The Aten asteroids are a dynamical group of

asteroid An asteroid is a minor planet of the Solar System#Inner solar system, inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic o ...

s whose orbits bring them into proximity with Earth. By definition, Atens are Earth-crossing asteroids . The group is named after

2062 Aten 2062 Aten , provisional designation , is a stony sub-kilometer asteroid and namesake of the Aten asteroids, a subgroup of near-Earth objects. The asteroid was named after Aten from Egyptian mythology. It was discovered on 7 January 1976, at the ...

, the first of its kind, discovered on 7 January 1976 by American astronomer Eleanor Helin at

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

. As of 2020, 1841 Atens have been discovered, of which 13 are named. Many Atens are classified as potentially hazardous asteroids.

Description

Aten asteroids are defined by having a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the lo ...

(a) of less than 1.0

astronomical unit The astronomical unit (symbol: au, or or AU) is a unit of length, roughly the distance from Earth to the Sun and approximately equal to or 8.3 light-minutes. The actual distance from Earth to the Sun varies by about 3% as Earth orbi ...

(AU), the roughly average distance from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

to the Sun. They also have an

aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. For example, the apsides of the Earth are called the aphelion and perihelion. General description There are two apsides in any e ...

(Q; furthest distance from the Sun) greater than 0.983 AU. This defines them as Earth-crossing asteroids as the orbit of Earth varies between 0.983 and 1.017 AU. Asteroids' orbits can be highly eccentric. Nearly all known Aten asteroids have an

greater than 1 AU. Observation of objects

inferior Inferior may refer to: * Inferiority complex * An Anatomical terms of location#Superior and inferior, anatomical term of location * Inferior angle of the scapula, in the human skeleton *Inferior (book), ''Inferior'' (book), by Angela Saini * ''The ...

to the Earth's orbit is difficult, and this difficulty may contribute to

sampling bias In statistics, sampling bias is a bias (statistics), bias in which a sample is collected in such a way that some members of the intended statistical population, population have a lower or higher sampling probability than others. It results in a bia ...

in the apparent preponderance of eccentric Atens. Aten asteroids account for only about 7.4% of the known near-Earth asteroid population. Many more Apollo-class asteroids are known than Aten-class asteroids, possibly because of the sampling bias. The shortest semi-major axis for any known Aten asteroid is 0.580 AU, for object . The Aten asteroid with the smallest known perihelion is also the one with the highest known

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off- center, in geometry * Eccentricity (graph theory) of a ...

: has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within Mercury's orbit, to an aphelion of 1.66 AU, which is greater than the semi-major axis of

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin atmos ...

(1.53 AU). For a brief time near the end of 2004, the asteroid 99942 Apophis (then known only by its

provisional designation Provisional designation in astronomy is the naming convention applied to astronomical objects immediately following their discovery. The provisional designation is usually superseded by a permanent designation once a reliable orbit has been calc ...

) apparently posed a threat of impacting Earth in 2029 or 2036, but earlier observations were found that eliminated those possibilities.

NEO types

References

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Description

NEO types

See also

References