sequential deformation of plains at the margins of alpha regio venus implications for tessera formation abstract the boundaries between the highly deformed tessera terrain and adjacent volcanic plains are primarily those of embayment where the tessera are stratigraphically older than the plains previous studies show that 3 of these boundaries display evidence of tectonic tilting after the emplacement of the plains one of these unusual boundaries is the western margin of alpha regio tessera a zone 100 km in width that separates the plains from the interior structures of alpha this zone is characterized by margin parallel fine scale 1 5 km fractures graben and ridges that truncate and postdate the broad scale 10 30 km ridges and troughs of the interior of alpha the western margin is embayed by several volcanic plains units that are progressively tilted and deformed by graben with closer proximity to alpha regio the earliest deformation of the plains consists of northeast trending graben 1 km in width that are similar in morphology and spacing to graben that deform intratessera plains and plains at the eastern boundary of alpha northwest trending graben then formed over an interval marked by the emplacement of two additional plains units their similarity to northwest trending structures emanating from eve corona and the lada terra rift suggests a possible genetic relationship the tilting of the plains adjacent to western alpha implies relative vertical movement of the margin either uplift of tessera or downwarping of plains subsequent to the formation and relaxation of the interior of alpha regio subsidence of plains at this locale is supported by the presence of a basin to the west of alpha surrounded by a fracture belt contiguous with western alpha thus the fractures and deformation at the western boundary of alpha may be related to the formation of a basin to the west of alpha with some influence from the northernmost extension of the lada terra rift such a basin is not present at a section along the eastern boundary of alpha regio where the origin of tilted plains remains equivocal we conclude that the deformation along the western margin of alpha regio is not directly related to the process of tessera formation but is an example of tessera modification and is consistent with the stratigraphic position of tessera as the oldest unit observed on venus

venus the nature of the surface from venera panoramas images of the surface of venus obtained by the soviet venera 9 10 13 and 14 landers have been analyzed to provide a basis for understanding the nature of geologic processes operating there the four spacecraft landed in the beta phoebe region at median elevations in the upland rolling plains province the landing points are each separated by distances of more than a thousand kilometers the venera panoramas were digitized and transformed into various perspectives in order to facilitate analysis and comparison with other planetary surfaces bedrock is exposed at the venera 10 13 and 14 sites and is characterized by semicontinuous flat polygonal to subrounded patches up to several meters in width the bedrock surface is often dominated by subhorizontal to horizontal layered plates with thicknesses of several centimeters and abundant linear and polygonal vertical fractures angular to subangular layered to platy blocks in the 5 to 70 cm range dominate the venera 9 site and occur much less frequently at the other sites blocks appear to share many characteristics with the exposed bedrock and are interpreted to be largely derived from it soils particles 1 cm are abundant at the venera 9 10 and 13 sites but are uncommon at venera 14 features indicative of a strong eolian influence moats dunes wind tails are not observed a striking aspect of the venera landing sites is their extreme similarity despite separation distances of thousands of kilometers several hypotheses are considered for the origin of the bedrock surfaces and we investigate in detail the hypothesis that bedrock originated from surface lava flows in this interpretation the broadly platy nature of the surface is analogous to the rolling and undulating nature of terrestrial pahoehoe flows caused by the formation and deformation of a semisolid crust the layering is interpreted to be formed by a combination of upper thermal boundary layer formation and horizontal sheets formed by cooling and shearing during flow emplacement vertical fractures are attributed largely to joint patterns formed during cooling this interpretation made on the basis of surface morphology is consistent with venera 13 and 14 geochemical results which reported high potassium basalt and tholeiitic basalt compositions respectively if this interpretation is correct large regions of the beta phoebe area are likely to be characterized by lava flows the relative freshness of features observed by venera 14 suggests that some bedrock surfaces are geologically young or that erosion rates are low

