modeling the sar backscatter of linear dunes on earth and titan abstract we modeled the synthetic aperture radar sar response of linear dunes of the great sand sea in egypt using a single surface scattering term based on integral equation and physical optics models using multi frequency sir c x sar radar scenes and topography obtained from the shuttle radar topography mission srtm we were able to estimate reasonable values for the parameters describing the surface roughness of the dunes as the linear dunes of the great sand sea are relevant analogs for the linear dunes observed on titan by the cassini radar instrument these results were thus used as a starting point to simulate the radar response of titan s dunes as imaged by the radar instrument onboard the cassini spacecraft during the t8 flyby in october 2005 we show that a single surface scattering term is not sufficient to simulate the radar signal backscattered by the dunes on titan one has to add a diffuse scattering term indicating that titan s dunes are likely to have somewhat inhomogeneous internal structures related to porosity and or internal layering our results also indicate that the dunes on titan should be close to perfectly smooth possibly because of the formation of smaller ripples than on earth plus smoothing resulting from precipitation events

the landscape of titan as witness to its climate evolution we investigated the range of titan climate evolution hypotheses regulated by the role sources and availability of methane we analyzed all available image data principally synthetic aperture radar sar of titan s landscape through the t 86 encounter starting with focused examinations of terrains that carry the markers of climate evolution traditional geologic and geomorphic landscape analysis was used to perform morphometric characterization establish time stratigraphic relationships and interpret local and regional geologic process oriented evolutionary histories we then assayed the distribution of terrains we identified with respect to both their latitudinal and altimetric occurrence our analysis of the terrain types and distributions was used to evaluate and rank the various climate evolution scenarios we favor progressive hypotheses which include a relatively brief period in which precipitation was able to affect geomorphic change in low latitudes at scales perceivable in sar data with subsequent gradual decline of precipitation intensity coupled with an increasing poleward restriction

loess and life out of earth abstract loess is a homogeneous typically nonstratified porous friable slightly coherent often calcareous fine grained silty pale yellow wind blown aeolian and often by water reworked sediment that is distributed on continents world wide recent studies have highlighted the importance of biological loess crusts in trapping and transforming aeolian material into loess and also in prevention from wind and water erosion of deposited material some planets and satellites in our solar system are characterized by conditions comparable to those related to loess formation in terrestrial environments given the requirements for loess deposition on earth this study aims to ask the following questions 1 if loess like sediment formation is possible outside earth what are the mechanisms of sediment deposition and preservation 2 could the possible loess like sediments be stabilized through the activity of extraterrestrial equivalents of biological loess crusts found on earth as loess formation on earth is related to biological activity we propose a new direction in the search for extraterrestrial life evidence about extraterrestrial loess might indicate extraterrestrial life connected to loess formation on the basis of comparative analysis of some astrophysical conditions of seven celestial bodies we propose mars and titan and possibly venus and io to be assessed for evidence of loess deposition and the possible presence of related life forms and their biomarkers following recent advances in our understanding of terrestrial loess deposition we propose new indicators of extraterrestrial life research biomarkers in loess cyanobacterial and other microbial

titan radar mapper observations from cassini s t3 fly by cassini s titan radar mapper imaged the surface of saturn s moon titan on its february 2005 fly by denoted t3 collecting high resolution synthetic aperture radar and larger scale radiometry and scatterometry data these data provide the first definitive identification of impact craters on the surface of titan networks of fluvial channels and surficial dark streaks that may be longitudinal dunes here we describe this great diversity of landforms we conclude that much of the surface thus far imaged by radar of the haze shrouded titan is very young with persistent geologic activity

focused magma supply at the intersection of the cobb hotspot and the juan de fuca ridge 1 we examine the interplay between the cobb hotspot and the juan de fuca ridge by mapping the base of the crust at their intersection near axial volcano pmp traveltimes from an extensive active source seismic experiment are used in conjunction with prior crustal tomography to map crustal thickness a cross section along the ridge axis consists of two distinct trends in addition to 1 2 km of excess crust inferred from gravity along a 100 km section of the central ridge we find a narrow 20 40 km diameter root extending to 11 km directly beneath the volcano focused magma flux from the cobb hotspot 0 3 0 8 m3 s is inferred to be the cause of both the narrow root and the large magma reservoir at axial the rapid return to thinner crust away from the intersection marks a transition back to ridge dominated magmatism

venus tectonics an overview of magellan observations the nearly global radar imaging and altimetry measurements of the surface of venus obtained by the magellan spacecraft have revealed that deformational features of a wide variety of styles and spatial scales are nearly ubiquitous on the planet many areas of venus record a superposition of different episodes of deformation and volcanism this deformation is manifested both in areally distributed strain of modest magnitude such as families of graben and wrinkle ridges at a few to a few tens of kilometers spacing in many plains regions as well as in zones of concentrated lithospheric extension and shortening the common coherence of strain patterns over hundreds of kilometers implies that even many local features reflect a crustal response to mantle dynamic processes ridge belts and mountain belts which have characteristic widths and spacings of hundreds of kilometers represent successive degrees of lithospheric shortening and crustal thickening the mountain belts of venus as on earth show widespread evidence for lateral extension both during and following active crustal compression venus displays two principal geometrical variations on lithospheric extension the quasi circular coronae 75 2600 km diameter and broad rises with linear rift zones having dimensions of hundreds to thousands of kilometers both are sites of significant volcanic flux but horizontal displacements may be limited to only a few tens of kilometers few large offset strike slip faults have been observed but limited local horizontal shear is accommodated across many zones of crustal stretching or shortening several large scale tectonic features have extremely steep topographic slopes in excess of 20 30 over a 10 km horizontal scale because of the tendency for such slopes to relax by ductile flow in the middle to lower crust such regions are likely to be tectonically active in general the preserved record of global tectonics of venus does not resemble oceanic plate tectonics on earth wherein large rigid plates are separated by narrow zones of deformation along plate boundaries rather tectonic strain on venus typically involves deformation distributed across broad zones tens to a few hundred kilometers wide separated by comparatively undeformed blocks having dimensions of hundreds of kilometers these characteristics are shared with actively deforming continental regions on earth the styles and scales of tectonic deformation on venus may be consequences of three differences from the earth 1 the absence of a hydrological cycle and significant erosion dictates that multiple episodes of deformation are typically well preserved 2 a high surface temperature and thus a significantly shallower onset of ductile behavior in the middle to lower crust gives rise to a rich spectrum of smaller scale deformational features 3 a strong coupling of mantle convection to the upper mantle portion of the lithosphere probably because venus lacks a mantle low viscosity zone leads to crustal stress fields that are coherent over large distances the lack of a global system of tectonic plates on venus is likely a combined consequence of a generally lesser strength and more limited horizontal mobility of the lithosphere than on earth

nature distribution and origin of titan s undifferentiated plains abstract the undifferentiated plains on titan first mapped by lopes et al lopes r m c et al 2010 icarus 205 540 588 are vast expanses of terrains that appear radar dark and fairly uniform in cassini synthetic aperture radar sar images as a result these terrains are often referred to as blandlands while the interpretation of several other geologic units on titan such as dunes lakes and well preserved impact craters has been relatively straightforward the origin of the undifferentiated plains has remained elusive sar images show that these blandlands are mostly found at mid latitudes and appear relatively featureless at radar wavelengths with no major topographic features their gradational boundaries and paucity of recognizable features in sar data make geologic interpretation particularly challenging we have mapped the distribution of these terrains using sar swaths up to flyby t92 july 2013 which cover 50 of titan s surface we compared sar images with other data sets where available including topography derived from the sartopo method and stereo dems the response from radar radiometry hyperspectral imaging data from cassini s visual and infrared mapping spectrometer vims and near infrared imaging from the imaging science subsystem iss we examined and evaluated different formation mechanisms including i cryovolcanic origin consisting of overlapping flows of low relief or ii sedimentary origins resulting from fluvial lacustrine or aeolian deposition or accumulation of photolysis products created in the atmosphere our analysis indicates that the undifferentiated plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and or sedimentary processes we conclude that aeolian processes played a major part in the formation of the undifferentiated plains however other processes fluvial deposition of photolysis products are likely to have contributed possibly in differing proportions depending on location

