clustered impacts experiments and implications impact by clusters of projectiles rather than a single projectile can result from several processes atmospheric breakup tidal breakup and ejecta from a large primary impact experiments have been performed in order to establish the characteristics of such events over a wide range of impact velocities 15 m s to 6 km s at very low impact velocities 15 200 m s clustered impacts were produced by launching a grouped projectiles of aluminum shot steel shot iron filings and sand at moderate to high velocities 0 8 6 km s pyrex spheres were shattered above the target during passage through aluminum foil or paper thereby forming a well defined cluster of fragments of overall radius rc the ratio of the overall radius rc of the cluster to the radius rs of a solid impactor of the same mass provides a measure of the cluster dispersion sand and compacted pumice targets were used in order to compare qualitatively the additional effect of slight differences in target strength the experiments reveal marked contrasts between impacts by clusters of projectiles and impacts by a single solid body tight clusters rc rs 20 displace a factor of 10 less mass this reduction in cratering efficiency is largely expressed as a shallow crater with an aspect ratio diameter depth as large as 30 for open clusters the size and velocity of the cluster as well as the density and strength contrast between the impactor and target can dramatically affect crater morphology open clusters impacting compacted pumice produce a flat hummocky floor with an incipient multiring pattern whereas a tight cluster impacting the same target produces a central floor mound oblique impacts by symmetrical clusters form a characteristic array of v shaped ridges pointing uprange the apex angle of the ridges depends on the cluster dispersion and impact angle inventories of postimpact projectile material reveal that the projectile is largely retained on the surface and spread downrange from the impact direction the amount of projectile material retained on the surfaces increases with decreasing impact angle from the horizontal and with increasing strength of the target relative to the projectile clustered impact craters and lunar secondary craters bear striking similarities over a broad range of morphologic features on this basis and on the basis of reasonable models of ejecta curtain structure we suggest that these experiments provide new clues for understanding ejecta emplacement around large lunar impact craters when the ejecta curtain around large impacts is viewed as a thick wall of debris and clustered impactors are viewed as a unit section of such a curtain then experimental results indicate that the continuous ejecta facies even for lunar craters larger than 100 km could contain as much as 90 primary material such a conclusion contrasts with many existing models that derive mixing ratios implicitly based on single noninteracting impact events beyond the continuous ejecta facies impacting clusters of ejecta provide a physical basis for understanding the wide variety of secondary morphologies and the large range in spectral signatures of primary material in crater rays

geologic structure generated by large impact basin formation observed at the south pole aitken basin on the moon the south pole aitken spa basin is the largest clearly recognized basin on the lunar surface determining the composition and structure of the spa basin interior provides critical constraints on the deep crustal and or mantle composition of the moon and improves our understanding of large basin forming impact processes here we present a new mineralogical map of the spa basin interior based on high spatial resolution reflectance spectra using the selene kaguya multiband imager which is combined with topographic data in order to interpret the geologic context the derived mineralogical map suggests extensive distribution of ejected low ca pyroxene dominant mantle material with the presence of purest anorthosite crustal materials surrounding a possible melt pool of 0 26 to 0 33 of the basin diameter near the basin center which is significantly smaller than that suggested by the crater scaling law the absence of clear evidence of lower crustal material is consistent with recent impact simulation results

