A minor planet moon is a minor planet that orbits another minor planet as its natural satellite. It is thought that many asteroids and Kuiper belt objects may possess moons, in some cases quite substantial in size. Discoveries of asteroid moons (and binary objects, in general) are important because the determination of their orbits provides estimates on the mass and density of the primary, allowing insights of their physical properties that is generally not otherwise possible.
Terminology
In addition to the terms satellite and moon, the term binary is sometimes used for minor planets with moons (or triple for minor planets with two moons). If one object is much bigger it is usually referred to as the primary and its companion as secondary. The term double asteroid is sometimes used for systems in which the asteroid and its moon are roughly the same size, while binary tends to be used independently from the relative sizes of the components.
Discovery milestones
As early as 1978, following a stellar occultation, 532 Herculina had been suggested to have a moon and there were reports of other asteroids having companions (usually referred to as satellites) in the following years. A letter in Sky & Telescope magazine at this time pointed to pairs of large craters (e.g. the Clearwater Lakes in Quebec) also suggesting asteroids having companions. However, it was not until 1993 that the first asteroid moon was confirmed when the Galileo probe discovered Dactyl orbiting 243 Ida. The second was discovered around 45 Eugenia in 1998. The first Trans-Neptunian binary, 1998 WW31 was optically resolved in 2002.[1]
As of September 2008[update], 104 asteroid moons had been discovered, 60 in the main belt, 2 orbiting Trojan asteroids, 42 near-Earth objects and Mars-crossers. There were at that time also 58 Trans-Neptunian moons. In 2005, the asteroid 87 Sylvia was discovered to have two moons, making it the first known triple asteroid. This was followed by the discovery of a second moon orbiting 45 Eugenia. Also in 2005, the KBO Haumea was discovered to have two moons, making it the second KBO after Pluto known to have more than one moon.[2]
An example of a double asteroid is 90 Antiope, where two roughly equal-sized components orbit the common centre of gravity. 617 Patroclus and its same-sized companion Menoetius is the only known binary system in the Trojan population.
Commonality
The data about the populations of binary objects are still patchy. In addition to the inevitable observational bias (dependence on the distance from Earth, size, albedo and separation of the components) the frequency appears to be different among different categories of objects. Among asteroids, an estimated 2% would have satellites. Among trans-Neptunian objects (TNO), an estimated 11% are believed to be binary or multiple objects, but three of the four known large TNO (75%) have at least one satellite.
More than 20 binaries are known in each of the main groupings: Near Earth asteroids, Main belt asteroids, and Trans-Neptunians, not including numerous claims based solely on the light curve variation.
No binaries have been found so far among Centaurs with semi-major axis smaller than Neptune.[3] However, using an extended definition of Centaurs, as the objects on instable orbits with the perihelion inside the orbit of Neptune, the first binary Centaur 42355_Typhon (previously known as 2002 CR46) was identified in 2006.[4]
Origin
The origin of asteroid moons is not currently known with certainty, and a variety of theories exist. A widely accepted theory is that asteroid moons are formed from debris knocked off of the primary asteroid by an impact. Other pairings may be formed when a small object is captured by the gravity of a larger one.
Formation by collision is constrained by the angular momentum of components i.e. by the masses and their separation. Close binaries fit this model (e.g. Pluto/Charon). Distant binaries however, with components of comparable size, are unlikely to have followed this scenario, unless considerable mass has been lost in the event.
The distances of the components for the known binaries vary from a few hundreds of kilometres (243 Ida, 3749 Balam) to more than 3000 km (379 Huenna) for the asteroids. Among TNOs, the known separations vary from 3,000 to 50,000 km.[3]
Populations
What is "typical" for a binary asteroid system tends to depend on its location in the Solar System (presumably because of different modes of origin and lifetimes of such systems in different populations of minor planets).[5]
- Among Near-Earth Asteroids, satellites tend to orbit at distances of the order of 3-7 primary radii, and have diameters two to several times smaller than the primary. Since these binaries are all inner-planet crossers, it is thought that tidal stresses that occurred when the parent object passed close to a planet may be responsible for the formation of many of them, although collisions are thought to also be a factor in the creation of these satellites.
