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ABSTRACT: The Cassini Imaging Science Sub-system (ISS) acquired many high-resolution images (﹤ 1 km/pixel) during close flybys of Dione and Tethys in 2005 and 2007. We combined these images with lower-resolution coverage and a few images taken by Voyager cameras to produce high-resolution semi-controlled mosaics of Dione and Tethys. These global mosaics are the baseline for high-resolution Dione and Tethys atlases that consist of 15 tiles each mapped at a scale of 1: 1,000,000. A few examples of these map tiles will be shown in this presentation. The nomenclature used in this atlas was suggested by the Cassini-ISS team and is currently under evaluation by the International Astronomical Union (IAU). The whole atlases will become available to the public through the Imaging Team’s website (http://ciclops.org/maps/).
EGU General Assembly;
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Thomas Roatsch,
Marita Wählisch,
Bernd Giese,
Angelika Hoffmeister,
Klaus-Dieter Matz,
Frank Scholten,
Roland Wagner,
Anne Kuhn,
Gerhard Neukum,
Paul Helfenstein, Carolyn Porco
XXIII International Cartographic Conference;
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Thomas Roatsch,
Marita Wählisch,
Bernd Giese,
Angelika Hoffmeister,
Klaus-Dieter Matz,
Frank Scholten,
Anne Kuhn,
Roland Wagner,
Gerhard Neukum,
Paul Helfenstein, Carolyn Porco
[show abstract]
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ABSTRACT: The Cassini Imaging Science Subsystem (ISS) acquired 377 high-resolution images (o1 km/pixel) during three close flybys of
Enceladus in 2005 [Porco, C.C., et al., 2006. Cassini observes the active south pole of Enceladus. Science 311, 1393–1401.]. We combined
these images with lower resolution Cassini images and four others taken by Voyager cameras to produce a high-resolution global
controlled mosaic of Enceladus. This global mosaic is the baseline for a high-resolution Enceladus atlas that consists of 15 tiles mapped
at a scale of 1:500,000. The nomenclature used in this atlas was proposed by the Cassini imaging team and was approved by the
International Astronomical Union (IAU). The whole atlas is available to the public through the Imaging Team’s website (http://
ciclops.org/maps).
Planetary and Space Science. 56(2008-01):109-116.
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ABSTRACT: The Institute of Planetary Research (IPR) at DLR has a long tradition in image processing and archiving. The major starting point in the early 1990’s was the development of the the image processing system for the Mars96 misison. Unfortunately, this mission failed shortly after launch. In parallel IPR developed software to analyze the imaging data from the Galileo and Clementine mission.In the late 1990’s IPR started to participate in the Cassini imaging experiment. IPR has been in charge for the processing of the camera data from the MarsExpress mission since 2004 and also for the imaging data from the VenusExpress mission since 2006.This work has been supplemented since 2007 by the software development for the DAWN data processing. The main focus of the IPR software development has been the systematic processing (telemetry processing and radiometric calibration), map projection and mosaicking, photogrammetric and cartographic processing. IPR also contributes to the archiving products from a variety of missions. These archiving products are released to the scientific community via the planteray archives at ESA and NASA (PSA and PDS).
COSPAR 2008;
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ABSTRACT: The Cassini Imaging Science Sub-system (ISS) acquired many high-resolution im-ages of Iapetus during the new year flyby in 2004/2005 and during the targeted flyby in September 2007. We combined these images with lower-resolution coverage and a few images taken by Voyager cameras to produce a high-resolution semi-controlled mosaic of Iapetus. This mosaic was calculated in equidistant projection with a resolution of 800 m/pixels. The Cassini-ISS team suggested names for the features which were detected during these two flybys. The nomenclature was ap-proved by the International Astronomical Union (IAU). In this presentation we will show the high resolution mosaic together with the most prominent feature names. The mosaic is available to the public through the Imaging Team's website (http://ciclops.org/maps/).
Saturn Book Symposium entitled "Saturn After Cassini-Huygens";
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ABSTRACT: The first version of the high-resolution Enceladus atlas was released back in 2006
[1]. The Cassini Imaging Science Sub-system (ISS) acquired more high-resolution
images (< 1 km/pixel) during four close flybys of Enceladus in 2008. We combined
these images with lower-resolution coverage taken between 2007 and 2009 to improve
the high-resolution global mosaic of Enceladus. The whole mosaic was finally
shifted by 3.5° to the West to be consistent with IAU longitude definition. This new
global mosaic is the baseline for the second release of the high-resolution Enceladus
atlas that consists again of 15 tiles mapped at a scale of 1:500,000. We proposed 29
additional names for features which will be used as nomenclature in the atlas. We
are awaiting validation of the new nomenclature by the IAU. The new release of the
atlas will be made available to the public through CICLOPS (http://ciclops.org) and
PDS (http://pds.jpl.nasa.gov).