major lunar crustal terranes surface expressions and crust mantle origins in light of global remotely sensed data the igneous crust of the moon can no longer be viewed as a simple globally stratified cumulus structure composed of a flotation upper crust of anorthosite underlain by progressively more mafic rocks and a residual melt kreep sandwich horizon near the base of the lower crust instead global geochemical information derived from clementine multispectral data and lunar prospector gamma ray data reveals at least three distinct provinces whose geochemistry and petrologic history make them geologically unique 1 the procellarum kreep terrane pkt 2 the feldspathic high lands terrane fht and 3 the south pole aitken terrane spat the pkt is a mafic province coincident with the largely resurfaced area in the procellarum imbrium region whose petrogenesis relates to the early differentiation of the moon here some 40 of the th in the moon s crust is concentrated into a region that constitutes only about 10 of the crustal volume this concentration of th average 5 ppm and by implication the other heat producing elements u and k led to a fundamentally different thermal and igneous evolution within this region compared to other parts of the lunar crust lower crustal materials within the pkt likely interacted with underlying mantle materials to produce hybrid magmatism leading to the magnesian suite of lunar rocks and possibly kreep basalt although rare in the apollo sample collection widespread mare volcanic rocks having substantial th enrichment are indicated by the remote data and may reflect further interaction between enriched crustal residues and mantle sources the fht is characterized by a central anorthositic region that constitutes the remnant of an anorthositic craton resulting from early lunar differentiation basin impacts into this region do not excavate significantly more mafic material suggesting a thickness of tens of kilometers of anorthositic crust the feldspathic lunar meteorites may represent samples from the anorthositic central region of the fht ejecta from deep penetrating basin impacts outside of the central anorthositic region however indicate an increasingly mafic composition with depth the spat a mafic anomaly of great magnitude may include material of the upper mantle as well as lower crust thus it is designated a separate terrane whether the spa basin impact simply uncovered lower crust such as we infer for the fht remains to be determined

volcanic eruptions on io nine eruption plumes were observed over a period of 6 1 2 days during the voyager 1 encounter with io during the voyager 2 encounter 4 months later eight of these eruptions were still active the largest plume viewed by voyager 1 became inactive sometime between the two encounters however a major eruption occurred at surt sometime between the two encounters and deposited an ejecta blanket comparable in size to those associated with the largest plumes the plumes range in height from about 60 to over 300 km with corresponding ejection velocities of about 0 5 to 1 0 km s where topographic information exists plumes 1 and 8 the plume source is located on level plains rather than topographic highs and consists of either fissures or calderas with the exception of plume 1 pele the brightness distribution monotonically decreases from the core to the top of the plume the shape and brightness distribution together with the pattern of the surface deposit of at least plume 3 prometheus can be simulated by a ballistic model in which the ejection velocity is constant 0 5 km s and ejection angles vary from vertical 0 to 55 the brightness distribution of plume 1 is probably better explained by a shock front near the top of the plume numerous surface deposits similar to those associated with active plumes probably mark the sites of recent eruptions the distribution of active and recent eruptions appears to be concentrated in the equatorial regions and indicates the volcanic activity is more frequent and intense in the equatorial regions than the polar regions this suggests that the depositional rate is greater and the surface age younger in the equatorial regions which may account for the darker polar regions the geologic setting of certain plume sources and the very large reservoirs of volatiles required for the active eruptions suggests that sulphur volcanism rather than silicate volcanism is the most likely driving mechanism for the eruption plumes

feo and tio2 concentrations in the south pole aitken basin implications for mantle composition and basin formation we use newly developed spectroscopic methods for determining feo and tio2 abundances to study the huge 2500 km diameter south pole aitken basin the floor of this basin shows iron and titanium values which are weakly correlated and largely range from 7 to 14 wt feo and from 0 5 to 1 5 wt tio2 this composition is consistent with an approximate 1 1 mixture of lower crustal material like that found elsewhere on the moon and mantle rock containing 10 16 wt feo and 0 1 wt tio2 although mantle rock appears to compose about 50 of the floor deposits models of the formation of large impact basins predict that virtually all the floor materials ought to be derived from the mantle

post voyager brightness variations on io imaging of io with the faint object and planetary cameras of the hubble space telescope in 1992 and 1993 at wavelengths of 3450 3700 and 4100 a shows two surface areas that have undergone significant large scale change in reflectivity since the 1979 voyager encounters the first is located in colchis regio and covers 106 km2 between longitudes 150 180 and latitudes 25 to 30 the second is centered at longitude 130 latitude 30 and extends for 105 km2 both areas have darkened by 45 since 1979 in light of the active volcanism discovered on io by the voyager 1 encounter it seems reasonable to infer that these large scale changes in surface morphology are due to some type of volcanic activity in the intervening 14 years we hypothesize two possible causes for these darkenings either large scale eruptions of the pele type have covered areas of existing so2 surface frost with new much darker deposits or previously active eruptions of the prometheus type or smaller scale venting which apparently produce so2 gas that is bright in the visible when it condenses as surface frost have become inactive

