Editing Tethys (moon) (section)

== Physical characteristics ==
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[[File:Map of Tethys PIA 14931 Jun 2012.jpg|thumb|left|300px|Tethys basemap (trailing hemisphere on the right)]]
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[[File:Tethys_size_corrected.png|left|thumb|Size comparison between Tethys(lower left), the [[Moon]] (upper left) and Earth]]
Tethys is the [[List of moons|16th-largest moon]] in the [[Solar System]], with a radius of 531&nbsp;km.{{sfn|Roatsch Jaumann et al.|2009|p=765|loc=Tables 24.1–2}} Its mass is about {{val|6.17|e=20|u=kg}} (0.000103 Earth mass),<ref name="Jacobson2022"/> which is less than 1% of the [[Moon]]. Despite its relatively small mass, it is more massive than all known moons smaller than itself combined.<ref>{{Cite web |last=Williams |first=Matt |date=23 October 2015 |title=Saturn's Moon Tethys |url=https://www.universetoday.com/15430/saturns-moon-tethys/ |access-date=14 November 2023 |website=Universe Today |language=en-US}}</ref>

The density of Tethys is 0.98&nbsp;g/cm<sup>3</sup>, indicating that it is composed almost entirely of water-ice.{{sfn|Thomas Burns et al.|2007}}
It is also the fifth-largest of Saturn's moons.
It is not known whether Tethys is differentiated into a rocky core and ice [[mantle (geology)|mantle]]. However, if it is differentiated, the radius of the core does not exceed 145&nbsp;km, and its mass is below 6% of the total mass. Due to the action of tidal and rotational forces, Tethys has the shape of [[triaxial ellipsoid]]. The dimensions of this ellipsoid are consistent with it having a homogeneous interior.{{sfn|Thomas Burns et al.|2007}} The existence of a subsurface ocean—a layer of liquid salt water in the interior of Tethys—is considered unlikely.{{sfn|Hussmann Sohl et al.|2006}}

The surface of Tethys is one of the most reflective (at visual wavelengths) in the Solar System, with a visual albedo of 1.229. This very high albedo is the result of the sandblasting of particles from Saturn's E-ring, a faint ring composed of small, water-ice particles generated by [[Enceladus]]'s south polar geysers.{{sfn|Verbiscer French et al.|2007}} The radar albedo of the Tethyan surface is also very high.{{sfn|Ostro West et al.|2006}} The leading hemisphere of Tethys is brighter by 10–15% than the trailing one.{{sfn|Filacchione Capaccioni et al.|2007}}

The high albedo indicates that the surface of Tethys is composed of almost pure water ice with only a small amount of darker materials. The visible spectrum of Tethys is flat and featureless, whereas in the [[near-infrared]] strong water ice absorption bands at 1.25, 1.5, 2.0 and 3.0&nbsp;μm wavelengths are visible.{{sfn|Filacchione Capaccioni et al.|2007}} No compound other than crystalline water ice has been unambiguously identified on Tethys.{{sfn|Jaumann Clark et al.|2009|pp=651–654}} (Possible constituents include [[Organic compound|organics]], [[ammonia]] and [[carbon dioxide]].) The dark material in the ice has the same spectral properties as seen on the surfaces of the dark Saturnian moons—[[Iapetus (moon)|Iapetus]] and [[Hyperion (moon)|Hyperion]]. The most probable candidate is [[nanophase]] iron or [[hematite]].{{sfn|Jaumann Clark et al.|2009|pp=654–656}} Measurements of the [[thermal emission]] as well as radar observations by the Cassini spacecraft show that the icy [[regolith]] on the surface of Tethys is structurally complex{{sfn|Ostro West et al.|2006}} and has a large [[porosity]] exceeding 95%.{{sfn|Carvano Migliorini et al.|2007}}

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| caption     = {{center|Enhanced-color maps<br/>northern and southern hemispheres}}
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{{Gallery |align=center |width=180
|File:PIA19638-Tethys-SaturnMoon-TrailingHemisphere-Standard-20150411.jpg|{{center|Tethys—Trailing hemisphere—Standard processing<br/>(11 April 2015).}}
|File:PIA19638-Tethys-SaturnMoon-TrailingHemisphere-Enhanced-20150411.jpg|{{center|Tethys—Trailing hemisphere—Enhanced processing<br/>(11 April 2015).}}
|File:PIA19636-SaturnMoon-Tethys-Cassini-20150411.jpg|{{center|Tethys—Trailing hemisphere—Enhanced-color<br/>(11 April 2014)}}}}