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Diagram of generic quasi-satellite orbit

A quasi-satellite is an object in a specific type of co-orbital configuration (1:1 orbital resonance) with a planet where the object stays close to that planet over many orbital periods.

A quasi-satellite's orbit around the Sun takes exactly the same time as the planet's, but has a different eccentricity (usually greater), as shown in the diagram. When viewed from the perspective of the planet, the quasi-satellite will appear to travel in an oblong retrograde loop around the planet. (See Analemma § Of quasi-satellites).

In contrast to true satellites, quasi-satellite orbits lie outside the planet's Hill sphere, and are unstable. Over time they tend to evolve to other types of resonant motion, where they no longer remain in the planet's neighborhood, then possibly later move back to a quasi-satellite orbit, etc.

Other types of orbit in a 1:1 resonance with the planet include horseshoe orbits and tadpole orbits around the Lagrangian points, but objects in these orbits do not stay near the planet's longitude over many revolutions about the star. Objects in horseshoe orbits are known to sometimes periodically transfer to a relatively short-lived quasi-satellite orbit,[1] and are sometimes confused with them. An example of such an object is 2002 AA29.

The word "geosynchronous" is sometimes used to describe quasi-satellites of the Earth, because their motion around the Sun is synchronized with Earth's. However, this usage is unconventional and confusing. Conventionally, geosynchronous satellites revolve in the prograde sense around the Earth, with orbital periods that are synchronized to the Earth's rotation.



Venus has one known quasi-satellite, (524522) 2002 VE68. This asteroid is also a Mercury- and Earth-crosser; it seems to have been a "companion" to Venus for approximately the last 7000 years only, and is destined to be ejected from this orbital arrangement about 500 years from now.[2]


The oscillating path of asteroid 469219 Kamoʻoalewa viewed from Earth's perspective as it orbits around the Sun. The traced path of Kamoʻoalewa makes it appear as a constant companion of the Earth.

As of 2016, Earth had five known quasi-satellites:

On the longer term, asteroids can transfer between quasi-satellite orbits and horseshoe orbits, which circulate around Lagrangian points L4 and L5. By 2016, orbital calculations showed that all five of Earth's then known quasi-satellites repeatedly transfer between horseshoe and quasi-satellite orbits.[8] 3753 Cruithne,[9] 2002 AA29,[1] 2003 YN107 and 2015 SO2[5] are minor planets in horseshoe orbits that might evolve into a quasi-satellite orbit. The time spent in the quasi-satellite phase differs from asteroid to asteroid. Quasi-satellite 2016 HO3 is predicted to be stable in this orbital state for several hundred years, in contrast to 2003 YN107 which was a quasi-satellite from 1996 to 2006 but then departed Earth's vicinity on a horseshoe orbit.[8][10]

469219 Kamoʻoalewa (2016 HO3) is thought to be one of the most stable quasi-satellites found yet of Earth. It stays between 38 and 100 lunar distances from the Earth.[10]

