Editing 9 Metis

{{Short description|Main-belt asteroid}}
{{Distinguish|text=Jupiter's moon [[Metis (moon)|Metis]]}}
{{Use dmy dates|date=September 2019}}
{{Infobox planet
| minorplanet = yes
| background=#D6D6D6 
| name=9 Metis
| image= 9 Metis VLT (2021), deconvolved.pdf
| image_size= 
| caption=
| symbol=[[Image:Metis symbol (bold).svg|24px]] (historical)
| discoverer=[[Andrew Graham (astronomer)|A. Graham]]
| discovered=25 April 1848
| mpc_name=(9) Metis
| alt_names={{mp|1974 QU|2}}
| pronounced = {{IPAc-en|ˈ|m|iː|t|ᵻ|s}}<ref>Noah Webster (1884) ''A Practical Dictionary of the English Language''</ref>
| named_after = [[Metis (mythology)|Mētis]]
| adjectives = Metidian {{IPAc-en|m|ɛ|ˈ|t|ɪ|d|i|ə|n}}
| mp_category=[[Main belt]]
| orbit_ref =<ref name="jpldata">{{cite web
  |type=last observation: 2023-08-13
  |title=JPL Small-Body Database Browser: 9 Metis
  |url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=9
  |access-date=2023-09-18}}</ref>
| epoch=13 September 2023<br/>([[Julian day|JD]]&nbsp;2453300.5)
| semimajor={{Convert|2.387|AU|e6km|abbr=unit}}
| perihelion={{Convert|2.093|AU|e6km|abbr=unit}}
| time_periastron=6 November 2023
| aphelion={{Convert|2.68|AU|e6km|abbr=unit|lk=on}}
| eccentricity=0.1231
| period=3.69 [[Julian year (astronomy)|yr]] (1346.74 d)
| inclination=5.577°
| asc_node=68.87°
| arg_peri=5.75°
| mean_anomaly=345.43°
| moid = {{Convert|1.1|AU|e6km|abbr=unit}}
| p_orbit_ref =<ref name=Metis-POE>{{cite web
  |title=AstDyS-2 Metis Synthetic Proper Orbital Elements
  |publisher=Department of Mathematics, University of Pisa, Italy
  |url=https://newton.spacedys.com/astdys/index.php?pc=1.1.6&n=9
  |access-date=1 October 2011}}</ref>
| p_semimajor = 2.3864354
| p_eccentricity = 0.1271833
| p_inclination = 4.6853629°
| p_mean_motion = 97.638314
| perihelion_rate = 38.754973
| node_rate = −41.998090
| mean_diameter={{val|173|2|u=km}}<ref name=VLT>P. Vernazza et al. (2021) VLT/SPHERE imaging survey of the largest main-belt asteroids: Final results and synthesis. ''Astronomy & Astrophysics'' 54, A56</ref><br />190±? km (Dunham)<ref name="jpldata" />
| dimensions=(222 × 182 × 130) ± 12 km<ref name="Baer2011" />
| flattening = 0.39{{efn|1=Flattening derived from the maximum aspect ratio (c/a): <math>f=1-\frac{c}{a}</math>, where (c/a) = {{val|0.61|0.05}}.<ref name=VLT/>}}
|mass={{val|8.0|1.9|e=18|u=kg}}<ref name=VLT/><br />{{val|11.3|2.2|e=18|u=kg}}{{refn|group=lower-alpha|{{val|5.7|1.1|e=−12|u={{Solar mass}}}}}}<ref name="Baer2011">James Baer, Steven Chesley & Robert Matson (2011) "Astrometric masses of 26 asteroids and observations on asteroid porosity." ''The Astronomical Journal'', Volume 141, Number 5</ref>
|density={{val|2.94|0.70|u=g/cm3}}<ref name=VLT/><br />{{val|4.12|1.17|u=g/cm3}}<ref name="Baer2011"/>
| rotation=0.2116 d (5.079 h)<ref name="jpldata" />
| spectral_type=[[S-type asteroid|S]]<ref name="spiff">[http://spiff.rit.edu/richmond/parallax/phot/LCSUMPUB.TXT asteroid lightcurve data file (March 2001)]</ref>
| magnitude = 8.1<ref name="Pasachoff1983">{{cite book | author=Donald H. Menzel | author2=Jay M. Pasachoff | name-list-style=amp | date=1983 | title=A Field Guide to the Stars and Planets | edition=2nd | publisher=Houghton Mifflin | pages=[https://archive.org/details/fieldguidetostar00menz_0/page/391 391] | location=Boston, MA | isbn=0-395-34835-8 | url-access=registration | url=https://archive.org/details/fieldguidetostar00menz_0/page/391 }}</ref> to 11.83
| abs_magnitude=6.33<ref name="jpldata" />
| albedo=0.18<ref name=VLT/><br />0.118<ref name="jpldata" />
| angular_size = 0.23" <!-- Horizons 2012-Dec-24 --> to 0.071"
| single_temperature=''max:'' 282 K (+9&nbsp;°C)<ref name="Lim05">L. F. Lim et al., ''Thermal infrared (8–13 μm) spectra of 29 asteroids: the Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) Survey'', Icarus Vol. 173, p. 385 (2005).</ref>
}}

