photometric changes on saturn s titan evidence for active cryovolcanism 1 we report infrared spectrophotometric variability on the surface of saturn s moon titan detected in images returned by the visual and infrared mapping spectrometer vims onboard the cassini saturn orbiter the changes were observed at 7 s 138 w and occurred between october 27 2005 and january 15 2006 after that date the surface was unchanged until the most recent observation march 18 2006 we previously reported spectrophotometric variability at another location 26 s 78 w cassini synthetic aperture radar sar images find that the surface morphology at both locations is consistent with surface flows possibly resulting from cryovolcanic activity wall et al companion paper this issue the vims reported time variability and sar morphology results suggest that titan currently exhibits intermittent surface changes consistent with present ongoing surface processes we suggest that these processes involve material from titan s interior being extruded or effused and deposited on the surface as might be expected from cryovolcanism

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

dune forming winds on titan and the influence of topography abstract numerous extended dunes on saturn s moon titan detected by the cassini radar constrain the long term pattern of surface winds we analyse the statistics of surface wind speed and direction and their spatial and temporal variability predicted by a general circulation model gcm in order to constrain surface wind predictions of this gcm by dune observations the model shows that modern winds are sufficient for saltation and dune formation at low latitudes in agreement with the presence of dunes there the best condition for the dune forming wind occurs with a threshold friction speed of 0 02 m s 1 or slightly less the equatorial region is conducive to longitudinal dunes because of a combined effect of a high sand drift potential and obtuse bimodal wind pattern oblique to the equator caused by the seasonal reversal of the hadley circulation the cross equatorial wind is steady and is characterised by a high weibull shape parameter k 4 the wind pattern at higher latitudes is more complex and gusty and neither longitudinal nor transversal dunes would be able to form putative large scale topography is found to have a profound influence on the near surface wind pattern generally mountains cause a convergence and speeding up on the flank while basins weaken the wind and cause a divergent flow longitudinal dunes can be deflected on the foot of mountains by up to 90 if xanadu is a hypothetical large mountain a wind pattern converging in xanadu that entirely disagrees with the dune observations is predicted if instead xanadu is a large basin the wind arcs clockwise north of xanadu and anti clockwise west and southwest of xanadu in agreement with the dune orientations in the vicinity of xanadu the albedo pattern has comparatively little influence on the wind field isolated mountain chains cause only local scale change in the wind pattern however the persistent surface easterlies in belet which are in conflict with the dune orientations do not disappear by any combination of large scale topography

anomalous radar backscatter from titan s surface abstract since cassini arrived at saturn in 2004 its moon titan has been thoroughly mapped by the radar instrument at 2 cm wavelength in both active and passive modes some regions on titan including xanadu and various bright hummocky bright terrains contain surfaces that are among the most radar bright encountered in the solar system this high brightness has been generally attributed to volume scattering processes in the inhomogeneous low loss medium expected for a cold icy satellite surface we can test this assumption now that the emissivity has been obtained from the concurrent radiometric measurements for nearly all the surface with unprecedented accuracy janssen et al and the cassini radar team 2009 icarus 200 222 239 kirchhoff s law of thermal radiation relates the radar and radiometric properties in a way that has never been fully exploited in this paper we examine here how this law may be applied in this case to better understand the nature of titan s radar bright regions we develop a quantitative model that when compared to the observational data allows us to conclude that either the reflective characteristics of the putative volume scattering subsurface must be highly constrained or more likely organized structure on or in the surface is present that enhances the backscatter

some thermal and mechanical consequences of rapid uplift an example from the southern alps new zealand abstract the thermal evolution of continental crust during active collision is modeled through numerical solutions of the two dimensional heat conduction equation for a rapidly moving medium the boundary conditions used in the modeling are derived from geological and geophysical observations from the active collision zone in the south island of new zealand the problem domain over which the solutions are obtained consists of a 40 km horizontal by 25 km vertical spatial plane with a vertical discontinuity at 10 km from the western boundary to the east of this discontinuity vertical uplift rates of up to 10 mm a occur over a timespan of up to 4 ma temperature distributions are calculated at 10 ka intervals over the 4 ma duration a two dimensional high temperature region is established upon initiation of uplift of the eastern block due to the advective component carrying heat upwards more rapidly than it can be dissipated laterally from the problem domain temperatures within the upper 5 km are greater than 400 c after 2 25 ma with geothermal gradients of up to 200 c km attained within the upper 3 km at times greater than 2 5 ma the vertical temperature distribution changes little while the anomalously high temperatures spread laterally into the stationary crust using rheological equations to describe the brittle behaviour of a water saturated upper crust and the ductile behaviour of a quartz dominated lower crust together with the thermal distribution of the conduction models the mechanical evolution of a collision zone is investigated in addition to high crustal temperatures and associated high heat flow rapid uplift produces a weakening of the crust by raising of the depth of transition from brittle to ductile behaviour within the zone of most rapid uplift the brittle ductile transition rises from 13 km to less than 5 km after 1 5 ma of uplift further uplift reduces the brittle layer to 3 km thickness and causes lateral spreading of the low strength zone the reductions in crustal strength caused by the thermal weakening produce a high strain zone within the region of maximum uplift which is incapable of sustaining large differential stresses this causes horizontal and vertical stress transfer and results in shallow seismicity increases in the adjacent crust as well as in intermediate depth seismicity within the high strength upper mantle because the thermal and mechanical anomalies discussed are a function of rapid uplift all regions of active continental collision may be expected to exhibit similar behaviour some mechanical and thermal characteristics of the himalayan collision zone are briefly examined in light of the numerical modeling

