Asteroid family
An asteroid family is a population of asteroids that share similar proper orbital elements, such as semimajor axis, eccentricity, and orbital inclination. The members of the families are thought to be fragments of past asteroid collisions. An asteroid family is a more specific term than asteroid group whose members, while sharing some broad orbital characteristics, may be otherwise unrelated to each other.
General properties
Large prominent families contain several hundred recognized asteroids. Small, compact families may have only about ten identified members. About 33% to 35% of asteroids in the main belt are family members.There are about 20 to 30 reliably recognized families, with several tens of less certain groupings. Most asteroid families are found in the main asteroid belt, although several family-like groups such as the Pallas family, Hungaria family, and the Phocaea family lie at smaller semi-major axis or larger inclination than the main belt.
One family has been identified associated with the dwarf planet. Some studies have tried to find evidence of collisional families among the trojan asteroids, but at present the evidence is inconclusive.
Origin and evolution
The families are thought to form as a result of collisions between asteroids. In many or most cases the parent body was shattered, but there are also several families which resulted from a large cratering event which did not disrupt the parent body. Such cratering families typically consist of a single large body and a swarm of asteroids that are much smaller. Some families have complex internal structures which are not satisfactorily explained at the moment, but may be due to several collisions in the same region at different times.Due to the method of origin, all the members have closely matching compositions for most families. Notable exceptions are those families which formed from a large differentiated parent body.
Asteroid families are thought to have lifetimes of the order of a billion years, depending on various factors. This is significantly shorter than the Solar System's age, so few if any are relics of the early Solar System. Decay of families occurs both because of slow dissipation of the orbits due to perturbations from Jupiter or other large bodies, and because of collisions between asteroids which grind them down to small bodies. Such small asteroids then become subject to perturbations such as the Yarkovsky effect that can push them towards orbital resonances with Jupiter over time. Once there, they are relatively rapidly ejected from the asteroid belt. Tentative age estimates have been obtained for some families, ranging from hundreds of millions of years to less than several million years as for the compact Karin family. Old families are thought to contain few small members, and this is the basis of the age determinations.
It is supposed that many very old families have lost all the smaller and medium-sized members, leaving only a few of the largest intact. A suggested example of such old family remains are the 9 Metis and 113 Amalthea pair. Further evidence for a large number of past families comes from analysis of chemical ratios in iron meteorites. These show that there must have once been at least 50 to 100 parent bodies large enough to be differentiated, that have since been shattered to expose their cores and produce the actual meteorites.
Identification of members, interlopers and background asteroids
When the orbital elements of main belt asteroids are plotted, a number of distinct concentrations are seen against the rather uniform distribution of non-family background asteroids. These concentrations are the asteroid families '. Interlopers''' are asteroids classified as family members based on their so-called proper orbital elements but having spectroscopic properties distinct from the bulk of the family, suggesting that they, contrary to the true family members, did not originate from the same parent body that once fragmented upon a collisional impact.Description
Strictly speaking, families and their membership are identified by analysing the proper orbital elements rather than the current osculating orbital elements, which regularly fluctuate on timescales of tens of thousands of years. The proper elements are related constants of motion that remain almost constant for times of at least tens of millions of years, and perhaps longer.The Japanese astronomer Kiyotsugu Hirayama pioneered the estimation of proper elements for asteroids, and first identified several of the most prominent families in 1918. In his honor, asteroid families are sometimes called Hirayama families. This particularly applies to the five prominent groupings discovered by him.
Hierarchical clustering method
Present day computer-assisted searches have identified [|more than a hundred asteroid families]. The most prominent algorithms have been the hierarchical clustering method, which looks for groupings with small nearest-neighbour distances in orbital element space, and wavelet analysis, which builds a density-of-asteroids map in orbital element space, and looks for density peaks.The boundaries of the families are somewhat vague because at the edges they blend into the background density of asteroids in the main belt. For this reason the number of members even among discovered asteroids is usually only known approximately, and membership is uncertain for asteroids near the edges.
Additionally, some interlopers from the heterogeneous background asteroid population are expected even in the central regions of a family. Since the true family members caused by the collision are expected to have similar compositions, most such interlopers can in principle be recognised by spectral properties which do not match those of the bulk of family members. A prominent example is 1 Ceres, the largest asteroid, which is an interloper in the family once named after it.