AGU Fall Meeting 2009;
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Tilmann Denk,
Gerhard Neukum,
Thomas Roatsch, carolyn Porco,
Joseph Burns,
Goetz Galuba,
Nico Schmedemann,
Paul Helfenstein,
Peter Thomas,
Roland Wagner,
Robert West
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ABSTRACT: Since 2004, Saturn’s moon Iapetus has been observed repeatedly with the Imaging Science Subsystem of the Cassini spacecraft. The images show numerous impact craters down to the resolution limit of ~10 meters per pixel. Small, bright craters within the dark hemisphere indicate a dark blanket thickness on the order of meters or less. Dark, equator-facing and bright, poleward-facing crater walls suggest temperature-driven water-ice sublimation as the process responsible for local albedo patterns. Imaging data also reveal a global color dichotomy, wherein both dark and bright materials on the leading side have a substantially redder color than the respective trailing-side materials. This global pattern indicates an exogenic origin for the redder leading-side parts and suggests that the global color dichotomy initiated the thermal formation of the global albedo dichotomy.
Science. 327(2010-01-22-5964):435-439.
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ABSTRACT: High resolution images of Enceladus and its south polar jets taken with the Cassini ISS cameras in the last year have provided an opportunity for detailed study of the jetting phenomenon and its relationship to features and thermal hot spots on the moons south polar terrain. We have identified ~ 30 individual jets in a series of images, ranging from 43 to 100 m per pixel, taken in November 2009. All jets are found to be erupting through `tiger stripe fractures that cross the south polar terrain. The most intense jetting activity generally corresponds to the hottest regions on the fractures. One of the brightest, most prominent jets observed in this image series vents from a region on the Damascus Sulcus fracture that was imaged at 16 m/pixel during Cassinis August 13, 2010 flyby; it is also one of the hottest places found so far on the south polar region.
Several jets were selected for dynamical modeling. These were jets whose source regions were on the limb as seen from Cassini, allowing extraction of brightness profiles down to a few hundred meters of the surface. We infer the velocity distribution of the particles as they leave the surface by modeling the integrated brightness vs. altitude. The particles are assumed to follow ballistic trajectories, and their contribution to the brightness in each thin layer is proportional to the time that they spend in the layer.
We find slow jets, fast jets, and jets in between. After a rapid ~ 2-km-scale-height decrease near the surface, the most prominent jet (mentioned above) extends with constant integrated brightness to the edge of the image 25 km above the surface; some of the particles in this jet appear to have mean velocities that exceed the 235 m/sec escape speed from Enceladus. Further analysis of higher-altitude images from the November flyby is in progress to verify this result.
The integrated brightness of slow jets falls off with a scale height of 5 km or less, implying mean vertical velocities of order 30 m/s or less, much less than either the escape speed or the thermal speed for a temperature of 273 K. From the collimation of the vapor in the jets, the Cassini UVIS team infers vertical velocities of 1000 m/s or more [Hansen et al. (2008) Nature 456, 477-479]. Schmidt et al. [(2008) Nature 451, 685-688] account for the slow particle speeds by invoking collisions with the walls of the vent. Ingersoll and Pankine [(2010) Icarus 206, 594-607] invoke short distances during which the gas velocity is high; the particles dont have time reach escape speed. The third possibility is that the particles are so large that the gas cannot accelerate them to escape speed. This possibility is testable with Cassini ISS high-resolution images, which span phase angles up to 176 degrees and wavelengths from UV to near-IR.
Our ultimate goal is to test models of how the jets form. The particles form either by condensing directly from vapor, by spallation from the icy walls of the vent, or by freezing of liquid water droplets. Images collected by Cassini thus far will help us choose among the possibilities.
AGU Fall Meeting;
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ABSTRACT: Until November 2009 the relation of the tectonic styles on the leading hemisphere of Enceladus to those elsewhere on the satellite were unclear. Cassini's ISS Narrow Angle Camera (NAC) acquired high-resolution mosaics of the leading hemisphere for the first time during three close flybys, one on November 21, 2009, another on May 18, 2010, and a third on August 13, 2010, respectively.
