The Aten asteroids are a dynamical group of

asteroid An asteroid is a minor planet—an object larger than a meteoroid that is neither a planet nor an identified comet—that orbits within the Solar System#Inner Solar System, inner Solar System or is co-orbital with Jupiter (Trojan asteroids). As ...

s whose orbits bring them into proximity with Earth. By definition, Atens are

Earth-crossing asteroid An Earth-crosser is a near-Earth asteroid whose orbit crosses that of Earth as observed from the ecliptic pole of Earth's orbit. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semi-major axes are smaller than E ...

s . The group is named after 2062 Aten, the first of its kind, discovered on 7 January 1976 by American astronomer

Eleanor Helin Eleanor Francis "Glo" Helin (née Francis, 19 November 1932 – 25 January 2009) was an American astronomer. She was principal investigator of the Near-Earth Asteroid Tracking (NEAT) program of NASA's Jet Propulsion Laboratory. (Some sources gi ...

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

. As of January 2025, 2,966 Atens have been discovered, of which 271 are numbered, 14 are named, and 197 are classified as

potentially hazardous asteroids A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and which is large enough to cause significant regional damage in the Impact event, event ...

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 longe ...

(a) of less than 1.0

astronomical unit The astronomical unit (symbol: au or AU) is a unit of length defined to be exactly equal to . Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its m ...

(AU), the roughly average distance from the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

to the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

. They also have an

aphelion An apsis (; ) is the farthest or nearest point in the orbit of a planetary body about its primary body. The line of apsides (also called apse line, or major axis of the orbit) is the line connecting the two extreme values. Apsides perta ...

(Q; furthest distance from the Sun) greater than 0.983 AU. This defines them as

s 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 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 b ...

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-Centre (geometry), center, in geometry * Eccentricity (g ...

: 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. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

(1.53 AU).

NEO types

References

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Description

NEO types

See also

References