evidence for the exposure of water ice on titan s surface the smoggy stratosphere of saturn9s largest moon titan veils its surface from view except at narrow wavelengths centered at 0 83 0 94 1 07 1 28 1 58 2 0 2 9 and 5 0 micrometers we derived a spectrum of titan9s surface within these windows and detected features characteristic of water ice therefore despite the hundreds of meters of organic liquids and solids hypothesized to exist on titan9s surface its icy bedrock lies extensively exposed

hypsometry of titan cassini radar topography data are used to evaluate titan s hypsometric profile and to make comparisons with other planetary bodies titan s hypsogram is unimodal and strikingly narrow compared with the terrestrial planets to investigate topographic extremes a novel variant on the classic hypsogram is introduced with a logarithmic abscissa to highlight mountainous terrain in such a plot the top of the terrestrial hypsogram is quite distinct from those of mars and venus due to the glacial buzz saw that clips terrestrial topography above the snowline in contrast to the positive skew seen in other hypsograms with a long tail of positive relief due to mountains there is an indication weak given the limited data for titan so far that the titan hypsogram appears slightly negatively skewed suggesting a significant population of unfilled depressions limited data permit only a simplistic comparison of titan topography with other icy satellites but we find that the standard deviation of terrain height albeit at different scales is similar to those of ganymede and europa

crater relaxation on titan aided by low thermal conductivity sand infill abstract titan s few impact craters are currently many hundreds of meters shallower than the depths expected assuming these craters initially had depths equal to that of similar size fresh craters on ganymede and callisto moons of similar size composition and target lithology then some process has shallowed them over time since nearly all of titan s recognized craters are located within the arid equatorial sand seas of organic rich dunes where rain is infrequent and atmospheric sedimentation is expected to be low it has been suggested that aeolian infill plays a major role in shallowing the craters topographic relaxation at titan s current heat flow was previously assumed to be an unimportant process on titan due to its low surface temperature 94 k however our estimate of the thermal conductivity of titan s organic rich sand is remarkably low 0 025 w m 1 k 1 and when in thick deposits will result in a thermal blanketing effect that can aid relaxation here we simulate the relaxation of titan s craters afekan soi and sinlap including thermal effects of various amounts of sand inside and around titan s craters we find that the combination of aeolian infill and subsequent relaxation can produce the current crater depths in a geologically reasonable period of time using titan s current heat flow instead of needing to fill completely the missing volume with 100 sand only 62 71 and 97 of the volume need be sand at the current basal heat flux for afekan soi and sinlap respectively we conclude that both processes are likely at work shallowing these craters and this finding contributes to why titan overall lacks impact craters in the arid equatorial regions

the dynamics of titan s troposphere while the voyager mission could essentially not reveal the dynamics of titan s troposphere useful information was obtained by the cassini spacecraft and particularly by the huygens probe that landed on titan s surface this information can be interpreted by means of numerical models of atmospheric circulation the meridional circulation is likely to consist of a large hadley circulation asymmetric about the equator but is susceptible to disruption by turbulence in clouds the zonal wind in the troposphere is comparable to or even weaker than that in the terrestrial troposphere and contains zones of easterlies much in contrast to the super rotating stratosphere unique to titan is the transition from a geostrophic to cyclostrophic wind balance in the upper troposphere while earth like storm systems associated with baroclinic instability are absent saturn s gravitational tide introduces a planetary wave of wavenumber 2 and a periodical variation in the wind direction in the troposphere unlike on earth the wind over the equatorial surface is westerly the seasonal reversal in the hadley circulation sense and zonal wind direction is predicted to have a substantial influence on the formation of dunes as well as variation of titan s rotation rate and length of day

impact cratering on titan ii global melt escaping ejecta and aqueous alteration of surface organics abstract new three dimensional hydrodynamic simulations of hypervelocity impacts into the crust of titan were undertaken to determine the fraction of liquid water generated on the surface of saturn s largest moon over its history and hence the potential for surface modification of hydrocarbons and nitriles by exposure to liquid water we model in detail an individual impact event in terms of ejecta produced and melt generated and use this to estimate melt production over titan s history taking into account the total flux of the impactors and its decay over time our estimates show that a global melt layer at any time after the very beginning of titan s history is improbable but transient melting local to newly formed craters has occurred over large parts of the surface local maxima of the melt are connected with the largest impact events we also calculate the amount of volatiles delivered at the impact with various impact velocities from 3 km s for possible hyperion fragments to 11 km s for jupiter family comets and their retention as a possible source of titan s atmosphere we find the probability of impact ejecta escaping titan with its modern dense and thick atmosphere is rather low and dispersal of titan organics throughout the rest of the solar system requires impactors tens of kilometers in diameter water ice melting and exposure of organics to liquid water has been widespread because of impacts but burial or obscuration of craters by organic deposits or cryovolcanism is aided by viscous relaxation the largest impactors may breach an ammonia water mantle layer creating a circular albedo contrast rather than a crater

near infrared spectral mapping of titan s mountains and channels 1 we investigate the spectral reflectance properties of channels and mountain ranges on titan using data from cassini s visual and infrared mapping spectrometer vims obtained during the t9 encounter 26 december 2005 we identify the location of channels and mountains using synthetic aperture radar maps obtained from cassini s radar instrument during the t13 30 april 2006 flyby channels are evident even in vims imaging with spatial resolution coarser than the channel size the channels share spectral characteristics with titan s dark blue terrain e g the huygens landing site that is consistent with an enhancement in water ice content relative to the rest of titan we use this fact to measure widths of 1 km for the largest channels comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of xanadu mountains are darker and bluer than surrounding smooth terrain these results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion we suggest a model for the geographic relationship of the dark blue dark brown and equatorial bright spectral units based on our findings

titan s cloud seasonal activity from winter to spring with cassini vims abstract since saturn orbital insertion in july 2004 the cassini orbiter has been observing titan throughout most of the northern winter season october 2002 august 2009 and the beginning of spring allowing a detailed monitoring of titan s cloud coverage at high spatial resolution with close flybys on a monthly basis this study reports on the analysis of all the near infrared images of titan s clouds acquired by the visual and infrared mapping spectrometer vims during 67 targeted flybys of titan between july 2004 and april 2010 the vims observations show numerous sporadic clouds at southern high and mid latitudes rare clouds in the equatorial region and reveal a long lived cloud cap above the north pole ubiquitous poleward of 60 n these observations allow us to follow the evolution of the cloud coverage during almost a 6 year period including the equinox and greatly help to further constrain global circulation models gcms after 4 years of regular outbursts observed by cassini between 2004 and 2008 southern polar cloud activity started declining and completely ceased 1 year before spring equinox the extensive cloud system over the north pole stable between 2004 and 2008 progressively fractionated and vanished as titan entered into northern spring at southern mid latitudes clouds were continuously observed throughout the vims observing period even after equinox in a latitude band between 30 s and 60 s during the whole period of observation only a dozen clouds were observed closer to the equator though they were slightly more frequent as equinox approached we also investigated the distribution of clouds with longitude we found that southern polar clouds before disappearing in mid 2008 were systematically concentrated in the leading hemisphere of titan in particular above and to the east of ontario lacus the largest reservoir of hydrocarbons in the area clouds are also non homogeneously distributed with longitude at southern mid latitudes the n 2 mode wave pattern of the distribution observed since 2003 by earth based telescopes and confirmed by our cassini observations may be attributed to saturn s tides although the latitudinal distribution of clouds is now relatively well reproduced and understood by the gcms the non homogeneous longitudinal distributions and the evolution of the cloud coverage with seasons still need investigation if the observation of a few single clouds at the tropics and at northern mid latitudes late in winter and at the start of spring cannot be further interpreted for the moment the obvious shutdown of the cloud activity at titan s poles provides clear signs of the onset of the general circulation turnover that is expected to accompany the beginning of titan s northern spring according to our gcm the persistence of clouds at certain latitudes rather suggests a sudden shift in near future of the meteorology into the more illuminated hemisphere finally the observed seasonal change in cloud activity occurred with a significant time lag that is not predicted by our model this may be due to an overall methane humidity at titan s surface higher than previously expected