latitudinal and altitudinal controls of titan s dune field morphometry dune fields dominate 13 of titan s surface and represent an important sink of carbon in the methane cycle herein we discuss correlations in dune morphometry with altitude and latitude these correlations which have important implications in terms of geological processes and climate on titan are investigated through the microwave electromagnetic signatures of dune fields using cassini radar and radiometry observations the backscatter and emissivity from titan s dune terrains are primarily controlled by the amount of interdune area within the radar footprint and are also expected to vary with the degree of the interdunal sand cover using sar derived topography we find that titan s main dune fields shangri la fensal belet and aztlan tend to occupy the lowest elevation areas in equatorial regions occurring at mean elevations between 400 and 0 m relative to the geoid in elevated dune terrains we show a definite trend towards a smaller dune to interdune ratio and possibly a thinner sand cover in the interdune areas a similar correlation is observed with latitude suggesting that the quantity of windblown sand in the dune fields tends to decrease as one moves farther north the altitudinal trend among titan s sand seas is consistent with the idea that sediment source zones most probably occur in lowlands which would reduce the sand supply toward elevated regions the latitudinal preference could result from a gradual increase in dampness with latitude due to the asymmetric seasonal forcing associated with titan s current orbital configuration unless it is indicative of a latitudinal preference in the sand source distribution or wind transport capacity

radar evidence for liquid surfaces on titan arecibo radar observations of titan at 13 centimeter wavelength indicate that most of the echo power is in a diffusely scattered component but that a small specular component is present for about 75 of the subearth locations observed these specular echoes have properties consistent with those expected for areas of liquid hydrocarbons knowledge of the areal extent and depth of any deposits of liquid hydrocarbons could strongly constrain the history of titan s atmosphere and surface

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

origin and lateral migration of linear dunes in the qaidam basin of nw china revealed by dune sediments internal structures and optically stimulated luminescence ages with implications for linear dunes on titan linear dunes which are widespread on earth and on some other planets are generally considered to have a depositional origin and to form by loose sand under a bidirectional wind regime or by stabilized sand under a unidirectional wind regime while the wind rift erosional origin model has commonly been rejected due largely to lack of sufficient evidence and difficulty in morphodynamic interpretations the linear dunes in the qaidam basin have been proposed to form as self extending lee dunes under a unidirectional wind regime owing to a high level of total silt clay and salt tscs content or cohesiveness of sediments and they have undergone southward lateral migration at rates of up to 3 m yr we present herein results from studies of the sediments internal structures and optically stimulated luminescence osl ages to show that 1 the linear dunes in the qaidam basin are most likely of erosional origin similar to yardangs with orientations controlled by strikes of joints 2 tscs content or related sediment cohesion is unlikely to be an important factor determining the formation of these linear dunes and 3 the linear dunes consist of 0 81 3 21 ka cross strata with small lateral migration rates of 0 02 0 04 m yr our findings evidently suggest that linear dunes can be of erosional origin we therefore propose that the possibility of erosional origin should not be ruled out for linear dunes in some other dune fields on earth as well as on titan if the control of tectonic structures on the orientation of wind eroded ridges is taken into account morphodynamic interpretations for the wind rift model may become much simpler

titan s surface from reconciled cassini microwave reflectivity and emissivity observations abstract the surface of titan saturn s largest moon appears to consist of solid hydrocarbons or co2 with considerable small scale structure according to a new electromagnetic scattering model that uses both cassini radar reflectivity and emissivity measurements our model resolves a well known ambiguity in active and passive observations of surfaces namely that the dielectric constant retrieved from radiometric data is usually less than that obtained from radar backscatter analysis we present here parameters of titan derived from radar and radiometric responses using a single set of surface physical descriptors the observed dielectric constant ranges from 1 75 2 5 consistent with the solids above but also with unconsolidated water or water ammonia ice inferred rms slopes of the surface range from 10 16 at cassini s 2 2 cm with radar albedos of about 30 emissivities of the surface are quite high on the order of 90 we find that the majority of the backscattered radar energy results from volume rather than surface scattering processes thus large scale variations in radar brightness are mainly diagnostic of composition and structure within titan s near subsurface the high level of volume scatter about 15 of incident energy and consequent high radar albedo suggest significant wavelength scale structure and multiple scatter within the medium this is most consistent with a surface composed either of ubiquitous mm size bubbles within the ice analogous to a vesicular cryolava or structures similar to ice pipes and lenses found in terrestrial ice sheets the cryovolcanic hypothesis suggests planet wide resurfacing by active volcanism to explain the large scale uniformity of observed backscatter if the lens pipe mechanism pertains it can imply percolation of precipitating liquid or surface melt through the titan firn

