2002 AA 29
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Asteroid 2002 AA 29 |
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| Properties of the orbit ( animation ) | |
| Orbit type | Near-Earth asteroid, Aten-type |
| Major semi-axis | 0.993 AU |
| eccentricity | 0.012 |
| Perihelion - aphelion | 0.988 AU - 1.012 AU |
| Inclination of the orbit plane | 10.739 ° |
| Sidereal period | 1 a 0 d |
| Mean orbital velocity | 29.784 km / s |
| Physical Properties | |
| Medium diameter | 50-110 m |
| Albedo | 0.04-0.20 |
| Rotation period | <33 min |
| Absolute brightness | 24.08-25.23 mag |
| Spectral class | C to S type |
| history | |
| Explorer | LINEAR |
| Date of discovery | January 9, 2002 |
| Source: Unless otherwise stated, the data comes from JPL Small-Body Database Browser . The affiliation to an asteroid family is automatically determined from the AstDyS-2 database . Please also note the note on asteroid items. | |
2002 AA 29 is a very small near-Earth asteroid , which was discovered on January 9, 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 in an orbit very similar to that of the earth , almost circular. It runs for the most part within the earth's orbit and crosses it at the point of the asteroid furthest from the sun, the aphelion . Because of this orbit, it is classified as an Aten-type after the eponymous asteroid Aten .
Another special feature is that its mean period around the sun corresponds exactly to a sidereal year . This means that it interacts with the earth , since such an orbit is only stable under certain conditions. So far, only a few such asteroids that interact with the earth in 1: 1 orbital resonance are known. The first was the (3753) Cruithne, discovered in 1986 . Asteroids that are in 1: 1 resonance with a planet are also called co-ordinate objects because they follow the planet's orbit. 2002 AA 29 is not one of the Trojans , which are the most well-known co-ordinate asteroids and are located in Lagrangian points L 4 and L 5 of the respective planet. Rather, it is in a so-called horseshoe orbit along the earth's orbit.
Orbit
Orbit data
Scientists from the Jet Propulsion Laboratory (JPL), Athabasca University ( Canada ), Queen's University in Kingston (Ontario, Canada) , York University in Toronto and the Tuorla Observatory at the University of Turku in Finland discovered the Unusual orbit from 2002 AA 29 confirmed by follow-up examinations at the Canada-France-Hawaii Telescope in Hawaii :
- Its orbit is for the most part within the Earth's orbit, in contrast to the orbits of most asteroids in the so-called asteroid belt between Mars and Jupiter or even further outside of Neptune's orbit in the so-called Kuiper belt .
- Due to orbital disturbances of the large gas planets , mainly by Jupiter, and by the Jarkowski effect (change of orbit due to asymmetrical irradiation and radiation of infrared radiation ) asteroids are deflected into the inner solar system , where their orbits can be further influenced by flying close to the inner planets. According to this mechanism, AA 29 probably also came into the sphere of influence of the earth from the outer solar system in 2002 . However, it is also speculated that the asteroid formed near Earth's orbit and has always been in a near-Earth orbit. One possibility in this case would be that it could be a detached fragment from the collision of a medium-sized asteroid with the earth or the moon .
- Its mean period of orbit is one sidereal year . After it was deflected into the inner solar system - or formed on an orbit near the earth's orbit - the asteroid must have found itself on an orbit corresponding to the earth. On this orbit it was repeatedly distracted from the earth in such a way that its own period of rotation was the same as that of the earth around the sun. In its current orbit, the earth will always keep it synchronized with its own orbit.
- The asteroid's orbit is almost circular and, at 0.012, has an even smaller eccentricity than the Earth's orbit at 0.0167. The other near-Earth asteroids have a much higher eccentricity of 0.29 on average. All other asteroids known before 2002 in 1: 1 resonance with the earth also have very strongly elliptical orbits - the eccentricity of (3753) Cruithne is 0.515, for example. The orbit of 2002 AA 29 was unique at the time of its discovery, which is why the asteroids are often referred to as the earth's first true co-ordinate companion , as the orbits of the other asteroids discovered before are not very similar to the earth's orbit. The very low orbital eccentricity of 2002 AA 29 is also an indication that it must have always been in a near-Earth orbit, or that the Jarkowski effect caused it to spiral into the inner solar system comparatively strongly over billions of years, since asteroids deflected by planets in the Usually have orbits with great eccentricity.