Spectral characteristics can also be used to determine the membership of asteroids in the outer regions of a family, as has been used e.g. for the Vesta family, whose members have an unusual composition.
Family types
As previously mentioned, families caused by an impact that did not disrupt the parent body but only ejected fragments are called cratering families. Other terminology has been used to distinguish various types of groups which are less distinct or less statistically certain from the most prominent "nominal families".Clusters, clumps, clans and tribes
The term cluster is also used to describe a small asteroid family, such as the Karin cluster. Clumps are groupings which have relatively few members but are clearly distinct from the background. Clans are groupings which merge very gradually into the background density and/or have a complex internal structure making it difficult to decide whether they are one complex group or several unrelated overlapping groups. Tribes are groups that are less certain to be statistically significant against the background either because of small density or large uncertainty in the orbital parameters of the members.List
Prominent families
Among the many asteroid families, the Eos, Eunomia, Flora, Hungaria, Hygiea, Koronis, Nysa, Themis and Vesta families are the most prominent ones in the asteroid belt. For a complete list, see .; Eos family
;Eunomia family
;Flora family
; Hungaria family
;Hygiea family
; [|Koronis family]
; Nysa family
; [|Themis family]
; Vesta family
All families
In 2015, a study identified 122 notable families with a total of approximately 100,000 member asteroids, based on the entire catalog of numbered minor planets, which consisted of almost 400,000 numbered bodies at the time '. The data has been made available at the "Small Bodies Data Ferret". The first column of this table contains the family identification number or family identifier number, which is an attempt for a numerical labeling of identified families, independent of their currently used name, as a family's name may change with refined observations, leading to multiple names used in literature and to subsequent confusion.| FIN | Family | Lbl | # of Members | Loc. | Taxonomy | mean- albedo | Parent bodyNotes | Cat | LoMP |
| 001 | Hilda family | HIL | 409 | rim | C | 0.04 | 153 Hilda; adj. Hildian; within the larger dynamical group with the same name. | :Category:Hilda asteroids|cat | |
| 002 | Schubart family | SHU | 352 | rim | C | 0.03 | 1911 Schubart | :Category:Schubart asteroids|cat | |
| 003 | Hungaria family | H | 2965 | rim | E | 0.35 | 434 Hungaria; located within the dynamical group of the same name. | :Category:Hungaria asteroids|cat | |
| 004 | Hektor family | HEK | 12 | rim | – | – | 624 Hektor | :Category:Hektor asteroids|cat | |
| 005 | Eurybates family | ERY | 218 | rim | CP | 0.06 | 3548 Eurybates | :Category:Eurybates asteroids|cat | |
| 006 | unnamed family | 006 | 7 | rim | – | 0.06 | 1996 RJ | — | |
| 007 | James Bond family | 007 | 1 | inner | ASP | – | 9007 James Bond | — | |
| 008 | Arkesilaos family | ARK | 37 | rim | – | – | 20961 Arkesilaos | :Category:Arkesilaos asteroids|cat | |
| 009 | Ennomos family | ENM | 30 | rim | – | 0.06 | 4709 Ennomos | :Category:Ennomos asteroids|cat | |