cassini radar images at hotei arcus and western xanadu titan evidence for geologically recent cryovolcanic activity 1 images obtained by the cassini titan radar mapper radar reveal lobate flowlike features in the hotei arcus region that embay and cover surrounding terrains and channels we conclude that they are cryovolcanic lava flows younger than surrounding terrain although we cannot reject the sedimentary alternative their appearance is grossly similar to another region in western xanadu and unlike most of the other volcanic regions on titan both regions correspond to those identified by cassini s visual and infrared mapping spectrometer vims as having variable infrared brightness strengthening the case that these are recent cryovolcanoes citation wall s d et al 2009 cassini radar images at hotei arcus and western xanadu titan evidence for geologically recent cryovolcanic activity geophys res lett 36 l04203 doi 10 1029 2008gl036415

cambrian ensialic rift related magmatism in the ossa morena zone evora aracena metamorphic belt sw iberian massif sm nd isotopes and shrimp zircon u th pb geochronology abstract the late ediacaran c 560 550 ma serie negra sediments of the evora aracena metamorphic belt ossa morena zone sw iberian massif preserve a record of the erosion of an avalonian cadomian magmatic arc and subsequent related turbiditic sedimentation detrital zircon from the serie negra is characterized by predominantly ediacaran and cryogenian ages with few paleoproterozoic and archean cores and a marked lack of grenvillian ages these features when combined with the metasediments enrichment in lree la yb 14 negative eu anomalies low 147 sm 144 nd values 0 121 and negative e nd 550 5 5 indicate that the protolith serie negra sediments were derived from a continental magmatic arc a period of late cadomian ca 560 540 ma tectonism was followed by an extended episode of widespread bimodal magmatism related to cambrian ca 540 500 ma rifting this tectonic inversion is expressed in the geological record by a regional early cambrian unconformity shrimp zircon u th pb ages from four felsic orthogneisses from the evora massif record cambrian 527 10 ma 522 5 ma 517 6 ma and 505 5 ma crystallization ages for their igneous protoliths this confirms the existence of widespread lower paleozoic igneous activity in the ossa morena zone i a lower cambrian ca 535 515 ma igneous felsic dominated sedimentary complex with calc alkaline signature and associated carbonate and siliciclastic deposition and ii a middle cambrian ordovician ca 515 490 ma igneous bimodal sedimentary complex with calc alkaline and tholeiitic signatures and associated dominant siliciclastic deposition but also carbonate sediments the cambrian felsic magmatism was characterized by negative eu anomalies la lu n 0 8 11 147 sm 144 nd 0 1289 0 1447 and e nd 500 ranging from 1 5 to 0 8 a tendency towards peraluminous compositions suggests late fractionation low degrees of partial melting or the mixing of crustal and mantle derived material in the magma source region some felsic rocks possibly represent the last residual melts of high temperature zircon undersaturated mafic magmas later affected by crustal contamination while others indicate partial melting of crustal metasediments variably contaminated by basaltic liquids the transition from early felsic dominated to later more mafic magmatism suggests the gradual opening of the system to tholeiitic n e morb products th n ta n 147 sm 144 nd 0 1478 0 1797 and e nd 500 values ranging from 6 4 to 7 3 while the n morb amphibolites have 147 sm 144 nd 0 1818 0 1979 and e nd 500 values of 5 8 and 7 0 reaching a maximum of 9 1 in contrast other amphibolites have a negative ta anomaly 1 35 n ta n 147 sm 144 nd values ranging from 0 1639 to 0 1946 and e nd 500 values of 3 5 to 5 2 suggesting derivation by crustal assimilation processes the sub alkaline igneous precursors of the amphibolites were most likely generated in a rift setting by asthenospheric upwelling these results strengthen the proposed geodynamic scenarios for the sw iberian massif by which cadomian accretion gave rise to an ensialic rift that developed into a proto oceanic basin and incipient spreading opening of the rheic ocean a similar transition from a convergent to a divergent plate boundary during the ediacaran to cambrian ordovician has also been reported in other segments of the northern gondwana margin

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

alluvial fan morphology distribution and formation on titan abstract titan is a hydrologically active world with dozens of alluvial fans that are evidence of sediment transport from high to low elevations however the distribution and requirements for the formation of fans on titan are not well understood we performed the first global survey of alluvial fans on titan using cassini synthetic aperture radar sar data which cover 61 of titan s surface we identified 82 fans with areas ranging from 28 km2 to 27 000 km2 a significant fraction 60 of the fans are restricted to latitudes of 50 80 suggesting that fluvial sediment transport may have been concentrated in the near polar terrains in the geologically recent past the density of fans is also found to be correlated with the latitudes predicted to have the highest precipitation rates by titan global circulation models in equatorial regions observable fans are not generally found in proximity to dune fields such observations suggest that sediment transport in these areas is dominated by aeolian transport mechanisms though with some degree of recent equatorial fluvial activity the fan area drainage area relationship on titan is more similar to that on earth than on mars suggesting that the fans on titan are smaller than what may be expected and that the transport of bedload sediment is limited we hypothesize that this has led to the development of a coarse gravel lag deposit over much of titan s surface such a model explains both the morphology of the fans and their latitudinal concentration yielding insight into the sediment transport regimes that operate across titan today