two classes of volcanic plumes on io abstract comparison of voyager 1 and voyager 2 images of the south polar region of io has revealed that a major volcanic eruption occured there during the period between the two spacecraft encounters an annular deposit 1400 km in diameter formed around the aten patera caldera 311 w 48 s the floor of which changed from orange to red black the characteristics of this eruption are remarkably similar to those described earlier for an eruption centered on surt caldera 338 w 45 n that occured during the same period also at high latitude but in the north both volcanic centers were evidently inactive during the voyager 1 and 2 encounters but were active sometime between the two the geometric and colorimetric characteristics as well as scale of the two annular deposits are virtually identical both resemble the surface features formed by the eruption of pele 255 w 18 s these three very large plume eruptions suggest a class of eruption distinct from that of six smaller plumes observed to be continously active by both voyagers 1 and 2 the smaller plumes of which prometheus is the type example are longer lived deposit bright whitish material erupt at velocities of 0 5 km sec 1 and are concentrated at low latitudes in an equatorial belt around the satellite the very large pele type plumes on the other hand are relatively short lived deposit darker red materials erupt at 1 0 km sec 1 and rather than restricted to a latitudinal band are restricted in longitude from 240 to 360 w both direct thermal infrared temperature measurements and the implied color temperatures for quenched liquid sulfur suggest that hot spot temperatures of 650 k are associated with the large plumes and temperatures 2 in their annuli whereas the large plumes apparently do not two other plumes that occur at either end of the linear feature loki may be intermediate or hybrid between the two classes exhibiting attributes of both additionally loki occurs in the area of overlap in the regional distributions of the two plume classes two distinct volcanic systems involving different volatiles may be responsible for the two classes we propose that the discrete temperatures associated with the two classes are a direct reflection of sulfur s peculiar variation in viscosity with temperature over two temperature ranges 400 to 430 k and 650 k sulfur is a low viscosity fluid orange and black respectively at other temperatures it is either solid or has a high viscosity as a result there will be two zones in io s crust in which liquid sulfur will flow freely a shallow zone of orange sulfur and a deeper zone of black sulfur a low temperature system driven by so 2 heated to 400 to 400 k by the orange sulfur zone seems the best model for the small plumes a system driven by sulfur heated to 650 k by hot or even molten silicates in the black sulfur zone seems the best explanation for the large plume class the large pele type plumes are apparently concentrated in a region of the satellite in which a thinner sulfur rich crust overlies the tidally heated silicate lithosphere so the black sulfur zone may be fairly shallow in this region the prometheus type plumes are possibly confined to the equatorial belt by some process that concentrates so 2 fluid in the equatorial crust

ultramafic impact melt sheet beneath the south pole aitken basin on the moon 1 the spectral profiler onboard the japanese lunar explorer kaguya conducted the first hyperspectral survey around the south pole aitken basin spa on the moon that is one of the largest impact structures in the solar system the radiative transfer modeling revealed that fresh crater central peaks inside spa are commonly composed of an ultramafic assemblage dominated by magnesium rich orthopyroxene suggesting a homogeneous layer buried under spa the extensive ultramafic layer could be a relic of a gigantic impact melt pool produced by the spa forming impact the preponderance of orthopyroxene could have resulted from significant fractional crystallization of the lunar magma ocean prior to the onset of plagioclase floatation