| 010 | unnamed family | 010 | 13 | rim | – | 0.09 | — | ||
| 401 | Vesta family | V | 15252 | inner | V | 0.35 | 4 Vesta | :Category:Vesta asteroids|cat | |
| 402 | Flora family | FLO | 13786 | inner | S | 0.30 | 8 Flora, also named after 43 Ariadne; typical asteroid clan. Not a legitimate asteroid family according to Carruba and Milani, instead, the Florian core region is labelled Belgica family and Duponta family, respectively. | :Category:Flora asteroids|cat | |
| 403 | Baptistina family | BAP | 2500 | inner | X | 0.16 | 298 Baptistina, merges with the Belgica family at 100 m/s according to Carruba | :Category:Baptistina asteroids|cat | |
| 404 | Massalia family | MAS | 6424 | inner | S | 0.22 | 20 Massalia, adj. Massalian, a-e-i: | :Category:Massalia asteroids|cat | |
| 405 | Nysa–Polana complex | NYS | 19073 | inner | SFC | 0.28 0.06 | 44 Nysa/142 Polana also known as the Hertha family. Includes the Eulalia family | :Category:Nysa asteroids|cat | |
| 406 | Erigone family | ERI | 1776 | inner | CX | 0.06 | 163 Erigone, adj. Erigonian. Can be joined with the dynamically different Martes family into a single collisional family. | :Category:Erigone asteroids|cat | |
| 407 | Clarissa family | CLA | 179 | inner | X | 0.05 | 302 Clarissa | :Category: Clarissa asteroids|cat | |
| 408 | Sulamitis family | SUL | 303 | inner | C | 0.04 | 752 Sulamitis | :Category:Sulamitis asteroids|cat | |
| 409 | Lucienne family | LCI | 142 | inner | S | 0.22 | 1892 Lucienne | :Category:Lucienne asteroids|cat | |
| 410 | Euterpe family | EUT | 474 | inner | S | 0.26 | 27 Euterpe | :Category:Euterpe asteroids|cat | |
| 411 | Datura family | DAT | 6 | inner | S | 0.21 | 1270 Datura; Recently formed family with members:,,, and | :Category:Datura asteroids|cat | |
| 412 | Lucascavin family | LCA | 3 | inner | S | – | 21509 Lucascavin; members:, | :Category:Lucascavin asteroids|cat | |
| 413 | Klio family | KLI | 330 | inner | C | 0.07 | 84 Klio | :Category:Klio asteroids|cat | |
| 414 | Chimaera family | CIM | 108 | inner | CX | 0.06 | 623 Chimaera | :Category:Chimaera asteroids|cat | |
| 415 | Chaldaea family | CHL | 132 | inner | C | 0.07 | 313 Chaldaea; alt. named after 1715 Salli by Masiero | :Category:Chaldaea asteroids|cat | |
| 416 | Svea family | SVE | 48 | inner | CX | 0.06 | 329 Svea | :Category:Svea asteroids|cat | |
| 417 | unnamed family | 417 | 9 | inner | – | – | — | ||
| 701 | Phocaea family | PHO | 1989 | inner | S | 0.22 | 25 Phocaea | :Category:Phocaea asteroids|cat | |
| 501 | Juno family | JUN | 1684 | middle | S | 0.25 | 3 Juno | :Category:Juno asteroids|cat | |
| 502 | Eunomia family | EUN | 5670 | middle | S | 0.19 | 15 Eunomia | :Category:Eunomia asteroids|cat | |
| 504 | Nemesis family | NEM | 1302 | middle | C | 0.05 | 128 Nemesis '; also named after 58 Concordia ' and 3827 Zdeněkhorský. Formerly Liberatrix family by Zappalà and Cellino | :Category:Nemesis asteroids|cat | |
| 505 | Adeona family | ADE | 2236 | middle | C | 0.07 | 145 Adeona | :Category:Adeona asteroids|cat | |
| 506 | Maria family | MAR | 2940 | middle | S | 0.25 | 170 Maria; alternatively named after 472 Roma. | :Category:Maria asteroids|cat | |
| 507 | Padua family | PAD | 1087 | middle | X | 0.10 | 363 Padua; also known as Lydia family110 Lydiaadj. Paduan; Lydian | :Category:Padua asteroids|cat | |