cassini radar observation of punga mare and environs bathymetry and composition abstract in january 2015 fly by t108 the cassini radar observed punga mare titan s northernmost and third largest sea in altimetry mode during closest approach the ground track intercepted a section of the mare and a system of channels and flooded areas connecting punga to kraken mare we use a processing technique successfully adopted for ligeia mare and ontario lacus for detecting echoes from the sea floor and constraining the depth and composition of these liquid bodies we find that along the radar transect punga mare has a maximum measured depth of 110 m the relative reduction in backscatter of the seafloor as a function of increasing depth suggests a liquid loss tangent of 3 1 10 5 while this value is within the formal uncertainty of the loss tangent derived for ligeia mare the best fit solution is lower and is consistent with a nearly pure binary methane nitrogen liquid with little to no ethane or higher order components the indication of very low amounts of ethane toward the pole suggests that atmospheric processes are controlling the surface liquid composition of titan s seas

morphology of fluvial networks on titan evidence for structural control abstract although titan s surface shows clear evidence of erosional modification such as fluvial incision evidence for tectonism has been less apparent on earth fluvial networks with strongly preferred orientations are often associated with structural features such as faults or joints that influence flow or erodibility we delineated and classified the morphologies of fluvial drainages on titan and discovered evidence of structural control fluvial networks were delineated both on synthetic aperture radar sar images covering 40 of titan from the cassini titan radar mapper up through t71 and on visible light images of the huygens landing site collected by the descent imager spectral radiometer disr the delineated networks were assigned to one of three morphologic classes dendritic parallel or rectangular using a quantitative terrestrial drainage pattern classification algorithm modified for use with titan data we validated our modified algorithm by applying it to synthetic fluvial networks produced by a landscape evolution model with no structural control of drainage orientations and confirmed that only a small fraction of the networks are falsely identified as structurally controlled as a second validation we confirmed that our modified algorithm correctly classifies terrestrial networks that are classified in multiple previous works as rectangular application of this modified algorithm to our titan networks results in a classification of rectangular for one half of the sar and disr networks a review of the geological context of the four terrestrial rectangular networks indicates that tensional stresses formed the structures controlling those terrestrial drainages based on the similar brittle response of rock and cryogenic ice to stress we infer that structures formed under tension are the most likely cause of the rectangular titan networks delineated here the distribution of these rectangular networks suggests that tensional stresses on titan may have been widespread

material transport map of titan the fate of dunes abstract using sar data from cassini s radar instrument we examined the orientations of three terrain units on titan bright lineated plains streak like plains and linear dunes from the overall integrated pattern of their orientation we were able to determine titan s global material transport vectors the analysis indicates that in both the northern and southern hemispheres materials from 0 to 35 deg latitude are transported poleward to a belt centred at roughly 35 deg materials from 60 to 35 deg latitude are transported equatorward to the belt at roughly 35 deg comparison with the global topographical gradient lorenz r d et al 2013 icarus 225 367 377 suggests that fluvial transport is not the dominant process for material transport on titan or that it is at least overprinted with another transport mechanism our results are consistent with aeolian transport being the dominant mechanism in the equatorial and mid latitude zones the zone at 35 deg is thus the ultimate sink for materials from the equator to low polar latitudes materials making up the equatorial dunes will be transported to the latitude 35 deg belts only plains units are observed at latitudes of 35 deg dunes and materials with the spectral characteristics of dunes are not observed at these latitudes this observation suggests that either dune materials are converted or modified into plains units or that the margins of dunes are transport limited

titan an exogenic world abstract all landforms on titan that are unambiguously identifiable can be explained by exogenic processes aeolian fluvial impact cratering and mass wasting previous suggestions of endogenically produced cryovolcanic constructs and flows have without exception lacked conclusive diagnostic evidence the modification of sparse recognizable impact craters themselves exogenic can be explained by aeolian and fluvial erosion tectonic activity could be driven by global thermal evolution or external forcing rather than by active interior processes a lack of cryovolcanism would be consistent with geophysical inferences of a relatively quiescent interior incomplete differentiation only minor tidal heating and possibly a lack of internal convection today titan might be most akin to callisto with weather an endogenically relatively inactive world with a cool interior we do not aim to disprove the existence of any and all endogenic activity at titan nor to provide definitive alternative hypotheses for all landforms but instead to inject a necessary level of caution into the discussion the hypothesis of titan as a predominantly exogenic world can be tested through additional cassini observations and analyses of putative cryovolcanic features geophysical and thermal modeling of titan s interior evolution modeling of icy satellite landscape evolution that is shaped by exogenic processes alone and consideration of possible means for supplying titan s atmospheric constituents that do not rely on cryovolcanism

evidence of titan s climate history from evaporite distribution abstract water ice poor 5 m bright material on saturn s moon titan has previously been geomorphologically identified as evaporitic here we present a global distribution of the occurrences of the 5 m bright spectral unit identified with cassini s visual infrared mapping spectrometer vims and examined with radar when possible we explore the possibility that each of these occurrences are evaporite deposits the 5 m bright material covers 1 of titan s surface and is not limited to the poles the only regions with extensive long lived surface liquid we find the greatest areal concentration to be in the equatorial basins tui regio and hotei regio our interpretations based on the correlation between 5 m bright material and lakebeds imply that there was enough liquid present at some time to create the observed 5 m bright material we address the climate implications surrounding a lack of evaporitic material at the south polar basins if the south pole basins were filled at some point in the past then where is the evaporite

the lakes of titan the surface of saturn s haze shrouded moon titan has long been proposed to have oceans or lakes on the basis of the stability of liquid methane at the surface1 2 initial visible3 and radar4 5 imaging failed to find any evidence of an ocean although abundant evidence was found that flowing liquids have existed on the surface5 6 here we provide definitive evidence for the presence of lakes on the surface of titan obtained during the cassini radar flyby of titan on 22 july 2006 t16 the radar imaging polewards of 70 north shows more than 75 circular to irregular radar dark patches in a region where liquid methane and ethane are expected to be abundant and stable on the surface2 7 the radar dark patches are interpreted as lakes on the basis of their very low radar reflectivity and morphological similarities to lakes including associated channels and location in topographic depressions some of the lakes do not completely fill the depressions in which they lie and apparently dry depressions are present we interpret this to indicate that lakes are present in a number of states including partly dry and liquid filled these northern hemisphere lakes constitute the strongest evidence yet that a condensable liquid hydrological cycle is active in titan s surface and atmosphere in which the lakes are filled through rainfall and or intersection with the subsurface liquid methane table

mountains on titan modeling and observations 1 we have developed a thermal model of titan s interior to study changes in volume during partial freezing or melting of a subsurface ocean due to heat flux variations from the interior we find that the long term cooling of titan can cause global volume contraction v v 0 01 we then simulate two dimensional contractional deformation of titan s icy lithosphere finding that contractional deformation can produce tectonic activity and fold formation folds could potentially achieve a topographic height of several kilometers for high local strain 0 16 and for high temperature gradients in the ice i shell order of 10 k km 1 corresponding to an ancient high heat flux from the interior order of 0 02 0 06 w m 2 examination of synthetic aperture radar sar imagery obtained by cassini radar shows possible evidence of contractional tectonism in the equatorial regions of titan although the moderate resolution of the cassini sar imagery does not permit an unambiguous geological interpretation

radar topography of domes on planetary surfaces abstract we investigate the possibility of measuring the heights and morphology of viscously emplaced domes using radar imagery we accurately reproduce the known height and shape of a terrestrial salt dome and estimate the heights of several venusian pancake domes to within a factor of two the terrestrial salt dome is consistent with a bingham flow while the much larger venusian pancake domes are consistent with a newtonian flow applying the same techniques to ganesa macula a potential cryovolcanic dome on titan we estimate a height between 2 0 4 9 km additional factors such as variable roughness and composition might account for some of the discrepancies observed

