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Last Updated
Jan 25, 2002
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NEO GROUPS
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In terms of orbital elements, NEOs are asteroids and comets with perihelion
distance q less than 1.3 AU.
Near-Earth Comets (NECs) are further restricted to include only short-period
comets (i.e orbital period P less than 200 years).
The vast majority of NEOs are asteroids, referred to as Near-Earth Asteroids (NEAs).
NEAs are divided into groups (Aten, Apollo, Amor) according to their
perihelion distance (q), aphelion distance (Q) and their semi-major axes (a).
| Group |
Description |
Definition |
|---|
| NECs |
Near-Earth Comets |
q<1.3 AU, P<200 years |
| NEAs |
Near-Earth Asteroids |
q<1.3 AU |
| Atens |
Earth-crossing NEAs with semi-major axes smaller than Earth's
(named after asteroid 2062 Aten). |
a<1.0 AU, Q>0.983 AU |
| Apollos |
Earth-crossing NEAs with semi-major axes larger than Earth's
(named after asteroid 1862 Apollo). |
a>1.0 AU, q<1.017 AU |
| Amors |
Earth-approaching NEAs with orbits exterior to Earth's but interior
to Mars' (named after asteroid 1221 Amor). |
a>1.0 AU, 1.017<q<1.3 AU |
| PHAs |
Potentially Hazardous Asteriods: NEAs whose
Minimum Orbit Intersection Distance (MOID)
with the Earth is 0.05 AU or less and whose absolute magnitude (H)
is 22.0 or brighter. |
MOID<=0.05 AU, H<=22.0 |
More information about PHAs can be found on the
PHA page, such as Earth close-approach tables including
uncertainties.
In addition,
tables of Earth close-approaches
are available for NEOs.
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Ron Baalke, Near-Earth Object Webmaster
Jet Propulsion Laboratory
Pasadena, California
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