View source for Asteroid radiation astronomy

'''Editor-In-Chief:''' Henry A. Hoff
[[Image:Asteroids by size and number.svg|center|thumb|500px|Asteroids in the solar system are categorized by size and number. Credit: Marco Colombo, DensityDesign Research Lab.{{tlx|free media}}]]
The center image is a log-log plot of frequency vs. size for asteroids in the solar system.
{{clear}}

==Theoretical asteroids==

'''Def.''' a "naturally occurring solid object, [which is] smaller than a planet<ref name=AsteroidWikt>{{ cite book
|author=[[wikt:User:Paul G|Paul G]]
|title=asteroid
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=18 August 2005
|url=https://en.wiktionary.org/wiki/asteroid
|accessdate=31 August 2015 }}</ref> and is not a comet,<ref name=AsteroidWikt2>{{ cite book
|author=[[wikt:User:Kwamikagami|Kwamikagami]]
|title=asteroid
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=19 January 2012
|url=https://en.wiktionary.org/wiki/asteroid
|accessdate=31 August 2015 }}</ref> that orbits a star"<ref name=AsteroidWikt1>{{ cite book
|author=[[wikt:User:41.240.160.214|41.240.160.214]]
|title=asteroid
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=19 March 2008
|url=https://en.wiktionary.org/wiki/asteroid
|accessdate=31 August 2015 }}</ref> is called an '''asteroid'''.

'''Usage notes'''

"The term "asteroid" has never been precisely defined. It was coined for objects which looked like stars in a telescope but moved like planets. These were known from the asteroid belt between Mars and Jupiter, and were later found co-orbiting with Jupiter (Trojan asteroids) and within the orbit of Mars. They were naturally distinguished from comets, which did not look at all starlike. Starting in the 1970s, small non-cometary bodies were found outside the orbit of Jupiter, and usage became divided as to whether to call these "asteroids" as well. Some astronomers restrict the term "asteroid" to rocky or rocky-icy bodies with orbits up to Jupiter. They may retain the term planetoid for all small bodies, and thus tend to use it for icy or rocky-icy bodies beyond Jupiter, or may use dedicated words such as centaurs, Kuiper belt objects, transneptunian objects, etc. for the latter. Other astronomers use "asteroid" for all non-cometary bodies smaller than a planet, even large ones such as Sedna and (occasionally) Pluto. However, the distinction between asteroid and comet is an artificial one; many outer "asteroids" would become comets if they ventured nearer the Sun. The official terminology since 2006 has been small Solar System body for any body that orbits the Sun directly and whose shape is not dominated by gravity."<ref name=AsteroidWikt/>

==Entities==
{{main|Radiation astronomy/Entities|Entities}}
"Asteroids in particularly large classes tend to be broken into subgroups with the first letter denoting the dominant group and the succeeding letters denoting less prominent spectral affinities or subgroups."<ref name=Weissman>{{ cite book
|author=Paul Robert Weissman, Torrence V. Johnson
|title=Encyclopedia of the Solar System, Second Edition
|publisher=Academic Press
|location=San Diego, California, USA
|date=2007
|editor=Lucy-Ann Adams McFadden, Paul Robert Weissman, Torrence V. Johnson
|pages=966
|url=http://books.google.com/books?id=G7UtYkLQoYoC&lr=&source=gbs_navlinks_s
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=0120885891
|accessdate=2012-12-11 }}</ref>

"From the dominant group, the asteroids evolve to intersect the Earth's orbit on a median time scale of about 60 Myr."<ref name=Michel>{{ cite journal
|author=Patrick Michel, Fabbio Migliorini, Alessandro Morbidelli, Vincenzo Zappalà
|title=The Population of Mars-Crossers: Classification and Dynamical Evolution
|journal=Icarus
|month=June
|year=2000
|volume=145
|issue=2
|pages=332-47
|url=http://www.obs-nice.fr/morby/papers/6358a.pdf
|bibcode=
|doi=10.1006/icar.2000.6358
|pmid=
|accessdate=2011-10-06 }}</ref>

==A asteroids==
{{main|Rocks/Rocky objects/Asteroids/As|A asteroids}}
Spectra "of several related asteroid classes (types A, R, and V) were also analyzed for comparison to various S-subtypes."<ref name=Gaffey>{{ cite journal
|author=Michael J. Gaffey, Jeffrey F. Bell, R. Hamilton Brown, Thomas H. Burbine, Jennifer L. Piatek, Kevin L. Reed, and Damon A. Chaky
|title=Mineralogical variations within the S-type asteroid class
|journal=Icarus
|month=December
|year=1993
|volume=106
|issue=2
|pages=573-602
|url=http://www.mtholyoke.edu/~tburbine/gaffey.icarus.1993.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2015-09-03 }}</ref>

"Observing 246 Asporina and 289 Nenetta, [6] were the first to identify A-type asteroids as nearly pure olivine assemblages based on their spectral characteristics. These asteroids display a single broad absorption feature centered at 1.06 μm (Band I) without any significant pyroxene feature at ~2.0 μm (Band II)."<ref name=Reddy/>

Only "a handful of A-type objects were discovered during the taxonomic surveys, assuming that all A-type asteroids are olivine-rich. The study of A-type asteroids may help solve the “missing mantle problem” in the asteroid belt."<ref name=Reddy/>

==Blue asteroids==
{{main|Rocks/Rocky objects/Asteroids/Blues|Blue asteroids}}
[[Image:PallasHST2007.jpg|thumb|right|250px|This is an [[w:Ultraviolet photography|ultraviolet image]] of Pallas showing its flattened shape taken by the [[w:Hubble Telescope|Hubble Space Telescope]]. Credit: NASA.]]
'''Pallas''', [[w:minor-planet designation|minor-planet designation]] '''2 Pallas''', is the second [[w:asteroid|asteroid]] to have been discovered (after [[Draft:Ceres|Ceres]]), and one of the largest in the [[Solar System]]. It is estimated to comprise 7% of the mass of the [[w:asteroid belt|asteroid belt]],<ref name="Pitjeva05">{{ cite journal
|author=Elena V. Pitjeva
|title=High-Precision Ephemerides of Planets—EPM and Determination of Some Astronomical Constants
|journal=Solar System Research
|year=2005
|volume=39
|issue=3
|page=176
|url=http://iau-comm4.jpl.nasa.gov/EPM2004.pdf
|doi=10.1007/s11208-005-0033-2
|bibcode = 2005SoSyR..39..176P }}</ref> and its diameter of {{convert|544|km}} is slightly larger than that of [[Draft:Vesta|4 Vesta]]. It is however 10–30% less massive than Vesta,<ref name="Baer2007">{{ cite journal
  |author=James Baer and Steven R. Chesley
  |title=Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris
  |journal=Celestial Mechanics and Dynamical Astronomy
  |volume=100
|issue=2008
|pages=27–42
  |url=http://www.springerlink.com/content/h747307j43863228/fulltext.pdf
  |doi=10.1007/s10569-007-9103-8
  |accessdate=2008-11-11
  |year=2008 
|bibcode = 2008CeMDA.100...27B }}</ref> placing it third among the asteroids.

"Spectrally blue (B-type) asteroids are rare, with the second discovered asteroid, Pallas, being the largest and most famous example."<ref name=Yang>{{ cite journal
|author=Bin Yang and David Jewitt
|title=Identification of Magnetite in B-type Asteroids
|journal=The Astronomical Journal
|month=September
|year=2010
|volume=140
|issue=3
|pages=692
|url=http://iopscience.iop.org/1538-3881/140/3/692
|arxiv=
|bibcode=
|doi=10.1088/0004-6256/140/3/692
|pmid=
|accessdate=2013-06-01 }}</ref>

"[T]he negative optical spectral slope of some B-type asteroids is due to the presence of a broad absorption band centered near 1.0 μm. The 1 μm band can be matched in position and shape using magnetite (Fe<sub>3</sub>O<sub>4</sub>), which is an important indicator of past aqueous alteration in the parent body. ... Observations of B-type asteroid (335) Roberta in the 3 μm region reveal an absorption feature centered at 2.9 μm, which is consistent with the absorption due to phyllosilicates (another hydration product) observed in CI chondrites. ... at least some B-type asteroids are likely to have incorporated significant amounts of water ice and to have experienced intensive aqueous alteration."<ref name=Yang/>

"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."<ref name=Yoshida>{{ cite journal
|author=F Yoshida, T Nakamura
|title=Subaru main belt asteroid survey (SMBAS)—size and color distributions of small main-belt asteroids
|journal=Planetary and Space Science
|month=June
|year=2007
|volume=55
|issue=9
|pages=1113-25
|url=http://www.sciencedirect.com/science/article/pii/S0032063306003357
|arxiv=
|bibcode=
|doi=10.1016/j.pss.2006.11.016
|pmid=
|accessdate=2013-06-01 }}</ref>

==Carbonaceous asteroids==
{{main|Rocks/Rocky objects/Asteroids/Carbonaceous|Carbonaceous asteroids}}
'''C-type asteroids''' are carbonaceous asteroids. They are the most common variety, forming around 75% of known asteroids,<ref name=Gradie>Gradie et al. pp. 316-335 in Asteroids II. edited by Richard P. Binzel, Tom Gehrels, and Mildred Shapley Matthews, Eds. University of Arizona Press, Tucson, 1989, {{ISBN|0-8165-1123-3}}</ref> and an even higher percentage in the outer part of the [[w:asteroid belt|asteroid belt]] beyond 2.7 [[w:astronomical unit|AU]], which is dominated by this asteroid type. The proportion of C-types may actually be greater than this, because C-types are much darker than most other asteroid types except [[w:D-type asteroid|D-types]] and others common only at the extreme outer edge of the asteroid belt. Their [[w:electromagnetic spectrum|spectra]] contain moderately strong ultraviolet absorption at wavelengths below about 0.4 μm to 0.5 μm, while at longer wavelengths they are largely featureless but slightly reddish. The so-called "water" absorption feature around 3 μm, which can be an indication of water content in minerals is also present.

==D asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ds|D asteroids}}
"Two comets observed at low activity (visible nuclei) also have properties more consistent with D asteroids than any other class (very low reported geometric albedos of 0.02 and red colors)."<ref name=Hartmann>{{ cite journal
|author=William K. Hartmann, David J. Tholen, Dale P. Cruikshank
|title=The relationship of active comets, “extinct” comets, and dark asteroids
|journal=Icarus
|month=January
|year=1987
|volume=69
|issue=1
|pages=33-50
|url=http://www.sciencedirect.com/science/article/pii/0019103587900054
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==E asteroids==
{{main|Rocks/Rocky objects/Asteroids/Es|E asteroids}}
The "enstatite achondrite-like E-asteroids almost certainly derive from the melting and differentiation of highly reduced parent materials analogous to enstatite chondrites (e.g., Keil 1989)."<ref name=Gaffey/>

==F asteroids==
{{main|Rocks/Rocky objects/Asteroids/Fs|F asteroids}}
F-type asteroids have spectra generally similar to those of the B-type asteroids, but lack the "water" absorption feature around 3 μm indicative of hydrated minerals, and differ in the low wavelength part of the ultraviolet spectrum below 0.4 μm.

==G asteroids==
{{main|Rocks/Rocky objects/Asteroids/Gs|G asteroids}}
"G-type asteroids are a relatively uncommon type of carbonaceous asteroid. The most notable asteroid in this class is 1 [[Draft:Ceres]]. Generally similar to the C-type objects, but containing a strong ultraviolet absorption feature below 0.5 μm.

==H asteroids==
{{main|Rocks/Rocky objects/Asteroids/Hs|H asteroids}}
"Group H asteroids are apparently olivine rich. In addition, this group exhibits the lowest mean value for the bend parameter. The asteroid 7 Iris is a typical member of this group."<ref name=Feierberg>{{ cite journal
|author=Michael A. Feierberg, Harod P. Larson, C. R. Chapman
|title=Spectroscopic evidence for undifferentiated S-type asteroids
|journal=The Astrophysical Journal
|month=1 June
|year=1982
|volume=257
|issue=6
|pages=361-72
|url=http://adsabs.harvard.edu/full/1982ApJ...257..361F
|arxiv=
|bibcode=1982ApJ...257..361F
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==I asteroids==
{{main|Rocks/Rocky objects/Asteroids/Is|I asteroids}}
Hardersen (2003) "started by dividing asteroids into two classes: Class I asteroids, which allow diagnostic determinations of their mineralogy, and Class II asteroids, where the determination is nondiagnostic and open to interpretation."<ref name=Ghosh>{{ cite journal
|author=A. Ghosh, S.J. Weidenschilling, H.Y. McSween Jr. and A. Rubin
|title=Asteroidal Heating and Thermal Stratification of the Asteroid Belt, In: ''Meteorites and the Early Solar System II''
|publisher=USRA
|location=
|month=
|year=2006
|volume=
|issue=
|pages=555-66
|url=http://www.lpi.usra.edu/books/MESSII/9017.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==J asteroids==
{{main|Rocks/Rocky objects/Asteroids/Js|J asteroids}}
"The remaining six are interpreted as diogenitic in composition and were designated as J asteroids (mnemonic for the Johnstown diogenite)."<ref name=Keil>{{ cite book
|author=K Keil
|title=Geological history of asteroid 4 Vesta: The “smallest terrestrial planet”, In: ''Asteroids III''
|volume=
|publisher=
|location=
|date=2002
|editor=
|pages=
|url=https://www.researchgate.net/profile/K_Keil/publication/259276198_Geological_History_of_Asteroid_4_Vesta_The_Smallest_Terrestrial_Planet/links/54d4f1380cf2970e4e63f1ba.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=2016-10-10 }}</ref>

==K asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ks|K asteroids}}
"Bell (1988) distinguished a new class (K-type) from previous members of the S-class and interpreted these objects as composed of material analogous to the undifferentiated CO3 ro CV3 carbonaceous chondrites."<ref name=Gaffey/>

