2002 AA29
Synodic rotation period | 0.55 h (33 min)[2] | |
0.2 ? | ||
Temperature | ~279 K | |
S-type asteroid[4] | ||
24.1 | ||
2002 AA29 (
A further characteristic is that its mean orbital period about the Sun is exactly one sidereal year. This means that it is locked into a relationship with the Earth, since such an orbit is only stable under particular conditions. As yet only a few asteroids of this sort are known, locked into a 1:1 resonance with the Earth. The first was 3753 Cruithne, discovered in 1986.
Asteroids that have a 1:1 orbital resonance with a planet are also called
Orbit
Orbital data
Shortly after the discovery by LINEAR, Scientists at the Jet Propulsion Laboratory (JPL), the Athabasca University (Canada), the Queen's University in Kingston (Ontario, Canada), the York University in Toronto and the Tuorla Observatory of the University of Turku in Finland determined the unusual orbit of 2002 AA29, and through further observations at the Canada–France–Hawaii Telescope in Hawaii it was confirmed that:
- Its orbit lies for the most part inside Earth's orbit. The orbits of most asteroids lie in the asteroid belt between Mars and Jupiter. Through orbital disturbances by the gas giant planets, mainly Jupiter and the Kirkwood gaps, and through the Yarkovsky effect (force due to asymmetrical absorption and emission of infrared radiation) asteroids are diverted into the inner Solar System, where their orbits are further influenced by close approaches with the inner planets. 2002 AA29 has probably been brought in the same way from the outer Solar System into Earth's influence. However, it is also suggested that the asteroid has always been on a near-Earth orbit and thus that it or a precursor body was formed near Earth's orbit. In this case one possibility is that it could be a fragment from a collision of a middle-sized asteroid with Earth or the Moon.[5]
- Its mean orbital period is one sidereal year. After it was diverted into the inner Solar System – or formed on a path near Earth's orbit – the asteroid must have been moved into an orbit corresponding with Earth. In this orbit it was repeatedly pulled by Earth in such a way that its own orbital period became the same as that of Earth. In the current orbit, Earth thus holds the asteroid in synchronicity with its own orbit.
- The orbit of the asteroid is almost circular, with an eccentricity of 0.012 which is even lower than that of the Earth at 0.0167. The other near-Earth asteroids have on average a significantly higher eccentricity of 0.29. Also, all other asteroids in 1:1 resonance with Earth known before 2002 have very strongly elliptical orbits – e.g. the eccentricity of (3753) Cruithne is 0.515. At the time of its discovery the orbit of 2002 AA29 was unique, because of which the asteroid is often called the first true co-orbital companion of Earth, since the paths of previously discovered asteroids are not very similar to Earth's orbit. The very low orbital eccentricity of 2002 AA29 is also an indication that it must always have been on a near-Earth orbit, or the Yarkovsky effect must have comparatively strongly caused it to spiral into the inner Solar System over billions of years, since as a rule asteroids which have been steered by planets have orbits with higher eccentricity.
- The orbital inclination with respect to the ecliptic (orbital plane of Earth) of 2002 AA29 is a moderate 10.739°. Hence its orbit is slightly tilted compared with that of Earth.
Shape of the orbit
If one looks at the orbit of 2002 AA29 from a point moving with the Earth around the Sun (the reference frame of the Earth–Sun system), it describes over the course of 95 years an arc of almost 360°, which during the next 95 years it retraces in reverse. The shape of this arc is reminiscent of a horseshoe, from which comes the name "horseshoe orbit". As it moves along the Earth's orbit, it winds in a spiral about it, in which each loop of the spiral takes one year. This spiral motion (in the Earth–Sun reference frame) arises from the slightly lower eccentricity and the tilt of the orbit: the inclination relative to the Earth's orbit is responsible for the vertical component of the spiral loop, and the difference in eccentricity for the horizontal component.
