2002 AA29

2002 AA29 is a very small near-Earth asteroid that was discovered on 9 January 2002 by the automatic sky monitoring LINEAR ( Lincoln Near Earth Asteroid Research). The diameter of the asteroid is only about 50 to 110 meters. It orbits the sun on one of the earth's orbit very similar, almost circular orbit. It runs for the most part within the orbit and crosses them in sonnenfernsten point of the asteroid, the aphelion. He is classified as an Aten type after the eponymous asteroid Aten because of this orbit. Another special feature is that its average orbital period around the Sun 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. The first was discovered 1986 (3753) Cruithne. 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, in 2002 AA29 is not one of them. He is rather on a so-called horseshoe orbit along the Earth's orbit.

• 2.1 brightness and size
• 2.2 Rotational Period

• 6.1 Article
• 6.2 databases

Orbit

Path data

Scientists at the Jet Propulsion Laboratory (JPL ), Athabasca University (Canada ), Queen's University in Kingston (Ontario, Canada ) York University in Toronto and the Tuorlaobservatoriums the University of Turku in Finland presented shortly after the discovery by LINEAR the unusual orbit determined from 2002 AA29, which was confirmed by follow-up examinations at the Canada -France - Hawaii Telescope in Hawaii:

• Its orbit is located mostly within the Earth's orbit. The orbits of most asteroids are located in the so-called asteroid belt between Mars and Jupiter or further out beyond the orbit of Neptune called the Kuiper belt. By perturbations of the large gas planet, mainly by Jupiter, and by the Yarkovsky effect (lane change by asymmetric radiation and irradiation of infrared radiation) asteroids are deflected into the inner solar system, where their orbits are then affected by other close flybys of the inner planets on. 2002 AA29 is also likely to come from the outer solar system in the sphere of influence of the Earth. However, it is also speculated that the asteroid has always been on a near-Earth path and he or a predecessor body is thus created near the Earth's orbit. One possibility would be in this case that he could be a abgesprengtes fragment of the crash of a medium asteroid with the Earth or the moon.
• Its average circulation period is one sidereal year. After being deflected into the inner solar system - or was on a path near the Earth's orbit - the asteroid must be advised on a corresponding to the Earth orbit. On this track, he was always distracted from the earth so that its own orbital period, the orbital period of the Earth around the sun accessible. At its current orbit so he will always be kept from the Earth in sync with their own circulation.

• The orbit of the asteroid is almost circular and has 0,012 an even lower eccentricity than the Earth's orbit with 0.0167. The other near-Earth asteroids have a much higher eccentricity of 0.29 on average. All the other known before 2002 asteroids in 1:1 resonance with the Earth have very highly elliptical orbits - the eccentricity of ( 3753 ) Cruithne is for example 0.515. The orbit of 2002 AA29 was unique at the time of discovery is why people often referred to the asteroid as a first real co-orbital companions of the earth, because the orbits of the other previously discovered asteroid the Earth's orbit are not very similar. The very low orbital eccentricity from 2002 AA29 is also an indication that it must have always been on a near-Earth orbit, or the Yarkovsky effect made ​​him comparatively strong spiralieren over billions of years into the inner solar system, since planet deflected asteroids usually have orbits with large eccentricity.
• The orbital inclination to the ecliptic ( the orbital plane of the Earth) 2002 AA29 is moderate at 10.7 °. Thus its orbit is slightly tilted with respect to the earth, otherwise both paths would directly lie on each other.

Web form

Looking at the one with the Earth's orbit were nearly the same orbit of 2002 AA29 from the sun moved along with the earth's motion reference system, he describes the course of 95 years along the Earth's orbit an arc of nearly 360 °, he swings back again in another 95 years. The shape of the arch is reminiscent of a horseshoe, hence the name horseshoe orbit for its orbit from the co-moving with the earth reference frame as seen. When moving along the Earth's orbit, he spirals around this, which he needs for a spiral rotation one year. This spiral movement in the co-moving with the Earth reference system comes about through his slightly different from the Earth's orbital eccentricity and orbital inclination, the difference in the orbital inclination for the vertical and one of eccentricity for the horizontal component of the projected spiral motion is responsible. If he comes to the earth from the beginning, ie in the direction of rotation of the earth, near, as it is conveyed by their attraction to a slightly faster, lying somewhat closer to the solar orbit. He rushes the earth in its orbit now ahead until it has almost overtaken again after 95 years and is now approaching her from behind. Now he falls again under its gravitational influence and is further elevated to a slower orbit slightly away from the sun. Wherein it can no longer keep up with the speed of the earth well, until it again reaches it after 95 years from the beginning. The Earth and 2002 AA29 thus traced alternately, come away but never too close. On 8 January 2003, the asteroid approached Earth from front to 5.9 million kilometers, which will be its closest approach for nearly a century. Since then he precedes it now, until he will have caught up from behind. Due to the subtle interaction with the earth but you do not have to worry that this asteroid might collide with the Earth's orbit as other cruiser with the earth. Calculations show that he will never get close closer than 4.5 million km in the next few millennia of the earth, which is about twelve times the Earth-Moon distance.

