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Iapetus: Major discoveries from the Cassini imaging experiment

Denk, Tilmann und Neukum, Gerhard und Schmedemann, Nico und Roatsch, Thomas und Thomas, Peter und Helfenstein, Paul und Turtle, Elizabeth und Porco, Carolyn (2008) Iapetus: Major discoveries from the Cassini imaging experiment. European Planetary Science Conference, 2008-09-22 - 2008-09-26, Muenster.

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Kurzfassung

Over the course of more than three years orbiting Saturn, the Imaging Subsystem (ISS) [1] of the Cassini spacecraft has acquired high-resolution images of the Saturnian moon Iapetus during a number of flybys. The most recent and only targeted Iapetus flyby occured on 10 September 2007, and allowed a >50x closer look at the surface than any previous observation. The surface of Iapetus is heavily cratered down to the resolution limit of ~10 meters per pixel. The crater size-frequency distribution shows no measurable difference between the leading and the trailing hemisphere, arguing for planetocentric projectiles as the main impactor source. The equatorial ridge can now be clearly tracked along half of Iapetus's circumference, from ~50°W to ~245°W; it is mainly absent on the other hemisphere. However, we argue that it presumably spanned the full globe shortly after formation. Very small bright-ray and bright-rim craters have been detected deep within the dark hemisphere, suggestive for a dark blanket with a thickness in the order of decimeters to meters only. On the trailing side at low and mid-latitudes, very dark terrain is located immediately adjacent to bright terrain, with almost no gray shading in between. In many cases, crater walls facing towards the equator are dark, while poleward-facing walls and slopes are bright. This effect vanishes at both north and south high latitudes. We interpret these observations to indicate that thermal segregation of water ice is responsible for these complex small-scale dark-bright patterns. On the trailing side, a bright polar cap has been observed at high latitudes on both hemispheres (north and south). A global color dichotomy has been detected in addition to the long-known global brightness dichotomy, with the leading side showing a significantly redder color than the trailing side. Unlike the more ellipsoidal-shaped brightness dichotomy, the color dichotomy is quite well separated into two different hemispheres, with the sub-Saturn (~0°W) and anti-Saturn (~180°W) meridians as the approximate boundaries [2]. This global pattern indicates an exogenic origin. Earlier hypotheses for the origin of the brightness dichotomy, like the infall of dust from retrograde outer moons, might actually offer a better explanation for the color dichotomy than for the brightness dichotomy. We propose that this so far unknown process forming the color dichotomy has also reddened and somewhat darkened Hyperion, another moon of Saturn. The color dichotomy also provides a key element to the explanation of the brightness dichotomy in the model of Spencer et al. [3]. References [1] Porco, C.C. et al. (2004) Space Sci. Rev.115, 363. [2] Denk, T. et al. (2006) EGU06-A-08352. [3] Spencer, J.R. et al. (2005) 37th DPS, abstract, 39.08.

elib-URL des Eintrags:https://elib.dlr.de/55733/
Dokumentart:Konferenzbeitrag (Vortrag)
Titel:Iapetus: Major discoveries from the Cassini imaging experiment
Autoren:
AutorenInstitution oder E-Mail-AdresseAutoren-ORCID-iDORCID Put Code
Denk, TilmannFU BerlinNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Neukum, GerhardFU BerlinNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Schmedemann, NicoFU BerlinNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Roatsch, ThomasNICHT SPEZIFIZIERTNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Thomas, PeterCornell UniversityNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Helfenstein, PaulCornell UniversityNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Turtle, ElizabethJohn Hopkins UniversityNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Porco, CarolynNICHT SPEZIFIZIERTNICHT SPEZIFIZIERTNICHT SPEZIFIZIERT
Datum:26 September 2008
Referierte Publikation:Nein
Open Access:Nein
Gold Open Access:Nein
In SCOPUS:Nein
In ISI Web of Science:Nein
Status:veröffentlicht
Stichwörter:Cassini, Iapetus, Icy Satellites
Veranstaltungstitel:European Planetary Science Conference
Veranstaltungsort:Muenster
Veranstaltungsart:internationale Konferenz
Veranstaltungsdatum:2008-09-22 - 2008-09-26
Veranstalter :Europlanet
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Weltraum (alt)
HGF - Programmthema:W EW - Erforschung des Weltraums
DLR - Schwerpunkt:Weltraum
DLR - Forschungsgebiet:W EW - Erforschung des Weltraums
DLR - Teilgebiet (Projekt, Vorhaben):W - Vorhaben CASSINI (alt)
Standort: Berlin-Adlershof
Institute & Einrichtungen:Institut für Planetenforschung > Planetengeologie
Hinterlegt von: Roatsch, Dr.rer.nat. Thomas
Hinterlegt am:07 Nov 2008
Letzte Änderung:27 Apr 2009 15:20

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