- The inclination of the orbit against the ecliptic (orbital plane of the earth) of 2002 AA 29 is moderate at 10.7 ° . Thus, its orbit is slightly tilted against that of the earth, otherwise both orbits would lie directly on top of one another.
Track shape
If you consider the orbit of 2002 AA 29, which is almost congruent with the earth's orbit, from the reference system that moves with the earth's movement around the sun , it describes an arc of almost 360 ° along the earth's orbit over the course of 95 years, which it swings back in another 95 years . The shape of the arch is reminiscent of a horseshoe , hence the name horseshoe orbit for its orbit as seen from the reference system that moves with the earth. When moving along the earth's orbit, it winds itself around it in a spiral, whereby it takes a year for a spiral turn.
This spiral movement in the reference system that moves with the earth is due to its eccentricity and orbital inclination, which is slightly different from the earth's orbit, whereby the difference in the orbital inclination is responsible for the vertical and that of the eccentricity for the horizontal part of the projected spiral movement. If it comes close to the earth from the front, i.e. in the direction of rotation of the earth, then it is transported into a slightly faster orbit slightly closer to the sun by its force of attraction. It now hurries ahead of the earth on its orbit until after 95 years it has almost lapped it and is now approaching it from behind. Now it comes under the influence of gravity again and is lifted into a slower orbit a little further away from the sun. As a result, it can no longer keep up with the speed of the earth until it reaches him again after 95 years. The earth and 2002 AA 29 follow each other alternately, but never come too close.
On January 8, 2003, the asteroid approached Earth from the front to within 5.9 million kilometers, which will be its closest approach for nearly a century. Since then he has been running ahead of her until he will have caught up with her from behind. However, due to the subtle interaction with Earth, one need not fear that this asteroid might collide with Earth like other Earth orbit cruisers. Calculations show that it will never get closer than 4.5 million kilometers to Earth in the next millennia, which is roughly twelve times the Earth-Moon distance.
In comparison, the larger co-ordinate companion (419624) 2010 SO 16 only approaches 50 times the lunar distance. It takes 175 years for the distance between the horseshoe points.
Due to its orbit inclination of 10.7 ° against the ecliptic, AA 29 is not always forced from the earth into its horseshoe orbit, but can sometimes slip through. It is then trapped near Earth for a while, which will happen next time in about 600 years, around the year 2600. It will then be within the small gap in the earth's orbit that it did not reach in its previous horseshoe orbit and no further than 0.2 astronomical units (30 million kilometers) from the earth. In doing so, it will slowly circle around the earth - almost like a second moon ; however, it takes a year to complete one cycle. After 45 years it finally switches back to horseshoe orbit, and then around the year 3750 and again around 6400 again to stay near the earth for 45 years. In these phases, in which he is outside his horseshoe orbit, he swings back and forth once within 15 years in the narrow area along the earth's orbit in which he is trapped. Since it is not firmly bound to the earth like the moon, but is mainly under the influence of gravity from the sun, these bodies are called quasi-satellites . This is roughly analogous to two cars that drive next to each other at the same speed and overtake each other, but are not firmly bound to each other.
Orbit calculations show that in 2002 AA 29 was already in this quasi-satellite orbit for 45 years from around 520 AD, but due to its tiny size too faint and therefore not visible. It thus changes approximately cyclically between the two orbit shapes, but always stays in quasi-satellite orbit for 45 years. Outside a period of time from approx. 520 to 6500 AD, the calculated orbits become chaotic , i.e. not calculable, which is why it is not possible to give precise information about periods beyond this. 2002 AA 29 was the first known celestial body to alternate between horseshoe and quasi-satellite orbit.
nature
Brightness and size
Little is known about 2002 AA 29 itself. With a size of around 50 to 110 meters, it is very small, which is why it only appears as a small point from Earth, even with large telescopes, and can only be observed with highly sensitive CCD cameras. At the time of closest approximation on January 8, 2003, it only had an apparent magnitude of around 20.4 orders of magnitude in the visual area .
So far nothing specific is known about the composition of 2002 AA 29 . Due to the proximity to the sun, however, it cannot consist of highly volatile substances such as water ice , as these would melt , evaporate or sublime , which can be clearly seen in comets on their tail. Presumably, like most asteroids, it will have a dark carbonaceous or slightly lighter, silicate-rich surface; in the former case the albedo would be around 0.05, in the latter a little higher at 0.15 to 0.25. Because of this uncertainty, the figures for its diameter have a relatively large range.