==L asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ls|L asteroids}}
"Color dependent photometry calibration, or the HK solar color, might be in error by 0.1 magnitude and cause the L asteroids not to coincide with the carbonaceous chondrites, but we do not think that this is a very likely possibility."<ref name=Matson>{{ cite journal
|author=Dennis L Matson, Glenn J Veeder, Larry A Lebofsky
|title=Infrared observations of asteroids from Earth and space
|journal=
|month=
|year=1978
|volume=
|issue=
|pages=127-44
|url=http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19780021072.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==M asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ms|M asteroids}}
"Exposure of compositionally distinct internal layers from within parent planetesimals may be an important source of the diversity within the S-population and is presumably the source of the M- and A-type."<ref name=Gaffey/>

"M-class [...] contains both metallic objects [...] 216 Kleopatra and [...] 16 Psyche".<ref name=Magri>{{ cite journal
|author=Christopher Magri, Steven J. Ostro, Keith D. Rosema, Michael L. Thomas, David L. Mitchell, Donald B. Campbell, John F. Chandler, Irwin I. Shapiro, Jon D. Giorgini, Donald K. Yeomans
|title=Mainbelt Asteroids: Results of Arecibo and Goldstone Radar Observations of 37 Objects during 1980–1995
|journal=Icarus
|month=August
|year=1999
|volume=140
|issue=2
|pages=379–407
|url=http://www.sciencedirect.com/science/article/pii/S0019103599961304
|arxiv=
|bibcode=
|doi=10.1006/icar.1999.6130
|pmid=
|accessdate=2017-01-09 }}</ref>

==N asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ns|N asteroids}}
"Emission features attributable to fine-grained silicates are seen in the spectra of two of the M-types and at least four of the C-types. This is the first positive evidence that N-type asteroids have a silicate component on their surface similar to that of other asteroids."<ref name=Tedesco>{{ cite journal
|author=E. F. Tedesco, G. J. Veeder, D. L. Matson, & L. A. Lebofsky,
|title=Infrared (JHK) colors for D class asteroids
|journal=Bulletin of the American Astronomical Society
|month=
|year=1983
|volume=15
|issue=6
|pages=825
|url=http://adsabs.harvard.edu/full/1983BAAS...15Q.825T
|arxiv=
|bibcode=1983BAAS...15Q.825T
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==O asteroids==
{{main|Rocks/Rocky objects/Asteroids/Os|O asteroids}}
"O-type asteroids 3628 Boznemcová and 7472 Kumakiri have absorption bands similar to pyroxenes but with band minima that are not typically found for terrestrial pyroxenes and known pyroxene-dominated meteorite assemblages."<ref name=Burbine>{{ cite journal
|author=Burbine, T. H.; Duffard, R.; Buchanan, P. C.; Cloutis, E. A.; Binzel, R. P.
|title=Spectroscopy of O-type asteroids, In: ''42nd Lunar and Planetary Science Conference''
|publisher=LPI
|location=The Woodlands, Texas
|month=3
|year=2011
|volume=
|issue=
|pages=2483
|url=http://adsabs.harvard.edu/abs/2011LPI....42.2483B
|arxiv=
|bibcode=
|doi= 
|pmid=
|accessdate=2016-10-10 }}</ref>

==P asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ps|P asteroids}}
"Whereas most of the P-type asteroids spectrally match the Tagish Lake meteorite in the wavelength range longer than 0.9 μm, they are different in the shorter wavelength range."<ref name=Hiroi>{{ cite journal
|author=T Hiroi, ME Zolensky, CM Pieters
|title=The Tagish Lake meteorite: A possible sample from a D-type asteroid
|journal=Science
|month=
|year=2001
|volume=293
|issue=5538
|pages=2234
|url=https://pdfs.semanticscholar.org/bf33/81d6ba1451f854f1f93c944de649ea405a2e.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==Q asteroids==
{{main|Rocks/Rocky objects/Asteroids/Qs|Q asteroids}}
lf "planetary encounters are important, the distribution of Q-type asteroids in the planet-crossing space should show a correlation with the perihelion distance, exactly as we have found here."<ref name=Marchi>{{ cite journal
|author=S. Marchi, S. Magrin, D. Nesvorný, P. Paolicchi and M. Lazzarin
|title=A spectral slope versus perihelion distance correlation for planet-crossing asteroids
|journal=Monthly Notices of the
|month=21November
|year=2006
|volume=368
|issue=1
|pages=L39-42
|url=http://mnrasl.oxfordjournals.org/content/368/1/L39.short
|arxiv=
|bibcode=
|doi=10.1111/j.1745-3933.2006.00152.x
|pmid=
|accessdate=2016-10-10 }}</ref>

==R asteroids==
{{main|Rocks/Rocky objects/Asteroids/Rs|R asteroids}}
"A-type asteroids are a relatively rare taxonomic class with no more than 17 known objects [1,2,3]. They were first identified as a separate group of R-type asteroids based on broadband spectrophotometry by [4], and were later classified based on ECAS data by Tholen (1984) [1]."<ref name=Reddy>{{ cite book
|author=V. Reddy, P. S. Hardersen, M. J. Gaffey, and P. A. Abell
|title=Mineralogic and Temperature-Induced Spectral Investigations of A-type Asteroids 246 Asporina and 446 Aeternitas, In: ''Lunar and Planetary Science''
|volume=36
|publisher=USRA
|location=
|date=2005
|editor=
|pages=2
|url=http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1375.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=2015-09-04 }}</ref>

==Siliceous asteroids==
{{main|Rocks/Rocky objects/Asteroids/Siliceous|Siliceous asteroids}}
[[Image:S class subtype asteroids.png|thumb|right|250px|This graph depicts carrier wavelength versus band ratios to divide or characterize the siliceous asteroids. Credit: Michael J. Gaffey, Jeffrey F. Bell, R. Hamilton Brown, Thomas H. Burbine, Jennifer L. Piatek, Kevin L. Reed, and Damon A. Chaky.]]
"The presence of trapped solar gas in stony meteorites places their origin in the regoliths of asteroidal-type bodies. The most plausible sources are the C (carbonaceous) and S (siliceous) asteroids, in spite of the differences between the spectra of S asteroids and ordinary chondrites."<ref name=Anders>{{ cite book
|author=E. Anders
|title=Most stony meteorites come from the asteroid belt, In: ''NASA, Washington Asteroids''
|volume=N78
|publisher=NASA
|location=Washington, DC USA
|date=1978
|editor=
|pages=57-75
|url=http://adsabs.harvard.edu/abs/1978astd.nasa...57A
|arxiv=
|bibcode=1978astd.nasa...57A
|doi=
|pmid=
|isbn=
|accessdate=2015-09-03 }}</ref>

"The S-asteroid class includes a number of distinct compositional subtypes [designated S(I)-S(VII)] which exhibit surface silicate assemblages ranging from pure olivine (dunites) through olivine-pyroxene mixtures to pure pyroxene or pyroxene-feldspar mixtures (basalts)."<ref name=Gaffey/> These are shown in the graph on the right.
{{clear}}

==T asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ts|T asteroids}}
The "T-type asteroids appear to contain at least two mineralogically distinct types."<ref name=Meibom>{{ cite journal
|author=Anders Meibom, Beth E Clark
|title=Evidence for the insignificance of ordinary chondritic material in the asteroid belt
|journal=Meteoritics and Planetary Science
|month=
|year=1999
|volume=34
|issue=1
|pages=7-24
|url=http://adsabs.harvard.edu/full/1999M%26PS...34....7M
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2016-10-10 }}</ref>

==U asteroids==
{{main|Rocks/Rocky objects/Asteroids/Us|U asteroids}}
"The SU type represents an ambiguous classification with parameters of both the S- and the [unusual] U-types but with the former more likely--Tholen 1984, 1989, Tholen and Barucci 1989."<ref name=Gaffey/>

==V asteroids==
{{main|Rocks/Rocky objects/Asteroids/Vs|V asteroids}}
[[Image:Vesta_full_mosaic.jpg|thumb|right|250px|As NASA's Dawn spacecraft takes off for its next destination, this mosaic synthesizes some of the best views the spacecraft had of the giant asteroid Vesta. Credit: NASA/JPL-Caltech/UCAL/MPS/DLR/IDA.]]
[[Image:Vesta family.png|right|thumb|400px|Location and structure of the Vesta family are depicted. Credit: [[w:User:Deuar|Deuar]].]]
In the full image of [[Draft:Vesta|Vesta]] at right, the rocky-object appears to have suffered from meteor damage.

'''Vesta''', [[w:minor-planet designation|minor-planet designation]] '''4 Vesta''', is one of the largest asteroids in the [[Solar System]]. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as [[w:HED meteorite|howardite–eucrite–diogenite (HED) meteorites]], a rich source of information about the asteroid.<ref name="Kelley2003">{{ cite journal
|author=Kelley, M. S. ''et al.''
|title=Quantified mineralogical evidence for a common origin of 1929 Kollaa with 4 Vesta and the HED meteorites
|journal=Icarus
|volume=165
|issue=1
|page=215
|year=2003
|doi=10.1016/S0019-1035(03)00149-0
|bibcode=2003Icar..165..215K}}</ref><ref name="nasa2011-vesta">{{ cite book
|date=12 July 2011
|title= Vesta
|publisher=NASA/JPL
|url=http://web.archive.org/web/20110629153841/http://www.nasa.gov/mission_pages/dawn/ceresvesta/index.html
|accessdate=30 July 2011 }}</ref>

"V-type asteroids are bodies whose surfaces are constituted of basalt. In the Main Asteroid Belt, most of these asteroids are assumed to come from the basaltic crust of Asteroid (4) Vesta."<ref name=Roig>{{ cite journal
|author=F Roig, D Nesvorný, R Gil-Hutton, D Lazzaro
|title=V-type asteroids in the middle main belt
|journal=Icarus
|month=March
|year=2008
|volume=194
|issue=1
|pages=125–36
|url=http://arxiv.org/pdf/0707.1012
|arxiv=
|bibcode=
|doi=10.1016/j.icarus.2007.10.004
|pmid=
|accessdate=2016-10-10 }}</ref>

The Vestian asteroids consist "of 4 Vesta, the second-most-massive of all asteroids (mean diameter of 530&nbsp;km), and many small asteroids below 10&nbsp;km diameter. The brightest of these, [[w:1929 Kollaa|1929 Kollaa]] and [[w:2045 Peking|2045 Peking]], have an [[w:absolute magnitude|absolute magnitude]] of 12.2, which would give them a radius of about 7.5&nbsp;km assuming the same high albedo as [[w:4 Vesta|4 Vesta]]."<ref name=VestaFamily>{{ cite book
|author=[[w:User:Deuar|Deuar]]
|title=Vesta family
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=12 February 2006
|url=https://en.wikipedia.org/wiki/Vesta_family
|accessdate=2018-05-04 }}</ref>

"A [[w:Hierarchical Clustering Method (asteroids)|HCM]] numerical analysis (by Zappala 1995) determined a large group of 'core' family members, whose [[w:proper orbital elements|proper orbital elements]] lie in the approximate ranges"<ref name=VestaFamily/>
{| align="center" style="border:1px solid #CCC; margin-left:15px;" cellpadding="5"
 ! !! ''[[w:semi-major axis|a<sub>p</sub>]]'' !! [[w:Orbital eccentricity|e<sub>p</sub>]]'' !! ''[[w:inclination|i<sub>p</sub>]]''
|-
|min || 2.26 [[w:Astronomical unit|AU]] || 0.075 || 5.6°
|-
|max || 2.48 AU || 0.122 || 7.9°
|}

"This gives the approximate boundaries of the family. At the present [[w:epoch (astronomy)|epoch]], the range of  [[w:osculating orbit|osculating]] orbital elements of these core members is"<ref name=VestaFamily/>
{| align="center" style="border:1px solid #CCC; margin-left:15px;" cellpadding="5"
! !! ''[[w:semi-major axis|a]]'' !! [[w:eccentricity (orbit)|e]]'' !! ''[[w:inclination|i]]''
|-
| min || 2.26 [[w:Astronomical unit|AU]] || 0.035 || 5.0°
|-
| max || 2.48 AU || 0.162 || 8.3°
|}

"The Zappala 1995 analysis<ref name=Vincenzo>{{ cite journal
|author=Vincenzo Zappalà, Philippe Bendjoya, Alberto Cellino, Paolo Farinella and Claude Froeschlé
|title=Asteroid Families: Search of a 12,487-Asteroid Sample Using Two Different Clustering Techniques
|journal=Icarus
|month=August
|year=1995
|volume=116
|issue=2
|pages=291-314
|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-45NJHPF-3C&_coverDate=08%2F31%2F1995&_alid=267428521&_rdoc=1&_fmt=&_orig=search&_qd=1&_cdi=6821&_sort=d&view=c&_acct=C000056973&_version=1&_urlVersion=0&_userid=2337731&md5=6a0ee5be29f8c0489e922cb06868ae45
|arxiv=
|bibcode=
|doi=
|pmid=
|accessdate=2018-5-04 }}</ref> found 235 core members. A search of a recent proper-element database ([https://web.archive.org/web/20060220070732/http://hamilton.dm.unipi.it/cgi-bin/astdys/astibo?proper_elements:0;main AstDys]) for 96944 [[w:minor planet|minor planet]]s in 2005 yielded 6051 objects (about 6% of the total) lying within the Vesta-family region as per the first table above."<ref name=VestaFamily/>
{{clear}}

==W asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ws|W asteroids}}
"Rivkin et al. also noted that W-type asteroids in their survey are lacking an FeO absorption band (0.4–0.5 μm), an expected feature if the hydrated minerals formed in the presence of significant free metal."<ref name=Ockert>{{ cite journal
|author=Maureen E. Ockert-Bella, Beth Ellen Clarka, Michael K. Shepardb,  Andrew S. Rivkin, Richard P. Binzeld, Cristina A. Thomas, Francesca E. DeMeo, S.J. Bus, Sweta Shah
|title=Observations of X/M asteroids across multiple wavelengths
|journal=Icarus
|month=May
|year=2008
|volume=195
|issue=1
|pages=206-19
|url=http://www.sciencedirect.com/science/article/pii/S0019103507005568
|arxiv=
|bibcode=
|doi=10.1016/j.icarus.2007.11.006
|pmid=
|accessdate=2016-10-10 }}</ref>

