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Line 1: − + + + + + + + + + + + + + + + + + + + + + + + − + − Hyperion is one of the largest highly irregular (non-spherical) bodies in the [[solar system]] (second to [[Proteus (moon)|Proteus]]). The largest [[crater]] on Hyperion is approximately 121.57 km in diameter and 10.2 km deep. A possible explanation for the irregular morphology is that Hyperion is a fragment of a larger body that was broken by a large impact in the distant past, an event which has been linked to the enigmatic darkening of [[Iapetus (moon) |Iapetus]].<ref name="Matthews1992">Robert A. J. Matthews; [http://adsabs.harvard.edu/abs/1992QJRAS..33..253M ''The Darkening of Iapetus and the Origin of Hyperion''], Quarterly Journal of the Royal Astronomical Society, Vol. 33 (September 1992), pp. 253–258</ref>+ − ==Name==+ − The moon is named after [[Hyperion (mythology)|Hyperion]], a [[Titan]] in [[Greek mythology]]. It is also designated '''Saturn VII'''. The adjectival form of the name is ''Hyperionian''. − Hyperion's discovery came shortly after [[John Herschel]] had suggested names for the seven previously-known satellites of Saturn in his 1847 publication ''Results of Astronomical Observations made at the Cape of Good Hope''.<ref>As reported by William Lassell, [http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000042.000.html Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 3, pp. 42–43] [[1848]] [[January 14]])</ref> [[William Lassell|Lassell]], who saw Hyperion two days after [[William Cranch Bond|Bond]], had already endorsed [[John Herschel|Herschel]]'s naming scheme and suggested the name Hyperion in accordance with it.<ref>Lassell, W.; [http://adsabs.harvard.edu//full/seri/MNRAS/0008//0000195.000.html ''Discovery of a New Satellite of Saturn''], Monthly Notices of the Royal Astronomical Society, Vol. 8, No. 9 (November 1848), pp. 195–197</ref> He also beat Bond to publication.<ref>Bond, W. C.; [http://adsabs.harvard.edu//full/seri/MNRAS/0009//0000001.000.html ''Discovery of a new satellite of Saturn''], Monthly Notices of the Royal Astronomical Society, Vol. 9, No. 1 ([[November 10]], [[1848]]) pp. 1–2</ref>+ − + − + + + + + + + + + + + + + + + + + + + + +
Expansion and original writing.
'''Hyperion''' is a [[moon]] of [[Saturn]] discovered by William Cranch Bond, George Phillips Bond and William Lassell in 1848. It is distinguished by its irregular shape, its chaotic rotation, and its unexplained sponge-like appearance.
{{Planet
|image=Hyperion2 cassini big.jpg
|caption=False-color image of Hyperion's sponge-like surface, taken by spacecraft [[Cassini Huygens mission|Cassini]]
|date=September 16, 1848<ref name=Bond>Bond, W. C. "[http://adsabs.harvard.edu//full/seri/MNRAS/0009//0000001.000.html Discovery of a new Satellite of Saturn]." ''Monthly Notices of the Royal Astronomical Society'', 9:1, November 10, 1848. Accessed June 9, 2008.</ref>
|discname=William Cranch Bond<ref name=usgs>"[http://planetarynames.wr.usgs.gov/append7.html Gazetteer of Planetary Nomenclature: Planetary Body Names and Discoverers]." US Geological Survey, Jennifer Blue, ed. March 31, 2008. Accessed May 9, 2008.</ref>
|origname=Member of the Titans, per an earlier suggestion by Sir John Herschel as reported by William Lassell<ref name=Bond/><ref name=Lassell1>Lassell, William. "[http://articles.adsabs.harvard.edu//full/seri/MNRAS/0008//0000043.000.html Satellites of Saturn]." ''Monthly Notices of the Royal Astronomical Society'', 8:42-43, 1848. Accessed June 9, 2008.</ref>
