Orbit Type Definition¶
The Minor Planet Center classifies orbits based on osculating orbital elements. Objects are grouped into three main regions of the solar system.
The following parameter definitions are used in the classification criteria: - a -- semimajor axis (AU) - q -- perihelion distance (AU) - Q -- aphelion distance (AU) - e -- eccentricity - i -- inclination (degrees) - T -- Tisserand parameter with respect to Jupiter - q_Mars = 1.405 AU (Mars perihelion distance) - a_Jupiter = 5.204 AU - a_Neptune = 30.178 AU
Inner Solar System¶
Objects with orbits primarily interior to Mars' orbit.
| Type | Code | Definition |
|---|---|---|
| Atira | 0 | a < 1 and Q < 0.983 |
| Aten | 1 | a < 1 and Q >= 0.983 |
| Apollo | 2 | a >= 1 and q < 1.017 |
| Amor | 3 | a >= 1 and 1.017 <= q < 1.3 |
| Other | 9 | a >= 1 and Q < q_Mars, unclassified otherwise |
Middle Solar System¶
OObjects that occupy the orbital region of Mars-crossers up to that of the Jovian Trojans.
| Type | Code | Definition |
|---|---|---|
| Mars Crosser | 10 | 1 <= a < 3.2 and 1.3 < q < 1.666 |
| Main Belt | 11 | 1 <= a < 3.27831 and i < 75 |
| Jupiter Trojan | 12 | 4.8 < a < 5.4 and e < 0.3 |
| Other | 19 | a < a_Jupiter, unclassified otherwise |
Outer Solar System¶
Objects beyond Jupiter, excluding Jupiter-Coupled objects which may have smaller semimajor axes.
| Type | Code | Definition |
|---|---|---|
| Jupiter Coupled | 20 | a >= 1 and 2 < T < 3 |
| Neptune Trojan | 21 | 29.8 < a < 30.4 |
| Centaur | 22 | a_Jupiter <= a < a_Neptune |
| TNO | 23 | a >= a_Neptune, unclassified otherwise |
Special and Unusual Orbits¶
| Type | Code | Definition |
|---|---|---|
| Hyperbolic | 30 | e > 1 |
| Parabolic | 31 | e = 1 |
| Other | 99 | Classification failure |