Known and suspected companions of Earth
Name Eccentricity Diameter
Discoverer Year of Discovery Type Current Type
Moon 0.055 1737400 ? ? Natural satellite Natural satellite
1913 Great Meteor Procession ? ? ? 9 February 1913 Possible Temporary satellite Destroyed
3753 Cruithne 0.515 5000 Duncan Waldron 10 October 1986 Quasi-satellite Horseshoe orbit
1991 VG 0.053 5–12 Spacewatch 6 November 1991 Temporary satellite Apollo asteroid
(85770) 1998 UP1 0.345 210–470 Lincoln Lab's ETS 18 October 1998 Horseshoe orbit Horseshoe orbit
54509 YORP 0.230 124 Lincoln Lab's ETS 3 August 2000 Horseshoe orbit Horseshoe orbit
2001 GO2 0.168 35–85 Lincoln Lab's ETS 13 April 2001 Possible Horseshoe orbit Possible Horseshoe orbit
2002 AA29 0.013 20–100 LINEAR 9 January 2002 Quasi-satellite Horseshoe orbit
2003 YN107 0.014 10–30 LINEAR 20 December 2003 Quasi-satellite Horseshoe orbit
(164207) 2004 GU9 0.136 160–360 LINEAR 13 April 2004 Quasi-satellite Quasi-satellite
(277810) 2006 FV35 0.377 140–320 Spacewatch 29 March 2006 Quasi-satellite Quasi-satellite
2006 JY26 0.083 6–13 Catalina Sky Survey 6 May 2006 Horseshoe orbit Horseshoe orbit
2006 RH120 0.024 2–3 Catalina Sky Survey 14 September 2006 Temporary satellite Apollo asteroid
(419624) 2010 SO16 0.075 357 WISE 17 September 2010 Horseshoe orbit Horseshoe orbit
2010 TK7 0.191 150–500 WISE 1 October 2010 Earth trojan Earth trojan
2013 BS45 0.083 20–40 Spacewatch 20 January 2010 Horseshoe orbit Horseshoe orbit
2013 LX28 0.452 130–300 Pan-STARRS 12 June 2013 Quasi-satellite temporary Quasi-satellite temporary
2014 OL339 0.461 70–160 EURONEAR 29 July 2014 Quasi-satellite temporary Quasi-satellite temporary
2015 SO2 0.108 50–110 Črni Vrh Observatory 21 September 2015 Quasi-satellite Horseshoe orbit temporary
2015 XX169 0.184 9–22 Mount Lemmon Survey 9 December 2015 Horseshoe orbit temporary Horseshoe orbit temporary
2015 YA 0.279 9–22 Catalina Sky Survey 16 December 2015 Horseshoe orbit temporary Horseshoe orbit temporary
2015 YQ1 0.404 7–16 Mount Lemmon Survey 19 December 2015 Horseshoe orbit temporary Horseshoe orbit temporary
469219 Kamoʻoalewa 0.104 40-100 Pan-STARRS 27 April 2016 Quasi-satellite stable Quasi-satellite stable
DN16082203 ? ? ? 22 August 2016 Possible Temporary satellite Destroyed
2020 CD3 0.017 1–6 Mount Lemmon Survey 15 February 2020 Temporary satellite Temporary satellite
2020 PN1 0.127 10–50 ATLAS-HKO 12 August 2020 Horseshoe orbit temporary Horseshoe orbit temporary
2020 PP1 0.074 10–20 Pan-STARRS 12 August 2020 Quasi-satellite stable Quasi-satellite stable
2020 VT1 0.167 70–150 Pan-STARRS 10 November 2020 Horseshoe orbit temporary Horseshoe orbit temporary
2020 XL5 0.387 250–550 Pan-STARRS 12 December 2020 Earth trojan (suspected) Earth trojan


(309239) 2007 RW10 is a temporary quasi-satellite of Neptune.[11] The object has been a quasi-satellite of Neptune for about 12,500 years and it will remain in that dynamical state for another 12,500 years.[11]

Other planets[edit]

Based on simulations, it is believed that Uranus and Neptune could potentially hold quasi-satellites for the age of the Solar System (about 4.5 billion years),[12] but a quasi-satellite's orbit would remain stable for only 10 million years near Jupiter and 100,000 years near Saturn. Jupiter and Saturn are known to have quasi-satellites.[clarification needed] 2015 OL106, a co-orbital to Jupiter, intermittently becomes a quasi satellite of the planet, and will next become one between 2380 and 2480.

Artificial quasi-satellites[edit]

In early 1989, the Soviet Phobos 2 spacecraft was injected into a quasi-satellite orbit around the Martian moon Phobos, with a mean orbital radius of about 100 kilometres (62 mi) from Phobos.[13] According to computations, it could have then stayed trapped in the vicinity of Phobos for many months. The spacecraft was lost due to a malfunction of the on-board control system.

Accidental quasi-satellites[edit]

Some objects are known to be accidental quasi-satellites, which means that they are not forced into the configuration by the gravitational influence of the body of which they are quasi-satellites.[14] The minor planets Ceres, Vesta, and Pluto are known to have accidental quasi-satellites.[14] In the case of Pluto, the known accidental quasi-satellite, 15810 Arawn, is, like Pluto, a plutino, and is forced into this configuration by the gravitational influence of Neptune.[14] This dynamical behavior is recurrent, Arawn becomes a quasi-satellite of Pluto every 2.4 Myr and remains in that configuration for nearly 350,000 years.[14][15][16]

See also[edit]