When 2002 AA29 is approaching the Earth from in front (i.e. it is moving slightly slower, and the Earth is catching it up), the gravitational attraction of the Earth shifts it onto a slightly faster orbit, a little nearer the Sun. It now hurries ahead of the Earth along its new orbit, until after 95 years it has almost lapped the Earth and is coming up from behind. Again it comes under the Earth's gravitational influence; this time it is lifted onto a slower orbit, further from the Sun. On this orbit it can no longer keep pace with the Earth, and it falls behind until in 95 years it is once again approaching the Earth from in front. The Earth and 2002 AA29 chase each other in turn around the Sun, but do not get close enough to break the pattern.
On 8 January 2003, the asteroid approached the Earth from in front to a distance of 0.0391
Because of its orbital inclination of 10.739° to the ecliptic, 2002 AA29 is not always forced by the Earth on its horseshoe orbit however but can sometimes slip out of this pattern. It is then caught for a while in the neighbourhood of the Earth. This will next happen in about 600 years i.e. in the 26th century. It will then stay within the small gap in the Earth's orbit which it does not reach in its previous horseshoe orbit, and will be no further than 0.2
Physical nature
Brightness and size
Relatively little is known about 2002 AA29 itself. With a size of about 20–100 metres (70–300 ft) it is very small, on account of which it is seen from the Earth as a small point even with large telescopes, and can only be observed using highly sensitive CCD cameras. At the time of its closest approach in January 2003 it had an apparent magnitude of about 20.4.[8]
So far nothing concrete is known about the composition of 2002 AA29. Because of its nearness to the Sun, it cannot however consist of
A further uncertainty arises from
Rotational period
Using radar echo measurements at the Arecibo radio telescope the rotational period of 2002 AA29 could be determined. In this radar astronomy procedure
- The asteroid rotates so quickly that the porous.[4]
- 2002 AA29 cannot possibly have been built up from individual small pieces, as these would be thrown apart by the rapid rotation. Therefore, it must be a fragment blown off in the collision of two heavenly bodies. giant impact hypothesis, collided with Earth in its early history.[9]
Outlook
Because its orbit is very similar to the Earth's, the asteroid is relatively easily reachable by
Related objects
- 6Q0B44E
- 2006 RH120
- 2003 YN107 – quasi-satellite of Earth
- 2010 TK7 – Trojan co-orbital companion of Earth
- 3753 Cruithne (1986 TO)
- 2001 GO2
- 2002 AA29
- 2006 JY26
- 2010 SO16
- 2012 FC71
See also
- Natural satellite
- Quasi-satellite
- List of asteroids
- Naming of Asteroids
- Orbital resonance
References
- IAU Minor Planet Center. 2002-01-15. (K02A29A)
- ^ a b c "JPL Small-Body Database Browser: (2002 AA29)" (last observation: 2004-01-15; arc: 2.02 yr). Jet Propulsion Laboratory. Retrieved 30 March 2016.
- ^ .
- ^ )
- ^ a b M. Connors, C. Veillet, R. Brasser, P. Wiegert, P. W. Chodas, S. Mikkola, K. Innanen: Horseshoe Asteroids and Quasi-satellites in Earth-like Orbits. in: 35th Lunar and Planetary Science Conference, 15.–19. März 2004. League City Texas 2004, 3., Abstract Nr. 1565 (PDF).
- ^ a b "JPL Close-Approach Data: (2002 AA29)" (last observation: 2004-01-15; arc: 2.02 yr). Retrieved 2015-02-28.
- )
- ^ "MPEC 2003-A17 : 2002 AA29". IAU Minor Planet Center. 2003-01-04.
- ^ Marcus Chown (2004-08-14). "The planet that stalked the Earth". New Scientist. JPG
- Tilmann Althaus: Ein zweiter Begleiter des Blauen Planeten. in: ISSN 0039-1263
External links
Articles
- MPEC 2003-A17
- Earth coorbital asteroid 2002 AA29
- Research paper describing horseshoe orbits. Recommend starting at page 105!