Near-Earth object#Near-Earth asteroids

As a near-Earth asteroids (English near- Earth asteroid, NEA) asteroids are known that can come near Earth. They do not move like most asteroids in the asteroid belt around the Sun, but in the region of the inner planets. The composition of the near-Earth asteroids but corresponds to the composition of the main belt asteroids.

The first of these unusual minor planet was discovered in 1898 as number 433 of the dumbbell-shaped Eros. In orbital radii from 1.13 to 1.78 AE ( Mars: 1.43 to 1.61 AE) he came to the earth to 0.15 AE close (58 lunar distances) and served in 1900 and 1931 for the accurate measurement of the solar system. In 2000, the meeting took place with the NEAR spacecraft. 1911 saw Johann Palisa # 719 Albert ( 1.19 to 4 AE), but was rediscovered only in 2000. Than 70 years ago, another " strange " tracks were discovered, people began to typify them.

Due to the high kinetic energy of the larger asteroids, or the large number of smaller runs a serious risk of an impact on the earth. New objects are typically found by one of the sky search programs such as CSS, NEAT, LONEOS, CINEOS, Spacewatch or LINEAR.

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Classification

The near-Earth asteroids are divided according to the length of their large semi-major axis and the perihelion and Apheldistanzen.

Amor - type

Asteroids of the Amor - type do not cross the Earth's orbit, come with her but close Periheldistanzen 1.017 to 1.3 AU from the outside. 1.017 is the Apheldistanz Earth 1.3 is an arbitrary limit ( " earthy "). Prototype of the group in 1932 discovered asteroid ( 1221 ) Amor, which moves at a distance from 1.08 to 2.76 AU around the Sun. Early members of this group are in 1898 discovered ( 433 ) Eros, the Earth's orbit comes within 0.15 AU, and ( 719) and Albert ( 887 ) Alinda. 30 December 2010 2854 asteroid Cupid type were known.

The asteroids of the Amor - type are divided into four subgroups according to the length of their large semi-major axis:

Amor I: This group consists of Amor asteroids whose semi-axes are shorter than those of the orbit of Mars (1.52 AU). If the orbital eccentricity is not too large, so they run completely between Earth and Mars orbit. Almost 20 % of Amor asteroids belong to the Cupid I type.

Amor II: The semi-axes of this subtype are longer to 2.12 AU, corresponding to the inner edge of the main belt, the eccentricity amount from 0.17 to 0.52. Therefore, these asteroids cross the orbit of Mars and its aphelion lies mostly within the asteroid belt. About a third of Amor asteroids belong to this group, including the namesake ( 1221 ) Amor.

Amor III: Your tracks have semi-axes as the asteroids of the asteroid belt, from 2.12 to 3.57 AE. However, their eccentricities ( 0.4-0.6 ) are large enough that their perihelion can be in up to an AE close to Jupiter in the vicinity of Earth's orbit and its aphelion. This group includes about half of all objects of the Amor - type, including the largest at 31.7 km in diameter Amor asteroid ( 1036 ) Ganymed. Some of the members of the Amor - III group are in 3:1 resonance with Jupiter, and are therefore counted as Alinda asteroids, which include some of the Apollo asteroids.

Amor IV: At this small group include Amor asteroids with even larger semi-major axes. Your straight runs they lead to areas outside the orbit of Jupiter. The best known representative is the asteroid ( 3552 ) Don Quixote.

Apollo - type

Objects with large semi-major axis > 1 AU and perihelion distance < 1.017 AE are designated according to (1862 ) Apollo as Apollo asteroids. You can cross the Earth's orbit, which means a risk of impact depending on the orbital plane.

Rail Regulations have shown that the asteroids of the main belt can go as a result of gravitational interference of Jupiter to Apollo trains. An example of this are the Alinda asteroids, which include some objects of the Apollo - type such as ( 4179 ) Toutatis. They move in 3:1 resonance with Jupiter and be disturbed in its orbit, so that the eccentricities of these objects are constantly increased until the resonance is resolved when approaching one of the inner planets. Even if that happens by Venus, creates a path from Apollo - type, because the definition does not exclude small perihelion distances.

The largest Apollo asteroid (1866 ) Sisyphus with 8.5 km in diameter. Other well-known representatives are ( 2101 ) and Adonis ( 69230 ) Hermes, the 1.5x Moon distance to the Earth vorbeizog 1937 and thereafter was considered lost until it was finally rediscovered in 2003. 1990 were 63 Apollo asteroids known, in 1999 already 415, November 2003 1190 and 30 December 2010 4111th

Aten - type

Aten asteroids of type have large semi-major axes < 1 AU and aphelion distances greater than 0.9833 AU, the perihelion distance of the earth. So you are also Earth's orbit cruiser. Some Aten asteroids have perihelion, which is within the Venus or even Mercury's orbit. Then you are considered as Venus or Mercury's orbit cruiser.

The 0.9 km wide namesake of the type class ( 2062 ) Aten, was discovered in 1976. He comes close to Earth in its orbit ( 0.79 to 1.14 AE) every 10,000 years. Other well-known representatives are ( 2100) Ra - Shalom ( 2340) Hathor ( 3753 ) Cruithne and ( 99942 ) Apophis.

1990 were known 9, 1999 already 60 and in November 2003, 196 asteroids of this type. 30 December 2010 678 Aten asteroids were known.

On February 15, 2013, the earth, the asteroid ( 367943 ) Duende approached up to 27,599 km. Until then classified as Apollo - type he changed his orbit by the close encounter with the Earth and became the Aten type.

Atira - type

A relatively small group of asteroids that orbit entirely within the Earth's orbit ( Inner Earth Objects ) and are therefore difficult to detect. Except for one, all known specimens are greater than 300 m (as of 2011):

( 163 693 ) Atira
(164294) 2004 XZ130
1998 DK36
2004 JG6
2005 TG45
2006 KZ39
2006 HS4
2007 EB26
2008 EA32
2008 UL90
2010 XB11

Arjuna asteroids

Arjuna asteroids represent a rare form of near-Earth asteroids and belong to one of four type classes described above. They move to a Earth-like orbit with synodic periods of more than ten years.

Sun Near asteroids

Some of these small bodies have their point nearest the Sun within the Venus or even within the orbit of Mercury.

30 December 2010 1746 asteroids were known to intersect the orbit of Venus. 507 of them have their point nearest the Sun even within the orbit of Mercury. Known representatives are:

Meteoric, discovered by IRAS 1984 (3200) Phaethon ( 0.14 to 2.40 AE). At perihelion it has a speed of 200 km / s, and despite temperatures of 600 ° C, no cometary emission ( ESA 2002).

Close encounters and impacts

The Apollo asteroid (29075) 1950 DA was the first object for which a positive value was determined on the Palermo scale for impact risks.
The Aten asteroid ( 99942 ) Apophis will fly by in just under 30,000 km at the morning of April 13, 2029 at the Earth. For this encounter, the classification was in December 2004 at the Turin scale for a few days at 4, one never since reached value.
The only about six feet small Aten asteroid 2004 FU162 coming to Earth on March 31, 2004 to 6,500 km. There is no known denser flyby of a small planet.
2008 TC3 was the first asteroid, for a collision with Earth was predicted incorrect. The 4- m very small object was discovered on 6 October 2008 still outside the moon's orbit and burned up 20 hours later almost completely in the atmosphere.

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