- Among main belt asteroids, the satellites are usually much smaller than the primary (a notable exception being 90 Antiope), and orbit around 10 primary radii away. Many of the binary systems here are members of asteroid families, and a good proportion of satellites are expected to be fragments of a parent body whose disruption after an asteroid collision produced both the primary and satellite.
- Among Trans-Neptunian Objects, it is common for the two orbiting components to be of comparable size, and for the semi-major axis of their orbits to be much larger − about 100 to 1000 primary radii. A significant proportion of these binaries are expected to be primordial.
List of minor planet moons
Near Earth objects
| Name | Type | Diameter (km) (or dimensions) | Name of moon | Diameter of moon (km) (or dimensions) | Separation (km) |
|---|---|---|---|---|---|
| 1862 Apollo | Apollo | 1.7 | S/2005 (1862) 1 | 0.08 | 3 |
| 3671 Dionysus | Amor | 1.5 | S/1997 (3671) 1 | 0.4 | 2.2 |
| 5381 Sekhmet | Aten | 1 | S/2003 (5381) 1 | 0.3 | 1.54 ± 0.12 |
| 7088 Ishtar | Amor | 1.5? | S/2006 (7088) 1 | ? | ? |
| (31345) 1998 PG | Amor | 0.9 | S/2001 (31345) 1 | 0.3 | 1.5 |
| (35107) 1991 VH | Apollo | 1.2 | S/2001 (35107) 1 | 0.5 | 3.2 |
| 65803 Didymos | Amor | 0.8 | S/2003 (65803) 1 | 0.15 ± 0.05 | 1.1 |
| (66063) 1998 RO1 | Aten | 0.9 | S/2001 (66063) 1 | 0.36 | 0.8 |
| (66391) 1999 KW4 | Aten | 1.2 | S/2001 (66391) 1 | > 0.36 | 2.6 |
| 69230 Hermes | Apollo | 0.4 | S/2003 (69230) 1 | 0.4 | 1 |
| (85938) 1999 DJ4 | Apollo | 0.7 | S/2004 (85938) 1 | 0.35 | 1.5 |
| (88710) 2001 SL9 | Apollo | 1 | S/2001 (88710) 1 | 0.31 | 1.8 |
| (137170) 1999 HF1 | Aten | 3.5 | S/1999 (137170) 1 | 0.8 | 7.0 |
| 1990 OS | Apollo | 0.3 | S/2003 (1990 OS) 1 | 0.045 | 0.6 |
| 1994 AW1 | Amor | 0.9 | S/2001 (1994 AW1) 1 | 0.5 | 2.1 |
| 1994 XD | Apollo | 1? | S/2005 (1994 XD) 1 | ? | ? |
| 1996 FG3 | Apollo | 1.4 | S/2001 (1996 FG3) 1 | 0.43 | 2.4 |
| 1998 ST27 | Aten | 0.8 | S/2002 (1998 ST27) 1 | 0.12 | 4.5 ± 0.5 |
| 2000 DP107 | Apollo | 0.80 (± 0.16) | S/2000 (2000 DP107) 1 | 0.30 (± 0.15) | 2.622 ± 0.162 |
| 2000 UG11 | Apollo | 0.23 ± 0.06 | S/2001 (2000 UG11) 1 | 0.10 | 0.337 ± 0.013 |
| 2002 BM26 | Amor | 0.6 | S/2002 (2002 BM26) 1 | 0.1 | 1.5 |
| 2002 CE26 | Apollo | 3 | S/2004 (2002 CE26) 1 | 0.2 | 5 |
| 2002 KK8 | Amor | 0.5 | S/2003 (2002 KK8) 1 | 0.1 | ? |