venus express mission 1 venus express is well and healthy and has now been providing exciting new data from venus our nearby twin planet for over 2 years many of the new results are presented and discussed in the subsequent papers in this special section the overall scientific objective of venus express is to carry out a detailed study of the atmosphere of venus including the interaction of the upper atmosphere with the solar wind and the interaction of the lowest part of the atmosphere with the surface of the planet in addition the plasma environment and magnetic fields as well as some aspects of the surface of the planet are addressed for the first time investigations make systematic use of the transparent infrared spectral windows in order to probe the atmosphere in four dimensions three spatial dimensions plus time the spacecraft design is taken from mars express with some modifications necessary owing to the specific environment around venus the payload is composed of three spectrometers a camera a magnetometer an instrument for detecting energetic particles and a radio science package the orbit is polar and highly elliptic with a pericenter altitude of about 200 km over the northern polar region and an apocenter altitude of 66 000 km presently the coverage of the southern hemisphere is very good but important gaps still do exist the coverage of the northern hemisphere is much less dense venus express is a part of the european space agency s program for the exploration of the inner solar system which includes missions to study the sun mercury venus the moon mars and comets and asteroids

surface modification of venus as inferred from magellan observations of plains in sedna planitia clear stratigraphic relations can be discerned among volcanic flow units young flows exhibit sar specific cross section values similar to fresh terrestrial basalt flows whereas older flows exhibit backscatter signatures similar to degraded terrestrial basalt flows total degradation of 1 m depth over 0 6 b y is inferred for the sedna area from radar signatures impact crater abundances and ejecta superposition relations with respect to volcanic flow units analyses of parabolic ejecta deposits associated with the crater stuart imply that the material is typically centimeters in thickness a relatively small fraction 10 of venusian impact craters exhibit prominent parabolic ejecta deposits these craters are interpreted to be relatively young and parabolic deposits are interpreted to be dispersed by aeolian activity over at least tens of millions of years the inferred dispersal rate 10 3 m yr is too low to produce the degradation of flows at sedna planitia and it is concluded that the dominant flow modification process is in situ weathering in addition elevation dependent weathering is inferred in western ovda regio where plains above 6054 km radius have enhanced reflection coefficients as compared to adjacent plains at lower elevations the inferred rate of generation of high reflection coefficient materials is no more than 10 2 m yr based on the inability of aeolian activity to cover high reflectivity surfaces with normal reflection coefficient materials and the ubiquitous nature of high reflectivity surfaces at high elevations surface modification rates on venus are orders of magnitude lower than on earth venusian rates are also much lower than the inferred rate of aeolian dispersal of friable materials on mars but are comparable to the estimated rate of weathering and erosion of martian bedrock low surface modification rates imply that it will be possible to determine regional scale age variations on venus based on the degree of preservation of volcanic landforms and microwave signatures

determining heights and slopes of fault scarps and other surfaces on venus using magellan stereo radar this report presents relationships and techniques for determining the heights and slopes of discretely dipping surfaces such as normal fault scarps on the surface of venus from measurements of their widths in magellan stereo synthetic aperture radar sar images these surfaces are clearly recognizable as distinct bands of increased or decreased radar backscatter relative to flat lying areas in the 120 to 280 m resolution magellan sar images but are not generally imaged in the 10 km resolution magellan altimetry our methods take into account radar distortion effects and allow one to determine whether a slope is foreshortened laid over elongated or in radar shadow the techniques make use of graphs constructed for the magellan incidence angle profiles so that investigators can determine the local height and slope of an individual surface in a straightforward manner but the techniques are applicable to any stereo radar data set if the radar incidence angles are known additionally the techniques can be used to improve digital elevation models constructed using radar stereoscopy in areas that have steep local terrain where stereoscopic fusion may be impossible due to the effects of layover or radar shadow using these techniques we show that there are normal fault scarps on venus with heights in the 700 m range that have remarkable topographic slopes of close to 60 something unheard of on earth and which suggests a high effective cohesive strength of the venusian crust