estimates of fluvial erosion on titan from sinuosity of lake shorelines 1 titan has few impact craters suggesting that its surface is geologically young titan s surface also has abundant landforms interpreted to be fluvial networks here we evaluate whether fluvial erosion has caused significant resurfacing by estimating the cumulative erosion around the margins of polar lakes a scarcity of detailed topographic data makes it difficult to measure fluvial incision on titan but images of drowned fluvial features around the lake margins where elevated levels of hydrocarbon liquids appear to have partly flooded fluvial valleys offer a constraint on the topography we mapped the shorelines of several lakes to obtain topographic contours that trace the fluvially dissected topography we then used a numerical landscape evolution model to calibrate a relationship between contour sinuosity which reflects the extent of fluvial valley incision and cumulative erosion we confirmed this relationship by analyzing a partially dissected surface adjacent to the minnesota river usa comparison of the mapped titan contours with the sinuosity erosion relationship suggests that cumulative fluvial erosion around the margins of titan s polar lakes including ligeia mare kraken mare and punga mare in the north and ontario lacus in the south ranges from 4 to 31 of the initial relief additional model simulations show that this amount of fluvial erosion does not render craters invisible at the resolution of currently available imagery suggesting that fluvial erosion is not the only major resurfacing mechanism operating in titan s polar regions

dynamics of an ice continent on titan 1 if the large high albedo surface feature on titan s leading hemisphere is an elevated continent composed mainly of water ice it will deform under its own weight we present a model for the axisymmetric spreading of this hypothesized continent based on the similarity solution of halfar 1983 and the approach of nye 2000 we find that the thickness of the model continent is dictated by the spreading time whereas topographic relief is controlled primarily by isostatic effects for a mantle density of 1000 kg m 3 the relief of an isostatically supported continent on titan is not likely to exceed 3 7 km

cassini radar views the surface of titan the cassini titan radar mapper imaged about 1 of titan s surface at a resolution of 0 5 kilometer and larger areas of the globe in lower resolution modes the images reveal a complex surface with areas of low relief and a variety of geologic features suggestive of dome like volcanic constructs flows and sinuous channels the surface appears to be young with few impact craters scattering and dielectric properties are consistent with porous ice or organics dark patches in the radar images show high brightness temperatures and high emissivity and are consistent with frozen hydrocarbons

structural and tidal models of titan and inferences on cryovolcanism titan saturn s largest satellite is subject to solid body tides exerted by saturn on the timescale of its orbital period the tide induced internal redistribution of mass results in tidal stress variations which could play a major role for titan s geologic surface record we construct models of titan s interior that are consistent with the satellite s mean density polar moment of inertia factor obliquity and tidal potential love number k2 as derived from cassini observations of titan s low degree gravity field and rotational state in the presence of a global liquid reservoir the tidal gravity field is found to be consistent with a subsurface water ammonia ocean more than 180 km thick and overlain by an outer ice shell of less than 110 km thickness the model calculations suggest comparatively low ocean ammonia contents of less than 5 wt and ocean temperatures in excess of 255 k i e higher than previously thought thereby substantially increasing titan s potential for habitable locations the calculated diurnal tidal stresses at titan s surface amount to 20 kpa almost comparable to those expected at enceladus and europa tidal shear stresses are concentrated in the polar areas while tensile stresses predominate in the near equatorial midlatitude areas of the sub and anti saturnian hemispheres the characteristic pattern of maximum diurnal tidal stresses is largely compliant with the distribution of active regions such as cryovolcanic candidate areas the latter could be important for titan s habitability since those may provide possible pathways for liquid water ammonia outbursts on the surface and the release of methane in the satellite s atmosphere

grooved terrain on ganymede first results from galileo high resolution imaging abstract high resolution galileo imaging has provided important insight into the origin and evolution of grooved terrain on ganymede the uruk sulcus target site was the first imaged at high resolution and considerations of resolution viewing geometry low image compression and complementary stereo imaging make this region extremely informative contrast variations in these low incidence angle images are extreme and give the visual impression of topographic shading however photometric analysis shows that the scene must owe its character to albedo variations a close correlation of albedo variations to topography is demonstrated by limited stereo coverage allowing extrapolation of the observed brightness and topographic relationships to the rest of the imaged area distinct geological units are apparent across the region and ridges and grooves are ubiquitous within these units the stratigraphically lowest and most heavily cratered units lineated grooved terrain generally show morphologies indicative of horst and graben style normal faulting the stratigraphically highest groove lanes parallel ridged terrain exhibit ridges of roughly triangular cross section suggesting that tilt block style normal faulting has shaped them these extensional tectonic models are supported by crosscutting relationships at the margins of groove lanes thus a change in tectonic style with time is suggested in the uruk sulcus region varying from horst and graben faulting for the oldest grooved terrain units to tilt block normal faulting for the latest units the morphologies and geometries of some stratigraphically high units indicate that a strike slip component of deformation has played an important role in shaping this region of grooved terrain the most recent tectonic episode is interpreted as right lateral transtension with its tectonic pattern of two contemporaneous structural orientations superimposed on older units of grooved terrain there is little direct evidence for cryovolcanic resurfacing in the uruk sulcus region instead tectonism appears to be the dominant geological process that has shaped the terrain a broad wavelength of deformation is indicated corresponding to the voyager observed topography and may be the result of ductile necking of the lithosphere while a finer scale of deformation probably reflects faulting of the brittle near surface the results here form a basis against which other galileo grooved terrain observations can be compared

alluvial and fluvial fans on saturn s moon titan reveal processes materials and regional geology fans landforms that record the storage and transport of sediment from uplands to depositional basins are found on saturn s moon titan a body of significantly different process rates and material compositions from earth images obtained by the cassini spacecraft s synthetic aperture radar reveal morphologies roughness textural patterns and other properties consistent with fan analogues on earth also viewed by synthetic aperture radar the observed fan characteristics on titan reveal some regions of high relative relief and others with gentle slopes over hundreds of kilometres exposing topographic variations and influences on fan formation there is evidence for a range of particle sizes across proximal to distal fan regions from c 2 cm or more to fine grained which can provide details on sedimentary processes some features are best described as alluvial fans which implies their proximity to high relief source areas while others are more likely to be fluvial fans drawing from larger catchment areas and frequently characterized by more prolonged runoff events the presence of fans corroborates the vast liquid storage capacity of the atmosphere and the resultant episodic behaviour fans join the growing list of landforms on titan derived from atmospheric and fluvial processes similar to those on earth strengthening comparisons between these two planetary bodies

geomorphologic mapping of the menrva region of titan using cassini radar data abstract we made a detailed geomorphologic map of the menrva region of titan using cassini radar data as our map base using similar techniques and approaches that were applied to mapping magellan radar images of venus and earlier more generalized titan maps we were able to define and characterize 10 radar morphologic units along with inferred dunes and fluvial channels from the radar data structural features such as scarps ridges and lineaments were also identified using principles of superposition cross cutting and embayment relations we created a sequence of map units for this region we interpret menrva to be a 440 km wide degraded impact basin in agreement with earlier studies by elachi et al elachi c et al 2006 nature 441 709 713 and wood et al wood c a lorenz r kirk r lopes r mitchell k stofan e and the cassini radar team 2010 icarus 206 334 344 and identify it as the oldest feature in the map region exogenic processes including hydrocarbon fluid channelization forming the elivagar flumina channel network and dune fields resulting from aeolian activity are the current geologic processes dominating our map area and these processes have contributed to the erosion of the crater s ejecta field there is evidence of multiple episodes of channel formation erosion and burial by aeolian deposits as observed elsewhere on titan by e g barnes et al barnes j w et al 2005 icarus 195 400 414 channel outflow regions have morphologies suggestive of streams formed by flash floods and dune fields are small and restricted rather than forming large dune seas consistent with a desert like environment for this region with low supply of hydrocarbon particles also consistent with other studies by e g lorenz et al lorenz r d et al 2008a planet space sci 56 1132 1144 there is no evidence of cryovolcanism or non impact related tectonic activity in the menrva region although this region is too small to infer anything about the roles of these processes elsewhere on titan this work suggests detailed geomorphologic mapping can confidently be applied to cassini radar data and we suggest that more extensive mapping should be done using radar iss and vims data geographically distributed across titan to assess its usefulness for a future combined radar iss vims based global geologic map

