Asteroid family

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Plot of proper inclination vs. semi-major axis for numbered asteroids. Asteroid families are visible as distinct clumps. Prominent Kirkwood gaps divide the core region. (A, B+C, D, E+F+G)

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[edit]

Plot of proper inclination vs. eccentricity for numbered asteroids.

Large prominent families contain several hundred recognized asteroids (and many more smaller objects which may be either not-yet-analyzed, or not-yet-discovered). 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 Haumea.[1] Some studies have tried to find evidence of collisional families among the trojan asteroids, but at present the evidence is inconclusive.

Origin and evolution[edit]

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 (e.g. the Vesta, Pallas, Hygiea, and Massalia families). Such cratering families typically consist of a single large body and a swarm of asteroids that are much smaller. Some families (e.g. the Flora family) 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 (such as the Vesta family) 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 (e.g. smaller asteroids are lost faster). 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 (now dispersed) 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 (Kelley & Gaffey 2000).

Identification of members and interlopers[edit]

When the orbital elements of main belt asteroids are plotted (typically inclination vs. eccentricity, or vs. semi-major axis), a number of distinct concentrations are seen against the rather uniform background distribution of generic 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 object that once fragmented upon a collisional impact.

Description[edit]

Asteroid orbital elements: standard Keplerian on the left (families indistinguishable) vs. proper elements on the right (families visible).

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 (1874–1943) 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[edit]

Present day computer-assisted searches have identified several tens of asteroid families. The most prominent algorithms have been the Hierarchical Clustering Method (HCM) which looks for groupings with small nearest-neighbour distances in orbital element space, and the Wavelet Analysis Method (WAM) 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 (the Ceres family, now the Gefion family).

Spectral characteristics can also be used to determine the membership (or otherwise) 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[edit]

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" (or clusters). The term cluster is also used to describe a small asteroid family, such as the Karin Cluster.[2] Clumps are groupings which have relatively few members but are clearly distinct from the background (e.g. the Juno clump). 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 (e.g. the Flora family has been called a clan). 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[edit]

Prominent families[edit]

Nysa family Vesta family Flora family Eos family Koronis family Eunomia family Hygiea family Themis family Hungaria family Asteroid family#All families Asteroid beltCircle frame.svg
  •   Nysa: 19,073 (4.8%)
  •   Vesta: 15,252 (3.8%)
  •   Flora: 13,786 (3.5%)
  •   Eos: 9,789 (2.5%)
  •   Koronis: 5,949 (1.5%)
  •   Eunomia: 5,670 (1.4%)
  •   Hygiea: 4,854 (1.2%)
  •   Themis: 4,782 (1.2%)
  •   Hungaria: 2,965 (0.7%)
  •   All other families: 21,500 (5.4%)
  •   Background: 295,000 (74.0%)
Distribution of the most prominent families, other families and background asteroids (up to number 398,000)[3]:23

Among the many asteroid family, the Eos, Eunomia, Flora, Hungaria, Hygiea, Koronis, Nysa, Themis and Vesta family are the most prominent ones in the asteroid belt. For a complete list, see § All families.

Eos family[edit]

The Eos family (adj. Eoan), 221 Eos , 9,789

Eunomia family[edit]

The Eunomia family (adj. Eunomia(n); FIN: 502) is a family of S-type asteroids, named after the asteroid 15 Eunomia. It is the most prominent family in the intermediate asteroid belt and the 6th-largest family with 5,670 known members, or approximately 1.4% of all main belt asteroids.[3]:23

Flora family[edit]

The Flora family (adj. Florian) 8 Flora 13,786; Ariadne(an) family after 43 Ariadne

Hungaria family[edit]

The Hungaria family (adj. Hungaria(n)) 434 Hungaria 2,965

Hygiea family[edit]

The Hygiea family (adj. ) 10 Hygiea 4,854

Koronis family[edit]

The Koronis family (adj. Koronian) 158 Koronis 5,949

Nysa family[edit]

The Nysa family (adj.Nysian) 44 Nysa 19,073; Hertha (Herthian) family after 135 Hertha

Themis family[edit]

The Themis family (adj. Themistian) 24 Themis 4,782

Vesta family[edit]

The Vesta family (adj. Vestian) 4 Vesta 15,252

All families[edit]

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 (see catalog index for a current listing of numbered minor planets).[3]:23 The data has been made available at the "Small Bodies Data Ferret".[4] The first column of this table contains the Family Identification Number (FIN).