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

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

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

spatially resolved images of titan by means of adaptive optics abstract images of titan were acquired with the adonis adaptive optics system installed at the eso 3 6 m telescope in la silla chile the near infrared range from 1 2 5 m was covered in 1994 and 1995 in the methane atmospheric windows at 1 3 1 6 and 2 0 m with narrow band filters and cvf diffraction limited images were obtained 0 14 arcsec at 2 m thus allowing us to resolve the titan disk we have corrected the images for systematic effects removed center to limb variation and applied deconvolution processes to our data the contrast on the images is on the order of 30 both the leading and trailing hemispheres were observed the 2 m images presented in this paper show a broad bright feature on the surface of titan s leading hemisphere near 114 lcm which is in agreement with the hst images and with spectroscopy performed at these longitudes from the ground that show a higher geometric albedo on titan s leading side high quality flat fielding of our data has highlighted the presence of at least two main bright spots within the equatorial region the trailing hemisphere of titan s surface is not completely dark but shows brightness near the poles with some north to south asymmetry the northern latitudes are uniformly brighter than the lower equatorial and southern latitudes factor of about 2 our results bring new constraints on the models of the satellite s surface

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

cassini observations of flow like features in western tui regio titan 1 a large 3 104 km2 lobate 5 m bright region seen by cassini on titan s leading equatorial region is best explained as a flow field we discuss observations from the visual and infrared mapping spectrometer and imaging science subsystem of the feature and present a map of the field we establish relative ages of flow features and discuss possible formation mechanisms and the implications of this finding for the evolution of titan s surface

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

low impact surface hardness testing equotip on porous surfaces advances in methodology with implications for rock weathering and stone deterioration research 2015 john wiley and sons ltd the equotip surface hardness tester is becoming a popular method for rock and stone weathering research in order to improve the reliability of equotip for on site application this study tested four porous limestones under laboratory conditions the range of stone porosity was chosen to represent likely porosities found in weathered limestones in the field we consider several key issues i its suitability for soft and porous stones ii the type of probe required for specific on site applications iii appropriate non parametrical statistical methods for equotip data iv sufficient sampling size this study shows that the equotip is suitable for soft and porous rock and stone from the two tested probes the dl probe has some advantages over the d probe as it correlates slightly better with open porosity and allows for more controlled sampling in recessed areas and rough or curved areas we show that appropriate sampling sizes and robust non parametric methods for subsequent data evaluation can produce meaningful measures of rock surface hardness derived from the equotip the novel hybrid dynamic hardness a combination of two measuring procedures single impact method sim and repeated impact method rim has been adapted and is based on median values to provide a more robust data evaluation for the tested stones in this study we propose a sample size of 45 readings for a confidence level of 95 this approach can certainly be transferred to stone and rock with similar porosities and hardness our approach also allows for consistent comparisons to be made across a wide variety of studies in the fields of rock weathering and stone deterioration research

storms in the tropics of titan methane clouds lakes and most fluvial features on saturn s moon titan have been observed in the moist high latitudes while the tropics have been nearly devoid of convective clouds and have shown an abundance of wind carved surface features like dunes the presence of small scale channels and dry riverbeds near the equator observed by the huygens probe at latitudes thought incapable of supporting convection and thus strong rain has been suggested to be due to geological seepage or other mechanisms not related to precipitation here we report the presence of bright transient tropospheric clouds in tropical latitudes we find that the initial pulse of cloud activity generated planetary waves that instigated cloud activity at other latitudes across titan that had been cloud free for at least several years these observations show that convective pulses at one latitude can trigger short term convection at other latitudes even those not generally considered capable of supporting convection and may also explain the presence of methane carved rivers and channels near the huygens landing site

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

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

fluvial geomorphology on earth like planetary surfaces a review morphological evidence for ancient channelized flows fluvial and fluvial like landforms exists on the surfaces of all of the inner planets and on some of the satellites of the solar system in some cases the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component water for earth and mars methane for saturn s moon titan in other cases as on mercury venus earth s moon and jupiter s moon io the flows were of highly fluid lava the discovery in 1972 of what are now known to be fluvial channels and valleys on mars sparked a major controversy over the role of water in shaping the surface of that planet the recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on mars including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history other fundamental questions posed by fluvial and fluvial like features on planetary bodies include the possible erosive action of large scale outpourings of very fluid lavas such as those that may have produced the remarkable canali forms on venus the ability of exotic fluids such as methane to create fluvial like landforms as observed on saturn s moon titan and the nature of sedimentation and erosion under different conditions of planetary surface gravity planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues including the role of analogy in geomorphological geological inquiry