komatiites as mercury surface analogues spectral measurements at pel article history the elemental composition of mercury s surface which has been recently measured by the nasa mercury surface space environment geochemistry and ranging messenger spacecraft suggests a mineralogy dominated by magnesium rich orthopyroxene and feldspar the most magnesium rich and aluminium poor regions of mercury s surface which are presumably orthopyroxene rich have compositions and possibly mineralogies analogous to terrestrial boninites and basaltic komatiites unfortunately little is known about the spectral properties of komatiites especially at the high surface temperatures of mercury we therefore have collected three terrestrial komatiites with different compositions plus a synthetic komatiitic sample and measured their reflectances in the visible and thermal infrared spectral ranges samples divided into four grain size ranges when enough material was available were measured fresh and after thermal processing in vacuum 10 pa at 500 c comparable to mercury peak surface temperatures our measurements show that spectral changes between fresh and thermally processed samples occur in both spectral channels but are stronger in the visible range with reddening affecting all the samples while darkening is more selective it is important to note that darkening and reddening after thermally processing the samples are independent of the komatiites ferrous iron content in fact the synthetic sample which is nearly iron free is most strongly affected from our study it turns out that thermally processing the samples in vacuum at mercury surface temperature produces the removal of samples colour centres the results of our study show also that the mercury atmospheric and surface composition spectrometer mascs instrument on messenger orbiting mercury currently cannot distinguish between different compositions of komatiites while the future mercury radiometer and thermal infrared imaging spectrometer mertis on the upcoming esa bepicolombo mission will resolve their differences in the 7 14 m spectral range

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

surface brightness variations seen by virtis on venus express and implications for the evolution of the lada terra region venus 1 venus express is since april 11 2006 in orbit around venus virtis visible and infrared thermal imaging spectrometer has started only hours after orbit insertion to collect an immense and unique data set of special interest is the wavelength range from 1 1 5 microns which includes the atmospheric windows by averaging several hundred multi spectral images obtained during the mission we have been able to map the surface temperatures for almost the whole southern hemisphere of venus blurring in the clouds limits the spatial resolution to approximately 100 km globally the most exciting and at the same time the most complex task is to retrieve compositional information for the surface of venus from the hyperspectral data obtained by virtis we report here about indication for variations in the surface composition in the lada terra region based on brightness variations mapped from virtis measurements and present some tentative links to the evolution of this region

contact metamorphism hydrothermal alteration of tertiary basalts from the isle of skye northwest scotland alkali olivine basalts from skye were simultaneously contact metamorphosed by tertiary gabbro and granite intrusions and altered by the hydrothermal convection system that the plutons induced four metamorphic zones were mapped around the plutons furthest from the intrusions in the primary olivine zone metabasalts are composed of combinations of igneous olivine augite plagioclase titaniferous magnetite ilmenite zeolites gyrolite sulfides and chlorite smectite intergrowths closer to the plutons in the smectite zone saponite and carbonate appear primary olivine and gyrolite disappear and zeolites decrease dramatically in abundance still closer to the plutons in the amphibole zone actinolite edenite chlorite sphene epidote andradite and quartz appear and saponite and chlorite smectite intergrowths disappear along parts of the contact between gabbro and basalt in the orthopyroxeneolivine zone orthopyroxene metamorphic olivine and biotite appear and amphibole chlorite sphene epidote andradite carbonate and quartz disappear whole rock chemical data indicate only minor change in the major element chemical composition of the metabasalts during progressive metamorphism hydrothermal alteration two pyroxene eothermometry and various mineral fluid equilibria suggest the range of peak temperatures attained in the metamorphic zones orthopyroxene olivine zone 900 1 030 c amphibole zone 400 900 c smectite and primary olivine zones 5 smow mineralogically more altered basalts from the smectite zone have whole rock 18o 2 to 5 still more mineralogically altered basalts from the amphibole zone with one exception have 18o 2 completely recrystallized hornfelses from the orthopyroxene olivine zone have 18o 0 the principal mechanism of isotope exchange between basalt and metamorphic hydrothermal fluid probably was heterogeneous mineralfluid reaction