FIN Family Lbl # of Members Loc. Taxonomy Parent body · Notes Cat LoMP
001 Hilda family HIL 409 rim C 153 Hilda; adj. Hildian; within the larger dynamical group with the same name of a-e-i: (3.7 to 4.2; > 0.07; < 20°) cat list
002 Schubart family SHU 352 rim C 1911 Schubart (within the dynamical Hilda group) cat list
003 Hungaria family H 2965 rim E 434 Hungaria cat list
004 Hektor family HEK 12 rim 624 Hektor (Jupiter trojan) list
005 Eurybates family ERY 218 rim CP 3548 Eurybates (Jupiter trojan) list
006 unnamed family 006 7 rim (9799) 1996 RJ (Jupiter trojan) list
007 James Bond family 007 1 inner ASP 9007 James Bond list
008 Arkesilaos family ARK 37 rim 20961 Arkesilaos (Jupiter trojan) list
009 Ennomos family ENM 30 rim 4709 Ennomos (Jupiter trojan) list
010 unnamed family 010 13 rim (247341) 2001 UV209 (Jupiter trojan) list
401 Vesta family V 15252 inner V 4 Vesta (adj. Vestian) cat list
402 Flora family FLO 13786 inner S 8 Flora cat list
403 Baptistina family BAP 2500 inner X 298 Baptistina cat list
404 Massalia family MAS 6424 inner S 20 Massalia, adj. Massalian, a-e-i: (2.37 to 2.45; 0.12 to 0.21; 0.4 to 2.4) cat list
405 Nysa family (Polana) NYS 19073 inner SFC Nysa-Polana complex; 44 Nysa/142 Polana; includes Eulalia family, 495 Eulalia cat list/(b)
406 Erigone family ERI 1776 inner CX 163 Erigone, adj. Erigonian cat list
407 Clarissa family CLA 179 inner X 302 Clarissa list
408 Sulamitis family SUL 303 inner C 752 Sulamitis cat list
409 Lucienne family LCI 142 inner S 1892 Lucienne list
410 Euterpe family EUT 474 inner S 27 Euterpe list
411 Datura family DAT 6 inner S 1270 Datura list
412 Lucascavin family LCA 3 inner S 21509 Lucascavin list
413 Klio family KLI 330 inner C 84 Klio list
414 Chimaera family CIM 108 inner CX 623 Chimaera list
415 Chaldaea family CHL 132 inner C 313 Chaldaea list
416 Svea family SVE 48 inner CX 329 Svea list
417 unnamed family 417 9 inner (108138) 2001 GB11 list
701 Phocaea family PHO 1989 inner S 25 Phocaea cat list
501 Juno family JUN 1684 middle S 3 Juno (adj. Junonian) cat list
502 Eunomia family EUN 5670 middle S 15 Eunomia cat list
504 Nemesis family NEM 1302 middle C 128 Nemesis, adj. Nemesian; also Concordia(n) family named after 58 Concordia cat list
505 Adeona family ADE 2236 middle C 145 Adeona cat list
506 Maria family MAR 2940 middle S 170 Maria cat list
507 Padua family PAD 1087 middle X 363 Padua; also known as Lydia family[C] · 110 Lydia · adj. Paduan; Lydian cat list
508 Aeolia family AEO 296 middle X 396 Aeolia cat list
509 Chloris family CLO 424 middle C 410 Chloris, adj. Chloridian cat list
