Near-Earth asteroid

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As near-Earth asteroids ( English near-Earth asteroid , NEA ) are asteroids called the near Earth can come. Unlike most asteroids, they do not move in the asteroid belt around the sun , but in the area of ​​the inner planets . The composition of the near-earth asteroids, however, corresponds to the composition of main belt asteroids.

As the first of these unusual small planets, the dumbbell-shaped Eros was discovered in 1898 as number 433 . With orbital radii between 1.13 and 1.78  AU (Mars: 1.43–1.61 AU) it came close to the earth up to 0.15 AU (58 lunar distances) and was used in 1900 and 1931 to precisely measure the solar system. The encounter with the NEAR space probe took place in 2000 . In 1911 Johann discovered Palisa No. 719 Albert (1.19–4 AU), but he was not found again until 2000. When more "strange" pathways were discovered 70 years ago, they began to be typified.

New objects are typically found by one of the sky search programs such as B. CSS , NEAT , LONEOS , CINEOS , Spacewatch or LINEAR found.

PHAs ( English Potentially Hazardous Asteroids , potentially dangerous asteroids) can be mentioned that about 20% of the NEAs, which in its orbit the Earth's orbit denser than 0.05 AE come and hence through on a time scale of 100 years perturbations may not fall on a collision course. The orbit calculations of the previously known objects have been highly automated with the Sentry monitoring system since 2002 and are listed in the Sentry Risk Table .

classification

Types of near-earth orbits
(433) Eros is an asteroid of the Cupid I-type

The near-earth asteroids are divided according to the length of their major orbit half-axis and the perihelion and aphelion distances.

Cupid type

Asteroids of the Cupid-type do not cross the earth's orbit, but come close to it from outside with perihelion distances between 1.017 and 1.3 AU. 1.017 is the apheld distance of the earth, 1.3 is an arbitrary limit (“close to the earth”). The group's prototype is the asteroid (1221) Amor , discovered in 1932, which moves around the sun at a distance of 1.08 to 2.76 AU. Early representatives of this group are (433) Eros , discovered in 1898 , which approaches the earth's orbit to within 0.15 AU, as well as (719) Albert and (887) Alinda . As of December 30, 2010, 2,854 Amor-type asteroids were known.

The asteroids of the Cupid type are divided into four subgroups depending on the length of their major semi-axis:

Cupid I.
This group includes Cupid asteroids whose semiaxes are shorter than those of Mars' orbit (1.52 AU). If the orbital eccentricity is not too great, they run completely between the orbit of Earth and Mars. Almost 20% of all Cupid asteroids belong to the Cupid I type.
Cupid II
The semi-axes of this subtype are longer, up to 2.12 AU, which corresponds to the inner edge of the main belt , the eccentricities are 0.17 to 0.52. These asteroids therefore cross the orbit of Mars and their aphelion is mostly within the asteroid belt. About a third of the Cupid asteroids belong to this group, including the namesake (1221) Amor.
Cupid III
Their orbits have semi-axes like the asteroids of the asteroid belt, between 2.12 and 3.57 AU. However, their eccentricities (0.4-0.6) are large enough that their perihelion can be close to the earth's orbit and their aphelion can be up to an AU close to Jupiter. About half of all objects of the Cupid type belong to this group, including the largest Cupid asteroid (1036) Ganymede with a diameter of 31.7 km . Some of the members of the Amor III group are in 3: 1 resonance with Jupiter and are therefore counted among the Alinda asteroids, which also includes some Apollo asteroids.
Cupid IV
This small group includes Cupid asteroids with even larger orbital half-axes. Their extended orbits lead them to areas outside of Jupiter's orbit. The best known representative is the asteroid (3552) Don Quixote .
Doppler delay method

Apollo type

Objects with a large orbit half-axis> 1 AU and perihelion distance <1.017 AU, the aphelion distance of the earth, are referred to as Apollo asteroids according to (1862) Apollo . They can cross the earth's orbit , which means a risk of impact depending on the level of the orbit .

Calculations have shown that the asteroids of the main belt can transition to Apollo orbits as a result of gravitational disturbances of Jupiter . An example of this are the Alinda asteroids, to which some Apollo-type objects such as B. (4179) Toutatis belong. They move in 3: 1 resonance to Jupiter and are thus disturbed in their orbit, whereby the eccentricities of these objects are constantly increased until the resonance is resolved when approaching one of the inner planets. Even if this happens through Venus, an Apollo-type orbit is created, because the definition does not exclude small perihelion distances.