dunes on titan observed by cassini radar thousands of longitudinal dunes have recently been discovered by the titan radar mapper on the surface of titan these are found mainly within 30 of the equator in optically near infrared and radar dark regions indicating a strong proportion of organics and cover well over 5 of titan s surface their longitudinal duneform interactions with topography and correlation with other aeolian forms indicate a single dominant wind direction aligned with the dune axis plus lesser off axis or seasonally alternating winds global compilations of dune orientations reveal the mean wind direction is dominantly eastwards with regional and local variations where winds are diverted around topographically high features such as mountain blocks or broad landforms global winds may carry sediments from high latitude regions to equatorial regions where relatively drier conditions prevail and the particles are reworked into dunes perhaps on timescales of thousands to tens of thousands of years on titan adequate sediment supply sufficient wind and the absence of sediment carriage and trapping by fluids are the dominant factors in the presence of dunes

geomorphologic mapping of titan s polar terrains constraining surface processes and landscape evolution abstract we present a geomorphologic map of titan s polar terrains the map was generated from a combination of cassini synthetic aperture radar sar and imaging science subsystem imaging products as well as altimetry sartopo and radargrammetry topographic datasets in combining imagery with topographic data our geomorphologic map reveals a stratigraphic sequence from which we infer process interactions between units in mapping both polar regions with the same geomorphologic units we conclude that processes that formed the terrains of the north polar region also acted to form the landscape we observe at the south uniform sar dark plains are interpreted as sedimentary deposits and are bounded by moderately dissected uplands these plains contain the highest density of filled and empty lake depressions and canyons these units unconformably overlay a basement rock that outcrops as mountains and sar bright dissected terrains at various elevations across both poles all these units are then superposed by surficial units that slope towards the seas suggestive of subsequent overland transport of sediment from estimates of the depths of the embedded empty depressions and canyons that drain into the seas the sar dark plains must be 600 m thick in places though the thickness may vary across the poles at the lowest elevations of each polar region there are large seas which are currently liquid methane ethane filled at the north and empty at the south the large plains deposits and the surrounding hillslopes may represent remnant landforms that are a result of previously vast polar oceans where larger liquid bodies may have allowed for a sustained accumulation of soluble and insoluble sediments potentially forming layered sedimentary deposits coupled with vertical crustal movements the resulting layers would be of varying solubilities and erosional resistances allowing formation of the complex landscape that we observe today

titan s surface from cassini radar sar and high resolution radiometry data of the first five flybys abstract the first five titan flybys with cassini s synthetic aperture radar sar and radiometer are examined with emphasis on the calibration and interpretation of the high resolution radiometry data acquired during the sar mode sar radiometry maps of the 2 cm wavelength brightness temperature are obtained coincident with the sar swath imaging with spatial resolution approaching 6 km a preliminary calibration shows that brightness temperature in these maps varies from 64 to 89 k surface features and physical properties derived from the sar radiometry maps and sar imaging are strongly correlated in general we find that surface features with high radar reflectivity are associated with radiometrically cold regions while surface features with low radar reflectivity correlate with radiometrically warm regions we examined scatterplots of the normalized radar cross section 0 versus brightness temperature finding differing signatures that characterize various terrains and surface features implications for the physical and compositional properties of these features are discussed the results indicate that volume scattering is important in many areas of titan s surface particularly xanadu while other areas exhibit complex brightness temperature variations consistent with variable slopes or surface material and compositional properties

radar scattering of linear dunes and mega yardangs application to titan the ku band 13 8 ghz 2 2 cm radar instrument onboard the cassini huygens spacecraft has revealed the richness of the surface of titan as numerous seas lakes rivers cryo volcanic flows and vast dune fields have been discovered linear dunes are a major geomorphological feature present on titan covering up to 17 of its surface mainly in equatorial regions however the resolution of the radar instrument is not good enough to allow a detailed study of the morphology of these features in addition other linear wind related landforms such as mega yardangs linear wind abraded ridges formed in cohesive rocks are likely to present a comparable radar signature that could be confused with the one of dunes we conducted a comparative study of the radar radiometry of both linear dunes and mega yardangs based on representative terrestrial analogues the linear dunes located in the great sand sea in western egypt and in the namib desert in namibia and the mega yardangs observed in the lut desert in eastern iran and in the borkou desert in northern chad we analysed the radar scattering of both terrestrial linear dunes and mega yardangs using high resolution radar images acquired by the x band 9 6 ghz 3 1 cm sensor of the terrasar x satellite variations seen in the radar response of dunes are the result of a contrast between the dune and interdune scattering while for mega yardangs these variations are the result of a contrast between ridges and erosion valleys we tested a simple surface scattering model with parameters derived from the local topography and surface roughness estimates to accurately reproduce the radar signal variations for both landforms it appears that we can discriminate between two types of dunes bare interdunes as in egypt and sand covered interdunes as in namibia and between two types of mega yardangs young yardangs as in iran and older ones as in chad we applied our understanding of the radar scattering to the analysis of cassini radar t8 acquisitions over the belet sand sea on titan and show that the linear dunes encountered there are likely to be of both egyptian and namibian type we also show that the radar bright linear features observed in cassini radar t64 and t83 acquisitions are very likely to be mega yardangs possible remnants of ancient lake basins at mid latitude formed when titan s climate was different

global contraction expansion and polar lithospheric thinning on titan from patterns of tectonism we investigate the underlying physical processes that govern the formation and evolution of titan s tectonic features this is done by mapping mountain chains and hills using cassini radar data obtained during titan flybys t3 to t69 our mapping of mountain chains and hills reveals a global pattern east west orientations within 30 of the equator and north south between 60 latitude and the poles this result makes titan one of the few solar system bodies where global processes rather than regional processes dominate tectonism after comparison with five global stress models showing theoretical mountain chain orientations we suggest that either global contraction coupled with spin up or global expansion coupled with despinning could explain our observations if coupled with a lithosphere thinner in titan s polar regions

linear dunes on titan and earth initial remote sensing comparisons thousands of dunes found in cassini radar images of the equatorial regions of titan a moon around saturn are similar in size and morphology to linear dunes on earth we present remote sensing images of terrestrial analogues to the dunes on titan obtained by landsat and radar both at considerably higher resolution than are available at titan that provide information about dune landforms and processes dunes are generally dark to radar indicating smooth surfaces and signal absorbing materials but at certain incidence angles dune surfaces can reflect the radar signal and lead to a bright return linear dunes on titan and earth diverge around topographic obstacles creating teardrop patterns that indicate mean direction of wind flow and sand transport when sand supply or wind conditions change in linear dune fields such as behind an obstacle or near the margin of the dune field dunes disappear change size and spacing or change dune type these comparisons of features on titan and earth provide a better understanding of the global sand transporting wind directions sand properties and supply and the nature of the underlying substrate on titan