An additional uncertainty arises from the fact that during radar echo measurements with the Arecibo radio telescope, only an unexpectedly weak radar echo could be picked up, i.e. 2002 AA 29 is either even smaller than expected or radio waves are only weakly reflected. In the former case it must have an unusually high albedo. This would be a further indication of the speculation that it, or at least the material it is made of, unlike most asteroids, has already been formed in a near-Earth orbit or even represents a fragment that was created by the collision of a medium-sized asteroid with the Earth or blasted off the moon.
Rotation time
With the help of the radar echo measurements on the Arecibo radio telescope , it was possible to determine the rotation period of 2002 AA 29 . With this method of radar astronomy , radio waves with a fixed wavelength are sent from a radio telescope to an asteroid. They are reflected there, whereby due to the Doppler effect, the part of the surface that moves towards the observer due to the rotation shortens the wavelength of the reflected radio waves, while the other part that turns away from the observer lengthen the wavelength. As a result, the wavelength of the reflected radio waves is “smeared”. From the width of this wavelength smear and the diameter of the asteroid, one can infer the duration of the rotation. For 2002 AA 29 you got 33 minutes as the upper limit of its rotation time, so the asteroid is probably rotating even faster. This rapid rotation together with the small diameter and thus the low mass allows some interesting conclusions:
- The asteroid rotates so fast that the centrifugal force on its surface is greater than its gravitational force. It is therefore under tensile stress and therefore cannot consist of a heap of loosely connected rubble or several fragments orbiting each other - which is suspected of some other asteroids or, for example , has also been proven for the asteroid (69230) Hermes . Instead, the body must be made up of a single relatively solid boulder or slightly baked piece. However, its tensile strength is probably much smaller than that of the earthly rock and the asteroid is also quite porous.
- 2002 AA 29 can never have accumulated from individual smaller pieces, as these would have been driven apart due to the rapid rotation. So it must be a detached fragment that was created when two celestial bodies collided.
outlook
Because of its very Earth-like orbit, the asteroid is relatively easy to reach for space probes . 2002 AA 29 would therefore be a suitable study object for a more detailed investigation of the structure and composition of asteroids and the development of their orbits around the sun over time. Other such co-ordinate companions of the earth located on horseshoe tracks or in orbit as a quasi-satellite have already been found in the meantime, such as the quasi-satellite 2003 YN 107 . Furthermore, around the Lagrangian points L 4 and L 5 of the Earth-Sun system, small Trojan companions of the earth with a diameter of 100 meters are suspected . The Erdtrojaner 2010 TK 7 was discovered and confirmed in 2010/2011, it is currently bound to L 4 ; At around 300 meters, however, its diameter is significantly larger than the size assumed for a terrestrial Trojan.
See also
literature
- M. Connors et al .: Discovery of an asteroid and quasi-satellite in an Earth-like horseshoe orbit. in: Meteoritics & Planetary Science . Allen Press, Lawrence Kan 37.2002, 10, 1435-1441. bibcode : 2002M & PS ... 37.1435C (English)
- Tilmann Althaus: A second companion of the blue planet. in: Stars and Space . Spektrum der Wiss., Heidelberg 42.2003, 2, pp. 22-24. ISSN 0039-1263
Web links
items
Databases
- Orbit data from 2002 AA 29 from the MPEC database (English)
- Physical data from 2002 AA 29 from the EARN database (English)
- Asteroid Orbital Elements Database of the Lowell Observatory (English)
Individual evidence
- ↑ a b M. Connors et al .: Horseshoe Asteroids and Quasi-satellites in Earth-like Orbits. In: 35th Lunar and Planetary Science Conference, 15. – 19. March 2004. League City Texas 2004, 3rd, Abstract No. 1565 (English, PDF; 933 kB).
- ↑ Asteroid 2010 SO16 is following Earth in its orbit around sun . earthsky.org. April 6, 2011. Retrieved April 10, 2011.
- ^ R. Brasser et al .: Transient co-orbital asteroids. In: Icarus . Elsevier, San Diego 171.2004, 9, p102-109. ISSN 0019-1035 (English, online on the Icarus server: doi : 10.1016 / j.icarus.2004.04.019 ).
- ^ A b Steven J. Ostro et al .: Radar detection of Asteroid 2002 AA29. In: Icarus . Elsevier, San Diego 166.2003, 12, p271-275. ISSN 0019-1035 (English, online on the Icarus server: doi : 10.1016 / j.icarus.2003.09.001 ).
