Odysseus (crater)

Coordinates: 32°49′N 128°53′W / 32.82°N 128.89°W / 32.82; -128.89^[1]

Odysseus is a large shallow crater at the bottom, as imaged by Cassini on February 14, 2010.

Odysseus is the largest crater on Saturn's moon Tethys. It is 445 km across, more than 2/5 of the moon's diameter, and is one of the larger craters in the Solar System. It is situated in the western part of 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 hero Odysseus.^[1]

Discovery

Odysseus was discovered by Voyager 2 spacecraft on 1 September 1981 during its flyby of Saturn.^[2] It was named after the Greek hero Odysseus from Homer's Odyssey and Iliad.^[1]

Geology

The Odysseus crater is now quite flat for its size of approximately 450 km or more precisely, its floor conforms to Tethys' spherical shape. This is most likely due to the viscous relaxation of the Tethyan icy crust over geologic time. The floor lies approximately 3 km below the mean radius, while its exterior rim is about 5 km above the mean radius—the relief of 6–9 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 km until the floor is reached. There are several graben radiating away from Odysseus, which are 10–20 km wide and hundreds kilometers long. They are likely to be cracks in the crust created by the impact.^[3] The most prominent among them is called Ogygia Chasma.^[4]

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 Tethys's surface, and the crater's rim and central peak have collapsed (similar relaxation is apparent on Jupiter's moons Callisto and 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, similar to the crater Herschel on Mimas.^[5][6]

The central complex of Odysseus (Scheria Montes)^[7] features a central pit-like depression,^[6] which is 2–4 km deep. It is surrounded by massifs elevated by 6–9 km above the crater floor, which itself is about 3 km below the average radius.^[3]

Relation to Ithaca Chasma

The immense trench called Ithaca Chasma, which approximately follows a great circle with a pole near Odyssues' center, had been hypothesized to have formed as a result of the Odysseus impact.^[3] However, a research based on high resolution 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.^[8][9]

Gallery

Odysseus as viewed by Voyager 2 on August 25, 1981.   Color image of Tethys taken by Cassini's narrow-angle camera on December 24, 2005.

Citations

1. ^ ^{a b c} "Tethys: Odysseus". Gazetteer of Planetary Nomenclature. USGS Astrogeology. http://planetarynames.wr.usgs.gov/Feature/4406. Retrieved 28 July 2011. 
2. ^ Stone, E. C.; Miner, E. D. (1982). "Voyager 2 Encounter with the Saturnian System". Science 215 (4532): 499–504. doi:10.1126/science.215.4532.499. PMID 17771272.  edit
3. ^ ^{a b c} Moore, 2004, pp.424–30
4. ^ "Tethys: Ogygia Chasma". Gazetteer of Planetary Nomenclature. USGS Astrogeology. http://planetarynames.wr.usgs.gov/Feature/14436. Retrieved 28 July 2011. 
5. ^ Calvin J. Hamilton. "Odysseus Basin on Saturn's Moon Tethys". SolarViews. http://www.solarviews.com/cap/sat/tethys5.htm. Retrieved 28 July 2011. 
6. ^ ^{a b} Jaumann, 2009, p.642
7. ^ "Tethys: Scheria Montes". Gazetteer of Planetary Nomenclature. USGS Astrogeology. http://planetarynames.wr.usgs.gov/Feature/14437. Retrieved 28 July 2011. 
8. ^ Giese, B.; Wagner, R.; Neukum, G.; Helfenstein, P.; Thomas, P. C. (2007). "Tethys: Lithospheric thickness and heat flux from flexurally supported topography at Ithaca Chasma". Geophysical Research Letters 34 (21). doi:10.1029/2007GL031467. http://ciclops.org/media/sp/2007/4702_10268_0.pdf.  edit
9. ^ Jaumann, 2009, p.669

References

• Jaumann, R.; Clark, R. N.; Nimmo, F.; Hendrix, A. R.; Buratti, B. J.; Denk, T.; Moore, J. M.; Schenk, P. M. et al. (2009). Icy Satellites: Geological Evolution and Surface Processes. pp. 637–681. doi:10.1007/978-1-4020-9217-6_20.  edit
• Moore, J. M.; Schenk, Paul M.; Bruesch, Lindsey S. et.al. (2004). "Large impact features on middle-sized icy satellites" (pdf). Icarus 171 (2): 421–43. Bibcode 2004Icar..171..421M. doi:10.1016/j.icarus.2004.05.009. http://planets.oma.be/ISY/pdf/article_Icy.pdf.  edit

External links

• Astronomy Picture of the Day for 9th September 2007