| 2003 SS84 | Apollo | 0.12 | S/2004 (2003 SS84) 1 | 0.06 | 0.3? |
| 2003 YT1 | Apollo | 1 | S/2004 (2003 YT1) 1 | 0.18 | ~2.7 |
| 2004 DC | Apollo | 0.3 | S/2006 (2004 DC) 1 | ? | ? |
| 2005 AB | Amor | 1.2? | S/2005 (2005 AB) 1 | 0.3 | 2.5? |
| 2005 NB7 | Apollo | 0.5 ± 0.1 | S/2008 (2005 NB7) 1 | 0.2 ± 0.1 | ≥ 0.6 |
| 2006 GY2 | Apollo | 0.45 | S/2006 (2006 GY2) 1 | ? | ? |
Mars crossers
| Name | Diameter (km) (or dimensions) | Name of moon | Diameter of moon (km) (or dimensions) | Separation (km) |
|---|---|---|---|---|
| 1139 Atami | 7 | S/2005 (1139) 1 | 7 | ? |
| 2044 Wirt | 8? | S/2006 (2044) 1 | ? | ? |
| (5407) 1992 AX | 4 | S/2001 (5407) 1 | 1.2 | 6.8 |
| (34706) 2001 OP83 | 4? | S/2005 (34706) 1 | 1? | 8? |
| (114319) 2002 XD58 | 3? | S/2005 (114319) 1 | ? | ? |
Main belt asteroids
| Name | Diameter (km) (or dimensions) | Name of moon | Diameter of moon (km) (or dimensions) | Separation (km) |
|---|---|---|---|---|
| 22 Kalliope | (215×180×150) | Linus | 38 ± 6 | 1,065 ± 8 |
| 45 Eugenia | (305×220×145) | Petit-Prince (Eugenia I) | 13 ± 1 | 1,184 ± 12 |
| S/2004 (45) 1 | ~6 | ~700(?) | ||
| 87 Sylvia | (385×265×230) | Remus (Sylvia II) | 7 ± 2 | 706 ± 5 |
| Romulus (Sylvia I) | 18 ± 4 | 1,356 ± 5 | ||
| 90 Antiope | 110±16 | S/2000 (90) 1 | 110 ± 16 | 170 ± 1 |
| 107 Camilla | (285×205×170) ± 20 | S/2001 (107) 1 | 11 ± 2 | 1,235 ± 16 |
| 121 Hermione | (254×125) | S/2002 (121) 1 | 12 ± 4 | 768 ± 11 |
| 130 Elektra | (215×155) | S/2003 (130) 1 | 6 ± 2 | 1,252 ± 30 |
| 243 Ida | (59.8×25.4×18.6) | Dactyl (Ida I) | (1.6×1.4×1.2) | 108 |
| 283 Emma | 148.1 ± 4.6 | S/2003 (283) 1 | 12 | 596 ± 3 |
| 379 Huenna | 92.3 ± 1.7 | S/2003 (379) 1 | 7 | 3,400 ± 11 |
| 762 Pulcova | 137.1 ± 3.2 | S/2000 (762) 1 | 20 | 810 |
| 809 Lundia | ~7 - 10 | S/2005 (809) 1 | ~7 - 10 | ~10 – 20 |
| 854 Frostia | 13.7 ± 5.6 | S/2004 (854) 1 | 10 | ~25 |
| 1089 Tama | 12.9 | S/2003 (1089) 1 | 9 | 20 |
| 1313 Berna | 11 | S/2004 (1313) 1 | 11 | 35 |
| 1509 Esclangona | 12 | S/2003 (1509) 1 | 4 | 140 |
| 1717 Arlon | 9? | S/2006 (1717) 1 | ? | 18? |
| 2006 Polonskaya | 10 | S/2005 (2006) 1 | ? | ? |
| 2478 Tokai | 10? | S/2007 (2478) 1 | ? | ? |
| 2486 Metsähovi | 12? | S/2007 (2486) 1 | ? | ? |
| 2754 Efimov | 7? | S/2006 (2754) 1 | ? | 12? |
| 3073 Kursk | 8? | S/2007 (3073) 1 | ? | ? |
| 3309 Brorfelde | 6? | S/2005 (3309) 1 | ? | ? |
| 3703 Volkonskaya | 3 | S/2003 (3703) 1 | 1.2 | ? |
