The Aten asteroids are a
dynamical group
In mathematics, a dynamical system is a system in which a Function (mathematics), function describes the time dependence of a Point (geometry), point in an ambient space. Examples include the mathematical models that describe the swinging of a ...
of
asteroid
An asteroid is a minor planet of the 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 or icy bodies with no atmosphere.
...
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 long ...
(a) of less than 1.0
astronomical unit (AU), the roughly average distance from the
Earth to the
Sun. They also have an
aphelion (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
aphelion 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 in which a sample is collected in such a way that some members of the intended population have a lower or higher sampling probability than others. It results in a biased sample of a population (or non-human fa ...
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: has an orbit with an eccentricity of 0.895, which takes it from a perihelion of 0.092 AU, well within
Mercury
Mercury commonly refers to:
* Mercury (planet), the nearest planet to the Sun
* Mercury (element), a metallic chemical element with the symbol Hg
* Mercury (mythology), a Roman god
Mercury or The Mercury may also refer to:
Companies
* Merc ...
's orbit, to an aphelion of 1.66 AU, which is greater than the semi-major axis of
Mars (1.53 AU). For a brief time near the end of 2004, the asteroid
99942 Apophis (then known only by its
provisional designation ) apparently posed a threat of
impacting Earth in 2029 or 2036, but earlier observations were found that eliminated those possibilities.
NEO types
See also
*
Alinda asteroid
*
Amor asteroid
*
Apollo asteroid
*
Atira asteroid
Atira asteroids or Apohele asteroids, also known as interior-Earth objects (IEOs), are asteroids whose orbits are entirely confined within Earth's orbit; that is, their orbit has an aphelion (farthest point from the Sun) smaller than Earth's peri ...
*
List of minor planets
References
{{Portal bar, Astronomy, Stars, Spaceflight, Outer space, Solar System
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