| 508 | Aeolia family | AEO | 296 | middle | X | 0.17 | 396 Aeolia | :Category:Aeolia asteroids|cat | |
| 509 | Chloris family | CLO | 424 | middle | C | 0.06 | 410 Chloris, adj. Chloridian | :Category:Chloris asteroids|cat | |
| 510 | Misa family | MIS | 702 | middle | C | 0.03 | 569 Misa, adj. Misian | :Category:Misa asteroids|cat | |
| 511 | Brangäne family | BRG | 195 | middle | S | 0.10 | 606 Brangäne | :Category:Brangäne asteroids|cat | |
| 512 | Dora family | DOR | 1259 | middle | C | 0.05 | 668 Dora, adj. Dorian | :Category:Dora asteroids|cat | |
| 513 | Merxia family | MRX | 1215 | middle | S | 0.23 | 808 Merxia, adj. Merxian | :Category:Merxia asteroids|cat | |
| 514 | Agnia family | AGN | 2125 | middle | S | 0.18 | 847 Agnia | :Category:Agnia asteroids|cat | |
| 515 | Astrid family | AST | 489 | middle | C | 0.08 | 1128 Astrid, adj. Astridian | :Category:Astrid asteroids|cat | |
| 516 | Gefion family | GEF | 2547 | middle | S | 0.20 | 1272 Gefion, adj. Gefionian; a-e-i: ; also known as Ceres family ' after 1 Ceres; and Minerva family after 93 Minerva | :Category:Gefion asteroids|cat | |
| 517 | König family | KON | 354 | middle | CX | 0.04 | 3815 König | :Category:König asteroids|cat | |
| 518 | Rafita family | RAF | 1295 | middle | S | 0.25 | 1644 Rafita, adj. Rafitian ; members and | :Category:Rafita asteroids|cat | |
| 519 | Hoffmeister family | HOF | 1819 | middle | CF | 0.04 | 1726 Hoffmeister | :Category:Hoffmeister asteroids|cat | |
| 520 | Iannini family | IAN | 150 | middle | S | 0.32 | 4652 Iannini | :Category:Iannini asteroids|cat | |
| 521 | Kazuya family | KAZ | 44 | middle | S | 0.21 | 7353 Kazuya | :Category:Kazuya asteroids|cat | |
| 522 | Ino family | INO | 463 | middle | S | 0.24 | 173 Ino | :Category:Ino asteroids|cat | |
| 523 | Emilkowalski family | EMI | 4 | middle | S | 0.20 | 14627 Emilkowalski; members:, and | :Category:Emilkowalski asteroids|cat | |
| 524 | Brugmansia family | 524 | 3 | middle | S | – | 16598 Brugmansia; members: and | :Category:Brugmansia asteroids|cat | |
| 525 | Schulhof family | SHF | 5 | middle | S | 0.27 | 2384 Schulhof; members:,,, | :Category:Schulhof asteroids|cat | |
| 526 | unnamed family | 526 | 58 | middle | C | 0.06 | — | ||
| 527 | Lorre family | LOR | 2 | middle | C | 0.05 | 5438 Lorre; other member: | :Category:Lorre asteroids|cat | |
| 528 | Leonidas family | [|LEO] | 135 | middle | CX | 0.07 | 2782 Leonidas; identical to the Vibilia family: [|VIB] ; | :Category:Leonidas asteroids|cat | |
| 529 | Vibilia family | VIB | 180 | middle | C | 0.06 | 144 Vibilia; namesake only listed in family by Zappalà, but not by Nesvorý; identical to the Leonidas family: LEO. | :Category:Vibilia asteroids|cat | |
| 530 | Phaeo family | PAE | 146 | middle | X | 0.06 | 322 Phaeo | :Category:Phaeo asteroids|cat | |
| 531 | Mitidika family | MIT | 653 | middle | C | 0.06 | 2262 Mitidika ; members: and | :Category:Mitidika asteroids|cat | |
| 532 | Henan family | HEN | 1872 | middle | L | 0.20 | 2085 Henan | :Category:Henan asteroids|cat | |
| 533 | Hanna family | HNA | 280 | middle | CX | 0.05 | 1668 Hanna | :Category:Hanna asteroids|cat | |
| 534 | Karma family | KRM | 124 | middle | CX | 0.05 | 3811 Karma | :Category:Karma asteroids|cat | |
| 535 | Witt family | WIT | 1618 | middle | S | 0.26 | 2732 Witt | :Category:Witt asteroids|cat | |