510 Misa family MIS 702 middle C 569 Misa, adj. Misian cat list
511 Brangane family BRG 195 middle S 606 Brangane list
512 Dora family DOR 1259 middle C 668 Dora, adj. Dorian cat list
513 Merxia family MRX 1215 middle S 808 Merxia, adj. Merxian cat list
514 Agnia family AGN 2125 middle S 847 Agnia cat list
515 Astrid family AST 489 middle C 1128 Astrid, adj. Astridian cat list
516 Gefion family GEF 2547 middle S 1272 Gefion, adj. Gefionian; a-e-i: (2.74 to 2.82; 0.08 to 0.18; 7.4 to 10.5); alt: Ceres (Cererian) family after 1 Ceres and Minerva (Minervian) family after 93 Minerva cat list
517 König family KON 354 middle CX 3815 König list
518 Rafita family RAF 1295 middle S 1644 Rafita, adj. Rafitian cat list
519 Hoffmeister family HOF 1819 middle CF 1726 Hoffmeister cat list
520 Iannini family IAN 150 middle S 4652 Iannini list
521 Kazuya family KAZ 44 middle S 7353 Kazuya list
522 Ino family INO 463 middle S 173 Ino list
523 Emilkowalski family EMI 4 middle S 14627 Emilkowalski list
524 Brugmansia family 524 3 middle S 16598 Brugmansia list
525 Schulhof family SHF 6 middle S 2384 Schulhof list
526 unnamed family 526 58 middle C (53546) 2000 BY6 list
527 Lorre family LOR 2 middle C 5438 Lorre list
528 Leonidas family LEO 135 middle CX 2782 Leonidas list
529 Vibilia family VIB 180 middle C 144 Vibilia cat list
530 Phaeo family PAE 146 middle X 322 Phaeo list
531 Mitidika family MIT 653 middle C 2262 Mitidika cat list
532 Henan family HEN 1872 middle L 2085 Henan cat list
533 Hanna family HNA 280 middle CX 1668 Hanna list
534 Karma family KRM 124 middle CX 3811 Karma list
535 Witt family WIT 1618 middle S 2732 Witt list
536 Xizang family XIZ 275 middle 2344 Xizang cat list
537 Watsonia family WAT 99 middle L 729 Watsonia cat list
538 Jones family (asteroids) JNS 22 middle T 3152 Jones list
539 Aëria family AER 272 middle X 369 Aeria cat list
540 Julia family (asteroids) JUL 33 middle S 89 Julia list
541 Postrema family POS 108 middle CX 1484 Postrema cat list
801 Pallas family PAL 128 middle B 2 Pallas (adj. Palladian) cat list
802 Gallia family GAL 182 middle S 148 Gallia list
803 Hansa family HNS 1094 middle S 480 Hansa adj. Hansian; a-e-i: (~2.66; ~0.06; ~22.0°)[5] list
804 Gersuind family GER 415 middle S 686 Gersuind list
805 Barcelona family BAR 306 middle S 945 Barcelona list
806 Tina family TIN 96 middle X 1222 Tina list
807 Brucato family BRU 342 middle CX 4203 Brucato list
601 Hygiea family HYG 4854 outer CB 10 Hygiea cat list
602 Themis family THM 4782 outer C 24 Themis (adj. Themistian) cat list