felsic highland crust on venus suggested by galileo near infrared mapping spectrometer data received 2 march 2008 revised 29 july 2008 accepted 18 september 2008 published 31 december 2008 1 we evaluated the spatial variation of venusian surface emissivity at 1 18 mm wavelength and that of near surface atmospheric temperature using multispectral images obtained by the near infrared mapping spectrometer nims on board the galileo spacecraft the galileo nims observed the nightside thermal emission from the surface and the deep atmosphere of venus which is attenuated by scattering from the overlying clouds to analyze the nims data we used a radiative transfer model based on the adding method although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere our analysis revealed that the horizontal temperature variation in the near surface atmosphere is no more than 2 k on the venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands one interpretation for the latter result is that highland materials are generally composed of felsic rocks since formation of a large body of granitic magmas requires water the presence of granitic terrains would imply that venus may have had an ocean and a mechanism to recycle water into the mantle in the past

chemical dieferentiation of a convecting planetary interior consequences for a one plate planet such as venus partial melting to generate the crust of a planet creates compostionally buoyant residual mantle in the absence of mantle flow associated with plate tectonics this buoyant refractory layer may collect at the top of the mantle with important implications for the evolution of the interior and surface in this study models of the thermal and chemical evolution of a planetary interior demonstrate the possible consequences of a chemically buoyant depleted mantle layer as the depleted layer thickens the melting temperature at the top of the underlying convecting mantle also increases and the degree of partial melting of mantle added to the depleted layer decreases as less depleted mantle with less positive compositional buoyancy is added negative thermal buoyancy of the layer eventually exceeds its positive compositional buoyancy the depleted layer then sinks into and mixes with the convecting interior the top of the convecting mantle then moves to a shallower depth larger degrees of melting resume and a new depleted layer accumulates this accumulation and instability of the depleted layer occurs repeatedly over a substantial portion of the planet s evolution with a period of 300 500 myr on venus the population of impacts craters is indistinguishable from a random distribution over the surface and give a surface age of about 500 myr we speculate that the mechanism described above may explain this episodic global resurfacing of venus

volatile transport on venus and implications for surface geochemistry and geology the high vapor pressure of volatile metal halides and chalcogenides e g of cu zn sn pb as sb bi at typical venus surface temperatures coupled with the altitude dependent temperature gradient of 8 5 k km 1 is calculated to transport volatile metal vapors to the highlands of venus where condensation and accumulation will occur the predicted geochemistry of volatile metals on venus is supported by observations of cu zn sn pb as sb and bi minerals around terrestrial volcanic vents spectroscopic observations of cucl in volcanic gases at kilauea and nyiragongo and large enrichments of these and other volatile elements in terrestrial volcanic aerosols a one dimensional finite difference vapor transport model shows the diffusive migration of a thickness of 0 01 to 10 m yr of moderately to highly volatile phases e g metal halides and chalcogenides from the hot lowlands 740 k to the cold highlands 660 k on venus the diffusive transport of volatile phases on venus may explain the observed low emissivity of the venusian highlands hazes at 6 km altitude observed by two pioneer venus entry probes and the pioneer venus entry probe anomalies at 12 5 km

an olistostrome melange belt formed along a suture bornova flysch zone western turkey abstract the bornova flysch zone bfz in western turkey is a regional olistostrome melange belt located between the izmir ankara tethyan suture in northwest and the menderes massif in the southeast the bfz consists mostly of tectonized gravity mass flows the blocks are mesozoic limestone and ophiolite which are enclosed in cretaceous paleocene sheared sandstone and shale the limestone blocks are of two types the first type consists of late triassic to cretaceous shallow marine carbonates the second type has an upper triassic shallow marine section overlain by jurassic to cretaceous pelagic limestones a semi intact part of the platform occurs in the karaburun peninsula and on the island of chios the ophiolitic blocks in the bfz include ultramafic rock gabbro basalt and radiolarian chert of middle triassic to cretaceous in age the formation of the bfz overlaps with the cretaceous subduction and hp lt metamorphism of the northern passive continental margin of the anatolide tauride block this subduction zone was bounded in the west by a strike slip tear fault the bfz formed in a narrow basin between this tear fault and the tethyan ocean the mass flows came from the southeast from the overriding ophiolite and accretionary complex and from the northwest from the uplifted segments of the platform margin this model provides an explanation as why the bfz is unmetamorphosed whereas the equivalent strata in the menderes massif were metamorphosed at depths of over 20 km it also explains the prominence of gravity flows and the southward younging in the bfz and for the apparently anomalous observation that although the tethyan ocean lay to the northwest the ophiolitic blocks are more common on the southeastern part of the bfz regions away from the tear fault such as the karaburun peninsula were least affected by subsidence and deformation during the cretaceous and paleocene

