Known populations of solar system objects: May 2009

compiled by Wm. Robert Johnston
last updated 8 May 2009

For related historical graphs see Historical known populations of solar system objects.

Summary

Star: 1

Planets*: 8
Dwarf planets*: 5 (5 named)
Asteroids*: 452,148 (214,872 numbered**, 237,276 provisional)
Outer solar system objects*: 1,338 (221 numbered**, 1,117 provisional)
Comets***: 3,648 (219 numbered***, 2,849 with designations, 580 without designations)

Moons of planets: 167 (145 named, 22 provisional)
Moons of dwarf planets: 6 (6 named)
Moons of asteroids: 117 (6 named, 111 provisional)
Moons of outer solar system objects: 54 (4 named, 50 provisional)

* Note: "dwarf planet" is a new classification designated by the International Astronomical Union on 24 August 2006; currently it includes the asteroid (1) Ceres, Pluto, and the trans-Neptunian objects (136108) Haumea, (136199) Eris, (136472) Makemake. These five objects are not included in the counts of asteroids and outer solar system objects, and Pluto is not included in the count of planets.

** Note: numbered asteroids include 15,155 with names, and numbered outer solar system objects include 30 with names. These counts do not include the 5 dwarf planets.

*** Note: excludes two objects with dual designations counted among Centaurs (Chiron and Echeclus).

Known populations of solar system objects--detail
object classpermanent designationprovisional designationtotalnotes
   Mercury moons: 0 0 0
   Venus moons: 0 0 0
asteroids, Aten: 72 435 507(#1)
   Aten asteroid moons: 0 6 6(#2)
   Earth moons: 1 0 1
asteroids, Earth coorbitals: 0 1 1(#3)
asteroids, Apollo: 458 2,620 3,078(#4)
   Apollo asteroid moons: 0 20 20(#5)
asteroids, Amor: 392 2,185 2,577(#6)
   Amor asteroid moons: 0 10 10(#7)
   Mars moons: 2 0 2(#8)
asteroids, Mars Trojans: 3 1 4(#9)
asteroids, main belt: 212,392230,631443,023(#10)
   Ceres moons: 0 0 0
   main belt asteroid moons: 5 72 77(#11)
   Jupiter moons: 49 14 63(#12)
asteroids, Jupiter Trojans: 1,555 1,403 2,958(#13)
   Jupiter Trojan asteroid moons: 1 3 4(#14)
   Saturn moons: 53 8 61(#15)
   Uranus moons: 27 0 27(#16)
comets, short period: 219 242 461(#17)
   Neptune moons: 13 0 13(#18)
KBOs, Neptune Trojans: 0 6 6(#19)
Centaurs and scattered disk objects: 78 163 241(#20)
   Centaur/scattered disk object moons: 2 6 8(#21)
Kuiper Belt objects: 142 948 1,090(#22)
   Kuiper Belt object moons: 2 44 46(#23)
   Pluto moons: 3 0 3(#24)
   Haumea moons: 2 0 2(#25)
   Makemake moons: 0 0 0
   Eris moons: 1 0 1(#26)
comets, long-period: 2,607 580 3,187(#27)
   Oort cloud objects: 1 0 1(#28)

Notes to table:

  1. Asteroids with semimajor axes less than 1.0 AU. First one discovered 1954.
  2. First one discovered 1999.
  3. Asteroid orbiting in horseshoe orbits with the Earth. First one (2002 AA29) discovered 2002. Does not include 2 possible coorbital objects.
  4. Asteroids (other than Amors) with perihelion distances less than 1.0 AU. First one discovered 1932.
  5. First one discovered 1997.
  6. Asteroids (other than Amors or Apollos) with perihelion distances less than 1.3 AU. First one discovered 1898.
  7. First one discovered 1997.
  8. First one discovered 1877.
  9. Asteroids orbiting in Mars' L4 and L5 positions (60 degrees ahead of and behind Mars, respectively). First one discovered 1990.
  10. Asteroids not counted elsewhere (some may cross the orbits of Mars, Jupiter, or other outer planets). Provisional asteroid figures include many objects counted more than once. First one discovered 1801. One is now classified as a dwarf planet.
  11. First one discovered 1993.
  12. First one discovered 1610. Does not include 7 objects observed near Amalthea in 2002.
  13. Asteroids orbiting in Jupiter's L4 and L5 positions (60 degrees ahead of and behind Jupiter, respectively). First one discovered 1906.
  14. First one discovered 2001.
  15. First one discovered 1655. Includes S/2004 S6 but excludes other provisional objects which may be clumps of ring material (e.g., S/2004 S3 and S/2004 S4) and excludes other objects detected in rings.
  16. First one discovered 1787.
  17. Comets with orbital periods less than 200 years. Excludes two objects with dual designations counted among Centaurs (Chiron and Echeclus).
  18. First one discovered 1846.
  19. Outer solar system objects orbiting in Neptune's L4 or L5 positions (60 degrees ahead of or behind Neptune, respectively). First one (2001 QR322) discovered 2001.
  20. Outer solar system objects beyond Saturn outside the main Kuiper Belt. Centaurs and scattered disk objects are included together since different delineations between the two categories exist. First one discovered 1977.
  21. First one discovered 2002.
  22. Outer solar system objects beyond Neptune in the main Kuiper Belt. First one discovered 1995.
  23. First one discovered 2000.
  24. First one discovered 1978. Pluto is now classified as a dwarf planet.
  25. First one discovered 2005. Haumea is now classified as a dwarf planet.
  26. First one discovered 2005. Eris is now classified as a dwarf planet.
  27. Comets with orbital periods over 200 years. A different criterion for permanent/provisional designations is used in this entry: "permanent" here includes long-period comets with computed orbits and IAU designations; "provisional" includes objects with no IAU designation: ancient comets with no computed orbit (449), modern comets with no computed orbit (72), and recently discovered comets awaiting designations (23).
  28. Outer solar system objects with perihelia greater than 70 AU. First one (90377 Sedna) discovered 2003.
Counts are up-to-date by category through the following dates: Note that most (448) of the 580 "other" provisional comets are from pre-modern observations and have no computed orbits. Provisional asteroid and comets numbers do not all represent unique objects (i.e. many provisional objects have been counted more than once in as yet unlinked observations).

In August 2006 the IAU reclassified Pluto (a still disputed decision) into a new category of "dwarf planet", along with Eris and (1) Ceres. In July 2008 Makemake was declared the fourth dwarf planet, and in September 2008 Haumea the fifth.

An estimated 189 man-made objects are orbiting the Sun, 6 are orbiting Venus, 14 are orbiting Mars, 1 is orbiting Saturn, and 8 are escaping the solar system. This is worth noting in this context since at least two Apollo "asteroids" with provisional designations--1991 VG and 2000 SG344--are suspected of being spent rocket boosters.

Counts are based on data from: the Minor Planet Center web site; The Catalogue of Cometary Orbits 1999 (Marsden and Williams); The Catalogue of Cometary Orbits 2005 (Marsden and Williams); Cometography, Vol. I (Kronk, 1999); International Comet Quarterly web site; the National Space Science Data Center web site; the Solar and Heliospheric Observatory web site; and the web site for the Asteroid Orbital Elements Database (Bowell) on Lowell Observatory's web site.

© 2001-2008, 2009 by Wm. Robert Johnston.
Last updated 8 May 2009.
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