2010 TK7

2010 TK7 is the provisional designation for an asteroid, which accompanied the Earth as a Trojan on its orbit. He is the first Erdtrojaner discovered.

Trojans

→ Main article: Lagrange points

Small celestial bodies that orbit the Sun close to the orbit of a planet be thrown by its gravitational influence sooner or later from this path. One of the possible exceptions to this are heavenly bodies that the planet in its orbit 60 ° ahead or lag behind, so that they form with the planets and the sun is an equilateral triangle.

At a distance of 60 ° from the planet are the so-called Lagrange points L4 and L5. In a rotating with the planetary reference system - in which the planet and the Lagrange points so stand still - stand out at these points the attractive forces of the planet and the sun and the centrifugal force straight so that there befindlicher body can force-free remain at rest. In the non-rotating inertial reference system, this means that it moves with the same orbital period as the planet and undisturbed by this around the sun.

The body can - considered in the co-rotating reference system - but only then remain at rest, if it is exactly located on the Lagrangian point and no further disturbance forces act. Both in practice is not the case, so that the body begins to drift. Then, however, to be considered in the rotating centrifugal and Coriolis forces begin to distract the body so that it describes an approximately kidney -shaped stable orbit around the Lagrange point. This revolved around the Lagrange point is also called libration ( " variation " ) (not to be confused with the libration of the Moon), the Lagrange points, therefore, are also called libration points.

There are not the Lagrange points L1 and L2 in the vicinity of the planet, as well as L3, which is opposite to the planetary in its path diametrically. To these points no stable orbits are possible.

Railway from 2010 TK7

2010 TK7 is bound to the Lagrangian point L4 of the earth and passes her with it on its path forward. It is only relatively weakly bound to L4 and therefore can be removed in the course of its libration far. He runs with a period of 390 years almost to the libration point L3 in 300 million km Erdentfernung and then back to just before the earth, without being able to get closer than 20 million kilometers. This represents more than 50 times the average distance of the moon ( 384,400 km ). Currently, the semi-major axis of the asteroid path has a length of 1.0004 AU, the asteroid is a slightly slower speed than the earth, and he drifts on its libration slowly to the earth. However, the interaction with the Earth reduced present its semi-major axis, so that increases in accordance with the third Kepler law its speed and it will be removed from the earth. Around the year 2200 will reach almost 2010 TK7 L3 and then converge with the earth.

Because of the appreciable eccentricity of 0.191 varies its distance from the Sun during a year between 0.8 and 1.2 AE, so that it is laterally away with a period of one year up to ± 0.2 AU from the Earth's orbit. Away Because of the significant orbital inclination of nearly 21 °, it is with a period of one year also to ± 0.4 AE in the vertical direction from the Earth's orbital plane. These two deflections run at the same annual period starting at the same time, so that the asteroid additional annual approximately perpendicular loops draws to its libration around the Earth's orbit. These additional loops that overlap the librational motion of the Trojan are also called epicycles, but are not earlier with the epicycles planetary theories to be confused.

Despite its very low Earth railway 2010 TK7 is difficult for spacecraft to reach than other near-Earth asteroids, because the strong inclination of its orbit would have such a large well double fuel consumption.

Physical Properties

From the measured brightness of the asteroid follows, assuming an albedo of 0.1, a diameter of 300 m, which is relatively big for a near-Earth asteroid. There are currently no color or even spectral measurements, so that still does not make any further classification.

Discovery

Objects in a libration around L4 or L5 are for a terrestrial observer on average, in only 60 ° distance from the sun and are therefore difficult to observe. The infrared satellite launched in 2009, WISE were searched from large areas of the sky at a distance of 90 ° from the sun, so it was hoped, a possibly existing Erdtrojaner could get on its libration in the field of WISE.

The mission WISE had Neowise connected project the task gained from WISE shots by moving objects, including near-Earth objects ( near- Earth objects - NEOs ) to search, and found objects with ground-based telescopes nachzubeobachten, so as not to lose again. On 1 and 2 October 2010 WISE observed an object that could be followed on October 6 and 7, also of three other telescopes. It was given the provisional designation 2010 TK7.

Astronomers who studied the database of WISE possible Erdtrojaner way could identify 2010 TK7 using the 6 -day observed orbital arc as probable Trojans. His pronounced annual epicycles had the asteroids so far away from its mean libration, that he had become visible to WISE. After the asteroid had spent several months in an unfavorable for ground-based observations of position, finally succeeded in April 2011, the retrieval with the Canada -France - Hawaii telescope, so that the improved orbit determination could clearly identify him as Erdtrojaner.

Career Development

2010 TK7 will be bound over at least 10,000 years stable at the Earth's orbit. An accurate prediction of its orbital motion is due to sensitive dependence on small perturbations but only about the next 250 years is possible. Over the period of pre-1800 's to 5000 years can be easily varied by computational tracking paths, however statistical statements about the possible behavior of the asteroid derived. Thus, the transition to a horseshoe alley, " has snapped " to the Lagrangian point L5 (since the asteroid near L3 shoot out in the course of one of his strong epicycles via L3 can ) or a short-term unstable libration around the point L3 is not completely ruled out. The calculations show that 2010 TK7 was already used to run to L5, but has jumped around the year 500 around on L4.