"CB chondrites have only very minor amounts of phyllosilicates and may come from W-type asteroids (“wet-M” asteroids)."<ref name=Scott>{{ cite book
|author=ERD Scott, AN Krot
|title=Meteorites, Comets, and Planets: Treatise
|publisher=
|location=
|date=2005
|editor=
|pages=
|url=http://www.higp.hawaii.edu/~escott/Scott%20Krot%20TOG2007.pdf
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=2016-10-10 }}</ref>

==X asteroids==
{{main|Rocks/Rocky objects/Asteroids/Xs|X asteroids}}
"Since the composition of X-type asteroids remains unclear and their relation to mineralogical type is unknown, [87] Sylvia's bulk porosity is not well constrained."<ref name=Marchis>{{ cite journal
|author=Franck Marchis, Pascal Descamps, Daniel Hestroffer & Jérome Berthier
|title=Discovery of the triple asteroidal system 87 Sylvia
|journal=Nature
|month=11 August
|year=2005
|volume=436
|issue=7052
|pages=822-4
|url=http://www.nature.com/nature/journal/v436/n7052/abs/nature04018.html
|arxiv=
|bibcode=
|doi=10.1038/nature04018
|pmid=
|accessdate=2016-10-10 }}</ref>

==Y asteroids==
{{main|Rocks/Rocky objects/Asteroids/Ys|Y asteroids}}
[[Image:YarkovskyEffect.svg|thumb|right|300px|Yarkovsky effect:<br />1. Radiation from asteroid's surface <br />2. Prograde rotating asteroid <br />2.1 Location with "Afternoon" <br />3. Asteroid's orbit <br />4. Radiation from Sun. Credit: [[w:user:Graevemoore|Graevemoore]].]]
The possible importance of the Yarkovsky effect is the movement of meteoroids about the [[Solar System]].<ref>{{cite journal |first=E. J. |last=Öpik |title=Collision probabilities with the planets and the distribution of interplanetary matter |journal=Proceedings of the Royal Irish Academy |volume=54A |issue= |pages=165–199 |year=1951 |jstor=20488532 }}</ref>

The diurnal effect is the dominant component for bodies with diameter greater than about 100 m.<ref name=Bottke06review>{{cite journal |last=Bottke, Jr. |first=William F., ''et al.'' |title=The Yarkovsky and YORP Effects: Implications for Asteroid Dynamics |journal=Annual Review of Earth and Planetary Sciences |volume=34 |pages=157–191 |year=2006 |doi=10.1146/annurev.earth.34.031405.125154 |bibcode = 2006AREPS..34..157B }}</ref>

On very long timescales over which the spin axis of the body may be repeatedly changed due to collisions (and hence also the direction of the diurnal effect changes), the seasonal effect will also tend to dominate.<ref name=Bottke06review />

The effect was first measured in 1991–2003 on the asteroid 6489 Golevka which drifted 15&nbsp;km from its predicted position over twelve years (the orbit was established with great precision by a series of radar observations in 1991, 1995 and 1999 from the Arecibo Observatory radio telescope).<ref>{{cite journal |last=Chesley |first=Steven R. |title=Direct Detection of the Yarkovsky Effect via Radar Ranging to Asteroid 6489 Golevka |journal=Science |volume=302 |issue=5651 |pages=1739–1742 |year=2003 |doi=10.1126/science.1091452 |bibcode = 2003Sci...302.1739C |display-authors=etal}}</ref>

The "population of asteroids in comet-like orbits using available asteroid size and albedo catalogs of data taken with the ''Infrared Astronomical Satellite'' [I], ''AKARI'' [A], and the ''Wide-field Infrared Survey Explorer'' [W] on the basis of their orbital properties (i.e., the Tisserand parameter with respect to Jupiter, T<sub>J</sub>, and the aphelion distance, Q, [is] 123 asteroids in comet-like orbits [with] Q < 4.5 AU and T<sub>J</sub> < 3, [including] a considerable number (i.e., 25 by our criteria) of asteroids in comet-like orbits have high albedo, pv > 0.1. [As] such high-albedo objects mostly consist of small (D < 3 km) bodies distributed in near-Earth space (with perihelion distance of q < 1.3 AU) [may be] susceptible to the Yarkovsky effect and drifted into comet-like orbits via chaotic resonances with planets."<ref name=Kim>{{ cite journal
|author=Yoonyoung Kim, Masateru Ishiguro and Fumihiko Usui
|title=Physical properties of asteroids in comet-like orbits in infrared asteroid survey catalogs
|journal=The Astrophysical Journal
|date=24 June 2014
|volume=789
|issue=2
|pages=151
|url=https://arxiv.org/pdf/1405.2989.pdf
|arxiv=
|bibcode=
|doi=10.1088/0004-637X/789/2/151
|pmid=
|accessdate=22 June 2019 }}</ref>

"There are 138,285 asteroids whose albedos and sizes are given in the I–A–W catalog. [...] nearly all high-albedo [asteroids in comet-like orbits] ACOs consist of small asteroids at q < 1.3 AU. This trend cannot be explained by the observational bias. Because the result is obtained based on the mid-infrared data, which, unlike optical observations, are less sensitive to albedo values, it provides reliable sets of asteroid albedo information. If there are big ACOs with high albedo beyond q = 1.3 AU, they would be detected easily. Although further dynamical study is essential to evaluate the population quantitatively, we propose that such ACOs with high albedos were injected from the domain of T<sub>J</sub> > 3 via the Yarkovsky effect, because small objects with higher surface temperature are susceptible to the thermal drag force and gradually change their orbital elements to be observed as ACOs in our list."<ref name=Kim/>

"Although there are uncertainties in the dynamical simulation such as the value of the Yarkovsky force and the rocket force (for active comets), we conservatively consider that these three objects (2000 SU236, 2008 UM7, and 2009 SC298) are ACOs and PDCs. ["potential dormant comet" (PDC) is one having a low albedo (pv < 0.1) among ACOs. The second term is a paronomasia associating the spectra of potential dormant comets with spectra similar to P-type, D-type, or C-type asteroids (Licandro et al. 2008; DeMeo & Binzel 2008).]"<ref name=Kim/>

"Let us consider how the Yarkovsky effect moves an asteroid into a comet-like orbit. As shown [...], high-albedo ACOs concentrate in a range of 2 < a < 3.5 AU, similar to main-belt asteroids and [Jupiter-family comets] JFCs. The Tisserand parameter is a function of a, e, and i, [the semimajor axis, eccentricity, and inclination, respectively] while the Yarkovsky effect changes a. Due to the similarity in a between high-albedo ACOs and main-belt asteroids, we conjecture that subsequent dynamical effects may change e and i. Widely known as a standard model for orbital evolution of near-Earth asteroids, the Yarkovsky effect could move small main-belt asteroids' orbits until they are close to resonances with planets, and subsequently, these resonances can push them into terrestrial planet crossing orbits (see, e.g., Morbidelli et al. 2002). Numerical simulations demonstrated that chaotic resonances cause a significant increase in the e and i of test particles in the resonance regions (Gladman et al. 1997). Bottke et al. (2002) suggested that some objects on T<sub>J</sub> < 3 (or even T<sub>J</sub> < 2) can result from chaotic resonances. [...] Although there are a couple of ACOs close to resonances, their semimajor axes are not related to these major resonances. Therefore, it may be reasonable to think that encounters with terrestrial planets as well as chaotic resonances with massive planets can drift main-belt asteroids into comet-like orbits."<ref name=Kim/>

"In particular, we stress again the significance of high-albedo ACOs. As we discussed through our ground-based observation with the Subaru Telescope, high-albedo ACOs, which may have composition similar to silicaceous asteroids, definitively exist in the I–A–W database. Considering the very low T<sub>J</sub> as well as the small size and perihelion distance, we suggest that such high-albedo ACOs have been injected via nongravitational forces, most likely the Yarkovsky effect."<ref name=Kim/>
{{clear}}

==Z asteroids==
{{main|Rocks/Rocky objects/Asteroids/Zs|Z asteroids}}
"There is a general increase in 'redness' with heliocentric distance in the outer belt asteroids going from the moderately red P asteroids, through the redder D asteroids, to the much redder Z asteroids."<ref name=Britt>{{ cite book
|author=Daniel T. Britt and Larry A. Lebofsky
|title=Meteorite parent bodies, In: ''Encyclopedia of Planetary Science''
|publisher=Springer
|location=
|date=1997
|editor=
|pages=486-9
|url=http://link.springer.com/referenceworkentry/10.1007%2F1-4020-4520-4_258
|arxiv=
|bibcode=
|doi=10.1007/1-4020-4520-4_258
|pmid=
|isbn=978-0-412-06951-2
|accessdate=2016-10-10 }}</ref>

==Earth crossers==
{{main|Rocks/Rocky objects/Asteroids/Earth crossers|Earth crossers}}
[[Image:2008VK184-year2014.png|thumb|right|250px|The close approach of apollo asteroid 2007 VK184 was in May 2014. Credit: Osamu Ajiki (AstroArts) and Ron Baalke (JPL).]]
EC denotes Earth-crossing.<ref name= Michel/>

"50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs".<ref name= Michel />

[[Image:SmallAsteroidImpacts-Frequency-Bolide-20141114.jpg|thumb|upright=2|center|500px|This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere. Credit: NASA/Planetary Science.]]
"This diagram [center] maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors, technically called "bolides" and commonly referred to as "fireballs". Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size."<ref name=Agle>{{ cite book
|author=DC Agle
|title=New Map Shows Frequency of Small Asteroid Impacts, Provides Clues on Larger Asteroid Population
|publisher=NASA's Jet Propulsion Laboratory
|location=Pasadena, California
|date=14 November 2014
|editor=
|pages=
|url=https://www.jpl.nasa.gov/news/news.php?release=2014-397
|arxiv=
|bibcode=
|doi=
|pmid=
|isbn=
|accessdate=2018-04-01 }}</ref>

"A map released [...] by NASA's Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in the Earth's atmosphere with random distribution around the globe. Released to the scientific community, the map visualizes data gathered by U.S. government sensors from 1994 to 2013. The data indicate that Earth's atmosphere was impacted by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event which was the largest asteroid to hit Earth in this period."<ref name=Agle/>
{{clear}}

==2019 OK==
[[Image:Asteroid 2019 OK misses Earth and Moon.jpg|right|thumb|300px|An asteroid dubbed a ‘city-killer’ narrowly missed colliding with the Earth on Thursday. Credit: Michael Brown, NASA.{{tlx|fairuse}}]]
"Asteroid 2019 OK - around 100 metres in diameter and racing at 24 kilometres a second - flew past Earth at around 11.22am on Thursday morning."<ref name=Gamp>{{ cite web
|author=Joe Gamp
|title=Earth just had a near-miss with a 'city killer' asteroid
|publisher=Yahoo! News
|location=
|date=25 July 2019
|url=https://news.yahoo.com/earth-just-had-a-near-miss-with-a-killer-asteroid-175546112.html?.tsrc=daily_mail&uh_test=1_04
|accessdate=26 July 2019 }}</ref>

"[If it hit Earth] it makes the bang of a very large nuclear weapon – a very large one."<ref name=Brown>{{ cite web
|author=Michael Brown
|title=Earth just had a near-miss with a 'city killer' asteroid
|publisher=Yahoo! News
|location=
|date=25 July 2019
|url=https://news.yahoo.com/earth-just-had-a-near-miss-with-a-killer-asteroid-175546112.html?.tsrc=daily_mail&uh_test=1_04
|accessdate=26 July 2019 }}</ref>

"It would have hit with over 30 times the energy of the atomic blast at Hiroshima. It's a city-killer asteroid. But because it's so small, it's incredibly hard to see until right at the last minute. It's threading tightly between the lunar orbit. Definitely too close for comfort."<ref name=Duffy>{{ cite web
|author=Alan Duffy
|title=Earth just had a near-miss with a 'city killer' asteroid
|publisher=Yahoo! News
|location=
|date=25 July 2019
|url=https://news.yahoo.com/earth-just-had-a-near-miss-with-a-killer-asteroid-175546112.html?.tsrc=daily_mail&uh_test=1_04
|accessdate=26 July 2019 }}</ref>
{{clear}}

