View source for Metis (moon)

{{Short description|Moon of Jupiter}}
{{Distinguish|9 Metis}}
{{Infobox planet
| name = Metis
| image = Metis.jpg
| caption = Image taken by ''[[Galileo (spacecraft)|Galileo]]'''s [[Galileo (spacecraft)#Solid-state imager (SSI)|Solid State Imager]] between November 1996 and June 1997
| pronounced = {{IPAc-en|ˈ|m|iː|t|ɪ|s}}<ref>{{cite book|author=Noah Webster|year=188|title=A Practical Dictionary of the English Language}}</ref> 
| adjective = Metidian, Metidean {{IPAc-en|m|ɛ|ˈ|t|ɪ|d|i|ə|n}}
| named_after = [[Metis (mythology)|Μήτις]] ''Mētis''
| discoverer = [[Stephen Synnott|S. Synnott]]
| discovered = 4 March 1979
| mean_orbit_radius = {{val|128000|u=km}} (1.792 R<sub>J</sub>){{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| eccentricity = {{val|0.0002}}{{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| period = {{val|0.294780|u=d}} {{nowrap|(7 h, 4.5 min)}}{{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| periapsis = {{val|127974|u=km}}{{efn|name=calculated}}
| apoapsis = {{val|128026|u=km}}{{efn|name=calculated}}
| avg_speed = 31.501 km/s{{efn|name=calculated}}
| inclination = 0.06° (to Jupiter's equator){{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}
| satellite_of = [[Jupiter]]
| physical_ref = {{sfn|Thomas Burns et al.|1998}}
| mean_radius = {{val|21.5|2.0|u=km}}
| dimensions = {{val|60|x|40|x|34|u=km}}
| volume = ≈&thinsp;{{val|42700|u=km<sup>3</sup>}}{{efn|name=calculated}}
| surface_area = ≈&thinsp;{{val|6200|u=km2}}{{efn|name=calculated}}
| mass = ≥{{val|6.4|e=16|u=kg}}{{efn|name=calculated}}
| density = ≥{{val|1.5|u=g/cm3}}
| surface_grav = ≥{{val|0.8|u=cm/s2}} (average)
| escape_velocity = 
| rotation = [[synchronous rotation|synchronous]]
| axial_tilt = zero
| albedo = {{val|0.061|0.003}}{{sfn|Simonelli Rossier et al.|2000}}
| single_temperature = ≈&thinsp;123 K
}}

'''Metis''' {{IPAc-en|ˈ|m|iː|t|ɪ|s}}, also known as '''{{nowrap|Jupiter XVI}}''', is the [[Jupiter's inner moons|innermost]] known [[moon of Jupiter]]. It was discovered in 1979 in images taken by ''[[Voyager 1]]'', and was named in 1983 after the Titaness [[Metis (mythology)|Metis]], the first wife of [[Zeus]] and the mother of [[Athena]]. Additional observations made between early 1996 and September 2003 by the [[Galileo spacecraft|''Galileo'' spacecraft]] allowed its surface to be imaged.

Metis is [[tidally locked]] to [[Jupiter]], and its shape is strongly asymmetrical, with the largest diameter being almost twice as large as the smallest one. It is also one of the two moons known to orbit Jupiter in less than the length of Jupiter's day, the other being [[Adrastea (moon)|Adrastea]]. It orbits within the [[Rings of Jupiter#Main ring|main ring of Jupiter]], and is thought to be a major contributor of ring material.

== Discovery and observations ==
[[File:Metis ontdekking.gif|thumb|left|''Voyager 1'' discovery image of Metis on 4 March 1979, showing the moon's tiny silhouette against the backdrop of Jupiter's clouds]]

Metis was discovered in 1979 by [[Stephen P. Synnott]] in images taken by the ''[[Voyager 1]]'' probe and was [[provisional designation|provisionally designated]] as '''{{nowrap|S/1979 J 3}}'''.{{sfn|IAUC 3507}}{{sfn|Synnott|1981}} In 1983, it was officially named after the mythological [[Metis (mythology)|Metis]], a [[Titan (mythology)|Titaness]] who was the first wife of [[Zeus]] (the [[Greek mythology|Greek]] prototype for the [[Roman mythology|Roman god]] [[Jupiter (mythology)|Jupiter]]) who between her and Zeus bore a daughter, [[Athena]].{{sfn|IAUC 3872}} The photographs taken by ''Voyager 1'' showed Metis only as a dot, and hence knowledge about Metis was very limited until the arrival of the [[Galileo spacecraft|''Galileo'' spacecraft]]. ''Galileo'' imaged almost all of the surface of Metis and put constraints on its composition by 1998.{{sfn|Thomas Burns et al.|1998}}