the geology of hotei regio titan correlation of cassini vims and radar abstract joint cassini vims and radar sar data of 700 km wide hotei regio reveal a rich collection of geological features that correlate between the two sets of images the degree of correlation is greater than anywhere else seen on titan central to hotei regio is a basin filled with cryovolcanic flows that are anomalously bright in vims data in particular at 5 m and quite variable in roughness in sar the edges of the flows are dark in sar data and appear to overrun a vims bright substrate sar stereo topography shows the flows to be viscous 100 200 m thick on its southern edge the basin is ringed by higher 1 km mountainous terrain the mountains show mixed texture in sar data some regions are extremely rough exhibit low and spectrally neutral albedo in vims data and may be partly coated with darker hydrocarbons around the southern margin of hotei regio the sar image shows several large dendritic radar bright channels that flow down from the mountainous terrain and terminate in dark blue patches seen in vims images whose infrared color is consistent with enrichment in water ice the patches are in depressions that we interpret to be filled with fluvial deposits eroded and transported by liquid methane in the channels in the vims images the dark blue patches are encased in a latticework of lighter bands that we suggest to demark a set of circumferential and radial fault systems bounding structural depressions conceivably the circular features are tectonic structures that are remnant from an ancient impact structure we suggest that impact generated structures may have simply served as zones of weakness no direct causal connection such as impact induced volcanism is implied we also speculate that two large dark features lying on the northern margin of hotei regio could be calderas in summary the preservation of such a broad suite of vims infrared color variations and the detailed correlation with features in the sar image and sar topography evidence a complex set of geological processes pluvial fluvial tectonic cryovolcanic impact that have likely remained active up to very recent geological time

titan s surface revealed by hst imaging we present for the first time relative albedo maps of titan s surface the maps were made from images taken by the hubble space telescope s planetary camera 295 km per pixel through atmospheric windows at 940 and 1080 nm coverage at all longitudes and between 45 s and 60 n was obtained with 14 orbits from 4 18 october 1994 each image is characterized by haze with both limb effects brightening and a large north south contrast subtracting an averaged image from each frame removes haze effects and reveals surface features of 10 maximum contrast many features are clearly visible in multiple images and in both filters but the surface map is dominated by a large bright roughly rectangular feature centered at 110 w 10 s and elongated in an east west direction 4000 2500 km2 this feature and others indicate the diversity of titan s surface we consider the origin of the bright feature in an otherwise dark landscape and suggest that highland washing by methane rainfall is a likely mechanism

use of soil catena field data for estimating relative ages of moraines soils at the crests of moraines are commonly used to estimate the relative ages of moraines however for various pedologic and geomorphic reasons soil development at crest sites may not truly reflect the time since moraine formation for example some crest soils on moraines of greatly different age are similar in morphology and development soil catena data for soils at several sites aligned downslope from the crest can greatly improve on the usefulness of soil data for estimating moraine ages for this purpose the authors use the weighted mean catena profile development index which condenses field data for all of the soils in each catena into a single value

fluvial erosion and post erosional processes on titan the surface of titan has been revealed by cassini observations in the infrared and radar wavelength ranges as well as locally by the huygens lander instruments sand seas recently discovered lakes distinct landscapes and dendritic erosion patterns indicate dynamic surface processes this study focus on erosional and depositional features that can be used to constrain the amount of liquids involved in the erosional process as well as on the compositional characteristics of depositional areas fluvial erosion channels on titan as identified at the huygens landing site and in radar and visible and infrared mapping spectrometer vims observations have been compared to analogous channel widths on earth yielding average discharges of up to 1600 m3 s for short recurrence intervals that are sufficient to move centimeter sized sediment and significantly higher discharges for long intervals with respect to the associated drainage areas this roughly translates to 1 150 cm day runoff production rates with 10 years recurrence intervals and by assuming precipitation this implies 0 6 60 mm h rainfall rates thus the observed surface erosion fits with the methane convective storm models as well as with the rates needed to transport sediment during cassini s t20 fly by the vims observed an extremely eroded area at 30 w 7 s with resolutions of up to 500 m pixel that extends over thousands of square kilometers the spectral characteristics of this area change systematically reflecting continuous compositional and or particle size variations indicative of transported sediment settling out while flow capacities cease to account for the estimated runoff production and widespread alluvial deposits of fine grained material release of area dependent large fluid volumes are required only frequent storms with heavy rainfall or cryovolcanic induced melting can explain these erosional features

role of fluids in the tectonic evolution of titan abstract detailed analyses of slopes and arcuate planform morphologies of titan s equatorial mountain ridge belts are consistent with formation by contractional tectonism however contractional structures in ice require large stresses 4 10 mpa the sources of which are not likely to exist on titan cassini spacecraft imagery reveals a methane based hydrological cycle on titan that likely includes movement of fluids through the subsurface these crustal liquids may enable contractional tectonic features to form as groundwater has for thrust belts on earth in this study we show that liquid hydrocarbons in titan s near subsurface can lead to fluid overpressures that facilitate contractional deformation at smaller stresses

the sand seas of titan cassini radar observations of longitudinal dunes the most recent cassini radar images of titan show widespread regions up to 1500 kilometers by 200 kilometers of near parallel radar dark linear features that appear to be seas of longitudinal dunes similar to those seen in the namib desert on earth the ku band 2 17 centimeter wavelength images show 100 meter ridges consistent with duneforms and reveal flow interactions with underlying hills the distribution and orientation of the dunes support a model of fluctuating surface winds of 0 5 meter per second resulting from the combination of an eastward flow with a variable tidal wind the existence of dunes also requires geological processes that create sand sized 100 to 300 micrometer particulates and a lack of persistent equatorial surface liquids to act as sand traps

distribution and interplay of geologic processes on titan from cassini radar data abstract the cassini titan radar mapper is providing an unprecedented view of titan s surface geology here we use synthetic aperture radar sar image swaths ta t30 obtained from october 2004 to december 2007 to infer the geologic processes that have shaped titan s surface these sar swaths cover about 20 of the surface at a spatial resolution ranging from 350 m to 2 km the sar data are distributed over a wide latitudinal and longitudinal range enabling some conclusions to be drawn about the global distribution of processes they reveal a geologically complex surface that has been modified by all the major geologic processes seen on earth volcanism tectonism impact cratering and erosion and deposition by fluvial and aeolian activity in this paper we map geomorphological units from sar data and analyze their areal distribution and relative ages of modification in order to infer the geologic evolution of titan s surface we find that dunes and hummocky and mountainous terrains are more widespread than lakes putative cryovolcanic features mottled plains and craters and crateriform structures that may be due to impact undifferentiated plains are the largest areal unit their origin is uncertain in terms of latitudinal distribution dunes and hummocky and mountainous terrains are located mostly at low latitudes less than 30 with no dunes being present above 60 channels formed by fluvial activity are present at all latitudes but lakes are at high latitudes only crateriform structures that may have been formed by impact appear to be uniformly distributed with latitude but the well preserved impact craters are all located at low latitudes possibly indicating that more resurfacing has occurred at higher latitudes cryovolcanic features are not ubiquitous and are mostly located between 30 and 60 north we examine temporal relationships between units wherever possible and conclude that aeolian and fluvial pluvial lacustrine processes are the most recent while tectonic processes that led to the formation of mountains and xanadu are likely the most ancient

surface albedo spectral properties of geologically interesting areas on titan we investigate the nature and possible formation processes of three areas on titan s surface which have been suggested as geologically interesting hotei regio tui regio and sotra patera we also reanalyze the spectral characteristics of the huygens landing site we apply a statistical principal component analysis pca and a radiative transfer rt method on the visual and infrared mapping spectrometer datacubes in order to retrieve the surface albedo of distinct spectral units in the near infrared we have been able to exploit only a subset of the currently available hotei regio data which are in general not optimal in terms of geometry for an analysis with a plane parallel rt code our inferred surface albedos present generally higher values from 1 to 2 m and lower ones at 0 94 and in the 2 6 5 m region the regions of interest rois within hotei regio tui regio and sotra patera are always significantly brighter than the surrounding areas the largest variations are found longward of 2 m and mainly at 5 m this higher surface albedo with respect to the surrounding area and in general the fact that the spectral behavior is different for each of these areas is probably indicative of diverse chemical compositions and origins we compare the spectral albedos with some suggested surface candidates on titan such as h2o co2 and ch4 ices as well as tholin and discuss possible chemical composition variations as well as other interpretations

