Quasi-satellite
A quasi-satellite is a small co-ordinate companion of a larger celestial body (such as a planet), which it orbits at a greater distance with the same orbital period as it moves around a central star (the sun ).
Most of them are asteroids that are near a planet . Its orbit around the sun therefore has the same orbital period and almost the same orbit axis as the planet, but appears a bit eccentric "seen from the sun" (see also Lagrange points and restricted three-body problem ).
Track shape
Quasi satellites are mainly under the gravitational influence of the common central body - and not like a moon under the influence of the planet . Strictly speaking, the earth's moon is also under the main influence of the sun. However, the lunar orbit - in contrast to a co-orbital orbit - lies in the gravitational field of the sun so that its influence is almost constant. The influence of the earth therefore largely determines the small, regular "disturbances" of the lunar orbit: In the stationary reference system , the lunar orbit describes a "snaking" curve around the earth's orbit. In contrast, the orbit of a quasi-satellite looks like a normal Kepler , elliptical orbit in this reference system .
From the point of view of an inhabitant of the larger object (planet), if one takes as the reference system the movement of the larger object (planet) around the central star (the planet thus seems to be at rest), the differences are more difficult to recognize. You can only see the relative movement of the quasi-satellite. In this reference system, it describes a loop around the larger celestial body within one orbit around the central star - so it has a slightly different orbit in terms of eccentricity and orbital inclination towards the ecliptic . The radial movement component is caused directly by the difference in the eccentricities between the planet and the quasi-satellite, while the movement component along the planetary orbit is caused by the slightly different speed in perihelion and aphelion . In perihelion it overtakes the planet from within, while in aphelion it falls further outside in relation to the planet. In the course of a year, this results in a complete orbit around the planet (which is ultimately synonymous with an orbital resonance of 1: 1), unlike a real satellite: The above-mentioned "serpentine shape" also exists, strictly speaking, in the orbit of a quasi-satellite, but has the same period length as its actual orbit (unlike the moon with around 13 lunar orbits around the earth per year). The orbits of the planet and the quasi-satellite are vividly similar to two cars on a motorway that drive next to each other at the same speed and overtake each other, but are not firmly bound to each other.
stability
Even if quasi-satellites are mainly subject to the gravity of the central body (the sun), they are influenced by the planet they are near. Since the ratio of the orbital times of the planet and the quasi-satellite is exactly 1: 1, i.e. they always meet in a similar constellation, the disturbance from the planet always acts in the same way and can therefore rock and throw the quasi-satellite off course.
However, computer simulations show that the orbits of quasi-satellites on the outer planets Uranus and Neptune are so stable that quasi-satellites have still been there since the formation of the solar system 4.5 billion years ago. For Jupiter, however , the time span to instability is only 10 million years and for Saturn , less than 100,000 years, even shorter. If the orbital eccentricity of the quasi-satellites is in a certain range (for Uranus and Neptune between 0.1 and 0.15) and the lower the inclination of their orbits to the orbital plane of the planet, the more stable the orbits of these quasi-satellites are. Because of this, Uranus and Neptune should still have original quasi-satellites, while Jupiter and Saturn should only have temporarily captured quasi-satellites.
Examples
earth
The small asteroid 2003 YN 107 is considered to be the first quasi-satellite to be discovered on earth from 1996 to 2006, which has since described a horseshoe orbit along the earth's orbit. In 2066 it will again become a quasi-satellite of the earth. At the subsequent encounter in the year 2120 it is even likely that it will be captured by the earth and thus become the second real moon on earth.
Another co-orbital object on earth, the asteroid 2002 AA 29 , alternates approximately cyclically between a horseshoe orbit and a quasi-satellite orbit, the next time it will be a quasi-satellite for 45 years around the year 2600.
On September 19, 2014, Cornell University published a study on the newly discovered asteroid 2014 OL 339 as another quasi-satellite on Earth. So far, the asteroids (164207) 2004 GU 9 , (277810) 2006 FV 35 and 2013 LX 28 were known as unbound earth companions.
On April 27, 2016, the automatic was under Pan-STARRS - sky survey the asteroid (469219) Kamo'oalewa discovered and recognized in the result as another quasi-satellite. Its diameter is given as around 40 to 100 meters and its distance from the earth varies between 38 and 100 times the distance from the earth to the moon. In addition, calculations have shown that the asteroid has been around Earth for around a century.
Other planets
The Venus has a quasi-satellite, the asteroid (524522) 2002 VE 68 . This is the first of its kind to be discovered and so far the only known coorbital companion of Venus. It is calculated that it has been in its current orbit for 7,000 years and will follow it for another 500 years. Due to the high eccentricity of about 0.4 and the inclination of around 9 °, its maximum distance from the sun is almost as great as that of the earth and its minimum distance smaller than the aphelion of Mercury ; it is also approaching the earth. The asteroid is believed to have been a near-Earth asteroid about 7,000 years ago that was brought into its current orbit by the Earth itself.
According to simulations, quasi-satellites have existed around the planets Uranus and Neptune since the formation of the solar system about 4.5 billion years ago. It is therefore assumed that these planets have quasi-satellites that they have not lost since they approached. So far, however, no quasi-satellites have been discovered by gas planets .
See also
Web links
- Articles about quasi-satellite (English)
- GIF animations of the orbital movements of the earth and the asteroid 2002 AA 29 (English)
Individual evidence
- ↑ Asteroid 2014 OL339: yet another Earth quasi-satellite . September 19, 2014, arxiv : 1409.5588 .
- ↑ Asteroid 2016 HO3 - a longtime companion of the earth. June 16, 2016, accessed June 18, 2016 .
- ↑ S. Mikkola, R. Brasser, P. Wiegert, K. Innanen: Asteroid 2002 VE68, a quasi-satellite of Venus . In: Monthly Notices of the Royal Astronomical Society . Issue 351, Topic 3. 2004. pp. L63-L65. doi : 10.1111 / j.1365-2966.2004.07994.x , bibcode : 2004MNRAS.351L..63M
- ^ Paul Wiegert, Kimmo Innanen, Seppo Mikkola: The stability of quasi satellites in the outer solar system . In: The Astronomical Journal . Issue 119. pp. 1978-1984.