The Kuiper Belt

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

The Kuiper Belt is a long-surmised and recently (1992) confirmed outer asteroid belt of rock and ice objects orbiting beyond Neptune. Many astronomers regard Pluto as merely the largest of the Kuiper Belt objects.

Kuiper Belt Objects

Data is adapted from a home page by Dave Jewitt (University of Hawaii), who discovered many of the objects listed. For such distant, faint, and slow-moving objects the data are somewhat provisional and subject to revision. Pluto is included for comparison. The table shows only the first few discovered; thousands are now known and active researchers maintain complete tabulations.

Explanation of Table Contents

Object
Provisional designation of the object: Year of discovery followed by letter-number identifiers. None of these objects have been formally named.
a (AU)
Semi-major axis in astronomical units: 1 AU = 149.6 million km, the distance from the Earth to the Sun. The semi-major axis is half the length of the long axis of the object's orbit, and is its average distance from the Sun.
a (mil km)
Semi-major axis in millions of kilometers.
perh (mil km)
Perihelion (minimum) distance in millions of kilometers.
aph (mil km)
Aphelion (maximum) distance in millions of kilometers.
period yr.
Orbital period in years.
e
Orbital eccentricity.
i (deg)
Inclination in degrees to plane of the ecliptic.
Mag (Mr)
Magnitude at average distance.
Diam. (km)
Diameter in kilometers. Estimated from magnitude and other optical data, hence, only approximate.

Interesting Features

Note the extremely faint magnitudes of all these objects. They are almost at the limit of our ability to detect them.

Note that their orbital inclinations are mostly small. These are objects that accreted like all the planets rather than objects formed somewhere else and then perturbed into their present orbits.

1996TL66 is in a class by itself and, apart from comets, is the most distant object in the Solar System. None of the other objects listed have aphelia beyond 8000 million km.

Object a (AU) a (mil km) perh (mil km) aph (mil km) period yr. e i (deg) Mag (Mr) Diam. (km)
Pluto 39.48 5900 4440 7350 248.02 0.249 17.14 14 2400
1992 QB1 44 6582 6122 7043 292 0.07 2 22.8 283
1993 FW 43.9 6567 6239 6896 291 0.05 8 22.8 286
1993 RO 39.4 5894 4715 7073 247 0.2 4 23.2 139
1993 RP 39.3 5879 5233 6526 246 0.11 3 24.5 96
1993 SB 39.4 5894 4008 7780 247 0.32 2 22.7 188
1993 SC 39.7 5939 4811 7068 250 0.19 5 21.7 319
1994 ES2 45.3 6777 6709 6845 305 0.01 1 24.3 159
1994 EV3 43.1 6448 6190 6706 283 0.04 2 23.3 267
1994 GV9 42.2 6313 6313 6313 274 0 0.1 23.1 264
1994 JQ1 43.3 6478 6478 6478 285 0 4 22.4 382
1994 JR1 39.8 5954 5180 6728 251 0.13 4 22.9 238
1994 JS 42.9 6418 4878 7958 281 0.24 14 22.4 263
1994 JV 39.5 5909 5141 6677 248 0.13 17 22.4 254
1994 TB 39.5 5909 4018 7800 248 0.32 12 21.5 258
1994 TG 42.3 6328 6328 6328 275 0 7 23 232
1994 TG2 42.5 6358 6358 6358 277 0 2 24 141
1994 TH 40.9 6119 6119 6119 262 0 16 23 217
1994 VK8 43.5 6508 6508 6508 287 0 1 22 389
1995 DA2 36.3 5430 4779 6082 219 0.12 7 23 169
1995 DB2 43.5 6508 6052 6963 287 0.07 4 22.5 266
1995 DC2 45.2 6762 6762 6762 304 0 2 22.5 338
1995 GA7 39.5 5909 5200 6618 248 0.12 4 23 202
1995 GY7 41.3 6178 6178 6178 265 0 0.9 23.5 TBD
1995 GJ 42.9 6418 5834 7002 281 0.091 23 22.5 301
1995 HM5 39.5 5909 4846 6973 248 0.18 5 23.1 161
1995 KJ1 43.5 6508 6508 6508 287 0 3 22.5 361
1995 KK1 39.5 5909 4786 7032 248 0.19 9 23 166
1995 FB21 42.43 6348 6348 6348 276 0 1 23.5 169
1995 QY9 39.4 5894 4480 7309 247 0.24 5 21.5 TBD
1995 QZ9 39.8 5954 5001 6907 251 0.16 19.5 22.5 TBD
1995WY2 45.87 6862 6588 7137 311 0.04 1.7 23.4 TBD
1995 YY3 39.24 5870 4591 7150 246 0.218 0.44 23.4 TBD
1996 KV1 43 6433 6175 6690 282 0.04 8.4 22.9 268
1996 KW1 46.6 6971 6971 6971 318 0 6 23.4 281
1996 KX1 39.5 5909 5318 6500 248 0.1 1.5 23.9 131
1996 KY1 39.5 5909 5318 6500 248 0.1 31 23.3 126
1996RQ20 39.4 5894 4244 7545 247 0.28 38 22.6 TBD
1996RR20 42.8 6403 6403 6403 280 0 5 22.8 TBD
1996SZ4 39.4 5894 4598 7191 247 0.22 5 23 TBD
1996TK66 42.5 6358 6358 6358 277 0 5 22 TBD
1996TL66 83.8 12536 5265 19808 767 0.58 24 21 500
1997CQ29 44.4 6642 6177 7107 296 0.07 3 22.5 TBD