| 536 | Xizang family | XIZ | 275 | middle | – | 0.12 | 2344 Xizang | :Category:Xizang asteroids|cat | |
| 537 | Watsonia family | WAT | 99 | middle | L | 0.13 | 729 Watsonia | :Category:Watsonia asteroids|cat | |
| 538 | Jones family | JNS | 22 | middle | T | 0.05 | 3152 Jones | :Category:Jones asteroids|cat | |
| 539 | Aëria family | AER | 272 | middle | X | 0.17 | 369 Aeria | :Category:Aeria asteroids|cat | |
| 540 | Julia family | JUL | 33 | middle | S | 0.19 | 89 Julia | :Category:Julia asteroids|cat | |
| 541 | Postrema family | POS | 108 | middle | CX | 0.05 | 1484 Postrema | :Category:Postrema asteroids|cat | |
| 801 | Pallas family | PAL | 128 | middle | B | 0.16 | 2 Pallas | :Category:Palladian asteroids|cat | |
| 802 | Gallia family | GAL | 182 | middle | S | 0.17 | 148 Gallia | :Category:Gallia asteroids|cat | |
| 803 | Hansa family | HNS | 1094 | middle | S | 0.26 | 480 Hansa adj. Hansian; a-e-i: | :Category:Hansa asteroids|cat | |
| 804 | Gersuind family | GER | 415 | middle | S | 0.15 | 686 Gersuind | :Category:Gersuind asteroids|cat | |
| 805 | Barcelona family | BAR | 306 | middle | S | 0.25 | 945 Barcelona | :Category:Barcelona asteroids|cat | |
| 806 | Tina family | TIN | 96 | middle | X | 0.34 | 1222 Tina | :Category:Tina asteroids|cat | |
| 807 | Brucato family | BRU | 342 | middle | CX | 0.06 | 4203 Brucato | :Category:Brucato asteroids|cat | |
| 601 | Hygiea family | HYG | 4854 | outer | CB | 0.06 | 10 Hygiea | :Category:Hygiea asteroids|cat | |
| 602 | Themis family | THM | 4782 | outer | C | 0.07 | 24 Themis | :Category:Themis asteroids|cat | |
| 603 | Sylvia family | SYL | 255 | outer | X | 0.05 | 87 Sylvia; family within Cybele group | :Category:Sylvia asteroids|cat | |
| 604 | Meliboea family | MEL | 444 | outer | C | 0.05 | 137 Meliboea, adj. Meliboean | :Category:Meliboea asteroids|cat | |
| 605 | Koronis family | KOR | 5949 | outer | S | 0.15 | 158 Koronis, also named after 208 Lacrimosa | :Category:Koronis asteroids|cat | |
| 606 | Eos family | EOS | 9789 | outer | K | 0.13 | 221 Eos | :Category:Eos asteroids|cat | |
| 607 | Emma family | EMA | 76 | outer | C | 0.05 | 283 Emma | :Category:Emma asteroids|cat | |
| 608 | Brasilia family | BRA | 579 | outer | X | 0.18 | 293 Brasilia, adj. Brazilian | :Category:Brasilia asteroids|cat | |
| 609 | Veritas family | VER | 1294 | outer | CPD | 0.07 | 490 Veritas, adj. Veritasian; alt: Undina family after 92 Undina | :Category:Veritas asteroids|cat | |
| 610 | Karin family | KAR | 541 | outer | S | 0.21 | 832 Karin. Recently formed family located within the Koronis family. | :Category:Karin asteroids|cat | |
| 611 | Naëma family | NAE | 301 | outer | C | 0.08 | 845 Naëma, adj. Naëmian | :Category:Naëma asteroids|cat | |
| 612 | Tirela family | TIR | 1395 | outer | S | 0.07 | 1400 Tirela, alternatively named after 1040 Klumpkea | :Category:Tirela asteroids|cat | |
| 613 | Lixiaohua family | LIX | 756 | outer | CX | 0.04 | 3556 Lixiaohua; although member 3330 Gantrisch is both larger and lower numbered ] | :Category:Lixiaohua asteroids|cat | |
| 614 | Telramund family | TEL | 468 | outer | S | 0.22 | 9506 Telramund; alternatively named after 179 Klytaemnestra by Masiero and by Milani | :Category:Telramund asteroids|cat | |
| 615 | unnamed family | 615 | 104 | outer | CX | 0.17 | — | ||