titan s surface at 2 18 cm wavelength imaged by the cassini radar radiometer results and interpretations through the first ten years of observation abstract a comprehensive calibration and mapping of the thermal microwave emission from titan s surface is reported based on radiometric data obtained at 2 18 cm wavelength by the passive radiometer included in the cassini radar instrument compared to previous work the present results incorporate the much larger data set obtained in the approximately ten years following saturn orbit insertion brightness temperature data including polarization were accumulated by segments in titan passes from ta october 2004 through t98 february 2014 the observational segments were analyzed to produce a mosaic of effective dielectric constant based on the measurement of thermal polarization covering 76 of the surface and brightness temperature at normal incidence covering titan s entire surface as part of the mosaicking process we also solved for the seasonal variation of physical temperature with latitude which we found to be smaller by a factor of 0 87 0 05 in relative amplitude compared to that reported in the thermal infrared by cassini s composite infrared spectrometer cirs we used the equatorial temperature obtained by the huygens probe and the seasonal dependence with latitude from cirs to convert the brightness mosaic to absolute emissivity from which we could infer global thermophysical properties of the surface in combination with the dielectric mosaic we see strong evidence for subsurface volume scattering as a dominant cause of the radar reflectivity in bright regions and elsewhere a surface composition consistent with the slow deposition and processing of organic compounds from the atmosphere the presence of water ice in the near subsurface is strongly indicated by the high degree of volume scattering observed in radar bright regions e g hummocky mountainous terrains constituting 10 of titan s surface a thermal analysis allowed us to infer a mean 2 18 cm emission depth in the range 40 100 cm for the dominant radar dark terrains the remainder of titan s surface at all latitudes of titan consistent with the deposition and possible processing and redistribution of tholin like atmospheric photochemical products

early cambrian granitoids of north gondwana margin in the transition from a convergent setting to intra continental rifting ossa morena zone sw iberia two distinct cambrian magmatic pulses are recognized in the ossa morena zone sw iberia an early rift er and a main rift related event this cambrian magmatism is related to intra continental rifting of north gondwana that is thought to have culminated in the opening of the rheic ocean in lower ordovician times new data of whole rock geochemistry 19 samples sm nd sr isotopes 4 samples and id tims u pb zircon geochronology 1 sample of the early cambrian er plutonic rocks of the ossa morena zone are presented in this contribution the er granitoids barreiros barquete calera salvatierra de los barros and tablada granitoid massifs are mostly peraluminous granites the sm nd isotopic data show moderate negative endt values ranging from 3 5 to 0 1 and tdm ages greatly in excess of emplacement ages most er granitoids are crustal melts however a subset of samples shows a transitional anorogenic alkaline tendency together with more primitive isotopic signatures documenting the participation of lower crust or mantle derived sources and suggesting a local transient advanced stage of rifting the barreiros granitoid is intrusive into the ediacaran basement of the ossa morena zone serie negra succession and has yielded a crystallization age of 524 7 0 8 ma consistent with other ages of er magmatic pulse this age 1 constrains the age of the metamorphism developed in the ediacaran back arc basins before the intrusion of granites and 2 defines the time of the transition from the ediacaran convergent setting to the lower cambrian intra continental rifting in north gondwana

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

a 5 micron bright spot on titan evidence for surface diversity observations from the cassini visual and infrared mapping spectrometer show an anomalously bright spot on titan located at 80 w and 20 s this area is bright in reflected light at all observed wavelengths but is most noticeable at 5 microns the spot is associated with a surface albedo feature identified in images taken by the cassini imaging science subsystem we discuss various hypotheses about the source of the spot reaching the conclusion that the spot is probably due to variation in surface composition perhaps associated with recent geophysical phenomena

the evolution of titan s mid latitude clouds spectra from cassini s visual and infrared mapping spectrometer reveal that the horizontal structure height and optical depth of titan s clouds are highly dynamic vigorous cloud centers are seen to rise from the middle to the upper troposphere within 30 minutes and dissipate within the next hour their development indicates that titan s clouds evolve convectively dissipate through rain and over the next several hours waft downwind to achieve their great longitude extents these and other characteristics suggest that temperate clouds originate from circulation induced convergence in addition to a forcing at the surface associated with saturn s tides geology and or surface composition

resurfacing of titan by ammonia water cryomagma the cassini titan radar mapper observed on titan several large features interpreted as cryovolcanic during the october 26 2004 pass at high northern latitudes lopes r m c and 43 colleagues 2007 icarus 186 395 412 to date models of ammonia water resurfacing have not been tied to specific events or evolutionary stages of titan we propose a model of cryovolcanism that involves cracking at the base of the ice shell and formation of ammonia water pockets in the ice as these ammonia water pockets undergo partial freezing in the cold ice shell the ammonia concentration in the pockets increases decreasing the negative buoyancy of the ammonia water mixture if the ice shell is contaminated by silicates delivered in impacts the liquid solid density difference would be even less while the liquid cannot easily become buoyant relative to the surrounding ice these concentrated ammonia water pockets are sufficiently close to the neutral buoyancy point that large scale tectonic stress patterns tides non synchronous rotation satellite volume changes solid state convection or subsurface pressure gradients associated with topography would enable the ammonia to erupt effusively onto the surface rather than suggesting steady state volcanism over the history of the solar system we favor a scenario where the cryovolcanic features could have been associated with episodic potentially late geological activity