  1. ^ a b Connors, Martin; Chodas, Paul; Mikkola, Seppo; Wiegert, Paul; Veillet, Christian; Innanen, Kimmo (2002). "Discovery of an asteroid and quasi-satellite in an Earth-like horseshoe orbit". Meteoritics & Planetary Science. 37 (10): 1435–1441. Bibcode:2002M&PS...37.1435C. doi:10.1111/j.1945-5100.2002.tb01039.x.
  2. ^ Mikkola, S.; Brasser, R.; Wiegert, P.; Innanen, K. (2004). "Asteroid 2002 VE68, a quasi-satellite of Venus". Monthly Notices of the Royal Astronomical Society. 351 (3): L63–L65. Bibcode:2004MNRAS.351L..63M. doi:10.1111/j.1365-2966.2004.07994.x.
  3. ^ Brasser, R.; et al. (September 2004). "Transient co-orbital asteroids". Icarus. 171 (1): 102–109. Bibcode:2004Icar..171..102B. doi:10.1016/j.icarus.2004.04.019.
  4. ^ Wajer, Paweł (October 2010). "Dynamical evolution of Earth's quasi-satellites: 2004 GU9 and 2006 FV35" (PDF). Icarus. 209 (2): 488–493. Bibcode:2010Icar..209..488W. doi:10.1016/j.icarus.2010.05.012.
  5. ^ a b de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2016). "From horseshoe to quasi-satellite and back again: The curious dynamics of Earth co-orbital asteroid 2015 SO2". Astrophysics and Space Science. 361. arXiv:1511.08360. Bibcode:2016Ap&SS.361...16D. doi:10.1007/s10509-015-2597-8.
  6. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2014). "Asteroid 2014 OL339: Yet another Earth quasi-satellite". Monthly Notices of the Royal Astronomical Society. 445 (3): 2985–2994. arXiv:1409.5588. Bibcode:2014MNRAS.445.2961D. doi:10.1093/mnras/stu1978.
  7. ^ Agle, D.C.; Brown, Dwayne; Cantillo, Laurie (15 June 2016). "Small asteroid is Earth's constant companion". NASA. Retrieved 15 June 2016.
  8. ^ a b c de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2016). "Asteroid (469219) 2016 HO3, the smallest and closest Earth quasi-satellite". Monthly Notices of the Royal Astronomical Society. 462 (4): 3441–3456. arXiv:1608.01518. Bibcode:2016MNRAS.462.3441D. doi:10.1093/mnras/stw1972.
  9. ^ Christou, Apostolos A.; Asher, David J. (2011). "A long-lived horseshoe companion to the Earth". Monthly Notices of the Royal Astronomical Society. 414 (4): 2965–2969. arXiv:1104.0036. Bibcode:2011MNRAS.414.2965C. doi:10.1111/j.1365-2966.2011.18595.x.
  10. ^ a b [1]
  11. ^ a b de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (September 2012). "(309239) 2007 RW10: a large temporary quasi-satellite of Neptune". Astronomy and Astrophysics Letters. 545: L9. arXiv:1209.1577. Bibcode:2012A&A...545L...9D. doi:10.1051/0004-6361/201219931.
  12. ^ Wiegert, P.; Innanen, K. (2000). "The stability of quasi satellites in the outer solar system". The Astronomical Journal. 119 (4): 1978–1984. Bibcode:2000AJ....119.1978W. doi:10.1086/301291.
  13. ^ Green, LM; Zakharov, AV; Pichkhadze, KM. Что мы ищем на Фобосе [What we are looking for [on] Phobos] (in Russian). Archived from the original on 2009-07-20.
  14. ^ a b c d de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2012). "Plutino 15810 (1994 JR1), an accidental quasi-satellite of Pluto". Monthly Notices of the Royal Astronomical Society: Letters. 427 (1): L85. arXiv:1209.3116. Bibcode:2012MNRAS.427L..85D. doi:10.1111/j.1745-3933.2012.01350.x.
  15. ^ "Pluto's fake moon". Archived from the original on 2013-01-05. Retrieved 2012-09-24.
  16. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2016). "The analemma criterion: accidental quasi-satellites are indeed true quasi-satellites". Monthly Notices of the Royal Astronomical Society. 462 (3): 3344–3349. arXiv:1607.06686. Bibcode:2016MNRAS.462.3344D. doi:10.1093/mnras/stw1833.

External links[edit]