the geology and geomorphology of the venus surface as revealed by the radar images obtained by veneras 15 and 16 a region by region condensed description of almost all of the area that was radar photographed by veneras 15 and 16 is presented using some generalizations the diversity of terrain was reduced to a discrete set from which a geological morphological map was constructed the predominant type of terrain of the studied area is a plain that was tentatively subdivided into five morphological types ridge and band patchy rolling plain dome and butte plain smooth plain and high smooth plain stratigraphically the ridge and band plains are the oldest and the smooth plains are the youngest the stratigraphic position of the other types is yet to be determined large sections of the plains show similarities to the mare type basaltic plains of the moon mercury and mars other types of terrain are combinations of ridges and grooves in various patterns linear parallel orthogonal diagonal or chevron like and chaotic in some places the ridge and groove terrain is stratigraphically below the plain material but in other places it appears to be plain material that has been subsequently deformed near the eastern and western boundaries of ishtar terra large several hundred kilometers in diameter ring like features can be seen that are named coronae or ovoids evidence of tectonic deformation and the presence of flow like patterns support their designation as volcano tectonic features beta regio seems to be an uplifted plain showing evidence of rifting and volcanism all types of terrain are sparesely peppered with craters of obvious impact morphology their average density gives the plain an age range of 0 5 to 1 109 years the fact that many impact craters are still in the pristine state indicates a very low rate of surface reworking at least for the last 0 5 to 1 109 years no evidence for water erosion sedimentation processes has been found the tectonic activity of venus has no equivalent on the moon mercury or even mars and can be compared only with that of the earth intensive horizontal deformation previously known only on earth occurs on venus but in a characteristic venusian style

highly silicic compositions on the moon using data from the diviner lunar radiometer experiment we show that four regions of the moon previously described as red spots exhibit mid infrared spectra best explained by quartz silica rich glass or alkali feldspar these lithologies are consistent with evolved rocks similar to lunar granites in the apollo samples the spectral character of these spots is distinct from surrounding mare and highlands material and from regions composed of pure plagioclase feldspar the variety of landforms associated with the silicic spectral character suggests that both extrusive and intrusive silicic magmatism occurred on the moon basaltic underplating is the preferred mechanism for silicic magma generation leading to the formation of extrusive landforms this mechanism or silicate liquid immiscibility could lead to the formation of intrusive bodies

venus surface thermal emission at 1 μm in virtis imaging observations evidence for variation of crust and mantle differentiation conditions 1 the venus express spacecraft images the nightside thermal emissions using the visible and infrared thermal imaging spectrometer virtis at 1 02 1 10 and 1 18 m thermal emission from the surface is observed the signal is attenuated by scattering and absorption in the dense atmosphere the measured flux at the top of the atmosphere is positively correlated with surface temperature and surface emissivity the surface temperature of venus is relatively well constrained as being mainly a function of altitude with a gradient lesser or equal to the adiabatic lapse rate this study examines the correlation of virtis images showing a signal of the surface at 1 02 m with viewing geometry stray sunlight cloud opacity and topography and applies semiempirical relations to remove their influence the remaining contrast can be either ascribed to surface emissivity or unexpected temperature variations temperature variations due to active volcanism are unlikely to be persistent over the time of observations therefore the mosaic of all processed images is here interpreted in terms of surface emissivity variation the emissivity variation found is correlated with geomorphological features established from magellan synthetic aperture radar images it is generally lower at tessera terrain some but not all volcanic edifices show increased emissivity large lava flows in the lada terra lavinia planitia region also show an increased thermal emission this might indicate a more felsic surface composition of tessera highlands and large scale extrusive volcanism of ultramafic composition

