Quasi-satellite


A quasi-satellite is an object in a specific type of co-orbital configuration 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, 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..
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, and are sometimes confused with them. An example of such an object is.
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.

Examples

Venus

Venus has one known quasi-satellite,. 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.

Earth

As of 2016, Earth had five known quasi-satellites:
and.
On the longer term, asteroids can transfer between quasi-satellite orbits and horseshoe orbits, which go 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. 3753 Cruithne,, and are minor planets in a horseshoe orbit that can evolve into a quasi-satellite orbit. The time spent in the quasi-satellite phase differs from asteroid to asteroid. Quasi-satellite is predicted to be stable in this orbital state for several hundred years, in contrast to which was a quasi-satellite from 1996 to 2006 but then departed Earth's vicinity on a horseshoe orbit.
469219 Kamoʻoalewa is thought to be one the most stable quasi-satellites found yet of Earth. It stays between 38 and 100 lunar distances from the Earth.
NameEccentricityDiameter
DiscovererYear of DiscoveryTypeCurrent Type
Moon0.0551737400??Natural satelliteNatural satellite
1913 Great Meteor Procession???1913 February 9Possible Temporary satelliteDestroyed
3753 Cruithne0.5155000Duncan Waldron1986 October 10Quasi-satelliteHorseshoe orbit
1991 VG0.0535–12Spacewatch1991 November 6Temporary satelliteApollo asteroid
1998 UP10.345210–470Lincoln Lab's ETS1998 October 18Horseshoe orbitHorseshoe orbit
54509 YORP0.230124Lincoln Lab's ETS2000 August 3Horseshoe orbitHorseshoe orbit
2001 GO20.16835–85Lincoln Lab's ETS2001 April 13Possible Horseshoe orbitPossible Horseshoe orbit
2002 AA290.01320–100LINEAR2002 January 9Quasi-satelliteHorseshoe orbit
2003 YN1070.01410–30LINEAR2003 December 20Quasi-satelliteHorseshoe orbit
2004 GU90.136160–360LINEAR2004 April 13Quasi-satelliteQuasi-satellite
2006 FV350.377140–320Spacewatch2006 March 29Quasi-satelliteQuasi-satellite
2006 JY260.0836–13Catalina Sky Survey2006 May 6Horseshoe orbitHorseshoe orbit
2006 RH1200.0242–3Catalina Sky Survey2006 September 14Temporary satelliteApollo asteroid
2010 SO160.075357WISE2010 September 17Horseshoe orbitHorseshoe orbit
2010 TK70.191150–500WISE2010 October 1Earth trojanEarth trojan
2013 BS450.08320–40Spacewatch2013 January 20Horseshoe orbitHorseshoe orbit
2013 LX280.452130–300Pan-STARRS2013 June 12Quasi-satellite temporaryQuasi-satellite temporary
2014 OL3390.461170EURONEAR2014 July 29Quasi-satellite temporaryQuasi-satellite temporary
2015 SO20.10850–111Črni Vrh Observatory2015 September 21Quasi-satelliteHorseshoe orbit temporary
2015 XX1690.1849–22Mount Lemmon Survey2015 December 9Horseshoe orbit temporaryHorseshoe orbit temporary
2015 YA0.2799–22Catalina Sky Survey2015 December 16Horseshoe orbit temporaryHorseshoe orbit temporary
2015 YQ10.4047–16Mount Lemmon Survey2015 December 19Horseshoe orbit temporaryHorseshoe orbit temporary
469219 Kamoʻoalewa0.10441-100Pan-STARRS2016 April 27Quasi-satellite stableQuasi-satellite stable
DN16082203???2016 August 22Possible Temporary satelliteDestroyed
2020 CD30.0171–6Mount Lemmon Survey2020 February 15Temporary satelliteTemporary satellite

Neptune

is a temporary quasi-satellite of Neptune. 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.

Other planets

Based on simulations, it is believed that Uranus and Neptune could potentially hold quasi-satellites for the age of the Solar System, 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.

Artificial quasi-satellites

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 from Phobos. 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

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. The minor planets Ceres, Vesta, and Pluto are known to have accidental quasi-satellites. 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. 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.