Quasi-satellite

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 on the right. 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 neighbourhood, 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.

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Examples

Earth

As of 2011, Earth has five known quasi-satellites: 3753 Cruithne, 2002 AA29, 2003 YN107, 2004 GU9[2] and 2010 SO16.[3] These objects remain in quasi-satellite orbits for periods of tens to hundreds of years or more.[1]

Venus

Venus has a quasi-satellite, 2002 VE68. This asteroid is also a Mercury- and Earth-crosser; it seems to have been a "companion" to Venus for the last 7000 years or so only, and is destined to be ejected from this orbital arrangement about 500 years from now.[4]

Other planets

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),[5] but a quasi-satellite's orbit would remain stable for only 10 million years near Jupiter and 100,000 years near Saturn. No actual quasi-satellites of these planets are currently known.

Artificial

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 km from Phobos.[6] 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.

See also

References

  1. ^ a b M. Connors et al. (2002). "Discovery of an asteroid and quasi-satellite in an Earth-like horseshoe orbit". Meteoritics & Planetary Science 37 (10): 1435. Bibcode 2002M&PS...37.1435C. doi:10.1111/j.1945-5100.2002.tb01039.x. 
  2. ^ 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. 
  3. ^ Braconnier, Deborah (April 6, 2011). "New horseshoe orbit Earth-companion asteroid discovered". PhysOrg. http://www.physorg.com/news/2011-04-horseshoe-orbit-earth-companion-asteroid.html. Retrieved 2011-04-06. 
  4. ^ Asteroid 2002 VE68, a quasi-satellite of Venus
  5. ^ P. Wiegert and K. Innanen (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. http://www.iop.org/EJ/article/1538-3881/119/4/1978/990367.html. 
  6. ^ The orbit is erroneously called "quasi-synchronous"

External links