Radar image of (4179) Toutatis , an Apollo-type asteroid

The largest Apollo asteroid is (1866) Sisyphus with a diameter of 8.5 km. Other well-known representatives are (2101) Adonis and (69230) Hermes , who passed Earth 1.5 times the lunar distance in 1937 and was then considered lost until he was finally found again in 2003. In 1990, 63 Apollo asteroids were known, 415 in 1999, 1190 in November 2003, and 4111 on December 30, 2010.

Aten type

Aten-type asteroids have large orbital semi-axes <1 AU and aphelion distances greater than 0.9833 AU, the perihelion distance on Earth. So you are also earth orbit cruiser . Some aten asteroids have a perihelion that lies within the orbit of Venus or even Mercury. They are then considered to be Venus or Mercury orbital cruisers .

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

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

On February 15, 2013, the asteroid (367943) Duende approached Earth to a distance of 27,599 km. Until then classified as an Apollo-type, it changed its orbit through the close encounter with the earth and became the Aten-type.

Atira type

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

Arjuna asteroid

Arjuna asteroids are a rare form of near-Earth asteroids and belong to one of the four types described above. Characteristic of asteroids of this class is their Earth-like orbit with a low orbital inclination , low eccentricity and orbital periods of about one Earth year . They are thus in resonance with the earth as earth trojans or on so-called horseshoe orbits . At times they can apparently orbit the earth as a quasi-satellite .

Asteroids near the Sun

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

As of December 30, 2010, 1746 asteroids were known to intersect Venus' orbit. 507 of them even have their point closest to the Sun within Mercury's orbit. Well-known representatives are:

  • (1566) Icarus (discovered in 1949; solar distance 0.19–1.97 AU)
  • (3200) Phaethon , discovered by IRAS in 1984 , 0.14-2.40 AU. In perihelion it has a speed of 110 km / s and defies temperatures of over 700 ° C.
  • 2005 HC4, discovered by LONEOS in 2005, comes closest to the sun, 0.071-3.571 AU, is heated to over 1500 ° C in the perihelion.

Close encounters and impacts

  • The Apollo asteroid (29075) 1950 DA was the first object to have a positive value on the Palermo scale for impact risk for March 16, 2880 Template: future / in 5 years.
  • The Aten asteroid (99942) Apophis will fly Template: future / in 5 yearspast the earth in almost 30,000 km on April 13, 2029 . For this encounter in December 2004 the rating on the Turin scale was 4 for a few days, a value that has not yet been achieved.
  • The only about six meters small Aten asteroid 2004 FU 162 approached the earth on March 31, 2004 up to 6,500 km and on February 4, 2011 the approx. 1-2 m tiny 2011 CQ1 to almost 5,500 km. No closer flyby of a minor planet has been observed since then, but there have been four cases of collisions.
  • 2008 TC 3 was the first asteroid for which a collision with the earth was correctly predicted. The very small object with 4 m was discovered on October 6th, 2008 while still outside the lunar orbit and 20 hours later it burned up almost completely in the atmosphere over Sudan .
  • 2019 OK is an Apollo asteroid a good 90 m in diameter that was discovered on July 25, 2019, just one day before it passed Earth in less than 72,000 kilometers. It flew at a speed of about 25 km / s relative to the earth.

Others

NASA has been researching the possible accessibility of near-earth asteroids with manned missions in the Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) since 2010 .

See also

literature

  • CT Russell: The Near Earth Asteroid Rendezvous Mission. Kluwer Acad. Publ., Dordrecht 1997, ISBN 0-7923-4957-1 .
  • Pierre Vernazza, et al .: Compositional differences between meteorites and near-Earth asteroids. Nature 454, 858-860, Aug. 14, 2008. Abstract
  • PART III - Near-Earth Objects in: John S. Lewis et al .: Resources of Near Earth Space. University of Arizona Press, Tucson 1993, ISBN 0-8165-1404-6 .

Web links

Commons : Near-Earth Asteroids  - Collection of images, videos and audio files

Videos

Individual evidence

  1. ↑ DF Lupishko and TA Lupishko: On the Origins of Earth-Approaching Asteroids . In: Solar System Research . 35, No. 3, May 2001, pp. 227-233. bibcode : 2001SoSyR..35..227L .
  2. ↑ NEO GROUPS neo.jpl.nasa.gov (accessed on September 2, 2010)
  3. ^ Spiegel Online
  4. ↑ https://arxiv.org/pdf/1410.4104.pdf
  5. ^ Meet the asteroid that might hit Earth in 2880. In: Fox News . October 9, 2013, accessed July 11, 2017 .
  6. ↑ Researchers find unique meteorite debris. In: Spiegel Online . March 26, 2009. Retrieved July 11, 2017 .
  7. ↑ Süddeutsche-Online: Large asteroid misses the earth almost unnoticed , July 28, 2019
  8. ↑ Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) jpl.nasa.gov, accessed April 28, 2015