elucidating the rate of volcanism on venus detection of lava eruptions using near infrared observations abstract lava eruptions can be observed remotely on venus nightside using a near infrared window at a 1 0 micrometer wavelength i e radiation at this wavelength emitted from the planetary surface traverses through the thick venus atmosphere and clouds due to the strong dependence of the intensity of thermal emission on temperature a hot surface produced by a lava eruption emits intense radiation with the intensity of the excess radiation depending on the surface area and temperature of the lava flow the excess emission from the hot surface is blurred by clouds yet a 1 km2 1500 k basaltic lava lake and a 50 km2 1000 k lava flow are readily detected using this technique rapid cooling of exposed lava results in excess surface radiation that is detectable for just one earth day after the end of an eruption hence short term eruptions are only detectable on the side of the planet where night is occurring eruptions lasting more than half a venus day i e more than about 60 earth days however are detectable across the globe as nighttime occurs sometime during this period for every such event due to limited observational geometries a complete global survey of active volcanos cannot be achieved from earth and in fact only about 10 of short lived major volcanic eruptions are observable alternatively a satellite orbiting high above venus 6 venus radii could detect virtually all short lived nighttime volcanic events or about half the events expected to occur across the globe

virtis emissivity of alpha regio venus with implications for tessera composition abstract the composition of venus tessera terrain is unknown the visible and infrared thermal imaging spectrometer virtis aboard venus express vex collects data that yields the surface emissivity at 1 m which contains information convolving a number of surface properties including composition we examine the variation of emissivity in the vicinity of alpha regio which is the largest exposure of tessera terrain imaged by virtis we find that the emissivity of alpha regio tessera is lower than adjacent plains materials and the deposits and flows of eve corona both of which have previously been interpreted to be basaltic the emissivity of the bulk of alpha is also lower than its western boundary which is interpreted to comprise plains structurally deformed to the same degree as tessera terrain this suggests that the lower emissivity of alpha is independent of structural elements macroscale roughness or local sedimentation processes and is due to material properties like composition or grain size the deviation of the emissivity of alpha from that of the plains for which a bulk basaltic composition is well supported corresponds to a significant difference in rock type or surface mineral assemblage the 1 m emissivity of alpha is consistent with rocks with low ferrous iron content this includes felsic igneous rocks like granitoids that form under either water rich or water poor conditions a water rich origin would require both a hydrosphere and a plate recycling mechanism and thus be limited to the lifetime of surface water on venus alternatively granitoids could form via the differentiation of basaltic melts the production of all tessera terrain by this mechanism would require the accumulation and preservation of felsic melts from a volume of mafic magma that exceeds what is preserved in the currently observed plains both mechanisms of granitoid formation would require that tessera terrain be formed prior to the emplacement of the plains consistent with their stratigraphic position anorthosites also satisfy the emissivity signature and can form from copious amounts of partial melting of a mafic source low emissivity values are also consistent with carbonates sulfates phyllosilicates and their dehydration products which may have formed via weathering of basalts under conditions of higher atmospheric p h2o all of these hypotheses suggest the mineralogy of alpha tessera records an extinct era of venus history and is a key target for future exploration

magellan observations of the venera and vega landing site regions geologic maps have been produced for each of the seven venera vega landing sites on venus the dominant terrain identified at all the sites is plains the sites contain minor amounts of complex ridge terrain crt complex terrain ct and an older plains po that are all embayed by younger plains py some of the sites venera 9 and vega 1 and 2 are made up of vast regional plains units while the other sites venera 8 10 13 and 14 contain more localized plains the venera 8 and 13 sites have unusual volcanic features associated with them and a nontholeiitic composition was measured by the landers at these sites at the other five sites where a tholeiitic composition was measured lava flows with morphologies that suggest an apparent low viscosity have been identified this indicates a good correspondence between the geochemistry measured by the landers and the magellan imagery a good correlation also exists between the tv panoramas taken by four of the landers and the magellan imagery at the venera 9 10 14 and vega 1 2 sites the most likely material sampled are plains composed of tholeiitic lavas a steep sided dome lamprophyre like lavas or ash beds are the most likely material sampled by the venera 8 lander the venera 13 lander may have sampled lava flows from a corona like feature or from a steep sided dome in the southeast of the landing circle radiophysical properties of the landing sites show a good correspondence with the local geology with most variations in backscatter emissivity and rms slopes reflecting differences in surface roughness the venera vega sites are good examples of typical venusian plains indicating that geochemical measurements and tv observations provide representative characteristics of this most abundant terrain type on venus