|primary=Saturn
|order=21
|periapsis=1,326,769 km<ref name=calc>Calculated</ref>
|apoapsis=1,635,431 km<ref name=calc/>
|semimajor=1,481,100 km<ref name=saturnsatfact>Williams, David R. "[http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html Saturnian Satellite Fact Sheet]." National Space Science Data Center, [[National Aeronautics and Space Administration|NASA]], November 23, 2007. Accessed June 4, 2008.</ref>
|eccentricity=0.1042<ref name=saturnsatfact/>
|sidereal=21.276609 da<ref name=saturnsatfact/>
|orbitspeed=5.07 km/s<ref name=Hamilton>Hamilton, Calvin J. "[http://www.solarviews.com/eng/hyperion.htm Entry for Hyperion]." ''Views of the Solar System'', 2001. Accessed June 9, 2008.</ref>
|inclination=0.43°<ref name=saturnsatfact/>
|mass=5.5 * 10<sup>18</sup> kg<ref name=saturnsatfact/>
|density=570 kg/m³<ref name=saturnsatfact/>
|meanradius=133 km<ref name=ssdphys>"[http://ssd.jpl.nasa.gov/?sat_phys_par Planetary Satellite Physical Parameters]." [[Jet Propulsion Laboratory|JPL]], [[National Aeronautics and Space Administration|NASA]]. Retrieved June 9, 2008.</ref>
|escapespeed=0.107 km/s<ref name=Hamilton/>
|composition=Water ice and little rock<ref name=Britannica>"[http://www.britannica.com/eb/article-9041800 Hyperion]." Encyclopædia Britannica. 2008. Encyclopædia Britannica Online. 9 June 2008.</ref>
|color=reddish rose tan
|albedo=0.3<ref name=saturnsatfact/><ref name=Hamilton/><ref name=Britannica/>
}}'''Hyperion''', or '''Saturn VII''', is the eighth [[moon]] of [[Saturn]] to be discovered, and the largest irregularly shaped body in the [[Solar system]]. ([[Proteus]], moon of [[Neptune]], is heavier but has a more nearly spheroid shape.) It is also highly porous, having the appearance of a [[sponge]], and displays a chaotic rotation.
==Physical characteristics==
== Discovery and naming ==
[[William Cranch Bond]] and [[George Phillips Bond]] first noticed Hyperion as a faint object in Saturn's ring plane, between the moons [[Titan]] and [[Iapetus]]. In the course of several days, the Bonds saw this object again, and it was clearly keeping station with Saturn at the time of Saturn's apparent retrograde motion. They determined its sidereal month with remarkable accuracy and reported their findings in the ''Monthly Notices''.<ref name=Bond/>
Independently of them, [[William Lassell]] first observed Hyperion on September 18, 1848. He was searching for Iapetus and found two objects, Iapetus and another, much fainter object. The next day, the faint object had appeared to approach Saturn, while the other object had not. Lassell was satisfied that the brighter object was Iapetus and determined that he had discovered a new object.<ref name=Lassell2>Lassell, William. "[http://articles.adsabs.harvard.edu/full/seri/MNRAS/0008//0000195.000.html Discovery of a new Satellite of Saturn]." ''Monthly Notices of the Royal Astronomical Society'', 8(9):195, November 1848. Accessed June 9, 2008.</ref>
Sir [[John Herschel]] had earlier suggested a naming convention for the seven satellites of Saturn already discovered. Lassell and the Bonds independently selected Hyperion as the name of the new object, in accordance with that convention.