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

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

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

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

impact craters on titan five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22 of titan s surface imaged by cassini s high resolution radar through december 2007 the certain craters have morphologies similar to impact craters on rocky planets as well as two with radar bright jagged rims the less certain craters often appear to be eroded versions of the certain ones titan s craters are modified by a variety of processes including fluvial erosion mass wasting burial by dunes and submergence in seas but there is no compelling evidence of isostatic adjustments as on other icy moons nor draping by thick atmospheric deposits the paucity of craters implies that titan s surface is quite young but the modeled age depends on which published crater production rate is assumed using the model of artemieva and lunine 2005 suggests that craters with diameters smaller than about 35 km are younger than 200 million years old and larger craters are older craters are not distributed uniformly xanadu has a crater density 2 9 times greater than the rest of titan and the density on equatorial dune areas is much lower than average there is a small excess of craters on the leading hemisphere and craters are deficient in the north polar region compared to the rest of the world the youthful age of titan overall and the various erosional states of its likely impact craters demonstrate that dynamic processes have destroyed most of the early history of the moon and that multiple processes continue to strongly modify its surface the existence of 24 possible impact craters with diameters less than 20 km appears consistent with the ivanov basilevsky and neukum 1997 model of the effectiveness of titan s atmosphere in destroying most but not all small projectiles

cryovolcanism on titan new results from cassini radar and vims 1 the existence of cryovolcanic features on titan has been the subject of some controversy here we use observations from the cassini radar including synthetic aperture radar sar imaging radiometry and topographic data as well as compositional data from the visible and infrared mapping spectrometer vims to reexamine several putative cryovolcanic features on titan in terms of likely processes of origin fluvial cryovolcanic or other we present evidence to support the cryovolcanic origin of features in the region formerly known as sotra facula which includes the deepest pit so far found on titan now known as sotra patera flow like features mohini fluctus and some of the highest mountains on titan doom and erebor montes we interpret this region to be a cryovolcanic complex of multiple cones craters and flows however we find that some other previously supposed cryovolcanic features were likely formed by other processes cryovolcanism is still a possible formation mechanism for several features including the flow like units in hotei regio we discuss implications for eruption style and composition of cryovolcanism on titan our analysis shows the great value of combining data sets when interpreting titan s geology and in particular stresses the value of radar stereogrammetry when combined with sar imaging and vims

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

titan s xanadu region geomorphology and formation scenario abstract based on comprehensive mapping of the region the recent theories of xanadu s origin are examined and a chronology of geologic processes is proposed the geologic history of titan s xanadu region is different from that of the other surface units on saturn s moon a previously proposed origin of western xanadu from a giant impact in the early history of the moon is difficult to confirm given the scarcity of morphologic indications of an impact basin the basic topographic structure of the landscape is controlled by tectonic processes that date back to the early history of titan more recently the surface is intensely reworked and resurfaced by fluvial processes which seem to have leveled out and compensated height differences although the surface age seems young at first view the underlying processes that created this surface and the topographic structure appear to be ancient

geodynamic evolution of a cadomian arc region the northern ossa morena zone iberian massif abstract ductile deformation and polyphase metamorphism in the ossa morena zone of the iberian massif are related to two major tectonothermal episodes of cadomian late neoproterozoic to early cambrian and variscan age middle to late paleozoic the available petrological structural and geochronological data suggest that a number of tectono metamorphic and magmatic episodes occurred during the 620 480 ma interval that would comprise a complete cadomian wilson cycle the geodynamic scenario was that of an andean type continental margin an evolutionary model is presented for this orogeny comprising stages of volcanic arc generation crustal thickening back arc extension tectonic inversion and cratonization a correlation with comparable areas from pre mesozoic massifs elsewhere in europe is proposed in particular with the armorican massif of northern france