imaging of volcanic activity on jupiter s moon io by galileo during the galileo europa mission and the galileo millennium mission the solid state imaging ssi instrument provided the first high and medium resolution views of io as the galileo spacecraft closed in on the volcanic body in late 1999 and early 2000 while each volcanic center has many unique features the majority can be placed into one of two broad categories the promethean eruptions typified by the volcanic center prometheus are characterized by long lived steady eruptions producing a compound flow field emplaced in an insulating manner over a period of years of decades in contrast pillanian eruptions are characterized by large pyroclastic deposits and short lived but high effusion rate eruptions from fissures feeding open channel or open sheet flows both types of eruptions commonly have 100 km tall bright so2 rich plumes forming near the flow fronts and smaller deposits of red material that mark the vent for the silicate lavas

global color and albedo variations on io abstract three multispectral mosaics of io have been produced from voyager imaging data a global mosaic from each of the voyager 1 and voyager 2 data sets and a high resolution mosaic of the region surrounding the volcano ra patera the mosaics are maps of normal albedo and color in accurate geometric map formats io s photometric behavior mapped with a two image technique is spatially variable especially in the bright white areas the disk integrated color and albedo of the satellite have been remarkably constant over recent decades despite the volcanic activity and the many differences between voyager 1 and 2 images acquired just 4 months apart this constancy is most likely due to the consistent occurrence of large pele type plumes with relatively dark red deposits in the region from long 240 to 360 a transient brightening southeast of pele during the voyager 1 encounter was probably due to real changes in surface and or atmospheric materials rather than to photometric behavior the intrinsic spectral variability of io as seen in a series of two dimensional histograms of the multispectral mosaics consists of continuous variation among three major spectral end members the data were mapped into five spectral units to compare them with laboratory measurements of candidate surface materials and to show the planimetric distributions unit 1 is best fit by the spectral reflectance of ordinary elemental sulfur and it is closely associated with the peletype plume deposits unit 2 is strongly confined to the polar caps above about latitude 50 but its composition is unknown unit 5 is probably so 2 with relatively minor contamination it is concentrated in the equatorial region and near the long lived prometheus type plumes units 3 and 4 are gradational between units 1 and 5 in addition to so 2 and elemental sulfur other plausible components of the surface are polysulfur oxides fecl 2 na 2 s and nahs

space weathering on airless bodies resolving a mystery with lunar samples using new techniques to examine the products of space weathering of lunar soils we demonstrate that nanophase reduced iron npfe0 is produced on the surface of grains by a combination of vapor deposition and irradiation effects the optical properties of soils both measured and modeled are shown to be highly dependent on the cumulative amount of npfe0 which varies with different starting materials and the energetics of different parts of the solar system the measured properties of intermediate albedo asteroids the abundant s type asteroids in particular are shown to directly mimic the effects predicted for small amounts of npfe0 on grains of an ordinary chondrite regolith this measurement and characterization of space weathering products seems to remove a final obstacle hindering a link between the abundant ordinary chondrite meteorites and common asteroids

reflectance spectroscopy of plagioclase dominated mineral mixtures implications for characterizing lunar anorthosites remotely anorthositic rocks dominate the moon s upper crust as remnants of the lunar magma ocean lmo small variations in the mineralogy of these rocks may hold key information about the homogeneity of lmo composition and solidification processes orbital near infrared nir sensors are sensitive to mineralogy but technologic advances have only recently enabled detection of the plagioclase component in crustal rocks based on an absorption band centered near 1250 nm anorthosites occupy a unique mineralogic range that is well suited for nir studies the highly transparent component plagioclase is present in high abundances while the spectrally dominant mafic or oxide minerals are present in only minor abundance as a result spectra of anorthosites are more likely than many other rock types to contain visually discernable signatures from more than one mineral component facilitating their identification and characterization in nir data in support of new nir measurements for the moon we present laboratory spectral analyses of well controlled plagioclase dominated mineral mixtures we focus on the spectral effects of varying mafic and oxide composition and abundance in mixtures with a common plagioclase end member the results demonstrate that plagioclase can be a significant contributor to reflectance spectra when strongly absorbing minerals are present in low abundance we show that the contribution of plagioclase is more pronounced in mixtures with pyroxenes and certain spinels but more easily masked in mixtures containing small amounts of olivine differences in minor mineral composition are clearly expressed in bulk spectra modeling of mixtures using a hapke nonlinear approach accurately estimates mineral abundances in laboratory spectra to within 5 vol for mixtures with 90 vol plagioclase together these results imply that not only should orbital nir data sets be able to discern the presence of plagioclase in anorthositic crustal exposures but also that detailed information about anorthosite mineral assemblages can be reliably accessed in reflectance spectra