==2008 TC<sub>3</sub>==
[[Image:2008TC3-groundpath-rev.png|right|thumb|300px|Estimated path and altitude of the meteor in red, with the possible location for the METEOSAT IR fireball (bolide) as orange crosshairs and the infrasound detection of the explosion in green. Credit: George William Herbert (graphic overlay) / US Government (original map).{{tlx|free media}}]]
[[Image:2008 TC3 Tumbling (reduced).gif|thumb|left|250px|An animation of 2008 TC3's excited rotation prior to entering the atmosphere is shown. Credit: Astronomical Institute of the Charles University: Josef Ďurech, Vojtěch Sidorin.]]
[[Image:Eumetsat-composite-2008TC3-impact.jpg|thumb|left|250px|Meteosat 8/EUMETSAT infrared image is of the explosion. Credit: .]]
[[Image:ELG webcam record of 2008 TC3 frame 0005.png|thumb|right|250px|This webcam frame was shot. Credit: Webcam at [http://www.kitepower-elgouna.com/en/ kitepower], Mangroovy Beach, El Gouna, Red Sea governate, Egypt.]]
[[Image:323213main Petersmeteorites 946-710.jpg|thumb|250px|2008 TC<sub>3</sub> fragment was found on February 28, 2009 by Peter Jenniskens, with help from students and staff of the University of Khartoum. Nubian Desert, Sudan. Credit: .]]
[[Image:M8-HRV-200810070245.jpg|thumb|right|250px|Meteosat 8 / EUMETSAT visual image is first light flare from 2008 TC<sub>3</sub> with lat/long reference. Credit: .]]
[[Image:M8-NCOL-200810070245.jpg|thumb|right|250px|Meteosat 8 / EUMETSAT IR image of main fireball from 2008 TC<sub>3</sub>. Credit: .]]
[[Image:Img asteroid hrv ir108.jpg|thumb|right|250px|Meteosat images combined, showing offset from first light flare to main IR flare. Credit: ]]
2008 TC<sub>3</sub> (Catalina Sky Survey temporary designation 8TA9D69) was an {{convert|80|t|ton|sigfig=1|adj=on}}, {{convert|4.1|m|ft|sigfig=2|sp=us|adj=on}} diameter asteroid<ref name=" Jenniskens2009">{{Cite journal
 |last=Jenniskens |first=P.
 |date=2009
 |volume=458 |issue=7237 |pages=485–488
 |title=The impact and recovery of asteroid 2008 TC<sub>3</sub>
 |journal=Nature
 |bibcode=2009Natur.458..485J
 |doi=10.1038/nature07920
 |pmid=19325630
 |display-authors=etal}}</ref> that entered Earth's atmosphere on October 7, 2008.<ref name="discovermagazine">{{cite web
 |last=Plait |first=P.
 |date=October 6, 2008
 |title=Incoming!!!
 |url=http://blogs.discovermagazine.com/badastronomy/2008/10/06/incoming-2/
 |publisher=Bad Astronomy
 |accessdate=October 8, 2008
|archiveurl=https://web.archive.org/web/20081007190747/http://blogs.discovermagazine.com/badastronomy/2008/10/06/incoming-2/
 |archivedate=October 7, 2008
 |deadurl=no }}</ref> It exploded at an estimated {{convert|37|km|sigfig=2|sp=us}} above the Nubian Desert in Sudan. Some 600 meteorites, weighing a total of {{convert|10.5|kg|sigfig=3}}, were recovered; many of these belonged to a rare type known as ureilites, which contain, among other minerals, nanodiamonds.<ref name="Jenniskens2009"/><ref name="nytimes">{{cite news
 |last=Chang |first=K.
 |date=March 25, 2009
 |title=Recovered Pieces of Asteroid Hold Clues to Early History
 |url=https://www.nytimes.com/2009/03/26/science/space/26asteroid.html?ref=us
 |work=The New York Times
 |accessdate=March 26, 2009
|archiveurl=https://web.archive.org/web/20131113234704/http://www.nytimes.com/2009/03/26/science/space/26asteroid.html?ref=us |archivedate=November 13, 2013
 |deadurl=no }}</ref><ref name=AP>{{cite news|last=Borenstein |first=S. |date=March 26, 2009 |title=Astronomers catch a shooting star for 1st time |url=http://abcnews.go.com/Technology/Space/WireStory?id=7175837&page=2 |publisher=ABC news |agency=The Associated Press |accessdate=September 15, 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090329084214/http://abcnews.go.com/Technology/Space/WireStory?id=7175837&page=2 |archivedate=March 29, 2009 }}</ref>

It was the first time that an asteroid impact had been predicted prior to its entry into the atmosphere as a meteor.<ref name="Roylance2008">{{cite news
 |last=Roylance |first=F.
 |date=October 7, 2008
 |title=Predicted meteor may have been sighted
 |url=http://weblogs.marylandweather.com/2008/10/predicted_meteor_may_have_been.html
 |publisher=Maryland Weather
 |accessdate=October 8, 2008
|archiveurl=https://web.archive.org/web/20081010045620/http://weblogs.marylandweather.com/2008/10/predicted_meteor_may_have_been.html
 |archivedate=October 10, 2008 
 |deadurl=no}}</ref>

The asteroid was discovered by Richard A. Kowalski at the Catalina Sky Survey (CSS) 1.5-meter telescope at Mount Lemmon, north of Tucson, Arizona, US, on October 6, 06:39 UTC, 19 hours before the impact.<ref>{{cite web
 |last=Williams |first=G. V.
 |date=October 6, 2008
 |title=MPEC 2008-T50
 |url=http://www.cfa.harvard.edu/mpec/K08/K08T50.html
 |publisher=Minor Planet Center
 |accessdate=October 8, 2008
|archiveurl=https://web.archive.org/web/20081009221534/http://www.cfa.harvard.edu/mpec/K08/K08T50.html
 |archivedate=October 9, 2008 
 |deadurl=no }}</ref><ref>{{cite web
 |last=Huntington 
 |first=J. 
 |date=October 7, 2008 
 |url=http://www.efluxmedia.com/news_Small_Asteroid_Enters_Earths_Atmosphere_26024.html 
 |title=Small Asteroid Enters Earth's Atmosphere 
 |publisher=eFluxMedia 
 |accessdate=October 8, 2008 
|archiveurl=https://web.archive.org/web/20081010095304/http://www.efluxmedia.com/news_Small_Asteroid_Enters_Earths_Atmosphere_26024.html 
 |archivedate=October 10, 2008 
 |deadurl=yes 
 |df= }}</ref><ref name="jplneo">{{cite web
 |last1=Chesley |first1=S.
 |last2=Chodas |first2=P.
 |last3=Yeomans  |first3=D.
 |date=November 4, 2008
 |title=Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree
 |url=http://neo.jpl.nasa.gov/news/2008tc3.html
 |work=Near Earth Object Program
 |publisher=NASA
 |accessdate=June 18, 2009
 |archiveurl=https://web.archive.org/web/20090618045538/http://neo.jpl.nasa.gov/news/2008tc3.html
 |archivedate=June 18, 2009 
 |deadurl=no }}</ref>

It was notable as the first such body to be observed and tracked prior to reaching Earth.<ref name="Roylance2008" /> The process of detecting and tracking a near-Earth object, an effort sometimes referred to as Spaceguard, was put to the test. In total, 586 astrometric and almost as many photometric observations were performed by 27 amateur and professional observers in less than 19 hours and reported to the Minor Planet Center, which in eleven hours issued 25 Minor Planet Electronic Circulars with new orbit solutions as observations poured in. On October 7, 01:49 UTC,<ref name="jplneo"/> the asteroid entered the shadow of the Earth, which made further observations impossible.

Impact predictions were performed by University of Pisa's CLOMON 2 semi-automatic monitoring system<ref>{{cite web
 |title=NEODys Main Risk Page
 |url=http://newton.dm.unipi.it/neodys/
 |accessdate=October 8, 2008 }}</ref><ref>{{cite web
 |title=NEODys 2008 TC<sub>3</sub> page
 |url=http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:2008TC3;main
 |accessdate=October 8, 2008 }}</ref> as well as Jet Propulsion Laboratory's Sentry system. Spectral observations that were performed by astronomers at the 4.2-meter William Herschel Telescope at La Palma, Canary Islands are consistent with either a C-type or M-type asteroid.

The meteor entered Earth's atmosphere above northern Sudan at 02:46 UTC (05:46 local time) on October 7, 2008 with a velocity of {{convert|12.8|km/s|mph|sp=us}} at an azimuth of 281 degrees and an altitude angle of 19 degrees to the local horizon. It exploded tens of kilometers above the ground with the energy of 0.9 to 2.1 kilotons of TNT over a remote area of the Nubian Desert, causing a large fireball or bolide.<ref>{{cite web
 |date=October 6, 2008 
 |title=Astronomers predict shooting star over Sudan from space boulder 
 |url=http://afp.google.com/article/ALeqM5jOHHF4wcyteiUj5AlJP69dIMb0yA 
 |publisher=Agence France-Presse
 |accessdate=October 8, 2008 
|archiveurl=https://web.archive.org/web/20081011054910/http://afp.google.com/article/ALeqM5jOHHF4wcyteiUj5AlJP69dIMb0yA 
 |archivedate=October 11, 2008 
 |deadurl=yes 
 |df= }}</ref>

The meteor's "light was so intense that it lit up the sky like a full moon and an airliner {{convert|1,400|km|mi|abbr=on}} away reported seeing the bright flash."<ref>{{cite news
 |last=Simon |first=P.
 |date=October 8, 2008
 |title=Weather Eye: NASA spots asteroid before annihilation
 |url=http://www.timesonline.co.uk/tol/news/weather/article4902427.ece
 |work=The Times
 |accessdate=October 8, 2008 }}</ref> A webcam captured the flash lighting up El-Gouna beach 725 kilometres north of the explosion (see [[:File:ELG webcam record of 2008 TC3 frame 0005.png|this webcam frame]]).<ref name=Javaux>{{cite web
 |last=Javaux |first=G.
 |title=2008 TC3... Première détection d'un astéroïde avant son impact sur Terre... quelques heures plus tard
 |url=http://pagesperso-orange.fr/pgj/2008_TC3.htm
 |language=French
 |accessdate=September 15, 2009 }}</ref>

"Une webcam de surveillance, située sur la plage de la Mer Rouge à El Gouna en Egypte, a enregistré indirectement le flash de l'explosion qui s'est produit à environ 725 km plus au sud."<ref name=Javaux/>

A low-resolution image of the explosion was captured by the weather satellite Meteosat 8.<ref name="SpaceWeather.com">{{cite web
 |date=October 8, 2008
 |title=Asteroid Impact
 |url=http://www.spaceweather.com/archive.php?view=1&day=08&month=10&year=2008
 |publisher=SpaceWeather.com
 |accessdate=October 8, 2008
|archiveurl=https://web.archive.org/web/20081010193852/http://www.spaceweather.com/archive.php?view=1&day=08&month=10&year=2008
 |archivedate=October 10, 2008 
 |deadurl=no }}</ref> The Meteosat images place the fireball at {{Coord|21.00|32.15|name=2008 TC<sub>3</sub> fireball}}.<ref name="Meteosat 8 HRV">{{cite web
 |date=October 8, 2008
 |title=m8 HRV 200810070245
 |url=http://www.eumetsat.int/groups/ops/documents/image/img_asteroid_impact_hrv.jpg
 |accessdate=October 8, 2008
|archiveurl=https://web.archive.org/web/20081017142511/http://www.eumetsat.int/groups/ops/documents/image/img_asteroid_impact_hrv.jpg
 |archivedate=October 17, 2008 
 |deadurl=yes}}</ref> Infrasound detector arrays in Kenya also detected a sound wave from the direction of the expected impact corresponding to energy of 1.1 to 2.1 kilotons of TNT.<ref name="NASA-160">{{cite web
 |date=October 7, 2008 
 |title=Impact of Asteroid 2008 TC3 Confirmed 
 |url=http://neo.jpl.nasa.gov/news/news160.html 
 |publisher=Near Earth Object Program]
 |accessdate=October 8, 2008 
 |archiveurl=https://web.archive.org/web/20081010010227/http://neo.jpl.nasa.gov/news/news160.html 
 |archivedate=October 10, 2008 
 |deadurl=yes 
 |df= }}</ref> Asteroids of this size hit Earth about two or three times a year.<ref>{{cite news
 |last=Borenstein |first=S.
 |date=October 6, 2008
 |title=Small Asteroid Headed for Light Show Over Africa
 |url=http://abcnews.go.com/Technology/wireStory?id=5968166
 |publisher=ABC News
 |agency=The Associated Press
 |accessdate=September 15, 2009 }} {{Dead link|date=September 2010|bot=H3llBot}}</ref>

The trajectory showed intersection with Earth's surface at roughly {{Coord|20.3|N|33.5|E|name=2008 TC<sub>3</sub> projected impact}}<ref>{{cite web
 |author=Mike 
 |date=October 6, 2008 
 |title=Very near NEO Meteoroid impact! 
 |url=http://mkvh.de/ast/serendipity/index.php?/archives/9-Very-near-NEO-Meteoroid-impact-!.html 
|archive-url=https://web.archive.org/web/20081010123315/http://mkvh.de/ast/serendipity/index.php?%2Farchives%2F9-Very-near-NEO-Meteoroid-impact-%21.html 
 |dead-url=yes 
 |archive-date=October 10, 2008 
 |publisher=MKVH.de 
 |df= }}</ref> though the object was expected to break up perhaps {{convert|100|-|200|km|mi|-1|sp=us}} west as it descended, somewhat east of the Nile River, and about {{convert|100|km|mi|-1|sp=us}} south of the Egypt–Sudan border.

According to U.S. government sources<ref>{{cite web
 |date=October 15, 2008
 |title=Asteroid Update
 |url=http://www.spaceweather.com/archive.php?month=10&day=15&year=2008&view=view
 |publisher=SpaceWeather.com
 |accessdate=October 18, 2008}}</ref><ref>{{cite web
 |date=October 15, 2008
 |title=Fireball detection
 |url=http://meteor.uwo.ca/~pbrown/usaf/usg282.txt
 |publisher=University of Western Ontario
 |accessdate=October 18, 2008}}</ref> U.S. satellites detected the impact at 02:45:40 UT, with the initial detection at {{Coord|20.9|N|31.4|E|name=2008 TC<sub>3</sub> initial detection}} at {{convert|65.4|km|mi}} altitude and final explosion at {{Coord|20.8|N|32.2|E|name=2008 TC<sub>3</sub> final explosion}} at {{convert|37|km|mi}} altitude. These images have not been publicly released.