The new mosaics show that the leading side has distinct geological provinces that exhibit diverse tectonic styles and different cratering histories. The highly tectonised terrains are bounded by a prominent broad annulus of grooved and striated terrains that ranges from about 60 km to over 140 km in width. It surrounds a complex arrangement of tectonic structures, including a conspicuous province near 30°N, 90°W of curvilinear massifs and roughly orthogonal-trending ridged-troughs that define a crudely radial and concentric pattern relative to a point near 25°N, 125°W. This angular sector, about 65° in width, may be the partial remains of an ancient impact basin with a diameter of about 180 km. It could also be the surface expression of an ancient, large diapir. The peculiar quasi-radial ridged-troughs resemble extinct, topographically degraded examples of tiger stripes seen elsewhere on Enceladus. While these features may have a different fracture origin from tiger stripes, their comparable morphology suggests that long ago they may have expressed a similar style of fissure volcanism.
Among our other significant findings is a region near 10°S, 60°W of rounded, rope-like sub-parallel ridges similar to ropy (funiscular) plains materials previously found only in the South Polar Terrain region near active tiger stripes. We suggest that the pattern of ropy ridges on the leading hemisphere arose from a similar style of tectonic deformation that produced the South Polar funiscular plains – a terrain that is closely related to possible folding and tectonic spreading associated with the tiger stripes. These features may thus record an ancient episode of South Polar style tectonism and volcanism near the equator. This hypothesis is consistent with the observed presence of viscously relaxed impact craters at the boundaries of the tectonically modified leading-side terrains as probes of a formerly elevated regional heat flux.
AGU Fall Meeting;
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ABSTRACT: The Saturnian system contains 47 satellites of different sizes. This paper deals with the mapping of the so-called medium-sized icy satellites Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, and Phoebe. Voyager-1 and Voyager-2 obtained a large number of images from the icy Saturnian satellites during their journeys through the Saturnian system in 1980 and 1981. These images constitute the basis for the planning of mapping during the Cassini mission. The Cassini Imaging Science Subsys-tem (ISS) consists of two framing cameras. The narrow angle camera is a reflecting telescope with a focal length of 2000 mm and a field of view of 0.35 degrees. The wide angle camera is a refractor with a focal length of 200 mm and a field of view of 3.5 degrees. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 0.2 to 1.1 micrometers. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 microns on a side. The stated objective of the ISS team is to ob-tain global coverage for all medium-sized icy satellites with a resolution better than 1 km/pixel and high-resolution images. This goal is being achieved with image sequences obtained during close fly-bys supplemented by images from greater distances to complete the coverage. Close flybys of all me-dium sized satellites except Mimas are planned during the nominal mission of the Cassini spacecraft until summer 2008. The first flybys during the mission were those of Phoebe in June 2004 and Iapetus in December 2004 followed by three flybys of Enceladus in February, March, and July 2005 and fly-bys of Tethys, Dione, and Rhea in fall 2005.
Imaging of the medium-sized icy satellites is ongoing and will continue until the end of the Cassini mission, making it possible to improve the image mosaics during the tour. The starting points of global mosaics for any satellite are the Voyager mosaics in which areas can be replaced gradually by higher-resolution Cassini images as data become available. At some point in time new mosaics can be generated on the basis of Cassini image data, where Voyager data fill the gaps between the Cassini images. In these maps, the satellite coverage, as expected by the end of the nominal Cassini mission, can be visualized. The global mosaics are usually produced using images of a similar resolution. However, some areas of the satellites are imaged at very high resolution. The data set of Phoebe is the only one that is complete, as no more high-resolution images are expected during the mission. Also, we will not obtain new high-resolution Enceladus images until 2008. Therefore standard maps were generated for these two satellites. The nomenclature was proposed by the Cassini imaging team and has yet to be validated by the IAU.
European Planetary Science Congress 2006;
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ABSTRACT: The Cassini Imaging Science Sub-system (ISS) acquired many high-resolution im-ages (< 1 km/pixel) during two close targeted flybys of Enceladus in March and August 2008. More close flybys are planned this fall. These images gave us the possibility to improve the high-resolution global mosaic of Enceladus. We also could improve some map sheets of the Enceladus atlas. Crater Salih which defines the longitude system of Enceladus was observed with high-resolution during the March flyby. This gave us the possibility to determine the shift of our mosaic com-pared to the definition of the International Astronomical Union (IAU). The global mosaic was shifted 3.5° to the West to be consistent with the IAU definition. The global mosaic and the atlas will be made available to the public through CICLOPS (http://ciclops.org).
