View source for Odysseus (crater)

{{Short description|Massive crater on Saturn's moon Tethys}}
{{Use dmy dates|date=March 2017}}
{{Infobox feature on celestial object 
|name         = Odysseus
|titlecolor    =
|image         = Epic Odysseus (PIA12588).jpg
|caption       = Tethys, with Odysseus at the top, as imaged by ''[[Cassini (spacecraft)|Cassini]]'' on February 14, 2010
|coordinates   = {{coord|32.82|N|128.89|W|globe:tethys_type:landmark|display=inline,title}}
|coordinates_footnotes = <ref name=gpn>{{gpn|4406|Odysseus}} (Center Latitude: 32.82°, Center Longitude: 128.89°; Planetographic, +West)</ref>
|type          = Central peak impact crater
|quadrangle    = 
|diameter      = {{convert|445|km|mi|abbr=on}}<ref name=gpn/>
|depth         = 
|discoverer    = 
|eponym        = [[Odysseus]]
|location      = [[Tethys (moon)|Tethys]]
}}
'''Odysseus''' is the largest [[Impact crater|crater]] on [[Saturn]]'s [[natural satellite|moon]] [[Tethys (moon)|Tethys]]. It is 445&nbsp;km across, more than 2/5 of the moon's diameter, and is one of the [[largest craters in the Solar System]]. It is situated in the western part of the leading hemisphere of the moon—the latitude and longitude of its center are 32.8°N and 128.9°W, respectively. It is named after the [[Greek mythology|Greek]] hero [[Odysseus]] from Homer's the ''[[Iliad]]'' and the ''[[Odyssey]]''.<ref name=gpn/> Odysseus was discovered by the ''[[Voyager 2]]'' spacecraft on 1 September 1981 during its flyby of Saturn.<ref>{{cite journal| doi = 10.1126/science.215.4532.499| last1 = Stone| first1 = E. C.| last2 = Miner| first2 = E. D.| date = 29 January 1982| title = Voyager 2 Encounter with the Saturnian System| journal = Science| volume = 215| issue = 4532| pages = 499–504| pmid = 17771272| bibcode = 1982Sci...215..499S| s2cid = 33642529| url = https://authors.library.caltech.edu/43660/1/1685660.pdf}}</ref>

== Geology ==
[[File:Tethys high resolution color map and topography PIA13701.jpg|thumb|left|Enhanced-color map (''left'') and elevation map (''right''). In the elevation map, dark blue represents lower elevations and red represents higher elevations]]
The Odysseus crater is now quite flat for its size of approximately 450&nbsp;km. More precisely, its floor conforms to Tethys's spherical shape. This is most likely due to the viscous relaxation of the Tethyan icy crust over geologic time. The floor lies approximately 3&nbsp;km below the mean radius, while its exterior rim is about 5&nbsp;km above the mean radius—the relief of 6–9&nbsp;km is not very high for such a large crater. Inside the crater the rim is composed of arcuate scarps and extends for about 100&nbsp;km until the floor is reached. There are several graben radiating away from Odysseus, which are 10–20&nbsp;km wide and hundreds of kilometers long. They are likely to be cracks in the crust created by the impact.<ref name=moore>{{cite journal| doi = 10.1016/j.icarus.2004.05.009| last1 = Moore| first1 = Jeffrey M.| last2 = Schenk| first2 = Paul M.| last3 = Bruesch| first3 = Lindsey S.| last4 = Asphaug| first4 = Erik| last5 = McKinnon| first5 = William B.| date=October 2004 | title = Large impact features on middle-sized icy satellites| journal = Icarus| volume = 171| issue = 2| pages = 421–443| url = http://planets.oma.be/ISY/pdf/article_Icy.pdf| bibcode = 2004Icar..171..421M}}</ref> The most prominent among them is called ''Ogygia Chasma''.<ref>{{gpn|14436|Tethys: Ogygia Chasma}}</ref>