A search of the impact zone that began on December 6, 2008, turned up {{convert|10.5|kg}} of rock in some 600 fragments. These meteorites are collectively named '''Almahata Sitta''',<ref>{{cite web
 |date=August 12, 2013
 |title=Almahata Sitta
 |url=http://www.lpi.usra.edu/meteor/metbull.php?code=48915
 |work=Meteoritical Bulletin Database
 |accessdate=August 13, 2013}}</ref> which means "Station Six"<ref>{{cite web
 |last=Gebauer 
 |first=S. 
 |date=April 16, 2008 
 |title=Station Nr. 6. – Nubian Desert 
 |url=https://www.panoramio.com/photo/9417877 
 |publisher=Panoramio
 |accessdate=June 15, 2009 
 |archiveurl=https://www.webcitation.org/5hbspSSJd?url=http://www.panoramio.com/photo/9417877 
 |archivedate=June 17, 2009 
 |deadurl=no 
 |df= }}</ref> in Arabic and is a train station between Wadi Halfa and Khartoum, Sudan. This search was led by Peter Jenniskens from the SETI Institute, California and Muawia Shaddad of the University of Khartoum in Sudan and carried out with the collaboration of students and staff of the University of Khartoum. The initial 15 meteorites were found in the first three days of the search. Numerous witnesses were interviewed, and the hunt was guided with a search grid and specific target area produced by NASA's Jet Propulsion Laboratory in Pasadena, California.<ref name="NASA2009">{{cite web
 |date=March 27, 2009
 |title=NASA Team Finds Riches in Meteorite Treasure Hunt
 |url=http://www.nasa.gov/topics/solarsystem/features/asteroid_treasure_hunt.html
 |publisher=NASA
 |accessdate=April 5, 2009
|archiveurl=https://web.archive.org/web/20090331094810/http://www.nasa.gov/topics/solarsystem/features/asteroid_treasure_hunt.html
 |archivedate=March 31, 2009 
 |deadurl=no }}</ref><ref>{{cite journal
 |date=February 25, 2009
 |title=Found: Pieces of meteorite spotted before impact
|url=https://www.newscientist.com/article/mg20126974.800-found-pieces-of-meteorite-spotted-before-impact.html
 |journal=New Scientist
 |issue=2697 |page=15 }}</ref><ref>{{cite journal
 |last=Shiga |first=D.
 |date=February 19, 2009
 |title=First tracked space rock recovered after impact
|url=https://www.newscientist.com/article/dn16635-first-tracked-space-rock-recovered-after-impact.html
 |journal=New Scientist }}</ref><ref>{{cite journal
 |last=Courtland 
 |first=R. 
 |date=March 25, 2009 
 |title=Meteorite hunters 'strike gold' in Sudan 
 |url=https://www.newscientist.com/article/dn16843-meteorite-hunters-strike-gold-in-sudan.html 
 |journal=New Scientist
 |accessdate=April 4, 2009 
|archiveurl=https://www.webcitation.org/5hDZNqGfI?url=http://www.newscientist.com/article/dn16843-meteorite-hunters-strike-gold-in-sudan.html 
 |archivedate=June 1, 2009 
 |deadurl=no 
 |df= }}</ref><ref>{{cite journal
 |last=Kwok |first=R.
 |date=March 26, 2009
 |title=Astronomy: The Rock That Fell to Earth
 |url=http://www.nature.com/news/2009/090325/full/458401a.html
 |journal=Nature
 |volume=458 |issue= 7237|pages=401–403
 |doi=10.1038/458401a
 |pmid=19325604 }}</ref>

Samples of the Almahata Sitta meteorite were sent for analysis to a consortium of researchers led by Jenniskens, the Almahata Sitta consortium, including NASA Ames Research Center in California, the Johnson Space Center in Houston, the Carnegie Institution of Washington, and Fordham University in New York City. The first sample measured was an anomalous ultra-fine-grained porous polymict ureilite achondrite, with large carbonaceous grains. Reflectance spectra of the meteorite, combined with the astronomal observations, identified asteroid 2008 TC<sub>3</sub> as an F-type asteroid class. These fragile anomalous dark carbon-rich ureilites are now firmly linked to the group of F-class asteroids.<ref name="Jenniskens2009" /> Amino acids have been found on the meteorite.<ref>{{cite web
 |date=December 16, 2010
 |title=Life's Building Blocks Found on Surprising Meteorite
|url=http://www.space.com/scienceastronomy/asteroid-collision-meteoroid-amino-acids-life-101215.html
 |publisher=Space.com
 |accessdate=August 13, 2013}}</ref> The nanodiamonds found in the meteorite were shown to have grown slowly, implying that the source is another planet in the solar system.<ref>{{cite journal | last=Nabiei | first=Farhang | last2=Badro | first2=James | last3=Dennenwaldt | first3=Teresa | last4=Oveisi | first4=Emad | last5=Cantoni | first5=Marco | last6=Hébert | first6=Cécile | last7=El Goresy | first7=Ahmed | last8=Barrat | first8=Jean-Alix | last9=Gillet | first9=Philippe | title=A large planetary body inferred from diamond inclusions in a ureilite meteorite | journal=Nature Communications | publisher=Springer Nature | volume=9 | issue=1 | pages=1327 | date=April 17, 2018 | issn=2041-1723 | doi=10.1038/s41467-018-03808-6 | pmid=29666368 | pmc=5904174 |bibcode=2018NatCo...9.1327N|url=https://www.nature.com/articles/s41467-018-03808-6 |display-authors=1}}</ref>

Richard Kowalski, who discovered the object, received a tiny fragment of Almahatta Sitta, a gift from friends and well-wishers on the Minor Planet Mailing List, which Kowalski founded in order to help connect professional and amateur astronomers.<ref>{{cite web
 |last=Lakdawalla |first=E.
 |date=September 20, 2009
 |title=A piece of an asteroid returns to the telescope that discovered it
 |url=http://www.planetary.org/blog/article/00002104/
 |publisher=The Planetary Society
 |accessdate=October 7, 2009}}</ref>
{{clear}}

==Apollo asteroids==
{{main|Rocks/Rocky objects/Asteroids/Apollos|Apollos}}
[[Image:Minor Planets - Apollo.svg|thumb|right|250px|This a diagram showing the Apollo asteroids, compared to the orbits of the terrestrial planets of the [[Solar System]].
{| style="width: 100%; margin-bottom: 8px; margin-left: 12px;"
|-
| valign=top width=45% |
{{legend2|#e61d30|border=1px solid #770D18|[[Draft:Mars|Mars]]}}&nbsp;(M)<br>
{{legend2|#000000|border=1px solid black|[[Draft:Venus|Venus]]}}&nbsp;(V)
{{legend2|#aaa|border=1px solid #444|[[Draft:Mercury|Mercury]]}}&nbsp;(H)
| valign=top |
{{legend2|#FFFF00|border=1px solid #B3B300|[[Stars/Sun|Sun]]}}<br>
{{legend2|#00CC00|border=1px solid #003300|'''Apollo asteroids'''}}<br>
{{legend2|#1708a6|border=1px solid black|[[Draft:Earth|Earth]]}}&nbsp;(E)
|}
Credit: [[commons:User:AndrewBuck|AndrewBuck]].]]
[[Image:162173 Ryugu.jpg|left|thumb|300px|Photograph of the full disc of the asteroid 162173 Ryugu, as it appeared to the Hayabusa2 spacecraft's Optical Navigation Camera – Telescopic (ONC-T) at a distance of 20 kilometres (12 miles) at 03:50 UTC on 26 June 2018. Credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.{{tlx|fairuse}}]]
[[Image:Asteroid-Bennu-OSIRIS-RExArrival-GifAnimation-20181203.gif|right|thumb|300px|Asteroid Bennu imaged by the OSIRIS-REx probe on arrival 3 December 2018. Credit: NASA/Goddard/University of Arizona.{{tlx|free media}}]]
[[Image:Bennuarrival.png|thumb|left|250px|Photo of 101955 Bennu was taken by the OSIRIS-REx probe on 3 December 2018. Credit: NASA/Goddard/University of Arizona.]]
Note that sizes and distances of bodies and orbits are ''not'' to scale in the image on the right.

As of 2015, the Apollo asteroid group includes a total of 6,923 known objects of which 991 are numbered ([http://ssd.jpl.nasa.gov/sbdb_query.cgi JPL SBDB]).

Ryugu shown on the left was discovered on 10 May 1999 by astronomers with the Lincoln Near-Earth Asteroid Research at the Lincoln Laboratory's Experimental Test Site near Socorro, New Mexico, in the United States.<ref name="MPC-object">{{cite book
| title      = 162173 Ryugu (1999 JU3)
| url        = https://www.minorplanetcenter.net/db_search/show_object?object_id=162173
| access-date= 22 June 2018}}</ref>

The asteroid was officially named "Ryugu" by the Minor Planet Center on 28 September 2015.<ref name="MPC-Circulars-Archive">{{cite book
| title      = MPC/MPO/MPS Archive
| url        = https://www.minorplanetcenter.net/iau/ECS/MPCArchive/MPCArchive_TBL.html
| access-date= 22 June 2018}}</ref>

Initial images taken by the ''Hayabusa-2'' spacecraft on approach at a distance of 700&nbsp;km were released on 14 June 2018 and revealed a diamond shaped body and confirmed its retrograde rotation.<ref>{{cite book|title=From a distance of about 700km, Ryugu's rotation was observed|url=http://www.hayabusa2.jaxa.jp/topics/20180616je/index_e.html|publisher=JAXA|access-date= 18 June 2018}}</ref> 

Between 17 and 18 June 2018, Hayabusa 2 went from 330&nbsp;km to 240&nbsp;km from Ryugu and captured a series of additional images from the closer approach.<ref>Plait, Phil, [http://www.syfy.com/syfywire/asteroid-ryugu-starts-to-come-into-focus "Asteroid Ryugu Starts to Come Into Focus"], SyFy Wire, 20 June 2018. Accessed 20 June 2018.</ref>

On 21 September 2018, the first two of these rovers, which will hop around the surface of the asteroid, were released from ''Hayabusa2''.<ref>{{cite book |last1=Wall |first1=Mike |title=Japanese Probe Deploys Tiny Hopping Robots Toward Big Asteroid Ryugu |url=https://www.space.com/41898-hayabusa2-deploys-hopping-robots-asteroid-ryugu.html |accessdate=21 September 2018}}</ref>

On September 22, 2018, JAXA confirmed the two rovers had successfully touched down on Ryugu's surface which marks the first time a mission has completed a successful landing on a fast-moving asteroid body.<ref name="MINERVA-II-1 Landings">{{cite book |last1=Yoshimitsu |first1=Tetsuo |last2=Kubota |first2=Takashi |last3=Tsuda |first3=Yuichi |last4=Yoshikawa |first4=Makoto |title=MINERVA-II1: Successful image capture,  landing on Ryugu and hop! |url=http://www.hayabusa2.jaxa.jp/en/topics/20180922e/ |publisher=JAXA |accessdate=24 September 2018}}</ref>

"This series of images [second down on the right] taken by the OSIRIS-REx spacecraft shows Bennu in one full rotation from a distance of around 50 miles (80 km). The spacecraft’s PolyCam camera obtained the 36 2.2-millisecond frames over a period of four hours and 18 minutes."<ref name=Drake>{{ cite book
|author=Michael J. Drake
|title=Bennu Full Rotation at a Distance of 50 Miles
|publisher=NASA
|location=Washington, DC USA
|date=November 25, 2018
|url=https://www.asteroidmission.org/?attachment_id=12182
|accessdate=5 December 2018 }}</ref>

101955 Bennu (provisional designation 1999 RQ<sub>36</sub><ref name="contest">{{ cite book
|author=Diane Murphy
|title=Nine-Year-Old Names Asteroid Target of NASA Mission in Competition Run By The Planetary Society
|url=http://www.planetary.org/press-room/releases/2013/nine-year-old-names-asteroid.html
|access-date=20 August 2016
|publisher=The Planetary Society
|date=1 May 2013 }}</ref>, a C-type carbonaceous asteroid in the Apollo group discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) Project on September 11, 1999, is a potentially hazardous object that is listed on the Sentry monitoring system, Sentry Risk Table, with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale.<ref name="risk-table">{{ cite book
| title=Sentry Risk Table
| publisher=NASA/JPL Near-Earth Object Program Office
| accessdate=2018-03-20
|url=https://web.archive.org/web/20160911172609/http://neo.jpl.nasa.gov/risk/ }}</ref> It has a cumulative 1-in-2,700 chance of impacting Earth between 2175 and 2199.<ref name="Sentry">{{cite book
| url=https://cneos.jpl.nasa.gov/sentry/details.html#?des=101955
| title=101955 1999 RQ36: Earth Impact Risk Summary
| publisher=Jet Propulsion Laboratory
| date=25 March 2016
| access-date=20 March 2018 }}</ref><ref name="Meteoritics">{{ cite journal
|last1=Lauretta|first1=D. S.|last2=Bartels|first2=A. E.|last3=Barucci|first3=M. A.|last4=Bierhaus|first4=E. B.|last5=Binzel|first5=R. P.|last6=Bottke|first6=W. F.|last7=Campins|first7=H.|last8=Chesley|first8=S. R.|last9=Clark|first9=B. C.|last10=Clark|first10=B. E.|last11=Cloutis|first11=E. A.|last12=Connolly|first12=H. C.|last13=Crombie|first13=M. K.|last14=Delbó|first14=M.|last15=Dworkin|first15=J. P.|last16=Emery|first16=J. P.|last17=Glavin|first17=D. P.|last18=Hamilton|first18=V. E.|last19=Hergenrother|first19=C. W.|last20=Johnson|first20=C. L.|last21=Keller|first21=L. P.|last22=Michel|first22=P.|last23=Nolan|first23=M. C.|last24=Sandford|first24=S. A.|last25=Scheeres|first25=D. J.|last26=Simon|first26=A. A.|last27=Sutter|first27=B. M.|last28=Vokrouhlický|first28=D.|last29=Walsh|first29=K. J.
|title=The OSIRIS-REx target asteroid (101955) Bennu: Constraints on its physical, geological, and dynamical nature from astronomical observations
|journal=Meteoritics & Planetary Science
|date=April 2015
|volume=50
|issue=4
|pages=834–849
|doi=10.1111/maps.12353
|bibcode=2015M&PS...50..834L
|citeseerx=10.1.1.723.9955 }}</ref>
 