| 3749 Balam | 7 | S/2002 (3749) 1 | 1.5 | 310 ± 20 |
| 3782 Celle | 6 | S/2003 (3782) 1 | 2.5 | 30 |
| 3982 Kastel | ? | S/2005 (3982) 1 | ? | ? |
| 4029 Bridges | 10 | S/2006 (4029) 1 | ? | ? |
| 4492 Debussy | 10 | S/2004 (4492) 1 | ? | 25 |
| 4674 Pauling | 8 | S/2004 (4674) 1 | 2.5 | 250 |
| 4786 Tatianina | 8? | S/2006 (4786) 1 | ? | ? |
| (5477) 1989 UH2 | ~7 | S/2005 (5477) 1 | 2.5 | 15 |
| 5905 Johnson | 5 | S/2005 (5905) 1 | 2 | ? |
| 6084 Bascom | 9? | S/2006 (6084) 1 | 3.5? | 32? |
| 6244 Okamoto | 7? | S/2006 (6244) 1 | 1.7? | 15? |
| 9069 Hovland | 3 | S/2004 (9069) 1 | 0.9 | ? |
| 9260 Edwardolson | ~4 | S/2005 (9260) 1 | ? | ? |
| 9617 Grahamchapman | 5? | S/2006 (9617) 1 | 1.4? | ? |
| 11264 Claudiomaccone | 4 | S/2003 (11264) 1 | 1.2 | ? |
| (17246) 2000 GL74 | 4.5 | S/2004 (17246) 1 | 2 | ~230 |
| (17260) 2000 JQ58 | 6? | S/2006 (17260) 1 | 1.5? | 10? |
| (22899) 1999 TO14 | 4.5 | S/2003 (22899) 1 | 1.5 | ~170 |
| (76818) 2000 RG79 | 3.6 | S/2005 (76818) 1 | 1.1 | ? |
Jupiter trojans
| Name | Diameter (km) (or dimensions) | Name of moon | Diameter of moon (km) (or dimensions) | Separation (km) |
|---|---|---|---|---|
| 617 Patroclus | 121.8 ± 3.2 | Menoetius (Patroclus I) | 112.6 ± 3.2 | 685 ± 40 |
| 624 Hektor | (363×207) | S/2006 (624) 1 | 15 | 1,000? |
Trans-Neptunian objects
| Name | Type | Diameter (km) (or dimensions) | Name of moon | Diameter of moon (km) (or dimensions) | Separation (km) |
|---|---|---|---|---|---|
| Pluto | Plutino | 2306±20 | Charon (Pluto I) | 1207±3 | 19,571±4 |
| Nix (Pluto II) | 44-130 | 48,675±120 | |||
| Hydra (Pluto III) | 44-130 | 64,780±90 | |||
| (26308) 1998 SM165 | Plutino | 221? | S/2001 (26308) 1 | 88 | 11,310 ± 110 |
| 42355 Typhon | SDO | 134 | Echidna (Typhon I) | 78 | 1,300? |
| (47171) 1999 TC36 | Plutino | 375 ± 50 | S/2001 (47171) 1 | 140 | 7,640 ± 460 |
| (48639) 1995 TL8 | SDO | 352 | S/2005 (48639) 1 | 161 | 420 |
| 50000 Quaoar | Cubewano | 1260 | S/2007 (50000) 1 | 96? | ? |
| (55637) 2002 UX25 | Cubewano | 649 | S/2007 (55637) 1 | 205 | ? |
| 58534 Logos | Cubewano | 80 | Zoe (Logos I) | 66 | 8,010 ± 80 |
| (60458) 2000 CM114 | SDO | 150? | S/2006 (60458) 1 | 119? | 2,200? |
| (60621) 2000 FE8 | 2:5 resonance | 151? | S/2007 (60621) 1 | 115? | 1,200 |
| 65489 Ceto | SDO | 172 | Phorcys (Ceto I) | 134 | 1,840 |
| 66652 Borasisi | Cubewano | 166 | Pabu (Borasisi I) | 137 | 4,660 ± 170 |