the emissivity of a fine grained labradorite sample at typical mercury dayside temperatures abstract analyzing the surface composition of mercury s regolith from remote sensing measurements is a challenging task in support of the national aeronautics and space agency s mercury surface space environment geochemistry and ranging messenger mission and especially in preparation for the mercury radiometer and thermal infrared spectrometer mertis instrument on the bepicolombo mission of the european space agency and the japan aerospace exploration agency we are developing a planetary emissivity laboratory at deutsches zentrum fur luft und rahmfahrt dlr in berlin here we present the first measurements of labradorite as a mercury surface analog obtained with a test setup at a temperature of 420 c appropriate for the dayside of mercury because of limitations on the current test apparatus we present here data only for mid infrared wavelengths the spectra show strong indications of significant changes in spectral features in the mid infrared with changing temperature this result introduces an additional complication to the analysis of spectra obtained from the surface of mercury as the surface temperature and the thermal history of an observed area must be taken into account in the interpretation of the spectra this inference implies that the latitude and possibly also the time of day must be considered when analyzing a spectrum in particular the surface at the equator might exhibit different spectral characteristics than the surface at high latitudes even for the same composition these observations while still preliminary underscore strongly the need for temperature dependent measurements of emissivity of candidate planetary surface materials

style and sequence of extensional structures in tessera terrain venus recent studies have focused on the question of the stratigraphic sequence and thus the stages of tessera formation specifically if tessera are formed by contractional deformation followed by extensional deformation or vice versa a major question centers on the interpretation of specific lineaments within tesserae as graben bounded by faults 60 or alternatively open tension fractures dipping 90 we document and assess the origin of extensional structures in tesserae at several locations on venus noting the morphology continuity along strike parallelism of walls stratigraphic position and interaction with other structures and variability due to radar viewing geometry in each study area our analyses demonstrate that 1 the extensional structures have variable widths interior subparallel lineaments and ramp terminations 2 ridges and lineaments are continuous across the troughs where the floors of many of these structures contain the lowered sections of preexisting structures and 3 intratessera plains are seen to embay ridges and an impact crater is superposed on a ridge and in both cases these features are subsequently deformed by the extensional structures we conclude that the morphology of these extensional structures is consistent with an origin as graben not open tension fractures and that these graben postdate the ridges in each study area both the graben and the ridges of the sizes found in our survey can be formed when the brittle crust is of the order of 1 to 10 km thick to further test the tension fracture model we examine the conditions of a venus that could produce tension fractures of the dimension 1 km width of extensional structures found in tessera terrain and find that thermal gradients of a minimum of 400 to 1500 k km 1 heat flows of 800 to 3000 mw m 2 are required for a range of diabase rheologies and strain rates thought typical of venus during tessera formation such a thermal structure would favor partial melting at depths 1 km dike propagation from this region of shallow melting within the tensile stress field would produce vast quantities of volcanism mitigating against the preservation of the closely associated tension fractures this volcanism is not observed both the amplitude and sign of changes in surface temperature induced by atmospheric warming due to massive outpourings of lava are not consistent with the hotspot model on the basis of our analysis of tesserae we conclude that the ridges formed first in response to large scale contraction of the crust and that the graben formed contemporaneously and largely following this phase as the thickened crust relaxed in a manner to what is predicted and observed for plateau regions on earth such as tibet and the altiplano