101955 Bennu has a mean diameter of approximately {{convert|492|m|ft mi|abbr=on}} and has been observed extensively with the Arecibo Observatory planetary radar and the Goldstone Deep Space Communications Complex NASA Deep Space Network.<ref name="Nolan2013">{{cite journal
|last1=Nolan|first1=M. C.|last2=Magri|first2=C.|last3=Howell|first3=E. S.|last4=Benner|first4=L. A. M.|last5=Giorgini|first5=J. D.|last6=Hergenrother|first6=C. W.|last7=Hudson|first7=R. S.|last8=Lauretta|first8=D. S.|last9=Margot|first9=J. L.|last10=Ostro|first10=S. J.|last11=Scheeres|first11=D. J.
|title=Shape model and surface properties of the OSIRIS-REx target Asteroid (101955) Bennu from radar and lightcurve observations
|journal=Icarus
|volume=226
|issue=1
|year=2013
|pages=629–640
|issn=0019-1035
|doi=10.1016/j.icarus.2013.05.028
|bibcode=2013Icar..226..629N
| url=http://www.escholarship.org/uc/item/6mh8b2t5|format=Submitted manuscript }}</ref><ref name="GDSCC-img">{{cite book
| url= http://echo.jpl.nasa.gov/~lance/1999RQ36/1999RQ36.html
| title=Goldstone Delay-Doppler Images of 1999 RQ36
| publisher=Jet Propulsion Laboratory }}</ref><ref name="Hudson et al. 2000">{{cite journal |author=Hudson, R. S. |author2=Ostro, S. J. |author3=Benner, L. A. M. |bibcode=2000DPS....32.0710H |title=Recent Delay-Doppler Radar Asteroid Modeling Results: 1999 RQ36 and Craters on Toutatis |journal=Bulletin of the American Astronomical Society |volume=32 |page=1001
| year=2000}}</ref>

Asteroid Bennu has a roughly spheroidal shape, resembling a spinning top, with the direction of rotation about its axis retrograde  with respect to its orbit and a fairly smooth shape with one prominent 10–20 m boulder on its surface, in the southern hemisphere.<ref name="Meteoritics" />

There is a well-defined ridge along the equator of asteroid Bennu that suggests that fine-grained regolith particles have accumulated in this area, possibly because of its low gravity and fast rotation.<ref name="Meteoritics" />

Observations of this minor planet by the Spitzer Space Telescope in 2007 gave an effective diameter of {{Val|484|10|u=m}}, which is in line with other studies. It has a low visible geometric albedo of {{Val|0.046|0.005}}. The thermal inertia was measured and found to vary by ±19% during each rotational period suggesting that the regolith grain size is moderate, ranging from several millimeters up to a centimeter, and evenly distributed. No emission from a potential dust coma has been detected around asteroid Bennu, which puts a limit of 10<sup>6</sup>&nbsp;g of dust within a radius of 4750&nbsp;km.<ref name=Emery2014>{{ cite book
| title=Thermal infrared observations and thermophysical characterization of the OSIRIS-REx target asteroid (101955) Bennu, In: Conference Proceedings Asteroids, Comets, Meteors 2014
|last1=Emery | first1=J.
| last2=Fernandez | first2=Y. | last3=Kelley | first3=M.
| last4=Warden | first4=K. | last5=Hergenrother | first5=C.
| last6=Lauretta | first6=D. | last7=Drake | first7=M.
| last8=Campins | first8=H. | last9=Ziffer | first9=J.
| pages=148
| editor=K. Muinonen
| date=July 2014
| bibcode=2014acm..conf..148E }}</ref>

Astrometric observations between 1999 and 2013 have demonstrated that 101955 Bennu is influenced by the Yarkovsky effect, causing the semimajor axis to drift on average by {{Val|284|1.5}}&nbsp;meters/year; analysis of the gravitational and thermal effects give a bulk density of ρ = {{Val|1260|70}}&nbsp;kg/m<sup>3</sup>, which is only slightly denser than water, the predicted macroporosity is {{Val|40|10}}%, suggesting that the interior has a rubble pile structure, with an estimated mass is {{Val|7.8|0.9|e=10|u=kg}}.<ref name="ChesleyFarnocchia2014">{{cite journal|last1=Chesley|first1=Steven R.|last2=Farnocchia|first2=Davide|last3=Nolan|first3=Michael C.|last4=Vokrouhlický|first4=David|last5=Chodas|first5=Paul W.|last6=Milani|first6=Andrea|last7=Spoto|first7=Federica|last8=Rozitis|first8=Benjamin|last9=Benner|first9=Lance A.M.|last10=Bottke|first10=William F.|last11=Busch|first11=Michael W.|last12=Emery|first12=Joshua P.|last13=Howell|first13=Ellen S.|last14=Lauretta|first14=Dante S.|last15=Margot|first15=Jean-Luc|last16=Taylor|first16=Patrick A.|title=Orbit and bulk density of the OSIRIS-REx target Asteroid (101955) Bennu|journal=Icarus|volume=235|date=2014|pages=5–22|issn=0019-1035|doi=10.1016/j.icarus.2014.02.020
| bibcode=2014Icar..235....5C|arxiv=1402.5573 }}</ref>

Photometric observations of Bennu in 2005 yielded a synodic rotation period of {{Val|4.2905|0.0065|u=h}}, a B-type asteroid classification, which is a sub-category of C-type asteroid or carbonaceous asteroids. Polarimetric observations show that Bennu belongs to the rare F-type asteroid or F subclass of carbonaceous asteroids, which is usually associated with cometary features.<ref name="Cellino2018" /> Measurements over a range of phase angles show a phase function slope of 0.040 magnitudes per degree, which is similar to other near-Earth asteroids with low albedo.<ref name=Hergenrother2013>{{ cite journal
| title=Lightcurve, Color and Phase Function Photometry of the OSIRIS-REx Target Asteroid (101955) Bennu
| last1=Hergenrother | first1=Carl W. | last2=Nolan | first2=Michael C.
| last3=Binzel | first3=Richard P. | last4=Cloutis | first4=Edward A.
| last5=Barucci | first5=Maria Antonietta | last6=Michel | first6=Patrick
| last7=Scheeres | first7=Daniel J. | last8=d'Aubigny | first8=Christian Drouet
| last9=Lazzaro | first9=Daniela | last10=Pinilla-Alonso | first10=Noemi
| last11=Campins | first11=Humberto | last12=Licandro | first12=Javier
| last13=Clark | first13=Beth E. | last14=Rizk | first14=Bashar
| last15=Beshore | first15=Edward C. | last16=Lauretta | first16=Dante S.
| journal=Icarus | volume=226 | issue=1 | pages=663–670 | date=September 2013
| doi=10.1016/j.icarus.2013.05.044 | bibcode=2013Icar..226..663H }}</ref>

Asteroid Bennu's basic [[mineralogy]] and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation into more complex minerals.<ref name="Meteoritics" /> Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100&nbsp;km, where simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the 495 Eulalia (Eulalia family).<ref name=Bottke2015>{{cite journal
| title=In search of the source of asteroid (101955) Bennu: Applications of the stochastic YORP model
| last1=Bottke | first1=William F. | last2=Vokrouhlický | first2=David
| last3=Walsh | first3=Kevin J. | last4=Delbo | first4=Marco
| last5=Michel | first5=Patrick | last6=Lauretta | first6=Dante S.
| last7=Campins | first7=Humberto | last8=Connolly | first8=Harold C.
| last9=Scheeres | first9=Daniel J. | last10=Chelsey | first10=Steven R.
| journal=Icarus | volume=247 | pages=191–217 | date=February 2015
| doi=10.1016/j.icarus.2014.09.046 | bibcode=2015Icar..247..191B }}</ref>

Subsequently, the orbit drifted as a result of the Yarkovsky effect and mean motion resonances with the giant planets, such as Jupiter and Saturn modified the asteroid, possibly changing its spin, shape, and surface features.<ref name=Lauretta2015>{{ cite journal
| title=The OSIRIS-REx target asteroid (101955) Bennu: Constraints on its physical, geological, and dynamical nature from astronomical observations
| last1=Lauretta | first1=D. S.
| last2=Bartels | first2=A. E. | last3=Barucci | first3=M. A.
| last4=Bierhaus | first4=E. B. | last5=Binzel | first5=R. P.
| last6=Bottke | first6=W. F. | last7=Campins | first7=H.
| last8=Chesley | first8=S. R. | last9=Clark | first9=B. C.
| last10=Clark | first10=B. E. | last11=Cloutis | first11=E. A.
| last12=Connolly | first12=H. C. | last13=Crombie | first13=M. K.
| last14=Delbó | first14=M. | last15=Dworkin | first15=J. P.
| last16=Emery | first16=J. P. | last17=Glavin | first17=D. P.
| last18=Hamilton | first18=V. E. | last19=Hergenrother | first19=C. W.
| last20=Johnson | first20=C. L. | last21=Keller | first21=L. P.
| last22=Michel | first22=P. | last23=Nolan | first23=M. C.
| last24=Sandford | first24=S. A. | last25=Scheeres | first25=D. J.
| last26=Simon | first26=A. A. | last27=Sutter | first27=B. M.
| last28=Vokrouhlický | first28=D. | last29=Walsh | first29=K. J.
| journal=Meteoritics & Planetary Science
| volume=50 | issue=4 | pages=834–849 | date=April 2015
| doi=10.1111/maps.12353 | bibcode=2015M&PS...50..834L
| citeseerx=10.1.1.723.9955}}</ref>

A possible cometary origin for Bennu, based on similarities of its spectroscopic properties with known comets, with the estimated fraction of comets in the population of Near Earth asteroids is {{val|8|5|u=%}}.<ref name="Cellino2018">{{Cite arXiv
| title=Unusual polarimetric properties of (101955) Bennu: similarities with F-class asteroids and cometary bodies
| eprint=1808.07812
| last1=Hergenrother
| first1=Carl W
| author2=Maria Antonietta Barucci
| last3=Barnouin
| first3=Olivier
| last4=Bierhaus
| first4=Beau
| last5=Binzel
| first5=Richard P
| last6=Bottke
| first6=William F
| last7=Chesley
| first7=Steve
| last8=Clark
| first8=Ben C
| last9=Clark
| first9=Beth E
| last10=Cloutis
| first10=Ed
| author11=Christian Drouet d'Aubigny
| last12=Delbo
| first12=Marco
| last13=Emery
| first13=Josh
| last14=Gaskell
| first14=Bob
| last15=Howell
| first15=Ellen
| last16=Keller
| first16=Lindsay
| last17=Kelley
| first17=Michael
| last18=Marshall
| first18=John
| last19=Michel
| first19=Patrick
| last20=Nolan
| first20=Michael
| last21=Rizk
| first21=Bashar
| last22=Scheeres
| first22=Dan
| last23=Takir
| first23=Driss
| last24=Vokrouhlický
| first24=David D
| last25=Beshore
| first25=Ed
| last26=Lauretta
| first26=Dante S
| class=astro-ph.EP
| year=2018 }}</ref>
{{clear}}

==Mars crossers==
{{main|Rocks/Rocky objects/Asteroids/Mars crossers|Mars crossers}}
"50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr".<ref name= Michel />

==Amor asteroids==
{{main|Rocks/Rocky objects/Asteroids/Amors|Amors}}
[[Image:Minor Planets - Amor.svg|thumb|right|250px|This is a diagram showing the general location of the Amor asteroids and Mars trojans, compared to the orbits of the terrestrial planets Mercury (H), Venus (V), Earth (E) and Mars (M).
{{legend|#FFFF00|border=1px solid #B3B300|[[Stars/Sun|Sun]]}}
{{legend|#00CC00|border=1px solid #003300|'''Amor asteroids'''}}
{{legend|#CD9C6A|border=1px solid #9D6934|Mars trojans}}
{{legend|#1708a6|border=1px solid black|[[Earth]]&nbsp;(E)}}
{{legend|#e61d30|border=1px solid #770D18|[[Mars]]&nbsp;(M)}}
{{legend|#000000|border=1px solid black|[[Venus]]&nbsp;(V)}}
{{legend|#aaa|border=1px solid #444|[[Mercury]]&nbsp;(H)}}
<br>Note that sizes and distances of bodies and orbits are ''not'' to scale. Credit: [[commons:User:AndrewBuck|AndrewBuck]].]]
{{clear}}

==Mars Trojans==
{{main|Rocks/Rocky objects/Asteroids/Mars Trojans|Mars Trojans}}
From the diagram in the section [[Rocks/Rocky objects/Asteroids#Amor asteroids|Amor asteroids]], the Mars Trojans occupy comparable positions relative to [[Mars]] that the [[Rocks/Rocky objects/Asteroids#Trojan asteroids|Trojan asteroids]] do to [[Jupiter]].

==Asteroid belts==
{{main|Rocks/Rocky objects/Asteroids/Belts|Belts}}
[[Image:Asteroidsscale.jpg|thumb|right|250px|This is a composite image, to scale, of the asteroids which have been imaged at high resolution. As of 2011 they are, from largest to smallest: [[w:4 Vesta|4 Vesta]], [[w:21 Lutetia|21 Lutetia]], [[w:253 Mathilde|253 Mathilde]], [[w:243 Ida|243 Ida]] and its moon Dactyl, [[w:433 Eros|433 Eros]], [[w:951 Gaspra|951 Gaspra]], [[w:2867 Šteins|2867 Šteins]], [[w:25143 Itokawa|25143 Itokawa]]. Credit: NASA/JPL-Caltech/JAXA/ESA.]]
[[Image:InnerSolarSystem-en.png|250px|thumb|left|The [[w:asteroid belt|asteroid belt]] is shown in (white) and the [[w:Trojan asteroids|Trojan asteroids]] (green). Credit: .]]
[[Image:243 ida crop.jpg|thumb|right|250px|This is an approximately natural color picture of the asteroid 243 Ida on August 28, 1993. Credit: NASA/JPL.]]
'''Def.''' a "region of the orbital plane of the solar system located between the orbits of Mars and Jupiter which is occupied by numerous minor planets and the dwarf planet Ceres"<ref name=AsteroidBeltWikt>{{ cite book
|author=[[wikt:User:WikiPedant|WikiPedant]]
|title=asteroid belt
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=10 December 2007
|url=https://en.wiktionary.org/wiki/asteroid_belt
|accessdate=2015-08-31 }}</ref> is called an '''asteroid belt'''.