603 Sylvia family SYL 255 outer X 87 Sylvia list
604 Meliboea family MEL 444 outer C 137 Meliboea, adj. Meliboean cat list
605 Koronis family KOR 5949 outer S 158 Koronis cat list
606 Eos family EOS 9789 outer K 221 Eos cat list
607 Emma family EMA 76 outer C 283 Emma list
608 Brasilia family BRA 579 outer X 293 Brasilia, adj. Brazilian cat list
609 Veritas family VER 1294 outer CPD 490 Veritas, adj. Veritasian; alt: Undina (Undinian) family after 92 Undina cat list
610 Karin family KAR 541 outer S 832 Karin cat list
611 Naëma family NAE 301 outer C 845 Naëma, adj. Naëmian cat list
612 Tirela family TIR 1395 outer S 1400 Tirela (Klumpkea) cat list
613 Lixiaohua family LIX 756 outer CX 3556 Lixiaohua cat list
614 Telramund family TEL 468 outer S 9506 Telramund list
615 unnamed family 615 104 outer CX (18405) 1993 FY12 list
616 Charis family CHA 808 outer C 627 Charis list
617 Theobalda family THB 376 outer CX 778 Theobalda, adj. Theobaldian; a-e-i: (3.16 to 3.19; 0.24 to 0.27; 14 to 15) cat list
618 Terentia family TRE 79 outer C 1189 Terentia list
619 Lau family LAU 56 outer S 10811 Lau list
620 Beagle family BGL 148 outer C 656 Beagle list
621 Koronis family (II) K-2 246 outer S 158 Koronis "second family" cat list
622 Terpsichore family TRP 138 outer C 81 Terpsichore list
623 Fringilla family FIR 134 outer X 709 Fringilla list
624 Durisen family DUR 27 outer X 5567 Durisen list
625 Yakovlev family YAK 67 outer C 5614 Yakovlev list
626 San Marcello family SAN 144 outer X 7481 San Marcello list
627 unnamed family 627 38 outer CX (15454) 1998 YB3 list
628 unnamed family 628 248 outer S (15477) 1999 CG1 list
629 unnamed family 629 58 outer S (36256) 1999 XT17 list
630 Aegle family AEG 99 outer CX 96 Aegle cat list
631 Ursula family URS 1466 outer CX 375 Ursula cat list
632 Elfriede family ELF 63 outer C 618 Elfriede list
633 Itha family ITH 54 outer S 918 Itha cat list
634 Inarradas family INA 38 outer CX 3438 Inarradas list
635 Anfimov family ANF 58 outer S 7468 Anfimov list
636 Marconia family MRC 34 outer CX 1332 Marconia list
637 unnamed family 637 64 outer CX (106302) 2000 UJ87 list
638 Croatia family CRO 93 outer X 589 Croatia cat list
639 Imhilde family IMH 43 outer CX 926 Imhilde list
640 Gibbs family GBS 8 outer 331P/Gibbs "P/2012 F5 (Gibbs)"
641 Juliana family JLI 76 outer CX 816 Juliana list
901 Euphrosyne family EUP 2035 outer C 31 Euphrosyne cat list
902 Alauda family ALA 1294 outer B 702 Alauda cat list
903 Ulla family ULA 26 outer X 909 Ulla list
904 Luthera family LUT 163 outer X 1303 Luthera list
905 Armenia family ARM 40 outer C 780 Armenia list

