2010 TK 7

from Wikipedia, the free encyclopedia
Asteroid
2010 TK 7
PIA14405-full crop.jpg
Asteroid 2010 TK 7 on an image from the WISE infrared space telescope from October 2010.
Properties of the orbit ( animation )
Epoch:  July 31, 2016 ( JD 2,457,600.5)
Orbit type Earth Trojan (L 4 )
Major semi-axis 0.9997  AU
eccentricity 0.1906
Inclination of the orbit plane 20.8896 °
Length of the ascending node 96.4958 °
Argument of the periapsis 45.9185 °
Time of passage of the perihelion January 18, 2012
Sidereal period 1.0 a
Mean orbital velocity 29.77 km / s
Physical Properties
Medium diameter 379 m
Albedo 0.059
Absolute brightness 20.8 mag
history
Explorer WISE / NEOWISE
Date of discovery October 1, 2010
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.

2010 TK 7 is the provisional name for an asteroid that accompanies the earth as a Trojan horse on its orbit . It is the first terrestrial Trojan to be discovered and moves on an extensive orbit around the so-called fourth Lagrange point.

Trojans

2010 TK 7 orbits around L 4 and is thus on earth orbit in front of the earth.

Small celestial bodies that orbit the sun in close proximity to a planet's orbit are usually thrown out of this orbit sooner or later by the influence of gravity . One of the possible exceptions to this are celestial bodies that run 60 ° ahead or behind the planet on its orbit, so that they form an equilateral triangle with the planet and the sun.

The so-called Lagrange points L 4 and L 5 are at a distance of 60 ° from the planet . In a reference system rotating with the planet - in which the planet and the Lagrange points stand still - the forces of attraction of the planet and sun as well as the centrifugal force cancel each other out at these points, so that a body located there can remain at rest without force. In the non-rotating inertial frame of reference this means that it moves around the sun with the same orbital period as the planet and undisturbed by it.

The body can - viewed in the co-rotating reference system - remain at rest only if it is exactly on the Lagrangian point and no other disturbing forces act. Neither is the case in practice, so that the body begins to drift away. Then, however, the centrifugal and Coriolis forces to be taken into account in the rotating system begin to deflect the body in such a way that it describes a roughly kidney-shaped stable orbit around the Lagrange point. This revolving around the Lagrange point is also called libration ("fluctuation") (not to be confused with the libration of the moon), the Lagrange points are therefore also called libration points.

Railway from 2010 TK 7

2010 TK 7 is bound to the Lagrange point L 4 of the earth and thus runs ahead of it on its orbit. It is only relatively weakly bound to L 4 and can therefore move far away from it in the course of its libration. It runs with a period of 390 years to almost the libration point L 3 at a distance of 300 million km from the earth and then back again to just before the earth, but without being able to get closer than 20 million km (approx. 50 moon distances). The asteroid's major semiaxis currently has a length of 1,0004 AU , so the asteroid has a slightly slower speed than Earth, and it is slowly drifting towards Earth on its librational orbit. However, the interaction with the earth is currently reducing its semi-major axis, so that according to Kepler's Third Law, its speed will increase and it will move away from the earth again. Around the year 2200, TK 7 will almost reach L 3 in 2010 and then approach Earth again.

Because of the noticeable eccentricity of 0.191, its solar distance fluctuates between 0.8 and 1.2 AU during a year, so that it moves laterally from the earth's orbit by up to ± 0.2 AU over a period of one year. Because of the considerable orbit inclination of almost 21 °, it also moves away from the plane of the earth's orbit by up to ± 0.4 AU in a vertical direction over a period of one year. These two deflections take place simultaneously with the same annual period, so that the asteroid, in addition to its librational orbit, draws approximately vertical loops around the earth's orbit. These additional loops, which are superimposed on the Trojan's librational movement, are also called epicycles, but should not be confused with the epicycles of earlier planetary theories .

Despite its particularly near-Earth orbit, TK 7 is more difficult for spacecraft to reach in 2010 than other near-Earth asteroids because the steep incline of its orbit would result in fuel consumption that is more than twice as high.

Physical Properties

From the measured brightness of the asteroid, assuming an albedo of 0.1, a diameter of 300 m follows , which would be relatively large for a near-earth asteroid. No color or even spectral measurements are available so that no further classification can be made.

discovery

For an earthly observer, objects in a librational path around L 4 or L 5 are on average only 60 ° away from the sun and are therefore difficult to observe. The infrared satellite WISE , which was launched in 2009, searched large areas of the sky at a distance of 90 ° from the sun, so there was hope that a possibly existing terrestrial Trojan might get into WISE's field of view on its librational path.

The mission WISE connected project Neowise had the task of the lessons of WISE shots by moving objects, including near-Earth objects (near-Earth objects - NEOs) , search and nachzubeobachten found objects with ground-based telescopes, so as not to lose it again. On October 1st and 2nd, 2010, WISE observed an object that could also be tracked by three other telescopes on October 6th and 7th. It was given the provisional designation 2010 TK 7 .

Astronomers who examined the WISE database for possible earth trojans were able to identify TK 7 as a probable Trojan horse based on the 6-day arc of the orbit observed in 2010 . Its pronounced annual epicycles had removed the asteroid so far from its mean librational orbit that it had become visible to WISE. After the asteroid had spent several months in an unfavorable position for terrestrial observations, it was finally found in April 2011 with the Canada-France-Hawaii telescope , so that the improved orbit determinations could clearly identify it as an terrestrial Trojan.

Orbit development

2010 TK 7 will be stably bound to the earth's orbit for at least 10,000 years. A precise prediction of its orbital movement is only possible over the next 250 years due to sensitive dependencies on small disturbances. Over the period from 1,800 years ago to 5,000 years ago, however, statistical statements about the possible behavior of the asteroid can be derived by following slightly varied orbits. Accordingly, the transition to a horseshoe track , a "jump" to the Lagrange point L 5 (since the asteroid near L 3 can also shoot beyond L 3 in the course of one of its pronounced epicycles ) or a brief unstable libration around point L 3 cannot be completely ruled out. The calculations show that TK 7 had already run around L 5 earlier in 2010 , but jumped to L 4 around the year 500 .

See also

Individual evidence

  1. ↑ a b S. Keys: MPEC 2010-T45: 2010 TK7 . Minor Planet Electronic Circular of the Minor Planet Center, October 7, 2010 ( online , accessed August 8, 2011)
  2. ^ A. Chamberlin: WISE NEA / Comet Discovery Statistics. ( online , accessed August 8, 2011)
  3. ↑ Earth's first Trojan asteroid: 2010 TK7
  4. ↑ a b c d e f g M. Connors, P. Wiegert, Ch. Veillet: Earth's Trojan Asteroid . Nature 475, 481–483 (July 28, 2011) doi : 10.1038 / nature10233 ( preprint online ; PDF; 1.0 MB)
  5. ^ AK Mainzer et al .: NEOWISE - An Infrared View of the Solar System . 42nd Lunar and Planetary Science Conference, March 7-11, 2011, The Woodlands, Texas. LPI Contribution No. 1608, p. 1121 (2011) ( online ; PDF; 175 kB)

Web links