DPS 42nd Meeting Abs..

09.05: Color Photometry of the Small Saturnian Satellites: Global and Regional Variaons on Prometheus and CalypsoAuthor Block: Sarah J. Morrison 1 , P. Helfenstein 1 , P. C. Thomas 1 , J. Veverka 11 Cornell University.Presentaon Time: 10/4/2010 3:48 PM - 3:50 PMLocaon: Exhibit HallAbstract: We invesgate color variaons of Prometheus and Calypso using recent high resoluon calibrated Cassini Imaging Subsystem (ISS) images with theNarrow Angle Camera (NAC) broadband filters UV3 (338 nm) , GRN (568 nm), and IR3 (930 nm) in comparison to those of Pandora, Janus, Epimetheus, and Telestoexamined previously (Morrison et al., 2009, DPS 45.04). The average UV3/IR3 rao values are as follows: Prometheus- 0.47, Pandora- 0.53, Janus- 0.57,Epimetheus- 0.58, Telesto- 0.95, and Calypso- 0.77 with formal uncertaines < 0.01 due to noise. While both Prometheus and Calypso connue the trend ofincreasing blueness toward the E-ring, Calypso differs in color from Telesto with a lower UV3/IR3 rao and a mean UV3/GRN rao value of ~0.7 compared toTelesto’s mean UV3/GRN value of ~0.9 despite both being Trojans of Tethys. Calypso’s surface also exhibits wider color and albedo variaons than on Telesto anddisnct UV3-bright units undergoing downslope transport with UV3/IR3 rao values of ~0.05 greater than the mean. Calypso's mean global CLR (611 nm) albedoat normal incidence and 35° phase is ~13% higher than Telesto's, but its albedo range is broader and overlaps Telesto's. The color differences between these twomoons may reflect varying degrees of surface burial and contaminaon from ring parcles.09.06: Mapping the Thermal Inera of IapetusAuthor Block: Edgard G. Rivera-Valenn 1 , D. G. Blackburn 1 , R. Ulrich 11 University of Arkanss.Presentaon Time: 10/4/2010 3:50 PM - 3:52 PMLocaon: Exhibit HallAbstract: Nighme temperatures on a slow rotang airless body, such as Iapetus, are a crical indicator of the surface thermal inera since during this methe only acve heat source is the stored thermal energy within the surface material. During a PRIME data set for ISS in 2007, the Cassini CIRS instrument wasgiven the opportunity to record data at such a me. Surface temperatures deduced from thermal emissions are thus far the lowest recorded for Iapetus. Toaccount for the observed low temperatures, a much lower thermal inera than previously esmated is required. Surface thermal inera is expected to vary if darkmaterial overburden thickness varies on the surface of Iapetus. This arises from the finding that for a heterogeneous mixture where the surface material has alower thermal inera than the underlying layer, the surface proximity of the high thermal inera material strongly affects the observed surface thermal inera(Mellon et al., 2004, Icarus, 169, 324-340). Indeed, it has been suggested that albedo is a funcon of dark material thickness (Spencer and Denk, 2010, Science,327, 432-435) thus it can be shown that surface thermal inera is a funcon of albedo. Via the use of a heat transfer model and the recently published Iapetusbolometric Bond albedo map (Blackburn et al., 2010, Icarus, Submied), surface thermal inera can now be extrapolated for several albedo points on Iapetus.This allows for an esmate of the albedo/thermal inera relaonship and thus the development of a global thermal inera map. We will discuss the implicaonsfor surface material composion focusing on the material properes of the dark terrain.09.07: Resonant Structure and Chaoc Diffusion of the Jovian Irregular Satellites.Author Block: Julien Frouard 11 IM CCE/LAL - Paris Observatory, France.Presentaon Time: 10/4/2010 3:52 PM - 3:54 PMLocaon: Exhibit HallAbstract.Abstract: The dynamical region of the Jovian irregular satellites presents an interesng web of resonances. Along with secular and mean moonresonances which shape the stability regions, we report a number of resonances involving the Great Inequality which are present in the system thanks to thewide range of the frequency of pericenter value available for the satellites in the stable regions. Using extensive numerical integraons of the satellites alongwith an indicator of chaos (MEGNO), we give global and detailled views of the retrograde and prograde regions for various dynamical models and show theapparion of the different types of resonances. The chaoc diffusion of the satellites is also studied and shows the long term stability of the Ananke and Carmefamilies, in contrast with the Pasiphae family.09.08: Towards a Comprehensive Explanaon of Iapetus' Albedo AsymmetryAuthor Block: Charles A. Peterson 11 Atmospheric & Environmental Research, Inc..Presentaon Time: 10/4/2010 3:54 PM - 3:56 PMLocaon: Exhibit HallAbstract: Saturn’s satellite Iapetus, which is 6 mes brighter on its trailing hemisphere than on its leading hemisphere, has an albedo asymmetry that is uniquein our Solar System. From the me of its discovery by Cassini in 1671 unl the present, no explanaon for this extreme appearance has gained generalacceptance. An updated hypothesis, originally proposed in 1975 (Icarus 24, 499-503) and revisited in light of recent observaons, is presented with the centralassumpon that Iapetus started out with a dark surface that connues to be coated asymmetrically with bright reflecve water ice. This ice is stable for longperiods of me in the region of the outer Solar System that includes Saturn and, therefore, can be conveyed to the satellite’s surface by three disnct populaonsof exogenic impactors whose sources are all exterior to Iapetus’ orbit. Evidence for the existence of these populaons is provided by the recent discovery by theSpitzer Observatory of a very large dust ring orbing Saturn at the distance expected for ejecta from its 38 known irregular satellites including Phoebe. Althoughjust one parcular impactor populaon could account for a hemispherical albedo asymmetry, the combined effect of all three populaons acng togetherenhances and characterizes this asymmetry even further. Relevant aspects of impact dynamics involving the collision of these ice-bearing parcles with Iapetus’surface will be summarized. Proving this revised hypothesis will require the extensive modeling of ejecta modificaon and transport on the surface of Iapetus.Such an effort should contribute significantly towards not only resolving this 300-year old problem in planetary science, but also providing a beer understandingof the much less extreme hemispheric asymmetries observed for most other regular satellites in the Solar System.09.09: Heat Conducon: An Important Process for the Shape of Iapetus’s Dark Spots?Author Block: Goetz Galuba 1 , T. Denk 1 , G. Neukum 11 Freie Universität Berlin, Planetology & Remote Sensing, Germany.Presentaon Time: 10/4/2010 3:56 PM - 3:58 PMLocaon: Exhibit HallAbstract: The saturnian moon Iapetus is famous for its global black-and-white dichotomy. While its leading side (Cassini Regio) is covered by very darkmaterial, the poles and trailing side are relavely bright. However, craters and troughs with dark floors are located within the bright area, especially at lowlatudes. The boundaries of these smaller-scaled dark areas are very sharp. Even within the best-resolved images from the Cassini imaging experiment (ISS), thetypical length of a drop-off in albedo is below the resoluon limit.