AGU Fall Meeting 2008;
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ABSTRACT: The Cassini Imaging Science Sub-system (ISS) acquired many high-resolution images (below 1 km/pixel) during a close targeted flyby of Dione in October 2005 and two non-targeted flybys in December 2004 and April 2007. We combined 44 high-resolution clear filter images with lower-resolution coverage and two images taken by Voyager cameras to produce a high-resolution global semi-controlled mosaic of Dione. This global mosaic is the baseline for a high-resolution Dione atlas that con-sists of 15 tiles mapped at a scale of 1:1,000,000. The nomenclature used in this atlas was proposed by the Cassini imaging team and is awaiting validation by the IAU. The atlas will be made available to the public through CICLOPS (http://ciclops.org) and PDS (http://pds.jpl.nasa.gov).
AGU Fall Meeting;
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ABSTRACT: High-resolution Cassini stereo images of Saturn's moon Phoebe have been used to derive a regional Digital Terrain Model (DTM) and an orthoimage mosaic of the surface. For DTM-control, a network of 130 points measured in 14 images (70-390 m/pixel resolution) was established which was simultaneously used to determine the orientation of the spin-axis. The J2000 spin-axis was found at RA = 78.0°±0.1° and Dec = 356.6°±0.3°, substantially different from the former Voyager solution. The control points yield a mean figure radius of 107.2 km with RMS residuals of 6.2 km demonstrating the irregular shape of this body. The DTM obtained is based on methods of digital image correlation. It has a horizontal resolution of 1-2 km and vertical accuracies in the range of 50-100 m. Although limited in coverage, it is higher in resolution than the previously derived global shape model of Phoebe (Porco et al., 2005) and allows us to study the morphology of the surface in more detail. The most important feature revealed by the DTM is the conical shape of craters which has not been reported on planetary bodies so far. The formation of such craters may hint at highly porous material on the surface of Phoebe.
Planetary and Space Science. 54(2006-12):1156-1166.
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ABSTRACT: We have used Cassini stereo images to study the topography of Iapetus' leading side. A terrain model derived at resolutions of 4-8 km reveals that Iapetus has substantial topography with heights in the range of -10 km to +13 km, much more than observed on the other middle-sized satellites of Saturn so far. Most of the topography is older than 4 Ga (Neukum et al., 2005) which implies that Iapetus must have had a thick lithosphere early in its history to support this topography. Models of lithospheric deflection by topographic loads provide an estimate of the required elastic thickness in the range of 50-100 km. Iapetus' prominent equatorial ridge (Porco et al., 2005) reaches widths of 70 km and heights of up to 13 km from their base within the modeled area. The morphology of the ridge suggests an endogenous origin rather than a formation by collisional accretion of a ring remnant (Ip, 2006). The transition from simple to complex central peak craters on Iapetus occurs at diameters of 11±3 km. The central peaks have pronounced conical shapes with flanking slopes of typically 11° and heights that can rise above the surrounding plains. Crater depths seem to be systematically lower on Iapetus than on similarly sized Rhea, which if true, may be related to more pronounced crater-wall slumping (which widens the craters) on Iapetus than on Rhea. There are seven large impact basins with complex morphologies including central peak massifs and terraced walls, the largest one reaches 800 km in diameter and has rim topography of up to 10 km. Generally, no rings are observed with the basins consistent with a thick lithosphere but still thin enough to allow for viscous relaxation of the basin floors, which is inferred from crater depth-to-diameter measurements. In particular, a 400-km basin shows up-domed floor topography which is suggestive of viscous relaxation. A model of complex crater formation with a viscoplastic (Bingham) rheology (Melosh, 1989) of the impact-shocked icy material provides an estimate of the effective cohesion / viscosity at 0.04±0.01 MPa / 0.6±0.2 GPas. The local distribution of bright and dark material on the surface of Iapetus is largely controlled by topography and consistent with the dark material being a sublimation lag deposit originating from a bright icy substrate mixed with the dark components, but frost deposits are possible as well.
