Editing Hyperion (moon) (section)

== Physical characteristics ==
[[File:NotSoHyperHyperion.jpg|thumb|Saturn VII Hyperion compared to [[Ceres (dwarf planet)|Ceres]] and the [[Moon]]<ref name="Thomas2010" />]]

=== Shape ===
Hyperion is one of the largest bodies known to be highly irregularly shaped (non-ellipsoidal, i.e. not in [[hydrostatic equilibrium]]) in the [[Solar System]].<ref name="nb larger objects" group="lower-alpha"/> The only larger moon known to be irregular in shape is Neptune's moon [[Proteus (moon)|Proteus]]. Hyperion has about 15% of the mass of [[Mimas (moon)|Mimas]], the least massive known ellipsoidal body. The largest [[Impact crater|crater]] on Hyperion is approximately {{convert|121.57|km|mi|abbr=on}} in diameter and {{convert|10.2|km|mi|abbr=on}} deep. A possible explanation for the irregular shape is that Hyperion is a fragment of a larger body that was broken up by a large impact in the distant past.<ref name="Matthews1992">
{{cite journal
 |author=R.A.J. Matthews
 |date=1992
 |title=The Darkening of Iapetus and the Origin of Hyperion
 |journal=[[Quarterly Journal of the Royal Astronomical Society]]
 |volume=33 |pages=253–258
 |bibcode=1992QJRAS..33..253M
}}</ref> A proto-Hyperion could have been {{convert|350|–|1000|km|mi|abbr=on}} in diameter (which ranges from a little below the size of Mimas to a little below the size of [[Tethys (moon)|Tethys]]).<ref name=Farinella1997>{{cite journal
  |last=Farinella |first=P.
  |author2=Marzari, F. |author3=Matteoli, S.
   |title=The Disruption of Hyperion and the Origin of Titan's Atmosphere
  |journal=Astronomical Journal
  |volume=113 |issue=2 |pages=2312–2316 |date=1997
  |doi=10.1086/118441
  |bibcode=1997AJ....113.2312F
  |doi-access=free}}</ref> Over about 1,000&nbsp;years, ejecta from a presumed Hyperion breakup would have impacted [[Titan (moon)|Titan]] at low speeds, building up [[Volatile (astrogeology)|volatiles]] in the [[atmosphere of Titan]].<ref name="Farinella1997" />

=== Composition ===
[[File:Hyperion in natural colours.jpg|195px|thumb|right|True-color image of Hyperion, taken by the [[Cassini spacecraft|''Cassini'' spacecraft]]]]
Like most of [[Saturn's natural satellites|Saturn's moons]], Hyperion's low [[density]] indicates that it is composed largely of water ice with only a small amount of rock. It is thought that Hyperion may be similar to a loosely accreted [[Rubble pile|pile of rubble]] in its physical composition. However, unlike most of Saturn's moons, Hyperion has a low [[albedo]] (0.2–0.3), indicating that it is covered by at least a thin layer of dark material. This may be material from [[Phoebe (moon)|Phoebe]] (which is much darker) that got past [[Iapetus (moon)|Iapetus]]. Hyperion is redder than Phoebe and closely matches the color of the dark material on Iapetus.

Hyperion has a [[porosity]] of about 0.46.<ref name="Thomas2007" /> Although Hyperion is the eighth-largest moon of Saturn, it is only the ninth-most massive. [[Phoebe (moon)|Phoebe]] has a smaller radius, but it is more massive than Hyperion and thus denser.<ref name="Thomas2010" />

=== Surface features ===

{{See also|List of geological features on Hyperion}}

''[[Voyager 2]]'' passed through the Saturn system, but photographed Hyperion only from a distance. It discerned individual craters and an enormous ridge, but was not able to make out the texture of Hyperion's surface. Early images from the ''[[Cassini–Huygens|Cassini]]'' orbiter suggested an unusual appearance, but it was not until ''Cassini'''s first targeted flyby of Hyperion on 25 September 2005 that Hyperion's oddness was revealed in full.

Hyperion's surface is covered with deep, sharp-edged [[impact crater|crater]]s that give it the appearance of a giant sponge. Dark material fills the bottom of each crater. The reddish substance contains long chains of [[carbon]] and [[hydrogen]] and appears very similar to material found on other Saturnian satellites, most notably [[Iapetus (moon)|Iapetus]]. Scientists attribute Hyperion's unusual, sponge-like appearance to the fact that it has an unusually low density for such a large object. Its low density makes Hyperion quite porous, with a weak surface gravity. These characteristics mean impactors tend to compress the surface, rather than excavating it, and most material that is blown off the surface never returns.<ref name="next2015"/>

The latest analyses of data obtained by ''Cassini'' during its flybys of Hyperion in 2005 and 2006 show that about 40 percent of it is empty space. It was suggested in July 2007 that this [[porosity]] allows craters to remain nearly unchanged over the eons. The new analyses also confirmed that Hyperion is composed mostly of water ice with very little rock.<ref>
{{cite web
 |title=Key to Giant Space Sponge Revealed
 |url=http://www.space.com/scienceastronomy/070704_sponge_moon.html
 |work=[[Space.com]]
 |date=4 July 2007
 |access-date=October 26, 2007
}}</ref>

=== Static charge ===
Hyperion's surface is electrically charged and was the first discovered to be so other than the [[Moon]]'s surface.<ref>{{Cite web |last= |title=Cassini Caught in Hyperion's Particle Beam |url=https://www.jpl.nasa.gov/news/cassini-caught-in-hyperions-particle-beam |access-date=2024-02-19 |website=www.jpl.nasa.gov |publisher=NASA Jet Propulsion Laboratory (JPL) |language=en-US}}</ref>