| (79360) 1997 CS29 | Cubewano | 305 | S/2005 (79360) 1 | 292 | 2300 |
| (80806) 2000 CM105 | Cubewano | 224 | S/2005 (80806) 1 | 129 | 2700 |
| (82075) 2000 YW134 | SDO | 431 | S/2005 (82075) 1 | 237 | 1900 |
| 88611 Teharonhiawako | Cubewano | 176 ± 20 | Sawiskera (Teharonhiawako I) | 122 ± 14 | 27,300 ± 343 |
| 90482 Orcus | Plutino | 946 | S/2007 (90482) 1 | 262 ± 170 | 8,700 |
| (119979) 2002 WC19 | 1:2 resonance | 420? | S/2007 (119979) 1 | ? | ? |
| (120347) 2004 SB60 | Cubewano | 580? | S/2006 (120347) 1 | ? | 3,500? |
| (123509) 2000 WK183 | Cubewano | 221? | S/2007 (123509) 1 | ? | ? |
| (134860) 2000 OJ67 | Cubewano | 253? | S/2003 (134860) 1 | 175? | 2,300? |
| 136108 Haumea | Cubewano | 1400 | Hiʻiaka (136108 Haumea I) | 310 | 49,500 ± 400 |
| Namaka (136108 Haumea II) | 170 | 39,300 | |||
| Eris | SDO | 2,800 | Dysnomia (Eris I) | 300-400 | 30,000-36,000 |
| (139775) 2001 QG298 | Plutino | 171? | S/2004 (139775) 1 | 171? | 240? |
| (148780) Altjira | Cubewano | 340? | S/2007 (148780) 1 | 246? | 5,800? |
| 1998 WW31 | Cubewano | 133 ± 15 | S/2000 (1998 WW31) 1 | 110 ± 12 | 22,300 ± 800 |
| 1999 OJ4 | Cubewano? | 168 | S/2005 (1999 OJ4) 1 | 93 | 2,200 |
| 1999 RT214 | Cubewano | 120? | S/2006 (1999 RT214) 1 | ? | 3,300? |
| 2000 CF105 | Cubewano | 170 | S/2001 (2000 CF105) 1 | 120 | 23,000 |
| 2000 CQ114 | Cubewano | 164? | S/2004 (2000 CQ114) 1 | 133 | 5,880 ± 200 |
| 2000 QL251 | Cubewano? | 176? | S/2006 (2000 QL251) 1 | 176? | 7,000? |
| 2001 FL185 | Cubewano | 144? | S/2007 (2001 FL185) 1 | 100? | 1,900? |
| 2001 QY297 | Cubewano | 282? | S/2007 (2001 QY297) 1 | 233? | 2,800? |
| 2001 RZ143 | Cubewano | 201? | S/2007 (2001 RZ143) 1 | 192? | 1,400? |
| 2001 QC298 | Cubewano | 189 | S/2002 (2001 QC298) 1 | 155 | 3,690 ± 70 |
| 2001 QW322 | Cubewano | 86 | S/2003 (2001 QW322) 1 | 86 | ~130,000 |
| 2002 GZ31 | SDO | 187? | S/2007 (2002 GZ31) 1 | 118? | ~2,060 ± 270 |
| 2003 AZ84 | Plutino | 686 +99/-96 | S/2007 (2003 AZ84) 1 | 68 ± 20 | 7,200 |
| 2003 QW111 | Plutino | 265? | S/2006 (2003 QW111) 1 | ? | 10,000? |
| 2003 QY90 | SDO | 196 | S/2003 (2003 QY90) 1 | 178 | 10,000 |
| 2003 UN284 | Cubewano | 127 | S/2003 (2003 UN284) 1 | 97 | 60,000 |
| 2004 PB108 | Cubewano | 210? | S/2007 (2004 PB108) 1 | 121? | 5,400 |
| 2005 EO304 | Cubewano | 240 | S/2005 (2005 EO304) 1 | ? | 85,000 |
See also
www.iass.tkwww.ialo.tk
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