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The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten
2062 Aten

'2062 Aten' is an asteroid that was discovered at the Mount Palomar Observatory by Eleanor F. Helin, who is now the principal scientist for the NEAT project....
, discovered January 7, 1976 by Eleanor F. Helin
Eleanor F. Helin

Eleanor Francis Helin was an American astronomer. She was principal investigator of the Near Earth Asteroid Tracking program of NASA's Jet Propulsion Laboratory....
). They are defined by having semi-major axes
Semi-major axis

In geometry, the semi-major axis is used to describe the dimensions of ellipses and hyperbolae....
 of less than one astronomical unit
Astronomical unit

An astronomical unit is a unit of length based on the mean distance from the Earth to the Sun. The precise value of the AU is currently accepted as 149,597,870,691 Plus-minus sign 6 metres ....
 (the distance from the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 to the Sun
Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
). Note that, because asteroids' orbits can be highly eccentric, an Aten orbit need not be entirely contained within Earth's orbit; in fact, nearly all known Aten asteroids have their aphelion greater than one AU
Astronomical unit

An astronomical unit is a unit of length based on the mean distance from the Earth to the Sun. The precise value of the AU is currently accepted as 149,597,870,691 Plus-minus sign 6 metres ....
.






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The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered (2062 Aten
2062 Aten

'2062 Aten' is an asteroid that was discovered at the Mount Palomar Observatory by Eleanor F. Helin, who is now the principal scientist for the NEAT project....
, discovered January 7, 1976 by Eleanor F. Helin
Eleanor F. Helin

Eleanor Francis Helin was an American astronomer. She was principal investigator of the Near Earth Asteroid Tracking program of NASA's Jet Propulsion Laboratory....
). They are defined by having semi-major axes
Semi-major axis

In geometry, the semi-major axis is used to describe the dimensions of ellipses and hyperbolae....
 of less than one astronomical unit
Astronomical unit

An astronomical unit is a unit of length based on the mean distance from the Earth to the Sun. The precise value of the AU is currently accepted as 149,597,870,691 Plus-minus sign 6 metres ....
 (the distance from the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
 to the Sun
Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
). Note that, because asteroids' orbits can be highly eccentric, an Aten orbit need not be entirely contained within Earth's orbit; in fact, nearly all known Aten asteroids have their aphelion greater than one AU
Astronomical unit

An astronomical unit is a unit of length based on the mean distance from the Earth to the Sun. The precise value of the AU is currently accepted as 149,597,870,691 Plus-minus sign 6 metres ....
. Those that have their aphelion entirely within the Earth
Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's orbit are known as Apohele asteroid
Apohele asteroid

Apohele asteroids are a subclass of Aten asteroids. They have not only their perihelion at less than one astronomical unit , but also their aphelion; that is, their entire orbit is within Earth's....
s. As of March 2008 there are only five known Apoheles ((163693) Atira, , , and ) and four suspected Apoheles ( and ).

The smallest semi-major axis is that of , at 0.642 AU (its eccentricity of 0.688 takes it from a perihelion of 0.200 AU, well within Mercury
Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 88 days. The orbit of Mercury has the highest Orbital eccentricity of all the Solar System planets, and it has the smallest axial tilt....
's orbit, to an aphelion of 1.084 AU), although seems to have an even smaller one (0.635 AU; eccentricity 0.532 ranging from 0.297 to 0.973 AU —enough to cross Venus
Venus

Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....
' orbit but not Mercury's).

For a brief time near the end of 2004, the asteroid 99942 Apophis
99942 Apophis

99942 Apophis is a near-Earth asteroid that caused a brief period of concern in December 2004 because initial observations indicated a significant probability that it would strike the Earth in 2029....
 (then known only by its provisional designation ) appeared to pose a threat of causing an Earth impact event
Impact event

An impact event is the collision of a large meteoroid, asteroid or comet with the Earth. Impact events have been a plot and background element in science fiction since knowledge of real impacts became established in the scientific mainstream....
 in 2029, but earlier observations were found that eliminated that possibility, although a very small possibility remains for 2036.

See also

Aten asteroids (category)
  • List of numbered Aten asteroids
    List of numbered Aten asteroids

    This is a list of all numbered Aten asteroids as of June 2005. See also :Category:Aten_asteroids for a list of all Aten asteroids that have articles....
  • Aten asteroid records
    Aten asteroid records

    The following is a list of current records for Aten asteroids.External links...


External links