global mapping and characterization of titan s dune fields with cassini correlation between radar and vims observations abstract vast fields of linear dunes have been observed in the equatorial regions of titan saturn s largest moon as the cassini mission in orbit around saturn since july 2004 and extended until may 2017 carries on the high resolution coverage of titan s surface increases revealing new dune fields and allowing refinements in the examination of their properties in this paper we present the joint analysis of cassini s microwave and infrared global scale observations of titan integrating within an up to date global map of titan all the cassini radar and vims visual and infrared mapping spectrometer images the latter being empirically corrected for atmospheric scattering and surface photometry from july 2004 through july 2013 and june 2010 respectively we found very good qualitative and quantitative spatial matching between the geographic distribution of the dune fields and a specific infrared spectral unit namely the dark brown unit the high degree of spatial correlation between dunes and the dark brown unit has important implications for titan s geology and climate we found that radar mapped dunes and the dark brown unit are similarly confined within the equatorial belt 30 in latitudes with an equivalent distribution with latitude suggesting an increasing sediment availability and mobility at titan s tropics relative to higher latitudes compatible with the lower ground humidity predicted in equatorial regions by general circulation models furthermore the strong correlation between radar mapped dunes and the vims dark brown unit 72 allows us to better constrain the total surface area covered by dune material previously estimated from the extrapolation of the radar observations alone according to our calculations dune material cover 17 5 1 5 of titan s surface area equivalent to a total surface area of 14 6 1 2 million km2 1 5 times the surface area of earth s sahara desert the vims dark brown coloration of the dune material is here confirmed at large spatial scale if the sand particle composition is dominated by solid organics produced in and settling from the atmosphere as supported by our spectral modeling and by previous spectral analysis microwave radiometric data and atmospheric modeling dune fields are one of the major surface hydrocarbon reservoirs on titan assuming two possible scenarios for the sand distribution either the sand is 1 entirely trapped in dune landforms or 2 trapped in dunes at places where dune landforms are firmly observed and in sand sheets elsewhere we estimate the volume of hydrocarbons trapped in the dune sediment to be comprised between 1 7 and 4 4 105 km3 corresponding to an average total mass of 230 000 gt in comparison with 4000 30 000 gt of hydrocarbons in the polar lakes and seas this indicates a maximum age for the dune sediments of 730 myr consistent with estimations of the ages of the current titan s atmospheric methane and surface

elevation distribution of titan s craters suggests extensive wetlands abstract using a new global topographic map of titan we find that craters on titan preferentially lie at higher than average elevations we explore several explanations for this observed behavior and judge the most reasonable explanation to be the presence of widespread wetlands of liquid hydrocarbons at low elevations over much of geologic time impacts into a shallow marine environment or a saturated layer of sediments more than several hundred meters thick would produce crater morphologies similar to terrestrial submarine impacts these are known to lack significant topographic expression and would thus be difficult to observe with the cassini spacecraft since titan s near surface methane inventory likely fluctuated over geologic time with episodic delivery and continuous depletion a few craters at low elevations can nonetheless be expected

mountain torque and its influence on the atmospheric angular momentum on titan abstract the impact of titan s large scale topography and surface roughness on the atmospheric angular momentum budget is investigated by the cologne titan general circulation model that is run with and without topography constrained by cassini on seasonal timescales the angular momentum exchange is dominated by the friction torque which oscillates semi annually topography gives rise to a large diurnal and small seasonal mountain torque the diurnal mountain torque is caused by surface pressure variations associated with saturn s tide but has no net effect on the atmospheric angular momentum the seasonal mountain torque is mainly contributed by low latitude mountains that are hit by easterly surface winds the seasonal mountain torque causes a net transfer of angular momentum from the surface to the atmosphere which is counterbalanced by an opposite angular momentum transfer by the friction torque the atmospheric angular momentum is larger if topography is included

geological evolution of titan s equatorial regions possible nature and origin of the dune material in 13 years infrared observations from the visual and infrared mapping spectrometer onboard cassini provided significant hints about the spectral and geological diversity of titan s surface the analysis of the infrared ir signature of spectral units enables constraining the surface composition which is crucial for understanding possible interactions between titan s interior surface and atmosphere here we investigate a selection of areas in the equatorial regions imaged by cassini s instruments which exhibit an apparent transition from the visual and infrared mapping spectrometer ir bright to the ir blue and ir brown units from false color composites using red 1 57 1 27 m green 2 01 1 27 m and blue 1 27 1 08 m by applying an updated radiative transfer model we extract the surface albedo of ir units identified in these regions then we compare them with synthetic mixtures of two expected components on titan s surface namely water ice and laboratory tholins this allows us to reconnect the derived composition and grain size information to the geomorphology observed from radio detection and ranging instrument radar synthetic aperture radar images we interpret ir bright units as hills and plains coated by organic material and incised by fluvial networks erosion products are transported downstream to areas where ir blue units are seen near the ir bright units these units enriched in water ice are most likely outwash plains hosting debris from fluvial erosion farther away from the ir bright units the ir brown units are dominantly made of organics with varied grain sizes ranging from dust to sand sized particles that form the dune fields the transition areas therefore exhibit trends in water ice content and grain size supported by geomorphological observations

fluvial network analysis on titan evidence for subsurface structures and west to east wind flow southwestern xanadu 1 data of titan s surface from the cassini huygens mission show inferred fluvial networks interpreted as products of liquid alkane flow using synthetic aperture radar sar data we delineated drainage networks measured network parameters and used these measurements in a simplified algorithm for classifying terrestrial drainage patterns the results show a variety of patterns indicating that a variety of factors control fluvial drainage on titan drainage network patterns in southwestern xanadu are classified as rectangular suggesting control by a subsurface tectonic structural fabric link orientations also suggest that thissubsurfacetectonicfabricisorientedpredominantlyeastwest spatial variations in drainage networks are consistent with a west to east precipitation pattern supporting inferences from aeolian dune morphology these results illustrate how fluvial landform analysis can yield new information on both atmospheric and subsurface processes citation burr d m r e jacobsen d l roth c b phillips k l mitchell and d viola 2009 fluvial network analysis on titan evidence for subsurface structures and west to east wind flow southwestern xanadu geophys res lett 36 l22203