"The MB group is the most numerous group of MCs. ... 50 % of the MB Mars-crossers [MCs] become ECs within 59.9 Myr and [this] contribution ... dominates the production of ECs"<ref name= Michel />. MB denotes the main belt of asteroids.<ref name= Michel />

The interplanetary medium includes interplanetary [[w:Interplanetary dust cloud|dust]], cosmic rays and hot [[Plasmas|plasma]] from the [[w:solar wind|solar wind]]. The temperature of the interplanetary medium varies. For dust particles within the asteroid belt, typical temperatures range from 200&nbsp;K (−73 °C) at 2.2&nbsp;AU down to 165&nbsp;K (−108 °C) at 3.2&nbsp;AU<ref name=Low>{{ cite journal
  | author=Low, F. J.; ''et al.''
  | title=Infrared cirrus&nbsp;– New components of the extended infrared emission
  | journal=Astrophysical Journal, Part 2&nbsp;– Letters to the Editor
  | year=1984
  | volume=278
  | pages=L19–L22
|url=http://adsabs.harvard.edu//abs/1984ApJ...278L..19L
  | bibcode=1984ApJ...278L..19L
  | doi=10.1086/184213 }}</ref>
The density of the interplanetary medium is very low, about 5 particles per cubic centimeter in the vicinity of the [[Earth]]; it decreases with increasing distance from the sun, in inverse proportion to the square of the distance. It is variable, and may be affected by magnetic fields and events such as [[w:Coronal mass ejection|coronal mass ejection]]s. It may rise to as high as 100 particles/cm³.

"The hydromagnetic approach led to the discovery of two important observational regularities in the solar system: (1) the band structure [such as in the rings of Saturn and in the asteroid belt], and (2) the cosmogonic shadow effect (the two-thirds fall down effect)."<ref name=Alfven1981>{{ cite journal
|author=Hannes Alfvén
|title=The Voyager 1/Saturn Encounter and the Cosmogonic Shadow Effect
|journal=Astrophysics and Space Science
|month=October
|year=1981
|volume=79
|issue=2
|pages=491-505
|url=http://adsabs.harvard.edu/abs/1981Ap&SS..79..491A
|arxiv=
|bibcode=1981Ap&SS..79..491A
|doi=10.1007/BF00649444
|pmid=
|accessdate=2013-12-19 }}</ref>

The majority of known asteroids orbit within the asteroid belt between the orbits of [[Mars]] and [[Jupiter]] ... This belt is now estimated to contain between 1.1 and 1.9 million asteroids larger than 1 km in diameter,<ref name=Tedesco2002>{{ cite book
 | author=Edward Tedesco, Leo Metcalfe
 | title=New study reveals twice as many asteroids as previously believed
 | publisher=European Space Agency | date=April 4, 2002
 | url=http://www.spaceref.com/news/viewpr.html?pid=7925
 | accessdate=2008-02-21 }}</ref> and millions of smaller ones.<ref>[http://www.nasa.gov/worldbook/asteroid_worldbook.html World Book at NASA]</ref>

At second right is an approximately natural color image of the asteroid 243 Ida. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."<ref name=Lavoie96>{{ cite book
|author=Sue Lavoie
|title=PIA00069: Ida and Dactyl in Enhanced Color
|publisher=NASA/JPL
|location=Pasadena, California USA
|date=January 29, 1996
|url=http://photojournal.jpl.nasa.gov/catalog/?IDNumber=PIA00069
|accessdate=2013-06-01 }}</ref>

"The [Sloan Digital Sky Survey] SDSS “blue” asteroids are related to the C-type (carbonaceous) asteroids, but not all of them are C-type. They are a mixture of C-, E-, M-, and P-types."<ref name=Yoshida>{{ cite journal
|author=F Yoshida, T Nakamura
|title=Subaru main belt asteroid survey (SMBAS)—size and color distributions of small main-belt asteroids
|journal=Planetary and Space Science
|month=June
|year=2007
|volume=55
|issue=9
|pages=1113-25
|url=http://www.sciencedirect.com/science/article/pii/S0032063306003357
|arxiv=
|bibcode=
|doi=10.1016/j.pss.2006.11.016
|pmid=
|accessdate=2013-06-01 }}</ref>
{{clear}}

==Baptistina family==
[[Image:298Bap-LB1-mag15.jpg|thumb|right|250px|298 Baptistina (center) is one of the largest presumed remnants of the Baptistina family. Credit: .]]
The '''Baptistina family''' (Family identification number, FIN: [[w:FIN tbl#403|403]]) is an asteroid family of more than 2500 members that was probably produced by the breakup of an asteroid {{convert|170|km|mi|abbr=on}} across 80 million years ago following an impact with a smaller body. The two largest presumed remnants of the parent asteroid are main-belt asteroids 298 Baptistina and 1696 Nurmela. The Batistina family is part of the larger [[w:Flora family|Flora clan]].<ref name="Alvarez-Candal-2006">{{Cite journal
  |first1     = A. |last1 = Alvarez-Candal
  |first2     = R. |last2 = Duffard
  |first3     = D. |last3 = Lazzaro
  |first4     = T. |last4 = Michtchenko
  |date       = December 2006
  |title      = The inner region of the asteroid Main Belt: a spectroscopic and dynamic analysis
  |url        = https://www.aanda.org/articles/aa/pdf/2006/45/aa5518-06.pdf
  |journal    = Astronomy and Astrophysics
  |volume     = 459
  |issue      = 3
  |pages      = 969–976
  |bibcode    = 2006A&A...459..969A 
  |doi        = 10.1051/0004-6361:20065518
  |accessdate= 21 April 2018}}</ref><ref name="Nesvorny-2014">{{Cite journal
  |first1     = D. |last1 = Nesvorný
  |first2     = M. |last2 = Broz
  |first3     = V. |last3 = Carruba
  |date       = December 2014
  |title      = Identification and Dynamical Properties of Asteroid Families
  |url        = https://arxiv.org/pdf/1502.01628.pdf
  |journal    = Asteroids IV
  |page       = 23
  |bibcode    = 2015aste.book..297N 
  |doi        = 10.2458/azu_uapress_9780816532131-ch016
  |arxiv      = 1502.01628
  |accessdate= 23 June 2017}}</ref>

The Baptistina family consists of darkly colored asteroids and meteoroids in similar orbits. Many mountain-sized fragments from the collision would have leaked into the inner solar system through orbital resonances with Mars and Jupiter, causing a prolonged series of asteroid impacts. Previously, this collision was believed to have occurred about 160 million years ago, and many impacts between 100 and 50 million years ago were attributed to it. However, in 2011, data from WISE revised the date of the proposed collision which broke up the parent asteroid to about 80 million years ago.<ref name="Universe Today">{{cite book | first=Tammy | last=Plotner | title=Did Asteroid Baptistina Kill the Dinosaurs? Think other WISE... | url=http://www.universetoday.com/89050/did-asteroid-baptistina-kill-the-dinosaurs-think-other-wise/#more-89050 |date=2011| accessdate=2011-09-19}}</ref>

Following the impact of the Chelyabinsk meteor in 2013, a paper published in the journal ''Icarus'' showed that shock produced during impact of a large asteroid can darken otherwise bright silicate material. Spectral analysis of the darkly-colored portions of the non-carbonaceous Chelyabinsk meteorite closely matched the color of members of the Baptistina family, showing that a low albedo does not necessarily indicate the composition of the family.<ref>{{cite book|url=https://phys.org/news/2014-07-russian-meteorite-dinosaur-extinction-mystery.html|title=Russian meteorite sheds light on dinosaur extinction mystery|date=2014-07-17}}</ref>


==Eos family==
{{main|Rocks/Rocky objects/Asteroids/Eos|Eos family}}
Members include 221 Eos, 339 Dorothea, 450 Brigitta, 513 Centesima, 562 Salome, 579, 633 Zelima, 639 Latona, 651 Antikleia, 653 Berenike, 661 Cloelia, 669 Kypria, 742 Edisona, 807 Ceraskia, 876 Scott, 890 Waltraut, 1075, 1199, and 1364.

==Koronis family==
{{main|Rocks/Rocky objects/Asteroids/Koronis|Koronis family}}
[[Image:Koronis family.jpg|thumb|right|250px|These are some of the Koronis family asteroids. Credit: NASA.]]
[[Image:243 ida crop.jpg|thumb|right|250px|This is an approximately natural color picture of the asteroid 243 Ida on August 28, 1993. Credit: NASA/JPL.]]
Members include 158 Koronis, 167 Urda, 208 Lacrimosa, 243 Ida,<ref name="Holm1994">{{cite journal|last=Holm|first=Jeanne|editor=Jones, Jan|title=Discovery of Ida's Moon Indicates Possible "Families" of Asteroids|journal=The Galileo Messenger|issue=34|date=June 1994|url=http://www2.jpl.nasa.gov/galileo/mess34/Moon2.html|accessdate=2008-10-23|ref=CITEREFHolm1994|archive-date=20 January 2012|archive-url=http://planetary.s3.amazonaws.com/galileo_messenger/GM034.pdf}}</ref> 311, 321, 534, 720, and 1223.

At second right is an approximately natural color image of the asteroid 243 Ida. The dot to the right is its moon Dactyl. "There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas."<ref name=Lavoie96/>

Ida was discovered on 29 September 1884 by Austrian astronomer Johann Palisa at the Vienna Observatory.<ref name="Ridpath1897p206">{{cite book|last=Ridpath|first=John Clark|title=The Standard American Encyclopedia of Arts, Sciences, History, Biography, Geography, Statistics, and General Knowledge|publisher=Encyclopedia Publishing|year=1897|url=https://books.google.com/?id=1GMMAAAAYAAJ|ref=CITEREFRidpath1897}}</ref> It was his 45th asteroid discovery.<ref name="Raab2002">{{cite journal|last=Raab|first=Herbert|title=Johann Palisa, the most successful visual discoverer of asteroids|journal=Meeting on Asteroids and Comets in Europe|year=2002|url=http://www.astrometrica.at/Papers/Palisa.pdf|accessdate=2008-10-23|archiveurl=https://web.archive.org/web/20081030190303/http://www.astrometrica.at/Papers/Palisa.pdf|archivedate=2008-10-30|deadurl=yes }}</ref> Ida was named by Moriz von Kuffner, a Viennese brewer and amateur astronomer.<ref name="Schmadel2003p36">{{cite book|last=Schmadel|first=Lutz D.|chapter=Catalogue of Minor Planet Names and Discovery Circumstances|title=Dictionary of minor planet names|series=IAU commission|volume=20|publisher=Springer|year=2003|chapterurl=https://books.google.com/books?id=KWrB1jPCa8AC&printsec=frontcover#PPA13,M1|isbn=978-3-540-00238-3 }}</ref><ref name="Berger2003p241">{{cite book|last=Berger|first=Peter|editor-last=Gourvish|editor-first=Terry|year=2003|title=Business and Politics in Europe, 1900–1970|chapter=The Gildemeester Organisation for Assistance to Emigrants and the expulsion of Jews from Vienna, 1938–1942|publisher=Cambridge University Press|location=Cambridge, UK|url=https://books.google.com/?id=uK99Gg2zBRQC|isbn=978-0-521-82344-9 }}</ref> In Greek mythology, Ida was a nymph of Crete who raised the god Zeus.<ref name="NASA2005">{{cite web|title=Images of Asteroids Ida & Dactyl |publisher=National Aeronautics and Space Administration |date=23 August 2005 |url=http://neo.jpl.nasa.gov/images/ida.html |accessdate=2008-12-04 |archiveurl=https://web.archive.org/web/20081021211759/http://neo.jpl.nasa.gov/images/ida.html |archivedate=21 October 2008 |deadurl=yes }}</ref> Ida was recognized as a member of the Koronis family by Kiyotsugu Hirayama, who proposed in 1918 that the group comprised the remnants of a destroyed precursor body.<ref name="Chapman1996p700">{{cite journal|last=Thomas|first=Peter C.|author2=Belton, Michael J. S.|author3=Carcich, B.|author4=Chapman, Clark R.|author5=Davies, M. E.|author6=Sullivan, Robert J.|author7= Veverka, Joseph|title=The shape of Ida|journal=Icarus|issue=1|volume=120|pages=20–32|year=1996|bibcode=1996Icar..120...20T|doi=10.1006/icar.1996.0033 }}</ref>

Ida's reflection spectrum was measured on 16 September 1980 by astronomers David J. Tholen and Edward F. Tedesco as part of the eight-color asteroid survey (ECAS).<ref name="ZellnerTholenTedesco1985p357p373">{{cite journal|last=Zellner|first=Ben|author2=Tholen, David J.|author3= Tedesco, Edward F.|title=The eight-color asteroid survey: Results for 589 minor planets|journal=Icarus|date=March 1985|volume=61|issue=3|pages=355–416|doi=10.1016/0019-1035(85)90133-2|bibcode=1985Icar...61..355Z }}</ref>

"The Eos and Koronis families&nbsp;... are entirely of type S, which is rare at their heliocentric distances ..."<ref name="ZellnerTholenTedesco1985p357p373"/>

Its spectrum matched those of the asteroids in the S-type classification.<ref name="ZellnerTholenTedesco1985p357p373"/> Many observations of Ida were made in early 1993 by the United States Naval Observatory Flagstaff Station and the Oak Ridge Observatory. These improved the measurement of Ida's orbit around the Sun and reduced the uncertainty of its position during the ''Galileo'' flyby from {{convert|78|to|60|km|mi|abbr=on}}.<ref name="OwenYeomans1994p2295">{{cite journal|last=Owen|first=W. M., Jr.|author2=Yeomans, D. K.|title=The overlapping plates method applied to CCD observations of 243 Ida|journal=The Astronomical Journal|volume=107|issue=6|pages=2295–2298|date=June 1994|doi=10.1086/117037|bibcode=1994AJ....107.2295O }}</ref>

{{clear}}

==Maria family==
{{main|Rocks/Rocky objects/Asteroids/Maria|Maria family}}
Members include 170 Maria, 472, 660, 695, and 714.