==References==
== Orbital characteristics ==
<references/>
[Image:Hyperion true color.jpg|150px|left]]Hyperion is in a slightly eccentric orbit around Saturn and participates in a 4:3 orbital resonance with [[Titan]]. Its sidereal day is about 21.28 [[earth]] days.<ref name=Britannica/><ref name=planetsoc>"[http://www.planetary.org/explore/topics/saturn/hyperion.html Hyperion, Chaotic Moon]." The Planetary Society. Accessed June 9, 2008.</ref> Many astronomers believe that the 4:3 resonance with Titan is responsible for the eccentricity of Hyperion's orbit.<ref name=Britannica/>
== Rotational characteristics ==
Hyperion's rotation is chaotic and nearly unpredictable.<ref name=Wisdom>J. Wisdom, S.J. Peale, F. Mignard. "[http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-47313KS-YY&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=d42f224c66e0051b451986d67951aca5 The chaotic rotation of Hyperion]". (IAU, COSPAR, NASA, et al., Colloquium on Natural Satellites, 77th, Cornell University, Ithaca, NY, July 5-9, 1983) ''Icarus'' (ISSN 0019-1035) 58: 137-152. {{doi|0.1016/0019-1035(84)90032-0}} Accessed June 9, 2008.</ref> Astronomers cite a number of factors, including the 4:3 orbital resonance with Titan, to account for this.<ref name=Britannica/><ref name=Arnett>Arnett, Bill. "[http://www.nineplanets.org/hyperion.html Entry for Hyperion]." ''The <s>Nine</s> 8 Planets'', July 12, 2007. Accessed June 9, 2008.</ref><ref name=Piazza>Piazza, Eric. "[http://saturn.jpl.nasa.gov/science/moons/moonDetails.cfm?pageID=6 Cassini-Huygens: Moons: Hyperion]." November 3, 2006, Accessed June 9, 2008.</ref>
== Physical characteristics ==
Hyperion has an irregular shape, with dimensions 185 x 140 x 113 km.<ref name=saturnsatfact/> In fact it is the largest irregularly shaped body in the solar system. [[Proteus]], moon of [[Neptune]], is often cited as a larger irregular body, but in fact Proteus is not irregular and is almost spherical.<ref name=Arnett/> Hyperion is also highly porous, with a density only 57% of that of [[water]].<ref name=saturnsatfact/>
=== Surface ===
[[Image:Hyperion Meri green.jpg|thumb|150px|left|Hyperion in color enhancement]]Hyperion has craters that cover its surface completely, making it spongiform in appearance.<ref name=Thomas>Thomas, P. C.; et al. (2007). "[http://www.nature.com/nature/journal/v448/n7149/abs/nature05779.html;jsessionid=8884731760421E844AF551ABA6E2527F Hyperion's sponge-like appearance]". Nature 448: 50-56. {{doi|10.1038/nature05779}}. Accessed June 9, 2008.</ref> Those craters are remarkably well preserved, primarily on account of Hyperion's low density. The largest crater on Hyperion has a diameter of 120 km and a depth of 10 km.<ref name=Piazza/>
Hyperion is one of the least reflective of Saturn's moons, with an albedo of 30%. Many astronomers believe that Hyperion is covered with dark material that comes from [[Phoebe]], an outer moon.<ref name=Hamilton/> Recent data from the [[Cassini Huygens mission|Cassini]] probe indicates that this material consists of hydrocarbons.<ref name=scidaily>NASA/Ames Research Center. "[http://www.sciencedaily.com/releases/2007/07/070705125818.htm Hydrocarbons, Necessary For Life, Found On Saturn's Moon Hyperion]." ''ScienceDaily'' 6 July 2007. Accessed 9 June 2008.</ref>
The favorite theory of the origin of Hyperion is that it is a fragment of a larger body that suffered a collision.<ref name=Piazza/><ref name=Arnett/> At least one astronomer speculated that debris from this collision contributed to the dark material that covers the Cassini Region of [[Iapetus]].<ref name=Matthews>Matthews, Robert A. J. "[http://adsabs.harvard.edu/abs/1992QJRAS..33..253M The Darkening of Iapetus and the Origin of Hyperion]." ''Quarterly Journal of the Royal Astronomical Society'', 33:253–258, September 1992. Accessed June 9, 2008.</ref>
== Observation and Exploration ==
Hyperion was under observation for centuries, but only with modern rocket probes has detailed examination been possible. The first such probe to make rendezvous with Hyperion was [[Voyager 2]], on August 24, 1981. The best examination of Hyperion to date was by the Cassini spacecraft, which made rendezvous with Hyperion on September 26, 2005 and took the remarkable images of its spongiform surface.
== References ==
{{reflist|2}}
{{Solarsystem}}
[[Category:Astronomy]]
[[Category:Astronomy]]