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Titel |
Tectonic features on Rhea's trailing hemisphere: a first look at the Cassini ISS camera data from orbit 121, Nov. 21, 2009 |
VerfasserIn |
R. J. Wagner, B. Giese, T. Roatsch, G. Neukum, T. Denk, U. Wolf, C. C. Porco |
Konferenz |
EGU General Assembly 2010
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 12 (2010) |
Datensatznummer |
250037474
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Zusammenfassung |
Introduction: The trailing hemisphere of Rhea, the second-largest satellite of Saturn (1528
km in diameter) is characterized by a network of linear to arcuate, bright wispy markings
which were only poorly resolved by Voyager in the two flybys in 1980 and 1981. During the
nominal mission of Cassini (2004 – 2008), ISS data have revealed that these bright markings
represent tectonic features, mostly troughs and graben, with bright ice exposed along steep
scarps being responsible for the bright albedo. Similar bright markings were also observed on
the trailing hemisphere of Dione, Rhea’s inner neighbour, and were shown to be tectonic in
origin. Observations: New ISS data obtained during Cassini’s Extended Mission in orbit 121
on Nov. 21, 2009, show this tectonized region at much higher resolution [140 – 160
m/pixel] and in stereo. At least two major sets of troughs trending approximately
north-south are seen in these data, separated by an area showing less deformation.
Observed graben widths range from several kilometers up to 30 km. Minor graben
structures occur within major troughs and also in the area between major troughs.
In some parts of the graben structures, avalanches of fine-grained material have
created a thin deposit which subdues the topography underneath. Rhea’s cratered
plains show modifications of a kind also observed on Dione. Inter-crater plains
between large craters, groups of large craters, and the floors of these craters appear
smooth with a lower superimposed small crater frequency than in densely cratered
plains. As on Dione, this variety of cratered plains is preferentially found in or
near tectonized regions implying a resurfacing process connected to tectonism.
Stratigraphy: Most of Rhea’s surface is densely cratered indicating that it is very old, on the
order of 4 billion years. Rhea’s low state of differentiation implies that significant
endogenic processes most likely ceased early in the satellite’s history. However, tectonic
structures in the region covered in this recent orbit 121 transect fresh craters with a low
superimposed crater frequency, provide evidence that tectonic activity may have lasted
for a much longer period of time, at least in this part of the trailing hemisphere. |
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