The crater must have originally been deep, with a high mountainous rim and towering central peak. Over time the crater floor has relaxed to the spherical shape of the Tethyan surface, and the crater's rim and central peak have collapsed (similar relaxation is apparent on Jupiter's moons [[Callisto (moon)|Callisto]] and [[Ganymede (moon)|Ganymede]]). This indicates that at the time of the Odysseus impact, Tethys must have been sufficiently warm and malleable to allow the topography to collapse; its interior may have even been [[liquid]]. If Tethys had been colder and more brittle at the time of impact, the moon might have been shattered, and even if it survived the impact, the topography of the crater would have retained its shape, similarly to the crater [[Herschel (Mimantean crater)|Herschel]] on [[Mimas (moon)|Mimas]].<ref>{{cite web
  | last = Hamilton
  | first = Calvin J.
  | date = 19 February 1999
  | title = Odysseus Basin on Saturn's Moon Tethys
  | work = SolarViews.com
  | publisher = SolarViews
  | url = http://www.solarviews.com/cap/sat/tethys5.htm
  | access-date = 19 December 2011
  }}</ref><ref name=jaumann>{{cite book| doi = 10.1007/978-1-4020-9217-6_20| last1 = Jaumann| first1 = R.| last2 = Clark| first2 = R. N.| last3 = Nimmo| first3 = F.| last4 = Hendrix| first4 = A. R.| last5 = Buratti| first5 = B. J.| last6 = Denk| first6 = T.| last7 = Moore| first7 = J. M.| last8 = Schenk| first8 = P. M.| last9 = Ostro| first9 = S. J.| last10 = Srama| first10 = Ralf| date = 2009| chapter = Icy Satellites: Geological Evolution and Surface Processes| title = Saturn from Cassini-Huygens| pages = 637–681| isbn = 978-1-4020-9216-9}}</ref>{{rp|642}}

The central complex of Odysseus (''Scheria Montes'')<ref>{{gpn|14437|Tethys: Scheria Montes}}</ref> features a central pit-like depression,<ref name=jaumann/>{{rp|642}} which is 2–4&nbsp;km deep. It is surrounded by massifs elevated by 2–3&nbsp;km above the crater floor, which itself is about 3&nbsp;km below the average radius.<ref name=moore/>

=== Relation to Ithaca Chasma ===
The immense trench called [[Ithaca Chasma]], which approximately follows a great circle with a pole near Odysseus's center, had been hypothesized to have formed as a result of the Odysseus impact.<ref name=moore/> However, a study based on high resolution [[Cassini (spacecraft)|Cassini]] images indicated that this is unlikely—the crater counts inside Odysseus appear to be lower than in Ithaca Chasma, indicating that the latter is older than the former.<ref>{{Cite journal | last1 = Giese | first1 = B. | last2 = Wagner | first2 = R. | last3 = Neukum | first3 = G. | last4 = Helfenstein | first4 = P. | last5 = Thomas | first5 = P. C. | title = Tethys: Lithospheric thickness and heat flux from flexurally supported topography at Ithaca Chasma | doi = 10.1029/2007GL031467 | bibcode = 2007GeoRL..3421203G| url = http://ciclops.org/media/sp/2007/4702_10268_0.pdf| journal = Geophysical Research Letters | volume = 34 | issue = 21 | pages = 21203 | date = 2007 | doi-access = free }}</ref><ref name=jaumann/>{{rp|669}}

== See also ==
*[[Tirawa (crater)|Tirawa]] – A similar impact basin on [[Rhea (moon)|Rhea]]
*[[Herschel (Mimantean crater)|Herschel]] – A similarly-sized (proportionally) impact crater on [[Mimas]]

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

== External links ==
* {{APOD |date=8 February 2006|title=The Great Basin on Tethys}}
* [[Astronomy Picture of the Day]] for [http://antwrp.gsfc.nasa.gov/apod/ap070909.html 9 September 2007]
* {{APOD |date=5 February 2017|title=Odysseus Crater on Tethys}}

{{Tethys}}

[[Category:Impact craters on Saturn's moons]]
[[Category:Surface features of Tethys (moon)]]