'''9 Metis''' is one of the larger [[main-belt]] [[asteroid]]s. It is composed of [[silicate]]s and [[metal]]lic [[nickel]]-[[iron]], and may be the core remnant of a large asteroid that was destroyed by an ancient collision.<ref name="Kelley00">{{cite journal
  |last=Kelley |first=Michael S
  |author2=Michael J. Gaffey
  |title=9 Metis and 113 Amalthea: A Genetic Asteroid Pair
  |journal=Icarus
  |volume=144 |issue=1 |pages=27–38 |date=2000
  |doi=10.1006/icar.1999.6266 |bibcode=2000Icar..144...27K}}</ref> Metis is estimated to contain just under half a percent of the total mass of the asteroid belt.<ref name="Baer">
{{cite web
  |date=2010
  |title=Recent Asteroid Mass Determinations
  |publisher=Personal Website
  |author=Jim Baer
  |url=http://home.earthlink.net/~jimbaer1/astmass.txt
  |access-date=13 February 2011
  |archive-url=https://web.archive.org/web/20130702212735/http://home.earthlink.net/~jimbaer1/astmass.txt
  |archive-date=2 July 2013
  |url-status=dead
  }}
</ref>

==Discovery and naming==
[[Image:Moon and Asteroids 1 to 10.svg|thumb|left|The first 10 asteroids profiled against Earth's [[Moon]]. 9 Metis is second from right.]]

Metis was discovered by [[Andrew Graham (astronomer)|Andrew Graham]] on 25 April 1848, at [[Markree Observatory]] in Ireland; it was his only asteroid discovery.<ref>Graham, A.; [http://adsabs.harvard.edu/abs/1848MNRAS...8..146G ''New Planet''], Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 6 (dated 14 April 1848!), p. 146 (signed 29 April 1848; the discovery was first announced on 27 April)</ref> It also has been the only asteroid to have been discovered as a result of observations from Ireland until 7 October 2008, when, 160 years later, Dave McDonald from observatory J65 discovered (281507) 2008 TM<sub>9</sub>.<ref name="Ireland">{{cite web |date=10 October 2008 |title=Amateur Astronomer Becomes Second Ever to Discover Asteroid from Ireland, After 160 Years |publisher=International Year of Astronomy in Ireland |url=http://astronomy2009.ie/news/second_irish_amateur_astron.html |access-date=2 March 2009|archive-url=https://web.archive.org/web/20110721122044/http://astronomy2009.ie/news/second_irish_amateur_astron.html|archive-date=21 July 2011}}</ref> Its name comes from the mythological [[Metis (mythology)|Metis]], a [[Titan (mythology)|Titaness]] and [[Oceanid]], daughter of [[Tethys (mythology)|Tethys]] and [[Oceanus]].<ref>Graham, A.; [http://adsabs.harvard.edu/abs/1848MNRAS...8..148. ''Metis''], Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 7 (dated 12 May 1848), pp. 147–150</ref> The name ''Thetis'' was also considered and rejected (it would later devolve to [[17 Thetis]]).