| 616 | Charis family | CHA | 808 | outer | C | 0.08 | 627 Charis | :Category:Charis asteroids|cat | |
| 617 | Theobalda family | THB | 376 | outer | CX | 0.06 | 778 Theobalda, adj. Theobaldian; a-e-i: | :Category:Theobalda asteroids|cat | |
| 618 | Terentia family | TRE | 79 | outer | C | 0.07 | 1189 Terentia | :Category:Terentia asteroids|cat | |
| 619 | Lau family | LAU | 56 | outer | S | 0.27 | 10811 Lau | :Category:Lau asteroids|cat | |
| 620 | Beagle family | BGL | 148 | outer | C | 0.09 | 656 Beagle. Recently formed family is located within the Themis family. Includes 7968 Elst–Pizarro. | :Category:Beagle asteroids|cat | |
| 621 | Koronis family | K-2 | 246 | outer | S | 0.14 | 158 Koronis "second family" | :Category:Koronis asteroids|cat | |
| 622 | Terpsichore family | TRP | 138 | outer | C | 0.05 | 81 Terpsichore | :Category:Terpsichore asteroids|cat | |
| 623 | Fringilla family | FIR | 134 | outer | X | 0.05 | 709 Fringilla | :Category:Fringilla asteroids|cat | |
| 624 | Durisen family | DUR | 27 | outer | X | 0.04 | 5567 Durisen | :Category:Durisen asteroids|cat | |
| 625 | Yakovlev family | YAK | 67 | outer | C | 0.05 | 5614 Yakovlev | :Category:Yakovlev asteroids|cat | |
| 626 | San Marcello family | SAN | 144 | outer | X | 0.19 | 7481 San Marcello | :Category:San Marcello asteroids|cat | |
| 627 | unnamed family | 627 | 38 | outer | CX | 0.05 | — | ||
| 628 | unnamed family | 628 | 248 | outer | S | 0.10 | — | ||
| 629 | unnamed family | 629 | 58 | outer | S | 0.21 | — | ||
| 630 | Aegle family | AEG | 99 | outer | CX | 0.07 | 96 Aegle | :Category:Aegle asteroids|cat | |
| 631 | Ursula family | URS | 1466 | outer | CX | 0.06 | 375 Ursula | :Category:Ursula asteroids|cat | |
| 632 | Elfriede family | ELF | 63 | outer | C | 0.05 | 618 Elfriede | :Category:Elfriede asteroids|cat | |
| 633 | Itha family | ITH | 54 | outer | S | 0.23 | 918 Itha | :Category:Itha asteroids|cat | |
| 634 | Inarradas family | INA | 38 | outer | CX | 0.07 | 3438 Inarradas | :Category:Inarradas asteroids|cat | |
| 635 | Anfimov family | ANF | 58 | outer | S | 0.16 | 7468 Anfimov | :Category:Anfimov asteroids|cat | |
| 636 | Marconia family | MRC | 34 | outer | CX | 0.05 | 1332 Marconia | :Category:Marconia asteroids|cat | |
| 637 | unnamed family | 637 | 64 | outer | CX | 0.05 | — | ||
| 638 | Croatia family | CRO | 93 | outer | X | 0.07 | 589 Croatia | :Category:Croatia asteroids|cat | |
| 639 | Imhilde family | IMH | 43 | outer | CX | 0.05 | 926 Imhilde | :Category:Imhilde asteroids|cat | |
| 640 | Gibbs family | GBS | 8 | outer | – | – | 331P/Gibbs "P/2012 F5 " | — | – |
| 641 | Juliana family | JLI | 76 | outer | CX | 0.05 | 816 Juliana | :Category:Juliana asteroids|cat | |
| 901 | Euphrosyne family | EUP | 2035 | outer | C | 0.06 | 31 Euphrosyne | :Category:Euphrosyne asteroids|cat | |
| 902 | Alauda family | ALA | 1294 | outer | B | 0.07 | 702 Alauda | :Category:Alauda asteroids|cat | |
| 903 | Ulla family | ULA | 26 | outer | X | 0.05 | 909 Ulla; family within Cybele group | :Category:Ulla asteroids|cat | |
| 904 | Luthera family | LUT | 163 | outer | X | 0.04 | 1303 Luthera; fam. is also named after 781 Kartvelia | :Category:Luthera asteroids|cat | |
| 905 | Armenia family | ARM | 40 | outer | C | 0.05 | 780 Armenia | :Category:Armenia asteroids|cat |