== Physical characteristics ==
[[File:Metis moon.jpg|thumb|Metis imaged by [[Galileo (spacecraft)|''Galileo'']] on 4 January 2000]]

Metis has an irregular shape and measures {{val|60|x|40|x|34|u=km}} across, which makes it the second smallest of the four [[inner satellites of Jupiter]].{{sfn|Thomas Burns et al.|1998}} Therefore, a very rough estimate of its surface area could be placed between 5,800 and 11,600 square kilometers (approx. 8,700).{{Cn|date=March 2024|reason=Where does the range in estimation come from?}} The bulk composition and mass of Metis are not known, but it is likely that its mean density is 1.5&nbsp;g/cm<sup>3</sup> or higher,{{sfn|Anderson Johnson et al.|2005}} and its mass can therefore be estimated as ~6.4×10<sup>16</sup>&nbsp;kg or higher.

The surface of Metis is heavily cratered, dark, and appears to be reddish in color{{Failed verification|date=January 2025}}. There is a substantial asymmetry between the leading and trailing [[Sphere|hemispheres]]: the leading hemisphere is 1.3 times brighter than the trailing one. The asymmetry is probably caused by the higher velocity and frequency of impacts on the leading hemisphere, which excavates a bright material (presumably ice) from its interior.{{sfn|Simonelli Rossier et al.|2000}}

== Orbit and rotation ==
Metis is the innermost of Jupiter's four small [[inner satellites of Jupiter|inner moon]]s. It orbits Jupiter at a distance of ~128,000&nbsp;km (1.79 Jupiter radii) within Jupiter's [[Rings of Jupiter#Main ring|main ring]]. Metis's orbit has very small [[orbital eccentricity|eccentricity]] (~0.0002) and [[inclination]] (~ 0.06°) relative to the equator of Jupiter.{{sfn|Evans Porco et al.|2002}}{{sfn|Burns Simonelli et al.|2004}}

Due to [[tidal locking]], Metis rotates synchronously with its orbital period (about 7 hours), with its longest axis aligned towards Jupiter.{{sfn|Burns Simonelli et al.|2004}}{{sfn|Thomas Burns et al.|1998}} Jupiter casts a shadow on all of Metis for 68 minutes each Metian day.{{efn|name=calculated}}

Metis lies inside Jupiter's [[synchronous orbit]] radius (as does [[Adrastea (moon)|Adrastea]]), and as a result, [[tidal deceleration|tidal force]]s slowly cause its orbit to decay. If its density is similar to Amalthea's, Metis's orbit lies within the fluid [[Roche limit]]; however, because it has not broken up, it must lie outside its rigid Roche limit.{{sfn|Burns Simonelli et al.|2004}}

== Relationship with Jupiter's rings ==
[[File:PIA09921 Shepherd Moons.gif|thumb|Metis orbiting at the edge of Jupiter's Main Ring, as imaged by the ''[[New Horizons]]'' spacecraft on 24 February 2007]]

Metis's orbit lies ~1,000&nbsp;km within the main ring of Jupiter. It orbits within a ~500&nbsp;km wide "gap" or "notch" in the ring.{{sfn|Burns Simonelli et al.|2004}}{{sfn|Ockert-Bell Burns et al.|1999}} The gap is clearly somehow related to the moon but the origin of this connection has not been established. Metis supplies a significant part of the main ring's dust.{{sfn|Burns Showalter et al.|1999}} This material appears to consist primarily of material that is ejected from the surfaces of [[Inner satellites of Jupiter|Jupiter's four small inner satellites]] by meteorite impacts. It is easy for the impact ejecta to be lost from the satellites into space because the satellites' surfaces lie fairly close to the edge of their [[Roche sphere]]s due to their low density.{{sfn|Burns Simonelli et al.|2004}}

== See also ==
* [[Timeline of discovery of Solar System planets and their moons]]
* [[Inner satellite]]
* [[Rings of Jupiter]]

== Notes ==
{{notes
| notes =

{{efn
| name = calculated
| Calculated on the basis of other parameters.
}}
}}

==References==

=== Citations ===
{{reflist}}

===Sources===

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== External links ==

{{Commons category|Metis (moon)}}{{Spoken Wikipedia|date=2021-01-17|En-Metis (moon)-article.ogg}}
* [https://web.archive.org/web/20071109115650/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Jup_Metis Metis Profile] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]

{{Moons of Jupiter}}
{{Portal bar|Astronomy|Stars|Spaceflight|Outer space|Solar System}}
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{{DEFAULTSORT:Metis (Moon)}}
[[Category:Moons of Jupiter]]
[[Category:Astronomical objects discovered in 1979|19790304]]
[[Category:Discoveries by Stephen P. Synnott]]
[[Category:Moons with a prograde orbit]]