In comparison, the larger co-orbital companion approaches 2010 SO16 only to the 50-fold Moon distance. For the distance between the horseshoe points he needed 175 years.

Due to its orbital inclination of 10.7 ° to the ecliptic is 2002 AA29 but not always forced by the earth on its horseshoe orbit, but can sometimes slip through virtually. He is then trapped for a while in the vicinity of the earth, what will happen the next time in about 600 years, ie around the year 2600. He will then stay within the small gap of the earth's orbit, which he did not reach in his previous horseshoe orbit, and not more than 0.2 astronomical units ( 30 million kilometers ) away from Earth. Here it is - almost like a second moon - slowly revolve around the earth; for a round he needs but one year. After 45 years he finally goes back to the horseshoe orbit to then around the year 3750 and again by 6400 to stop again for 45 years in the vicinity of the earth. In these phases where he is staying outside its horseshoe orbit, it swings in the narrow region along the Earth's orbit, in which he is trapped, within 15 years once before and back. Since he is not like the moon tightly bound to the earth, but mainly under the gravitational influence of the sun, called this body quasi-satellite. This is analogous to two cars side by side drive with the same speed and overtake mutually, but are not tied to each other about. Show path calculations that 2002 AA29 as early as about 520 AD, was for 45 years in this quasi-satellite orbit, but due to its tiny size too faint and therefore not visible. He changes thus almost cyclically between the two orbit forms, but always sticks on for 45 years in quasi-satellite orbit. Outside a period of about 520-6500 AD, the calculated orbits are chaotic, that is not predictable, so you can make over periods that go beyond any exact information. 2002 AA29 was the first known celestial body that alternates between horseshoes and quasi-satellite orbit.

Nature

Brightness and size

About 2002 AA29 even relatively little is known. He is having a size of about 50 to 110 meters is very small, so it appears from the earth, even with large telescopes only as a small dot and can be observed only with highly sensitive CCD cameras. Around the time of closest approach on January 8, 2003, he had in the visual field only an apparent magnitude of about 20.4 magnitudes. About the composition of 2002 AA29 is so far nothing concrete known. However, due to the vicinity of the Sun, it can not consist of volatile substances such as water ice, as they melt, evaporate or sublimate would, what can be observed clearly visible at about comet at its tail. Presumably, he is like most asteroids have a dark carbonaceous or slightly lighter silicate- rich surface; in the former case would be the albedo at about 0.05, the latter slightly higher at 0.15 to 0.25. Because of this uncertainty, the data have a relatively large margin for its diameter. An additional uncertainty arises from the fact that when radar echo measurements with the Arecibo radio telescope only an unexpectedly weak radar echo was collected in 2002 AA29 so either is even smaller than expected or radio waves reflected only weakly. In the former case, he must have an unusually high albedo. This would be a further indication of the speculation that he, or at least the material from which it is made, unlike most asteroids has already been done on a near-Earth orbit, or even represents a fragment of it, or by the collision of a middle asteroid with the Earth the moon was blasted off.

Rotational period

Use the radar echo measurements at the Arecibo radio telescope could determine the rotation period of 2002 AA29. In this method, radio waves are emitted radar astronomy fixed wavelength of a radio telescope specifically to an asteroid. In this they are reflected, said shortened due to the Doppler effect, the part of the surface which is moving due to the rotation of the observer, the wavelength of the reflected radio wave, while the other part which rotates away from the observer, increases the wavelength. As a result, the wavelength of the reflected radio waves " smeared ." From the width and the diameter of this Wellenlängenverschmierung asteroid may be close to the rotation period. For 2002, AA29 so you got 33 minutes as the upper limit of its rotation period, probably rotates the asteroid that much sooner. This rapid rotation spins together with the small diameter and the small mass, thus some interesting conclusions:

• The asteroid rotates so fast that the centrifugal force on the surface thereof is greater than its gravitation. He is thus under tensile stress and thus can not consist of a bunch of loosely connected or debris from several to orbiting debris - has what is thought by some other asteroids or, for example, the asteroid ( 69230 ) Hermes also demonstrated. Instead, the body of a single relatively solid rock or slightly caked shall be composed of. However, its tensile strength is probably much smaller than the earthly rock and the asteroid probably quite porous.
• 2002 AA29 may have stored together from individual smaller pieces and never, as they would be driven apart due to the rapid rotation before. So he must be a abgesprengtes fragment, which was created in the collision of two celestial bodies.

View

Due to its very Earth-like orbit of the asteroid for space probes is relatively easy to reach. 2002 AA29 would be a suitable object of study for closer examination of the structure and composition of asteroids and the temporal evolution of their orbits around the sun. Other such located on horseshoe orbits, or on a co-orbital satellite orbit as quasi companion of the earth have been found in the meantime, such as the quasi- satellite in 2003 YN107. Furthermore, it is believed by the Lagrange points L4 and L5 of the Earth-Sun system small Trojan companion of Earth in the order of 100 meters in diameter. The Erdtrojaner 2010 TK7 was discovered in 2010/2011 and confirmed he is currently attached to L4; its diameter is about 300 meters, but with significantly higher than the assumed size for a Erdtrojaner.