the cassini vims archive of titan from browse products to global infrared color maps abstract we have analyzed the complete visual and infrared mapping spectrometer vims data archive of titan our objective is to build global surface cartographic products by combining all the data gathered during the 127 targeted flybys of titan into synthetic global maps interpolated on a grid at 32 pixels per degree 1 4 km pixel at the equator in seven infrared spectral atmospheric windows multispectral summary images have been computed for each single vims cube in order to rapidly identify their scientific content and assess their quality these summary images are made available to the community on a public website vims univ nantes fr the global mapping work faced several challenges due to the strong absorbing and scattering effects of the atmosphere coupled to the changing observing conditions linked to the orbital tour of the cassini mission we determined a surface photometric function which accounts for variations in incidence emergence and phase angles and which is able to mitigate brightness variations linked to the viewing geometry of the flybys the atmospheric contribution has been reduced using the subtraction of the methane absorption band wings considered as proxies for atmospheric haze scattering we present a new global three color composite map of band ratios red 1 59 1 27 m green 2 03 1 27 m blue 1 27 1 08 m which has also been empirically corrected from an airmass the solar photon path length through the atmosphere dependence this map provides a detailed global color view of titan s surface partially corrected from the atmosphere and gives a global insight of the spectral variability with the equatorial dunes fields appearing in brownish tones and several occurrences of bluish tones localized in areas such as sinlap menvra and selk craters this kind of spectral map can serve as a basis for further regional studies and comparisons with radiative transfer outputs such as surface albedos and other additional data sets acquired by the cassini radar radar and imaging science subsystem iss instruments

relative rates of fluvial bedrock incision on titan and earth 1 observations of likely fluvial channels on the surface of titan along with titan s geologically youthful surface motivate this study of comparative fluvial erosion rates on titan and the earth the roles of bedload abrasion suspended load abrasion plucking and cavitation are considered despite orders of magnitude differences in some of the physical parameters that control fluvial incision on titan and the earth incision rates on titan are likely to be similar to terrestrial rates given similar conditions of slope discharge and sediment supply

spectroscopy morphometry and photoclinometry of titan s dunefields from cassini vims fine resolution 500 m pixel cassini visual and infrared mapping spectrometer vims t20 observations of titan resolve that moon s sand dunes the spectral variability in some dune regions shows that there are sand free interdune areas wherein vims spectra reveal the exposed dune substrate the interdunes from t20 are variously materials that correspond to the equatorial bright 5 m bright and dark blue spectral units our observations show that an enigmatic dark red spectral unit seen in t5 in fact represents a macroscopic mixture with 5 m bright material and dunes as its spectral endmembers looking more broadly similar mixtures of varying amounts of dune and interdune units of varying composition can explain the spectral and albedo variability within the dark brown dune global spectral unit that is associated with dunes the presence of interdunes indicates that titan s dunefields are both mature and recently active the spectrum of the dune endmember reveals the sand to be composed of less water ice than the rest of titan various organics are consistent with the dunes measured reflectivity we measure a mean dune spacing of 2 1 km and find that the dunes are oriented on the average in an east west direction but angling up to 10 from parallel to the equator in specific cases where no interdunes are present we determine the height of one set of dunes photoclinometrically to be between 30 and 70 m these results pave the way for future exploration and interpretation of titan s sand dunes

natural controls of fluvial denudation rates in major world drainage basins we present a new compilation of estimates of modern rates of mechanical and chemical denudation for externally drained basins exceeding 5 105 km2 in area these estimates are based on sediment and solute load data selected in order to represent natural rates as far as possible chemical denudation rates have been calculated by deducting the nondenudational component of solute load mechanical denudation rates range from 1 mm kyr 1 for the st lawrence and dnepr basins to 670 mm kyr 1 for the brahmaputra basin chemical denudation rates vary from 1 mm kyr 1 kolyma niger nile and rio grande basins to 27 mm kyr 1 chiang jiang basin the kolyma basin has the lowest 4 mm kyr 1 and the brahmaputra basin the highest overall rate of denudation 688 mm kyr 1 relationships between denudation rates and a range of morphometric hydrologic and climatic variables are investigated through correlation and regression analysis morphometric variables such as mean local relief are accurately calculated for large basins for the first time by using the national geophysical data center 10 minute topographic database variables expressing basin relief characteristics and runoff are found to be most strongly associated with both mechanical and chemical denudation rates with more than 60 of the variance in total denudation being accounted for by basin relief ratio and runoff basin area runoff variability and mean temperature however are only weakly associated with rates of denudation although direct comparisons cannot be made it appears that rates of basin denudation derived from present day mass flux estimates are not overall significantly different from estimates of long term rates based on sediment volume and thermochronologic data it therefore appears that the key factors identified as controlling denudation rates here are also applicable to the geological time spans relevant to the interaction between tectonic and denudational processes

mapping of titan results from the first titan radar passes the first two swaths collected by cassini s titan radar mapper were obtained in october of 2004 ta and february of 2005 t3 the ta swath provides evidence for cryovolcanic processes the possible occurrence of fluvial channels and lakes and some tectonic activity the t3 swath has extensive areas of dunes and two large impact craters we interpret the brightness variations in much of the swaths to result from roughness variations caused by fracturing and erosion of titan s icy surface with additional contributions from a combination of volume scattering and compositional variations despite the small amount of titan mapped to date the significant differences between the terrains of the two swaths suggest that titan is geologically complex the overall scarcity of impact craters provides evidence that the surface imaged to date is relatively young with resurfacing by cryovolcanism fluvial erosion aeolian erosion and likely atmospheric deposition of materials future radar swaths will help to further define the nature of and extent to which internal and external processes have shaped titan s surface

microwave dielectric constant of liquid hydrocarbons application to the depth estimation of titan s lakes 1 cassini radar reveals the surface of titan since flyby ta acquired on october 2004 the radar instrument discovered volcanic structures craters dunes channels lakes and seas in particular flyby t16 realized in july 2006 imaged tens of radar dark features close to titan s north pole they are interpreted as lakes filled with liquid hydrocarbons mainly methane a key material in the geologic and climatic history of titan in order to perform quantitative analysis and modeling of the radar response of titan s lakes the dielectric constant of liquid hydrocarbons is a crucial parameter in particular to estimate the radar wave attenuation we present here first measurements of the dielectric constant of lng liquefied natural gas mainly composed of methane at ku band 10 13 ghz we obtained a value 1 75 0 002j this value is used to model the radar backscattering of lakes observed during t16 flyby using a two layer scattering model we derive a relationship that is used to estimate a minimum depth for titan s lakes the proposed relationship is also coherent with the observation that the larger and then the deeper lakes are also the darker in radar images

mountains on titan observed by cassini radar abstract the cassini titan radar mapper has observed elevated blocks and ridge forming block chains on saturn s moon titan demonstrating high topography we term mountains summit flanks measured from the t3 february 2005 and t8 october 2005 flybys have a mean maximum slope of 37 and total elevations up to 1930 m as derived from a shape from shading model corrected for the probable effects of image resolution mountain peak morphologies and surrounding diffuse blankets give evidence that erosion has acted upon these features perhaps in the form of fluvial runoff possible formation mechanisms for these mountains include crustal compressional tectonism and upthrusting of blocks extensional tectonism and formation of horst and graben deposition as blocks of impact ejecta or dissection and erosion of a preexisting layer of material all above processes may be at work given the diversity of geology evident across titan s surface comparisons of mountain and blanket volumes and erosion rate estimates for titan provide a typical mountain age as young as 20 100 million years

the tectonics of titan global structural mapping from cassini radar abstract the cassini radar mapper has imaged elevated mountain ridge belts on titan with a linear to arcuate morphology indicative of a tectonic origin systematic geomorphologic mapping of the ridges in synthetic aperture radar sar images reveals that the orientation of ridges is globally e w and the ridges are more common near the equator than the poles comparison with a global topographic map reveals the equatorial ridges are found to lie preferentially at higher than average elevations we conclude the most reasonable formation scenario for titan s ridges is that contractional tectonism built the ridges and thickened the icy lithosphere near the equator causing regional uplift the combination of global and regional tectonic events likely contractional in nature followed by erosion aeolian activity and enhanced sedimentation at mid to high latitudes would have led to regional infilling and perhaps covering of some mountain features thus shaping titan s tectonic landforms and surface morphology into what we see today