Plutinos

A surprising fraction - 40 % - of Kuiper Belt objects have orbital periods close to Pluto's. 246 years is 3/2 of Neptune's period of 164 years and is a stable resonance that allows the object to avoid being perturbed by Neptune. In the asteroid belt, similarly, there are gaps where Jupiter would have 2, 5/2, or 3 times the asteroid's period but a cluster of asteroids where Jupiter has 3/2 the asteroid's period.

Kuiper Belt objects with periods close to Pluto's have been dubbed "Plutinos". A list of known plutinos from the list above follows. Pluto is included for comparison.

Object a (AU) a (mil km) perh (mil km) aph (mil km) period yr. e i (deg) Mag (Mr) Diam. (km)
Pluto 39.48 5900 4440 7350 248.02 0.249 17.14 14 2400
1993 RO 39.4 5894 4715 7073 247 0.2 4 23.2 139
1993 RP 39.3 5879 5233 6526 246 0.11 3 24.5 96
1993 SB 39.4 5894 4008 7780 247 0.32 2 22.7 188
1993 SC 39.7 5939 4811 7068 250 0.19 5 21.7 319
1994 JR1 39.8 5954 5180 6728 251 0.13 4 22.9 238
1994 JV 39.5 5909 5141 6677 248 0.13 17 22.4 254
1994 TB 39.5 5909 4018 7800 248 0.32 12 21.5 258
1995 GA7 39.5 5909 5200 6618 248 0.12 4 23 202
1995 HM5 39.5 5909 4846 6973 248 0.18 5 23.1 161
1995 KK1 39.5 5909 4786 7032 248 0.19 9 23 166
1995 QY9 39.4 5894 4480 7309 247 0.24 5 21.5 TBD
1995 QZ9 39.8 5954 5001 6907 251 0.16 19.5 22.5 TBD
1995 YY3 39.24 5870 4591 7150 246 0.218 0.44 23.4 TBD
1996 KX1 39.5 5909 5318 6500 248 0.1 1.5 23.9 131
1996 KY1 39.5 5909 5318 6500 248 0.1 31 23.3 126
1996RQ20 39.4 5894 4244 7545 247 0.28 38 22.6 TBD
1996SZ4 39.4 5894 4598 7191 247 0.22 5 23 TBD

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Created 9 June 1997, Last Update 12 January 2020