The historical symbol for Metis was an eye with a star above it. It is in the pipeline for [[Unicode]] 17.0 as U+1CEC3 𜻃 ([[File:Metis symbol (fixed width).svg|12px]]).<ref name=astunicode>{{cite web |url=https://www.unicode.org/L2/L2023/23207-historical-asteroids.pdf |title=Unicode request for historical asteroid symbols |last1=Bala |first1=Gavin Jared |last2=Miller |first2=Kirk |date=18 September 2023 |website=unicode.org |publisher=Unicode |access-date=26 September 2023 |quote=}}</ref><ref name=pipeline>{{cite web |url=https://unicode.org/alloc/Pipeline.html |title=Proposed New Characters: The Pipeline |author=Unicode |date= |website=unicode.org |publisher=The Unicode Consortium |access-date=6 November 2023 |quote=}}</ref>

==Characteristics==
[[file:9Metis (Lightcurve Inversion).png|thumb|[[Lightcurve]]-based 3D-model of Metis]]
Metis's direction of rotation is unknown at present, due to ambiguous data. Lightcurve analysis indicates that the Metidian pole points towards either [[ecliptic coordinate system|ecliptic coordinates]] (β, λ) = (23°, 181°) or (9°, 359°) with a 10° uncertainty.<ref name="Torppa03">J. Torppa et al., [http://www.rni.helsinki.fi/~mjk/thirty.pdf ''Shapes and rotational properties of thirty asteroids from photometric data''], Icarus Vol. 164, p. 346 (2003).</ref> The equivalent [[equatorial coordinate system|equatorial coordinates]] are (α, δ) = (12.7 h, 21°) or (23.7 h, 8°). This gives an [[axial tilt]] of 72° or 76°, respectively.{{Citation needed|date=June 2007}}

[[Hubble Space Telescope]] images<ref name="Hubble05">A. D. Storrs et al., ''A closer look at main-belt asteroids 1: WF/PC images'', Icarus Vol. 173, p. 409 (2005).</ref><ref name="Hubble99">[http://web.media.mit.edu/~win/hstpub.pdf Hubble Space Telescope observations] {{webarchive|url=https://web.archive.org/web/20081030022816/http://web.media.mit.edu/~win/hstpub.pdf |date=30 October 2008 }}</ref> and lightcurve analyses<ref name="Torppa03" /> are in agreement that Metis has an irregular elongated shape with one pointed and one broad end.<ref name="Torppa03" /><ref name="Hubble99" /> Radar observations suggest the presence of a significant flat area,<ref name="Mitchell95">D. L. Mitchell et al., ''Radar Observations of Asteroids 7 Iris, 9 Metis, 12 Victoria, 216 Kleopatra, and 654 Zelinda'', Icarus Vol. 118, p. 105 (1995).</ref> in agreement with the shape model from lightcurves.

The Metidian surface composition has been estimated as 30–40% metal-bearing [[olivine]] and 60–70% [[Nickel|Ni]]-[[Iron|Fe]] metal.<ref name="Kelley00" />

[[Light curve]] data on Metis led to an assumption that it could have a [[natural satellite|satellite]]. However, subsequent observations failed to confirm this.<ref>[http://www.bdl.fr/observateur/binast/binary_ast.php research at IMCCE] {{webarchive|url=https://web.archive.org/web/20020612093733/http://www.bdl.fr/observateur/binast/binary_ast.php |date=12 June 2002 }} (in French)</ref><ref>[http://www.johnstonsarchive.net/astro/asteroidmoonsq.html "other" reports of asteroid companions]</ref> Later searches with the [[Hubble Space Telescope]] in 1993 found no satellites.<ref name="Hubble99" />

==Family relationships==
Metis was once considered to be a member of an [[asteroid family]] known as the Metis family,<ref name="Williams92">J. G. Williams, ''Asteroid Families – An Initial Search'', Icarus Vol. 96, p. 251 (1992).</ref> but more recent searches for prominent families did not recognize any such group, nor is a clump evident in the vicinity of Metis by visual inspection of [[proper orbital elements|proper orbital element]] diagrams.

However, a spectroscopic analysis found strong spectral similarities between Metis and [[113 Amalthea]], and it is suggested that these asteroids may be remnants of a very old (at least ~1 [[giga-annum|Ga]]) dynamical family whose smaller members have been pulverised by collisions or perturbed away from the vicinity. The putative parent body is estimated to have been 300 to 600&nbsp;km in diameter ([[4 Vesta|Vesta]]-sized) and [[planetary differentiation|differentiated]].<ref name="Kelley00" /> Metis would be the relatively intact core remnant (though smaller than [[16 Psyche]]), and Amalthea a fragment of the mantle, with 90% of the original body unaccounted for.<ref name="Kelley00" /> Coincidentally, both Metis and Amalthea have namesakes among [[Jupiter's inner moons]].