Icarus 193(2008-2):359-371. · 3.38 Impact Factor
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ABSTRACT: The Cassini spacecraft started to investigate the Saturnian icy satellites in June 2004
with the flyby of Phoebe. This flyby was followed by flybys of all medium sized Icy
satellites except Mimas. The images taken by the Cassini orbiter camera during
these flybys together with more distant observations allow the compilation of high
resolution image mosaics. These data can also be used to calculate new global mosaics
(e.g. Enceladus) or to improve the existing global mosaics based on Voyager
data (e.g. for Iapetus). These global mosaics can be used both for scientific interpretation
and for the planning of further flybys later in the tour. Furthermore, these
global mosaics can be extended to cartographic standard products.
We will show in this presentation both examples of new mosaics and cartographic
products and will demonstrate how the mosaics can be used for further planning
work.
AGU Fall Meeting;
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ABSTRACT: The Cassini imaging science subsystem (ISS) acquired 449 high-resolution images (o800 m/pixel) during one close flyby of Dione in
2005 and three non-targeted flybys in 2004, 2006, and 2007. We combined these images with lower-resolution Cassini images and one
other taken by Voyager cameras to produce a high-resolution semi-controlled mosaic of Dione. This global mosaic is the baseline for a
high-resolution Dione atlas that consists of 15 tiles mapped at a scale of 1:1,000,000. The nomenclature used in this atlas was proposed by
the Cassini imaging team and was approved by the International Astronomical Union (IAU). The whole atlas is available to the public
through the Imaging Team’s website [http://ciclops.org/maps].
Planetary and Space Science 56(2008-10):1499-1505. · 2.22 Impact Factor
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ABSTRACT: Since its arrival at the Saturn system in mid-2004, the Cassini orbiter has successfully
performed seven observation campaigns of Saturn’s strange satellite Iapetus at ranges
of 1.4 million km or closer. Large parts of the surface have now been observed at 9
km/pxl resolution or better. The closest flyby was taking place on 31 Dec 2004, when
Cassini passed the northern leading side of Iapetus at 124000 km altitude. The surface
of Iapetus is heavily cratered on both the bright and the dark hemispheres, with an
unusually high number of large basins of up to 800 km in size [1; 2; 3].
The irregular (non-spherical, rather ellipsoidal) shape of Iapetus [4] was confirmed
by Cassini data [1; 5], and is considered as a remnant of the despinning process [6].
A major surprise was the discovery of a large, up to 20 km high ridge system on
the leading side on 25 Dec 2004 [1; 2], which is located exactly at the equator, and
which might also be explained by despinning early in Iapetus’ history. An alternative
hypothesis considers an ancient ring system around Iapetus as the cause for the ridge
formation [7]. The ridge appears to be a geometric continuation of isolated bright
mountains, which have been discovered in Voyager images on the anti-Saturn side
[4], but remained unexplained at this time.
There is also progress in solving the centuries-old question of the formation of the
unique dark/bright albedo dichotomy. ISS data have not shown any "hole" (fresh
"punch-through" impact crater) at a resolution down to 750 m/pxl. RADAR data indicate
that the dark layer is rather thin (at the order of decimeters, [8]), suggesting
that it is either a young structure relative to major crater formation, or that an ongoing
process is responsible. Earlier ideas for the albedo dichotomy formation included dust
from retrograde outer satellites covering Iapetus’ leading side [9; 10]. The advantage
of this idea is that the exact alignment to the center of the leading side can be explained.
However, the bright poles are a problem here. A recent idea from Spencer
et al. [11] is based on data from the CIRS infrared spectrometer and suggests that a
thermal re-distribution of water ice towards the poles is responsible for the albedo dichotomy.
Here, the bright poles can be easily explained, but the leading/trailing side
asymmetry requires different starting conditions for each hemisphere. Outer satellite
dust was considered as a candidate.
This scenario is now supported by the ISS discovery of a color dichotomy in addition
to the albedo dichotomy [12]. Different to the albedo dichotomy, the color dichotomy
is quite precisely aligned to the leading side, including the bright poles. It allows to
link the Spencer et al. [11] and Buratti et al. [10] hypotheses. The dust from outer
satellites only causes a moderate darkening, but a significant reddening of the whole
leading side. This process once triggered the thermal re-distribution of water ice to
start on the leading side, but not on the trailing hemisphere, as suggested by Spencer
et al. [11].
While the described mechanism appears straightforward, it is still questionable if the
very complex albedo patterns at equatorial latitudes revealed by Cassini images [2]
have also been produced entirely by these two rather simple processes. Imaging of
the anti-Saturn side planned for the sole targeted flyby on 10 Sep 2007 will hopefully
provide information that may help to ultimately solve the Iapetus enigma.