titan s topography and shape at the end of the cassini mission with the conclusion of the cassini mission we present an updated topographic map of titan including all the available altimetry sartopo and stereo photogrammetry topographic datasets available from the mission we use radial basis functions to interpolate the sparse dataset which covers only 9 of titan s global area the most notable updates to the topography include higher coverage of the poles of titan improved fits to the global shape and a finer resolution of the global interpolation we also present a statistical analysis of the error in the derived products and perform a global minimization on a profile by profile basis to account for observed biases in the input dataset we find a greater flattening of titan than measured additional topographic rises in titan s southern hemisphere and better constrain the possible locations of past and present liquids on titan s surface

geomorphological map of the afekan crater region titan terrain relationships in the equatorial and mid latitude regions we carried out geomorphological mapping in a mid latitude area surrounding the afekan crater region on titan we used cassini radar synthetic aperture radar mode data as the basemap supplemented by cassini radar microwave emissivity imaging science subsystem iss infrared data visual and infrared mapping spectrometer vims spectral images and topography derived from synthetic aperture radar sar mapping was done at a spatial scale of 300 m pixel which corresponds to a map scale of 1 800 000 we describe multiple terrain units and their spatial relations we describe five broad classes of units that are in agreement with previous mapping efforts crater labyrinth hummocky mountainous plains and dune terrain classes we subdivide these into seven crater units four hummocky mountainous units six plains units and three dunes units our results show that plains are the dominant unit in titan s mid latitudes of the plains units the undifferentiated plains are the largest by total areal extent in the mapped region accounting for over 45 of the mapped area we developed a stratigraphic sequence that has the hummocky mountainous and labyrinth terrains as the oldest units the observed properties of the hummocky mountainous terrain are consistent with fractured water ice materials while the labyrinth terrains are consistent with organic materials the youngest units are the dune units and streak like plains units with the undifferentiated plains units being of intermediate age the microwave emissivity of the undifferentiated plains and dune units are consistent with organic materials given their properties and stratigraphic placement we conclude that the hummocky mountainous terrains are most consistent with the presumed crustal materials of titan the plains materials are consistent with deposits resulting from the transport and emplacement of organic rich materials predominantly by aeolian mechanisms our geomorphological mapping results are consistent with the equatorial and mid latitudes of titan being dominated by organic materials that have been deposited and emplaced by aeolian activity

regional geomorphology and history of titan s xanadu province titan s enigmatic xanadu province has been seen in some detail with instruments from the cassini spacecraft the region contains some of the most rugged mountainous terrain on titan with relief over 2000 m xanadu contains evolved and integrated river channels impact craters and dry basins filled with smooth radar dark material perhaps sediments from past lake beds arcuate and aligned mountain chains give evidence of compressional tectonism yet the overall elevation of xanadu is puzzlingly low compared to surrounding sand seas lineations associated with mountain fronts and valley floors give evidence of extension that probably contributed to this regional lowering several locations on xanadu s western and southern margins contain flow like features that may be cryovolcanic in origin perhaps ascended from lithospheric faults related to regional downdropping late in its history radiometry and scatterometry observations are consistent with a water ice or water ammonia ice composition to its exposed eroded fractured bedrock both microwave and visible to near infrared v nir data indicate a thin overcoating of organics likely derived from the atmosphere we suggest xanadu is one of the oldest terrains on titan and that its origin and evolution have been controlled and shaped by compressional and then extensional tectonism in the icy crust and ongoing erosion by methane rainfall

estimating erosional exhumation on titan from drainage network morphology 1 drainage networks on titan earth and mars provide the only known examples of non volcanic fluvial activity in our solar system the drainage networks on titan are apparently the result of a methane ethane cycle similar to earth s water cycle the scarcity of impact craters and the uneven distribution of fluvial dissection on titan suggest that the surface may be relatively young the purpose of this study is to assess the importance of erosion relative to other plausible mechanisms of resurfacing such as tectonic deformation cryovolcanism or deposition of aerosols we present a new method based on a measure of drainage network shape known as the width function to estimate cumulative erosion into an initially rough surface we calibrate this method with a numerical landscape evolution model and successfully test the method by applying it to river networks on earth with different exhumation histories to estimate erosional exhumation on titan we mapped fluvial networks in all synthetic aperture radar swaths obtained by the cassini spacecraft through t71 application of our method to the most completely imaged drainage networks indicates that for two of four regions analyzed titan s fluvial networks have produced only minor erosional modification of the surface for the best constrained region in the northern high latitudes we find that fluvial networks reflect spatially averaged erosion of more than 0 4 but less than 9 of the initial topographic relief this result implies either a recent non fluvial resurfacing event or long term fluvial incision rates that are slow relative to the rate of resurfacing

titan s diverse landscapes as evidenced by cassini radar s third and fourth looks at titan abstract cassini s third and fourth radar flybys t7 and t8 covered diverse terrains in the high southern and equatorial latitudes respectively the t7 synthetic aperture radar sar swath is somewhat more straightforward to understand in terms of a progressive poleward descent from a high dissected and partly hilly terrain down to a low flat plain with embayments and deposits suggestive of the past or even current presence of hydrocarbon liquids the t8 swath is dominated by dunes likely made of organic solids but also contain somewhat enigmatic probably tectonic features that may be partly buried or degraded by erosion or relaxation in a thin crust the dark areas in t7 show no dune morphology unlike the dark areas in t8 but are radiometrically warm like the dunes the huygens landing site lies on the edge of the t8 swath correlation of the radar and huygens disr images allows accurate determination of its coordinates and indicates that to the north of the landing site sit two large longitudinal dunes indeed had the huygens probe trajectory been just 10 km north of where it actually was images of large sand dunes would have been returned in place of the fluvially dissected terrain actually seen illustrating the strong diversity of titan s landscapes even at local scales

cryovolcanic features on titan s surface as revealed by the cassini titan radar mapper abstract the cassini titan radar mapper obtained synthetic aperture radar images of titan s surface during four fly bys during the mission s first year these images show that titan s surface is very complex geologically showing evidence of major planetary geologic processes including cryovolcanism this paper discusses the variety of cryovolcanic features identified from sar images their possible origin and their geologic context the features which we identify as cryovolcanic in origin include a large 180 km diameter volcanic construct dome or shield several extensive flows and three calderas which appear to be the source of flows the composition of the cryomagma on titan is still unknown but constraints on rheological properties can be estimated using flow thickness rheological properties of one flow were estimated and appear inconsistent with ammonia water slurries and possibly more consistent with ammonia water methanol slurries the extent of cryovolcanism on titan is still not known as only a small fraction of the surface has been imaged at sufficient resolution energetic considerations suggest that cryovolcanism may have been a dominant process in the resurfacing of titan

determining titan surface topography from cassini sar data a technique referred to as sartopo has been developed for obtaining surface height estimates with 10 km horizontal resolution and 75 m vertical resolution of the surface of titan along each cassini synthetic aperture radar sar swath we describe the technique and present maps of the co located data sets a global map and regional maps of xanadu and the northern hemisphere hydrocarbon lakes district are included in the results a strength of the technique is that it provides topographic information co located with sar imagery having a topographic context vastly improves the interpretability of the sar imagery and is essential for understanding titan sartopo is capable of estimating surface heights for most of the sar imaged surface of titan currently nearly 30 of the surface is within 100 km of a sartopo height profile other competing techniques provide orders of magnitude less coverage we validate the sartopo technique through comparison with known geomorphological features such as mountain ranges and craters and by comparison with co located nadir altimetry including a 3000 km strip that had been observed by sar a month earlier in this area the sartopo and nadir altimetry data sets are co located tightly within 5 10 km for one 500 km section have similar resolution and as expected agree closely in surface height furthermore the region contains prominent high spatial resolution topography so it provides an excellent test of the resolution and precision of both techniques