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Iapetus: Major discoveries from the Cassini imaging experiment

Denk, Tilmann and Neukum, Gerhard and Schmedemann, Nico and Roatsch, Thomas and Thomas, Peter and Helfenstein, Paul and Turtle, Elizabeth and 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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Abstract

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.

Item URL in elib:https://elib.dlr.de/55733/
Document Type:Conference or Workshop Item (Speech)
Title:Iapetus: Major discoveries from the Cassini imaging experiment
Authors:
AuthorsInstitution or Email of AuthorsAuthors ORCID iD
Denk, TilmannFU BerlinUNSPECIFIED
Neukum, GerhardFU BerlinUNSPECIFIED
Schmedemann, NicoFU BerlinUNSPECIFIED
Roatsch, ThomasUNSPECIFIEDUNSPECIFIED
Thomas, PeterCornell UniversityUNSPECIFIED
Helfenstein, PaulCornell UniversityUNSPECIFIED
Turtle, ElizabethJohn Hopkins UniversityUNSPECIFIED
Porco, CarolynUNSPECIFIEDUNSPECIFIED
Date:26 September 2008
Refereed publication:No
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Cassini, Iapetus, Icy Satellites
Event Title:European Planetary Science Conference
Event Location:Muenster
Event Type:international Conference
Event Dates:2008-09-22 - 2008-09-26
Organizer:Europlanet
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben CASSINI (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geology
Deposited By: Roatsch, Dr.rer.nat. Thomas
Deposited On:07 Nov 2008
Last Modified:27 Apr 2009 15:20

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