==Occultations==
In 1984 an occultation of a star produced seven [[Chord (astronomy)|chords]] that Kristensen used to derive an ellipsoidal profile of 210×170&nbsp;km.<ref name="occult">{{cite journal
  |last1=Kissling |first1=W.M
  |last2=Blow |first2=G. L.
  |last3=Allen |first3=W. H.
  |last4=Priestley |first4=J.
  |last5=Riley |first5=P.
  |last6=Daalder |first6=P.
  |last7=George |first7=M.
  |title=The Diameter of 9 Metis from the Occultation of SAO:190531
  |journal=Proceedings of the Astronomical Society of Australia
  |volume=9 |pages=150–152 |date=1991
  |issue=1
 |bibcode=1991PASA....9..150K
|doi=10.1017/S1323358000025352
 |s2cid=117689158
 }}</ref> On 6 August 1989, Metis occulted a [[apparent magnitude|magnitude]] 8.7 star producing five chords suggesting a diameter of 173.5&nbsp;km.<ref name="occult" /> Observations of an occultation on 11 February 2006, produced only two chords indicating a minimum diameter 156&nbsp;km.<ref name="RASNZ">{{cite web
 |title       = Occultation of TYC 0862-00695-1 by (9) Metis 2006 February 11
 |publisher   = Royal Astronomical Society of New Zealand
 |url         = http://occsec.wellington.net.nz/planet/2006/results/060211_Metis.htm
 |access-date  = 6 December 2008
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20080827155624/http://occsec.wellington.net.nz/planet/2006/results/060211_Metis.htm
 |archive-date = 27 August 2008
 |df          = dmy-all
}} [http://occsec.wellington.net.nz/planet/2006/results/060211_Metis_PlotColour.gif (Chords)] {{webarchive|url=https://web.archive.org/web/20110724205049/http://occsec.wellington.net.nz/planet/2006/results/060211_Metis_PlotColour.gif |date=24 July 2011 }}</ref> All three of these occultations fit the ellipsoid 222×182×130&nbsp;km suggested by Baer.<ref name="Baer" />

On 7 March 2014, Metis occulted the star HIP 78193 ([[Magnitude (astronomy)|magnitude]] 7.9) over parts of Europe and the Middle East.<ref>[http://www.asteroidoccultation.com/2014_03/0307_9_32274.htm Asteroid Occulations] {{webarchive|url=https://web.archive.org/web/20140306184634/http://www.asteroidoccultation.com/2014_03/0307_9_32274.htm |date=6 March 2014 }}</ref><ref>[http://www.asteroidoccultation.com/2014_03/0307_9_32274_MapE.gif Map] {{webarchive|url=https://web.archive.org/web/20140306185840/http://www.asteroidoccultation.com/2014_03/0307_9_32274_MapE.gif |date=6 March 2014 }}</ref>

==See also==
* [[List of former planets]]
* [[Comet seeker]]

== Notes ==
{{notelist}}

== References ==
{{Reflist|30em}}

== External links ==
* [http://www.rni.helsinki.fi/~mjk/thirty.pdf shape model deduced from lightcurve]
* [http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000146.000.html "Notice of discovery of Metis", MNRAS '''8''' (1848) 146]
* [https://web.archive.org/web/20040823231519/http://www.eaas.co.uk/news/metis.html Irish Astronomical History: Markree Castle Observatory and The Discovery of the Asteroid Metis]
* [http://ssd.jpl.nasa.gov/horizons.cgi?find_body=1&body_group=sb&sstr=9 JPL Ephemeris]
* {{cite web |title=Elements and Ephemeris for (9) Metis |publisher=Minor Planet Center |url=http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00009 |url-status=dead |archive-url=https://web.archive.org/web/20160304051845/http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=b2011&o=00009 |archive-date=4 March 2016  }} (displays [[Elongation (astronomy)|Elong]] from Sun and [[apparent magnitude|V mag]] for 2011)
* [http://www.astrode.de/metis2014d.htm Globe of 9 Metis]
* {{AstDys|9}}
* {{JPL small body}}

{{Minor planets navigator|8 Flora|number=9|10 Hygiea}}
{{Small Solar System bodies}}
{{Authority control}}

{{DEFAULTSORT:000009}}
[[Category:Flora asteroids]]
[[Category:Discoveries by Andrew Graham (astronomer)|Metis]]
[[Category:Named minor planets|Metis]]
[[Category:S-type asteroids (Tholen)]]
[[Category:Astronomical objects discovered in 1848|18480425]]