Other families[edit]

Other asteroid families from miscellaneous sources (not listed in the above table), as well as non-asteroid families include:

Family Parent Cat Description
Alinda family 887 Alinda cat Alinda group described by projectpluto.com
Amneris family 871 Amneris cat Small family of 22 asteroids identified by Zappalà (1995).[6] Most members have been assigned to the encompassing complex of the Flora family by Nesvorný (2014).[3]
Astraea family 5 Astraea cat Large family with 6,169 members up to number (494569), accordiny to AstDyS-2 (Src). Lowest-numbered members: (5), (91), (262), (355), (765) and (1121). Not a listed family in HCM by Zappalà (1995) and Nesvorný (2014).[6][3]
Augusta family 254 Augusta cat Small family of 23 asteroids identified by Zappalà (1995).[6] Most members have been assigned to the Flora family by Nesvorný (2014).[3]
Ausonia family 63 Ausonia cat Single member. Unsourced. Member of the Vesta family according to AstDyS-2 and Nesvorný (2014).[3]
Bower family 1639 Bower Micro-family with 10 members as per Zappalà (1995). Adj. Bowerian. Alternative name Endymion (Endymionian) family after 342 Endymion.[C] All members: (1639), (3815), (8832), (14306), (15666), (22286), (32637), (85133), (120446) and (145685).[6] This family corresponds in large parts with the König family by Nesvorný (2014).[3]
Clematis family 1101 Clematis cat Micro-family with 17 members up to number (494569), accordiny to AstDyS-2 (Src). Subset of the large Alauda family as per Nesvorný (2014).[3] All members: (1101), (5360), (22044), (25982), (29963), (32240), (37628), (66174), (71688), (83362), (83790), (97516), (110030), (132961), (147858), (181960) and (223933).
Cybele family 65 Cybele cat Cybele group according to Asteroids, Meteorites, and Comets – by Linda T. Elkins-Tanton and projectpluto.com. Corresponding wiki-category lists a total of 32 members. Not a listed family in HCM by Zappalà (1995), Nesvorný (2014) and AstDyS-2 (Src), where these bodies are predominantly assigned to the background population.[6][3]
Dejanira family 157 Dejanira cat Micro-family with 5 members as per Zappalà (1995). All members: (157), (2290), (5276), (10779) and (17377).[6] All belong to the background population according to Nesvorný (2014).[3]
Faïna family 751 Faïna cat Carbonaceous family with 12 identified members as per Zappalà (1995).[6] All members: (751), (2089), (2420), (3637), (3904), (5083), (8087), (10741), (10744), (11497), (12975) and (29086). Predominantly background population with 3 bodies belonging to the stony Maria family per Nesvorný (2014). Not a listed family at AstDyS-2 (Src)
Griqua group 1362 Griqua cat Griqua group (not a collisional family) described by projectpluto.com. A marginally unstable group of asteroids observed in the 2 :1 resonance with Jupiter.
Hestia family 46 Hestia cat Single member. Background asteroid according to both AstDyS-2 and Nesvorný.[3]
Laodica family 507 Laodica cat Category with 2 members. 507 Laodica and 635 Vundtia are core members of the Eos family according to AstDyS-2 (507; 635) and background asteroid per Nesvorný (507; 635), respectively.[3]
Liberatrix family 125 Liberatrix cat 3 listed members. 125 Liberatrix is a background asteroid according to AstDyS-2, and a member of the Nemesis family according to Nesvorný.[3] Background asteroid: 301 Bavaria (both AstDyS-2 and Nesvorný). 9923 Ronaldthiel is a core member of the Agnia family at AstDyS-2.
Haumea family Haumea (dwarf planet) cat This is a TNO-family. As of 2017, and current categorization, the family consists of 10 members (including parent body).[D]
Martes family 5026 Martes cat Two members. (5026) Martes is the parent body of a family, accordiny to AstDyS-2, with attributed member 9879 Mammuthus (AstDyS-2). Both asteroids are members of the Erigone family according to Nesvorný (5026; 9879).[3]
Nohavica family 6539 Nohavica cat Previously known as the "1982 QG" family. Second member: (9935) 1986 CP1; both are background asteroids according to AstDyS-2 and Nesvorný.
Reginita family 1117 Reginita cat Claimed subgroup of the Flora family. Background asteroid according to both AstDyS-2 and Nesvorný.[3]
Legend:
  • C These are families listed as "robustly" identified in Bendjoya and Zappala (2002).
  • D TNOs are not considered asteroids, but are included here for completeness.

See also[edit]

References[edit]

  1. ^ Michael E. Brown, Kristina M. Barkume, Darin Ragozzine & Emily L. Schaller, A collisional family of icy objects in the Kuiper belt, Nature, 446, (March 2007), pp 294-296.
  2. ^ David Nesvorný, Brian L. Enke, William F. Bottke, Daniel D. Durda, Erik Ashaug & Derek C. Richardson Karin cluster formation by asteroid impact, Icarus 183, (2006) pp 296-311.
  3. ^ a b c d e f g h i j k l m n o p Nesvorný, D.; Broz, M.; Carruba, V. (December 2014). "Identification and Dynamical Properties of Asteroid Families" (PDF). Asteroids IV: 297–321. arXiv:1502.01628Freely accessible. Bibcode:2015aste.book..297N. doi:10.2458/azu_uapress_9780816532131-ch016. Retrieved 23 June 2017. 
  4. ^ "Small Bodies Data Ferret". Nesvorny HCM Asteroid Families V3.0. Retrieved 22 July 2017. 
  5. ^ The Hansa Family: A New High-Inclination Asteroid Family
  6. ^ a b c d e f g V. Zappala (1995). "Asteroid Dynamical Families – EAR-A-5-DDR-FAMILY-V4.1". NASA Planetary Data System. Retrieved 7 December 2017. 

Further reading[edit]

External links[edit]