chenier type ridges in giralia bay exmouth gulf western australia processes chronostratigraphy and significance for recording past tropical cyclones abstract past coastal flooding events may be inferred from geomorphic and sedimentary archives including particular landforms e g beach ridges washover fans deposits e g washover sediments in lagoons or erosional features e g erosional scarps within strandplains in giralia bay southern exmouth gulf western australia sandy ridge sequences in supratidal elevations form the landward margin of extensive mudflats the formation of these ridges is assumed to be mainly driven by tropical cyclones tcs although their depositional processes need to be clarified we investigated the supratidal sandy ridge sequence in giralia bay by carrying out process monitoring geomorphological mapping by means of an unmanned aerial vehicle survey as well as sedimentological and geochronological investigations and multivariate statistics based on the resulting data this study aims at i identifying the most important driving processes to form the sandy ridges ii establishing their chronostratigraphy and iii understanding their significance for recording past tc activity trench excavations revealed sandy units that are interbedded with mud layers at the base similar to the present distal mudflat sediments on top mud intercalations recede and sand layers of varying grain size distribution dominate in the upper part of the trenches younger sediment layers onlap older ones documenting the stepwise seaward accretion of the ridges onto the mudflat while our data suggests that tidal processes have only limited effects on ridge activity sediment transport erosion and deposition seems to be driven by both tc induced storm surges and high magnitude precipitation events causing surface discharge most accretionary sand units are thus assumed to represent events of morphodynamic activity during tc induced flooding since the mid holocene ridge activity is recorded in a roughly decadal resolution and over historical as well as prehistorical holocene time scales while the ridges do not represent beach or chenier ridges sensu stricto they may be described as chenier type ridges due to their stratigraphical architecture ridge evolution however over a millennial time scale seems to be indicated by the landward rise of the sequence possibly corresponding to the mid holocene sea level highstand of western australia of at least 1 2 m above present mean sea level

the global resurfacing of venus the impact cratering record on venus is unique among the terrestrial planets fully 84 of the craters are in pristine condition and only 12 are fractured remarkably only 2 5 of the craters and crater related features are embayed by lava although intense volcanism and tectonism have affected the entire planet furthermore the spatial and hypsometric distribution of the craters is consistent with a completely random one including stochastic variations monte carlo simulations of equilibrium resurfacing models result in a minimum of 17 times more embayed craters than observed or unobserved nonrandom crater distributions for resurfacing areas between 0 03 and 100 of the planet s surface these models also are not consistent with the number and nonrandom distribution of volcanoes and the nonrandom distribution of embayed and heavily fractured craters the constraints imposed by the cratering record strongly indicate that venus experienced a global resurfacing event about 300 m y ago followed by a dramatic reduction of volcanism and tectonism this global resurfacing event ended abruptly 10 m y the present crater population has accumulated since then and remains largely intact thermal history models suggest that similar global resurfacing events probably occurred episodically in the past the tesserae statistically have the same average surface age crater retention age as the rest of the planet but they probably represent older rock units deformed by earlier episodes of global resurfacing although they largely survived the latest global resurfacing event their surfaces were severely deformed by it monte carlo simulations indicate that only about 4 6 of the planet has been volcanically resurfaced since the global event and that the lava production rate has been no more than 0 01 0 15 km3 yr during this time this rate is significantly less than the current rate of intraplate volcanism on earth 0 33 0 5 km3 yr most of venus recent volcanism occurs in the beta atla themis region and most of the recent tectonism is associated with the major global scale tectonic disruption zones that lie within and connect the equatorial highlands the approximately 33 of the planet s surface bounded by latitudes 30 n and 30 s longitudes 60 and 300 e contains twice as many heavily fractured craters and 1 4 times more lava embayed craters as the planetary average this region includes most of the major tectonic belts in the equatorial region because the craters are indistinguishable from a statistically random distribution both spatially and hypsometrically this concentration of strongly fractured and embayed craters is considered indicative of a continuing low level of limited extension and volcanic activity in this region over the past 300 m y however these craters are simply fractured and or embayed and very few have been subjected to complete tectonic disruption complete burial and subsequent removal from the surface as was the case during the global resurfacing event we show that neither the present level and style of geologic activity nor anything less than global resurfacing could have produced the observed cratering record the effects of recent geologic activity are much less than those of the earlier global resurfacing event when the record of all the early heavy bombardment and much of the later light bombardment was erased from the surface by massive volcanism and tectonic activity episodic regional resurfacing events that had global effects also occurred on earth e g the mid cretaceous superplume and probably on mars on mars they may have triggered the catastrophic releases of water that formed the outflow channels