Nesvorný, 12 aug 2013
  15. ^ a b Hecht, Jeff (1 May 2009). "Nearby asteroid found orbiting Sun backwards". NewScientist. Retrieved 10 October 2009. 
  16. ^ PRODUCTION OF NEAR-EARTH ASTEROIDS ON RETROGRADE ORBITS, S. Greenstreet, B. Gladman, H. Ngo, M. Granvik, and S. Larson, The Astrophysical Journal Letters, 749:L39 (5pp), 2012 April 20
  17. ^ Spin vectors of asteroids: Updated statistical properties and open problems, Paolo Paolicchia, Agnieszka Kryszczyńskab, Planetary and Space Science, Volume 73, Issue 1, December 2012, Pages 70–74
  18. ^ Physical studies of asteroids at Poznan Observatory
  20. ^ Rotational breakup as the origin of small binary asteroids, Kevin J. Walsh, Derek C. Richardson & Patrick Michel, Nature, Vol 454 10 July 2008
  21. ^ Asteroids with satellites: Analysis of observational data, N. M. Gaftonyuk, N. N. Gorkavyi, Solar System Research May 2013, Volume 47, Issue 3, pp 196-202
  22. ^ Namouni, M.H.M.; F. Namouni (1970). "Asteroids in retrograde resonance with Jupiter and Saturn". Monthly Notices of the Royal Astronomical Society Letters (in press) 436: L30. arXiv:arXiv:1308.0216. Bibcode:2013MNRAS.436L..30M. doi:10.1093/mnrasl/slt106. 
  23. ^ Halley's Comet
  24. ^ Hecht, Jeff (5 September 2008). "Distant object found orbiting Sun backwards". NewScientist. Retrieved 10 October 2009. 
  25. ^ Meteorites: A Journey Through Space and Time, Alex Bevan, John De Laeter, UNSW Press, 2002 ISBN 9780868404905
  26. ^ Javaraiah, J. (12 July 2005). "Sun's retrograde motion and violation of even-odd cycle rule in sunspot activity". Monthly Notices of the Royal Astronomical Society 362 (2005): 1311–1318. arXiv:astro-ph/0507269. Bibcode:2005MNRAS.362.1311J. doi:10.1111/j.1365-2966.2005.09403.x. 
  27. ^ Grossman, Lisa (13 August 2009). "Planet found orbiting its star backwards for first time". NewScientist. Retrieved 7 September 2010. 
  29. ^ Evolution of Spin Direction of Accreting Magnetic Protostars and Spin-Orbit Misalignment in Exoplanetary Systems, Dong Lai, Francois Foucart, Douglas N.C. Lin
  30. ^ Still-Forming Solar System May Have Planets Orbiting Star in Opposite Directions, Astronomers Say, National Radio Astronomy Observatory, February 13, 2006
  32. ^ Second backwards planet found, a day after the first, New Scientist, 13 August 2009
  33. ^ Kravtsov, V. V. (2001). "Globular clusters and dwarf spheroidal galaxies of the outer galactic halo: On the putative scenario of their formation". Astronomical and Astrophysical Transactions 20 (1): 89–92. Bibcode:2001A&AT...20...89K. doi:10.1080/10556790108208191. Retrieved 13 October 2009. 
  34. ^ Kravtsov, Valery V. (2002). "Second parameter globulars and dwarf spheroidals around the Local Group massive galaxies: What can they evidence?". Astronomy & Astrophysics 396: 117–123. arXiv:astro-ph/0209553. Bibcode:2002A&A...396..117K. doi:10.1051/0004-6361:20021404. 
  35. ^ Carollo, Daniela; Timothy C. Beers, Young Sun Lee, Masashi Chiba, John E. Norris, Ronald Wilhelm, Thirupathi Sivarani, Brian Marsteller, Jeffrey A. Munn, Coryn A. L. Bailer-Jones, Paola Re Fiorentin, Donald G. York (13 December 2007). "Two stellar components in the halo of the Milky Way". Nature 450 (7172): 1020–5. arXiv:0706.3005. Bibcode:2007Natur.450.1020C. doi:10.1038/nature06460. PMID 18075581. Retrieved 13 October 2009. 
  36. ^
  37. ^ Making Counter-Orbiting Tidal Debris - The Origin of the Milky Way Disc of Satellites, M. S. Pawlowski, P. Kroupa, and K. S. de Boer
  38. ^ Cain, Fraser (22 May 2003). "Galaxy Orbiting Milky Way in the Wrong Direction". Universe Today. Retrieved 13 October 2009. [dead link]
  39. ^ Lockman, Felix J. (2003). "High-velocity cloud Complex H: a satellite of the Milky Way in a retrograde orbit?". The Astrophysical Journal Letters 591 (1): L33–L36. arXiv:astro-ph/0305408. Bibcode:2003ApJ...591L..33L. doi:10.1086/376961. 
  40. ^ Prada, F.; C. Gutierrez, R. F. Peletier, C. D. McKeith (14 March 1996). "A Counter-rotating Bulge in the Sb Galaxy NGC 7331". arXiv:astro-ph/9602142 [astro-ph].
  42. ^ "Some black holes make stronger jets of gas". 1 June 2010. Retrieved 1 June 2010. 
  43. ^ Atkinson, Nancy (1 June 2010). "What's more powerful than a supermassive black hole? A supermassive black hole that spins backwards.". The Christian Science Monitor. Retrieved 1 June 2010. 

Further reading[edit]