geologic mapping of the chaac camaxtli region of io from galileo imaging data 1 we produced a geologic geomorphologic map of the chaac camaxtli region of io s leading anti jovian hemisphere using regional resolution 186 m pixel galileo imaging data collected during orbit i27 february 2000 integrated with lower resolution 1 4 km pixel color data along with other galileo imaging and spectral data this is the first regional map of io made from galileo data nine color and geomorphologic units have been mapped and the close proximity of dark and various colored bright materials suggests that there is an intimate interaction between presumably silicate magmas and sulfur bearing volatile materials that produced a variety of explosive and effusive deposits in the recent geologic past this region of io is dominated by 11 volcanic centers most of which are paterae that are analogous in morphology to terrestrial calderas but larger in size mapping of structural features indicates that most of the active regions occur in topographic lows and less active or inactive paterae are associated with topographic highs this indicates that crustal thickness variations influence magma access to the surface surface changes in this region since the voyager flybys 1979 are relatively minor additional bright and dark flows color changes although several active vents have migrated within paterae this observation along with the identification of the relatively regular spacing of paterae 100 150 km along a line may indicate there are multiple interlacing fractures in the crust that serve as magma conduits from the interior this connection between volcanism and tectonism may have implications for tidal heating mechanisms and their effect on io s lithosphere some inactive patera floors may be evolving into bright plains material which if composed of silicates might explain the strength of io s crust to support steep patera walls and tall mountains

size and shape of saturn s moon titan cassini observations show that saturn s moon titan is slightly oblate a fourth order spherical harmonic expansion yields north polar south polar and mean equatorial radii of 2574 32 0 05 kilometers km 2574 36 0 03 km and 2574 91 0 11 km respectively its mean radius is 2574 73 0 09 km titan s shape approximates a hydrostatic synchronously rotating triaxial ellipsoid but is best fit by such a body orbiting closer to saturn than titan presently does titan s lack of high relief implies that most but not all of the surface features observed with the cassini imaging subsystem and synthetic aperture radar are uncorrelated with topography and elevation titan s depressed polar radii suggest that a constant geopotential hydrocarbon table could explain the confinement of the hydrocarbon lakes to high latitudes

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

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

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

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

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

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

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

a global topographic map of titan abstract cassini radar sartopo and altimetry data are used to construct a global gridded 1 1 elevation map for use in global circulation models hydrological models and correlative studies the data are sparse and so most of the map domain 90 is populated with interpolated values using a spline algorithm the highest 520 m gridded point observed is at 48 s 12 w the lowest point observed 1700 m below a 2575 km sphere is at 59 s 317 w this may be a basin where liquids presently in the north could have resided in the past if the deepest point were once a sea with the areal extent of present day ligeia mare it would be 1000 m deep we find four prominent topographic rises each 200 km wide radar bright and heavily dissected distributed over a 3000 km arc in the southeastern quadrant of titan 40 60 s 15 150 w

fluvial features on titan insights from morphology and modeling fluvial features on titan have been identified in synthetic aperture radar sar data taken during spacecraft flybys by the cassini titan radar mapper radar and in descent imager spectral radiometer disr images taken during descent of the huygens probe to the surface interpretations using terrestrial analogs and process mechanics extend our perspective on fluvial geomorphology to another world and offer insight into their formative processes at the landscape scale the varied morphologies of titan s fluvial networks imply a variety of mechanical controls including structural influence on channelized flows at the reach scale the various morphologies of individual fluvial features implying a broad range of fluvial processes suggest that paleo flows did not occupy the entire observed width of the features disr images provide a spatially limited view of uplands dissected by valley networks also likely formed by overland flows which are not visible in lower resolution sar data this high resolution snapshot suggests that some fluvial features observed in sar data may be river valleys rather than channels and that uplands elsewhere on titan may also have fine scale fluvial dissection that is not resolved in sar data radar bright terrain with crenulated bright and dark bands is hypothesized here to be a signature of fine scale fluvial dissection fluvial deposition is inferred to occur in braided channels in paleo lake basins and on sar dark plains and disr images at the surface indicate the presence of fluvial sediment flow sufficient to move sediment is inferred from observations and modeling of atmospheric processes which support the inference from surface morphology of precipitation fed fluvial processes with material properties appropriate for titan terrestrial hydraulic equations are applicable to flow on titan for fully turbulent flow and rough boundaries for low reynolds number flow over smooth boundaries however knowledge of fluid kinematic viscosity is necessary sediment movement and bed form development should occur at lower bed shear stress on titan than on earth scaling bedrock erosion however is hampered by uncertainties regarding titan material properties overall observations of titan point to a world pervasively influenced by fluvial processes for which appropriate terrestrial analogs and formulations may provide insight