(3753) Cruithne

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( 3753 ) Cruithne is approximately 3.3 km large near-Earth asteroid.

Discovery

The asteroid was discovered on October 10, 1986 at the Siding Spring Observatory. He first received the provisional designation 1986 TO. In the subsequent calculation of its orbit it was recognized that it is identical with the object UH in 1983, which at the European Southern Observatory ( ESO) was discovered in Chile in 1983. Later he was named Cruithne after the first Celtic tribe that settled in the British Isles.

Orbit

( 3753 ) Cruithne orbits the sun on a highly eccentric orbit of the Aten - type. Another special feature is that ( 3753 ) Cruithne was the first asteroid discovered, the mean orbital period around the Sun almost exactly corresponds to a sidereal year. This means that it is in interaction with the earth, since such orbit is stable only under certain conditions. So far, few such in 1:1 orbital resonance interacting with Earth asteroids are known only. Asteroids that are in 1:1 resonance with a planet, also co-orbital objects are called because they follow the path of the planet. The best-known co-orbital asteroids are called Trojans, which reside in the Lagrangian points L4 and L5 of each planet. However Cruithne is not a trojan. In 1997, scientists at York University (Canada) and the University of Turku (Finland ) its orbit more precisely and found a complex interacting with the Earth horseshoe orbit. In the meantime, however, one expects him mainly because of its highly eccentric orbit no longer a real horseshoe orbit companions of the earth, but one of the asteroid 2002 AA29 as the first known real horseshoe companion of the Earth.

Cruithne moves at a distance of 0.484 AU ( perihelion ) to 1.511 AU aphelion around the sun. His eccentric train goes near the sun approach almost to the orbit of Mercury and crosses in the outer regions of the orbit of Mars.

Its orbit is inclined at 19.811 ° significantly to the ecliptic ( the orbital plane of the Earth). It is therefore usually well outside the orbital plane of the planets.

Cruithne is occasionally referred to as the " second moon of the Earth", but this is not correct. The asteroid is not running around the earth, but moves on a earth- co-orbital path around the sun, its orbital period is nearly one sidereal year and thus is almost equal to the earth.

The actual duration of the Cruithne orbits is only on average one year, the orbit is about 190 years, slightly shorter than a year and a bit in the next 190 years longer.

In the representation in which one chooses the connection between Earth and Sun as a fixed axis, the orbit of the asteroid has a complex horseshoe shape, that is, the asteroid approaches the Earth slowly " from scratch" ( from the motion direction of the web ), disappears again in the same direction, appeared 190 years later "from behind" on again and removed there to come back around again after 190 years back " from scratch". A complete cycle takes about 385 years. Cruithne was discovered in the current phase of such perigee and now moves away from the earth. Due to the subtle interaction with the earth, there is no risk of colliding with it. He can approach based on which the earth in its orbit no closer than 15 million kilometers up to - which is about 40 times the distance between Earth and the Moon. Because of its small size, it is not visible to the naked eye even at the time of closest approach.

Such an orbit is also called horseshoe orbit due to its horseshoe shape in that particular frame of reference. However, the orbit of Cruithne is even more complex due to the large eccentricity and his rather high orbital inclination, which is why they are not a real horseshoe orbit around the earth follows. Railway Simulations show that he had located some time in this orbit. Its orbit is by computer simulations but not stable in the long term. Presumably Cruithne this relationship with the Earth's orbit have only a few thousand years and then taking another train.

Similar asteroids

Meanwhile, several asteroids with such a relationship to the Earth's orbit are known: (85770) 1998 UP1, ( 54509 ) YORP and 2002 AA29. The latter has an almost circular path around the Earth and is considered the first true co-orbital companion of the Earth on a horseshoe orbit.