Temporary satellite


A temporary satellite is an object which has been captured by the gravitational field of a planet and thus became the planet's natural satellite, but, unlike irregular moons of the larger outer planets of the Solar System, will eventually either leave its orbit around the planet or collide with the planet. The only observed examples are, a temporary satellite of Earth for nine months in 2006 and 2007, and, which was discovered in 2020. Some defunct space probes or rockets have also been observed on temporary satellite orbits.
In astrophysics, a temporary satellite is any body that enters the Hill sphere of a planet at a sufficiently low velocity such that it becomes gravitationally bound to the planet for some period of time.

Capture of asteroids

The dynamics of the capture of asteroids by Earth was explored in simulations conducted on a supercomputer, with results published in 2012. Of 10 million virtual near-Earth asteroids, 18,000 have been temporarily captured. Earth has at least one temporary satellite across at any given time, but they are too faint to detect by current surveys.
According to the simulations, temporary satellites are typically caught and released when they pass one of two gravitational equilibrium points of the Sun and the planet along the line connecting the two, the L1 and L2 Lagrangian points. The captured asteroids typically have orbits very similar to the planet's and are captured most often when the planet is closest to the Sun or furthest from the Sun.
In strict sense, only bodies that complete a full orbit around a planet are considered temporary satellites, also called temporarily captured orbiters. However, asteroids not in a tight co-orbital configuration with a planet can be temporarily captured for less than a full orbit; such objects have been named temporarily-captured fly-bys. In a 2017 follow-up to the 2012 simulation study which also considered an improved model of near-Earth asteroid populations, 40% of captured objects were TCF. The combined number of TCO/TCF was found to be smaller than in the previous study, the maximum size of objects which can be expected to be orbiting Earth at any given moment was. In another 2017 study based on simulations with one million virtual co-orbital asteroids, 0.36% have been temporarily captured.

Examples

, two objects have been observed at the time when they were temporary satellites: and 2020 CD3. According to orbital calculations, on its solar orbit, passes Earth at low speed every 20 to 21 years, at which point it can become a temporary satellite again.
, there is one confirmed example of a temporarily captured asteroid that didn't complete a full orbit,. This asteroid was observed for a month after its discovery in November 1991, then again in April 1992, after which it wasn't seen until May 2017. After the re-discovery, orbital calculations confirmed that was a temporary satellite of Earth in February 1992.
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 CD30.0171–3Mount Lemmon Survey2020 February 15Temporary satelliteApollo asteroid

Artificial objects on temporary satellite orbits

The Earth can also temporarily capture defunct space probes or rockets travelling on solar orbits, in which case astronomers can't always immediately determine whether the object is artificial or natural. The possibility of an artificial origin has been considered for both and.
The artificial origin has been confirmed in other cases. In September 2002, astronomers found an object designated J002E3. The object was on a temporary satellite orbit around Earth, leaving for a solar orbit in June 2003. Calculations showed that it was also on a solar orbit before 2002, but was close to Earth in 1971. J002E3 was identified as the third stage of the Saturn V rocket that carried Apollo 12 to the Moon. In 2006, an object designated 6Q0B44E was discovered on a temporary satellite orbit, later its artificial nature was confirmed, but its identity is unknown. Another confirmed artificial temporary satellite with unidentified origin is.