References: [1] Porco et al. (2005), Science 307, 1237. [2] Denk et al. (2005), LPSC
abstract 2268. [3] Giese et al. (2005), DPS abstract 47.08. [4] Denk et al. (2000),
LPSC abstract 1596. [5] Thomas et al. (2006), LPSC abstract 1639. [6] Castillo et
al. (2005), DPS abstract 39.04. [7] Ip (2006), GRL, in press. [8] Ostro et al. (2006),
Icarus, in press. [9] Soter (1974), IAU Colloq. 28. [10] Buratti et al. (2002), Icarus
155, 375. [11] Spencer et al. (2005), LPSC abstract 2305. [12] Denk et al. (2006),
EGU 06-A-08352.
European Planetary Science Congress 2006;
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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.
European Planetary Science Conference;
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Paul Helfenstein,
Tilmann Denk,
Bernd Giese,
Andy Ingersoll,
Torrence Johnson,
Alfred McEwen,
Gerhard Neukum,
Jason Perry, Carolyn Porco,
Thomas Roatsch,
Peter Thomas,
Elizabeth Turtle,
Anne Verbiscer,
Joe Veverka
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ABSTRACT: The Cassini spacecraft executed a close flyby of Enceladus on August 11 (altitude: 50km); two more
are planned for October 9 (altitude: 25 km), and October 31 (altitude: 196 km). High resolution (as
fine as 7m/pixel) images of known geologically active features in the South Polar Terrain (SPT) have
been returned to investigate how plume eruptions, tectonism, and seismicity alter the surface and to
reveal how the SPT has evolved over time. We examined six known eruption sites (Spitale and Porco
2007, Nature 449, 695697)
along Cairo, Baghdad, and Damascus Sulci, as well as inactive portions of
the "tiger stripes" and bright fractured terrain in adjacent areas. We also obtained contiguous ISS
broadband multispectral
mosaics of the entire SPT region to refine our geological and digital terrain
maps and to search for volcanically and tectonically driven temporal changes.
The highestresolution
images show ice blocks up to tens of meters in size that are widely but nonuniformly
distributed over a variety of terrain units. The upraised flanks and valley walls of active
tiger stripes are mantled in places by smooth fluffylooking
deposits, most likely accumulations of
coarsegrained
plume fallout. With increasing lateral distance from the stripes, the smooth upraised
flank deposits grade into rounded, platytextured,
elongate hills and a conspicuous system of quasiparallel
knobby ridges and grooves that have spacings and dimensions comparable to the tiger stripe
flanks themselves. Peculiar narrow lenticular ridges, perhaps emplaced by extrusion or as icy
pyroclastic deposits, rise from tens to hundreds of meters along the medial fissures of some tiger
stripes. On regional scales, the ends of the tiger stripes are bounded by a complex network of fractured
terrain, within which can be found numerous transform faults that lie at high angles relative to the
trends of the tiger stripes. Observed offsets along these transforms and an absence of lateral symmetry
of the displaced terrains suggest that tiger stripes are not exact analogs to classic terrestrial oceanic
rifts. Instead, any possible tectonic divergence is more likely a result of the superposition of many
regionally and temporally distributed spreading centers.
AGU Fall Meeting 2008;
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Thomas Roatsch,
Marita Waehlisch,
Angelika Hoffmeister,
Elke Kersten,
Klaus-Dieter Matz,
Frank Scholten,
Roland Wagner,
Tilmann Denk,
Gerhard Neukum,
Paul Helfenstein, Carolyn Porco
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ABSTRACT: The Cassini Imaging Science Subsystem (ISS) acquired 282, 258, and 513 high-resolution images (less than 800 m/pixel) of Mimas, Tethys, and Iapetus, respectively during two close flyby of Tethys and Iapetus and 98 non-targeted flybys between 2004 and 2007. We combined these images with lower-resolution Cassini images and others taken by Voyager cameras to produce high-resolution semi-controlled mosaics of Mimas, Tethys, and Iapetus. These global mosaics are the baseline for high-resolution Mimas and Iapetus maps and a Tethys atlas. The nomenclature used in these maps was proposed by the Cassini imaging team and was approved by the International Astronomical Union (IAU). The two maps and the atlas are available to the public through the Imaging Team's website [http://ciclops.org/maps] and the Planetary Data System [http://pds.jpl.nasa.gov].
Planetary and Space Science. 57(2009-01):83-92.