==Nysian asteroids==
{{main|Rocks/Rocky objects/Asteroids/Nysians|Nysians}}
[[Image:Nysian asteroid family.png|thumb|right|250px|This is a screen shot of a computer plot for the Nysian family of asteroids. Credit: EasySky.]]
The Nysian asteroids occur primarily between the orbits of Mars and Jupiter but some are between Earth and Mars.
{{clear}}

==Trojan asteroids==
{{main|Rocks/Rocky objects/Asteroids/Trojans|Trojan asteroids}}
[[Image:Lagrange very massive.svg|thumb|right|250px|Diagram of Lagrange points is in a system where the primary is much more massive than the secondary. Credit: [[commons:User:Cmglee|Cmglee]].]]
'''Def.''' "the L4 and L5 Lagrange points of the Sun-Jupiter orbital configuration"<ref name=TrojanPointWikt>{{ cite book
|author=[[wikt:User:65.94.44.124|65.94.44.124]]
|title=Trojan point
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=11 December 2010
|url=https://en.wiktionary.org/wiki/Trojan_point
|accessdate=2015-08-31 }}</ref> are called the '''Trojan points'''.

'''Def.''' "an asteroid occupying the Trojan points of the Sun-Jupiter system"<ref name=TrojanAsteroidWikt>{{ cite book
|author=[[wikt:User:65.94.44.124|65.94.44.124]]
|title=Trojan asteroid
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=11 December 2010
|url=https://en.wiktionary.org/wiki/Trojan_asteroid
|accessdate=2015-08-31 }}</ref> is called a '''Trojan asteroid'''.

The Trojan asteroids orbit 60 degrees ahead of and behind Jupiter as it circles the Sun."<ref name=Porco>{{ cite book
|author=C. Porco
|title=Flying by Helene
|publisher=NASA's Science Mission Directorate
|location=Washington, D.C. USA
|date=31 January 2011
|url=http://www.ciclops.org/view/6723/Flying_by_Helene?js=1
|accessdate=2016-11-06 }}</ref>

Asteroid (514107) 2015 BZ509 may be a former interstellar object, captured some 4.5 billion years ago, as evidenced by its co-orbital motion with Jupiter and its retrograde orbit around the Sun.<ref>{{ cite web
|url=http://www.sciencemag.org/news/2018/05/asteroid-came-another-solar-system-and-it-s-here-stay
|title=This asteroid came from another solar system—and it’s here to stay
|publisher=Science }}</ref>
{{clear}}

==Centaurs==
{{main|Rocks/Rocky objects/Centaurs|Centaurs}}
'''Def.''' an "icy planetoid that orbits the Sun between [[Jupiter]] and [[Neptune]]"<ref name=CentaurWikt>{{ cite book
|author=[[wikt:User:SnoopY|SnoopY]]
|title=Centaur
|publisher=Wikimedia Foundation, Inc
|location=San Francisco, California
|date=21 December 2005
|url=https://en.wiktionary.org/wiki/Centaur
|accessdate=31 August 2015 }}</ref> is called a '''Centaur'''.

"The recent investigation of the orbital distribution of Centaurs (Emel’yanenko et al., 2005) showed that there are two dynamically distinct classes of Centaurs, a dominant group with semimajor axes a > 60 AU and a minority group with a < 60 AU."<ref name=Emelyanenko>{{ cite journal
|author=V. V. Emel’yanenko
|title=Structure and dynamics of the Centaur population: constraints on the origin of short-period comets
|journal=Earth, Moon, and Planets
|month=December
|year=2005
|volume=97
|issue=3-4
|pages=341-51
|url=http://dccm.susu.ac.ru/acm2005.pdf
|bibcode=
|doi=10.1007/s11038-006-9095-5
|pmid=
|accessdate=2011-10-06 }}</ref> "[T]he intrinsic number of such objects is roughly an order of magnitude greater than that for a<60 AU".<ref name=Emelyanenko/>

==Radars==
{{main|Radiation astronomy/Radars|Radar astronomy}}
[[Image:2012 LZ1.jpg|thumb|right|250px|This image is of asteroid 2012 LZ1 by the Arecibo Observatory in Puerto Rico using the Arecibo Planetary Radar. Credit: Arecibo Observatory.]]
'''Radar astronomy''' is used to detect and study astronomical objects that reflect radio rays.

"The advantages of radar in planetary astronomy result from (1) the observer's control of all the attributes of the coherent signal used to illuminate the target, especially the wave form's time/frequency modulation and polarization; (2) the ability of radar to resolve objects spatially via measurements of the distribution of echo power in time delay and Doppler frequency; (3) the pronounced degree to which delay-Doppler measurements constrain orbits and spin vectors; and (4) centimeter-to-meter wavelengths, which easily penetrate optically opaque planetary clouds and cometary comae, permit investigation of near-surface macrostructure and bulk density, and are sensitive to high concentrations of metal or, in certain situations, ice."<ref name="Ostro">{{cite journal
|author=Steven J. Ostro
|title=Planetary radar astronomy
|journal=Reviews of Modern Physics
|month=October-December
|year=1993
|volume=65
|issue=4
|pages=1235-79
|url=http://rmp.aps.org/abstract/RMP/v65/i4/p1235_1
|arxiv=
|bibcode=
|doi=10.1103/RevModPhys.65.1235
|pmid=
|accessdate=2012-02-09 }}</ref>
{{clear}}

==514107 Kaʻepaokaʻawela==
[[Image:2015 BZ509-orbit.png|right|thumb|300px|Retrograde orbit of 2015 BZ<sub>509</sub> has 100 day motion markers. Credit: [[c:user:Tomruen|Tomruen]].{{tlx|free media}}]]
[[Image:JupiterRetroAstroLookingDow.jpg|thumb|left|250px|Orbital diagram is shown. Credit: [[c:user:Nwbeeson|Nwbeeson]].]]
[[Image:JupiterRetroAsterSideView.jpg|thumb|left|250px|Orbit (side-view) is compared to Jupiter. Credit: [[c:user:Nwbeeson|Nwbeeson]].]]
[[Image:2015 BZ509-retrograde-near-sun.png|right|320px|thumb|''Kaʻepaokaʻawela'' shows apparent retrograde motion in the sky while it is on the far side of the sun, rather than at opposition with the sun. Credit: [[c:user:Tomruen|Tomruen]].]]
514107 Kaʻepaokaʻawela, provisional designation 2015 BZ<sub>509</sub>, also nicknamed Bee-Zed,<ref name=Phys.org>{{cite news
  |author     =<!--Staff writer(s); no by-line.-->
  |title      = The stable retrograde orbit of the Bee-Zed asteroid explained
  |url        = https://phys.org/news/2017-06-stable-retrograde-orbit-bee-zed-asteroid.html 
  |work       = Phys.org
  |date       = 28 June 2017}}</ref> is a small asteroid, approximately {{convert|3|km|mi|sigfig=1|abbr=off|sp=us}} in diameter,<ref name="CNRS">{{Cite press release
  |title      = Discovery of the first body in the Solar System with an extrasolar origin
  |date       = 22 May 2018
  |publisher  = CNRS
  |website    = www2.cnrs.fr
  |url        = http://www2.cnrs.fr/en/3117.htm
  |access-date= 31 May 2018}}</ref> in a resonant, co-orbital motion with Jupiter.<ref name="Wiegert-2017" /> Its orbit is retrograde, which is opposite to the direction of most other bodies in the [[Solar System]].<ref name="BadAstronomy">{{cite web
  |last1      = Plait |first1 = Phil
  |title      = Meet Jupiter's backwards little friend: Asteroid 2015 BZ509
  |publisher  = SyFy Wire
  |date       = Mar 30, 2017
  |url        = http://www.syfy.com/syfywire/meet-jupiters-backwards-little-friend-asteroid-2015-bz509
  |accessdate = 30 March 2017}}</ref> It was discovered on 26 November 2014, by astronomers of the Pan-STARRS survey at Haleakala Observatory on the island of Maui, United States.<ref name="MPC-object2015">{{cite web
  |title      = (514107) Ka`epaoka`awela = 2015 BZ509
  |work       = Minor Planet Center
  |url        = https://www.minorplanetcenter.net/db_search/show_object?object_id=514107
  |accessdate = 7 March 2018}}</ref> The unusual object is the first example of an asteroid in a 1:−1 resonance with any of the planets.<ref name="Wiegert-WesternUniversity">{{cite web
  |last       = Wiegert | first = Paul
  |title      = The first retrograde co-orbital asteroid: 2015 BZ509 – a Trojan in retreat
  |date       = 30 March 2017
  |publisher  = University of Western Ontario
  |url        = http://www.astro.uwo.ca/~wiegert/2015BZ509/
  |accessdate = 7 March 2018}}</ref>

''Kaʻepaokaʻawela'' orbits the Sun at a distance of 3.2–7.1&nbsp;AU once every 11 years and 8 months (4,256 days; semi-major axis of 5.14&nbsp;AU), has an eccentricity of 0.38 and an inclination of 163° with respect to the ecliptic.<ref name="jpldata">{{cite web
  |type       = 2017-09-17 last obs.
  |title      = JPL Small-Body Database Browser: 514107 Ka`epaoka`awela (2015 BZ509)
  |url        = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2514107
  |publisher  = Jet Propulsion Laboratory
  |accessdate = 3 December 2018}}</ref>

The orbit of this asteroid is shown in blue when it is above the plane of the orbit of Jupiter, and in magenta when it is below the plane of the orbit of Jupiter.<ref name="Wiegert-2017">{{Cite journal
  |first1     = Paul |last1 = Wiegert
  |first2     = Martin |last2 = Connors
  |first3     = Christian |last3 = Veillet
  |date       = March 2017
  |title      = A retrograde co-orbital asteroid of Jupiter
  |url        = http://www.nature.com/nature/journal/v543/n7647/full/nature22029.html#videos
  |journal    = Nature
  |volume     = 543
  |issue      = 7647
  |pages      = 687–689
  |bibcode    = 2017Natur.543..687W
  |doi        = 10.1038/nature22029
  |pmid = 28358083
  |accessdate= 7 March 2018}}</ref>

The plane of the orbit of Jupiter is shown in black, but in this frame of reference Jupiter (the red dot) stays at the right end of the black line. The orbit of this asteroid is shown in blue when it is above (north of) the plane of the orbit of Jupiter, and it is shown in magenta when it is below (south of) the plane of the orbit of Jupiter.<ref name="Wiegert-2017" />

''Kaʻepaokaʻawela'' has been in its retrograde resonance with Jupiter since the origin of the Solar System instead of it being an object that is only briefly in this orbit that was observed by chance using the Copernican principle.<ref name="Scientific-American" /><ref name="Namouni-2018">{{Cite journal
  |first1     = Fathi |last1 = Namouni
  |first2     = Maria Helena Moreira |last2 = Morais
  |date       = 21 May 2018
  |title      = An interstellar origin for Jupiter's retrograde co-orbital asteroid
  |journal    = Monthly Notices of the Royal Astronomical Society: Letters
  |volume     = 477
  |issue      = 1
  |pages      = L117–L121
  |bibcode    = 2018MNRAS.477L.117N 
  |doi        = 10.1093/mnrasl/sly057
  |arxiv      = 1805.09013
  |issn       = 1745-3925}}</ref> Since its retrograde orbit is in the opposite direction as objects that formed in the early Solar System they posit that ''Kaʻepaokaʻawela'' has an interstellar origin.<ref name="BBC">{{Cite news
  |last       = Halton
  |first      = Mary
  |date       = 21 May 2018
  |title      = 'Permanent' interstellar visitor found
  |work       = BBC News
  |url        = https://www.bbc.com/news/science-environment-44173403
  |accessdate= 1 June 2018}}</ref> If confirmed, this origin would have implications on current theories such as the detailed timing and mechanics of planet formation, and the delivery of water and organic molecules to Earth.<ref name="Scientific-American" /> Others suggest that ''Kaʻepaokaʻawela'' originated in the Oort cloud or that it acquired a retrograde orbit due to interactions with Planet Nine, and that it is a short term resident of its current resonance.<ref name="Scientific-American">{{Cite web
  |last       = Billings
  |first      = Lee
  |date       = 21 May 2018
  |title      = Astronomers Spot Potential "Interstellar" Asteroid Orbiting Backward around the Sun
  |publisher  = Scientific American
  |url        = https://www.scientificamerican.com/article/astronomers-spot-potential-interstellar-asteroid-orbiting-backward-around-the-sun/
  |accessdate = 1 June 2018}}</ref>
{{clear}}

==Acknowledgements==

The content on this page was first contributed by: Henry A. Hoff.

Initial content for this page in some instances came from [http://www.wikiversity.org Wikiversity].

==See also==
{{div col|colwidth=12em}}
* [[Asteroid mining]]
* [[Asteroid Surveys]]
* [[Earth-impact events]]
{{Div col end}}

==References==
{{reflist|2}}

==External links==
* [http://www.cfht.hawaii.edu Canada-France-Hawaii Telecope]
* [http://www.lpl.arizona.edu/css/ Catalina Sky Survey]
* [http://www.minorplanetcenter.net/iau/mpc.html Minor Planet Center]
* [http://neo.jpl.nasa.gov/risk Sentry Impact Risk]

<!-- footer templates -->
{{Radiation astronomy resources}}{{Sisterlinks|Asteroids}}

<!-- categories -->
[[Category:Radiation astronomy/Lectures]]
[[Category:Radiation/Lectures]]
[[Category:Resources last modified in October 2019]]
[[Category:Rocks/Lectures]]