io evidence for silicate volcanism in 1986 infrared observations of io during the 1986 apparition of jupiter indicate that a large eruptive event occurred on the leading side of io on 7 august 1986 universal time measurements made at 4 8 8 7 and 20 micrometers suggest that the source of the event was about 15 kilometers in radius with a model temperature of 900 kelvin together with previously reported events these measurements indicate that high temperature volcanic activity on the leading side of io may be more frequent than previously thought the inferred temperature is significantly above the boiling point of sulfur in a vacuum 715 kelvin and thus constitutes strong evidence for active silicate volcanism on the surface of io

differentiation of the south pole aitken basin impact melt sheet implications for lunar exploration we modeled the differentiation of the south pole aitken spa impact melt sheet to determine whether noritic lithologies observed within spa formed as a result of the impact results indicate differentiation of spa impact melt can produce noritic layers that may accommodate observed surface compositions but only in specific scenarios one of nine modeled impact melt compositions yielded layers of noritic materials that account for observations of noritic lithologies at depths of 6 km in this scenario impact occurred before a hypothesized lunar magma ocean cumulate overturn the 50 km deep melt sheet would have formed an insulating quenched layer at the surface before differentiating the uppermost differentiated layers in this scenario have feo and tio2 contents consistent with orbital observations if they were subsequently mixed with the uppermost quenched melt layer and with less feo and tio2 enriched materials such as ejecta emplaced during younger impacts these results verify that noritic lithologies observed within spa could have formed as a direct result of the impact therefore locations within spa that contain noritic materials represent potential destinations for collecting samples that can be analyzed to determine the age of the spa impact potential destinations include central peaks of bhabha bose finsen and antoniadi craters as well as walls of leibnitz and schrodinger basins additionally potential remnants of the uppermost quenched melt may be preserved in gabbroic material exposed in mafic mound exploring and sampling these locations can constrain the absolute age of spa a task that ranks among the highest priorities in lunar science

surface changes on io during the galileo mission abstract a careful survey of galileo ssi global monitoring images revealed more than 80 apparent surface changes that took place on io during the 5 year period of observation ranging from giant plume deposits to subtle changes in the color or albedo of patera surfaces explosive volcanic activity was discovered at four previously unrecognized centers an unnamed patera to the south of karei that produced a pele sized red ring a patera to the west of zal that produced a small circular bright deposit a large orange ring detected near the north pole of io and a small bright ring near io s south pole only a handful of io s many active volcanoes produced large scale explosive eruptions and several of these erupted repeatedly leaving at least 83 of io s surface unaltered throughout the galileo mission most of the hot spots detected from ssi nims and ground based thermal observations caused no noticeable surface changes greater than 10 km in extent over the five year period surface changes were found at every location where active plumes were identified including acala which was never seen in sunlight and was only detected through auroral emissions during eclipse two types of plumes are distinguished on the basis of the size and color of their deposits confirming post voyager suggestions by mcewen and soderblom icarus 55 1983 191 smaller plumes produce near circular rings typically 150 200 km in radius that are white or yellow in color unless contaminated with silicates and frequently coat their surroundings with frosts of fine grained so2 the larger plumes are much less numerous limited to a half dozen examples and produce oval orange or red sulfur rich rings with maximum radii in the north south direction that are typically in the range from 500 to 550 km both types of plumes can be either episodic or quasi continuous over a five year period repeated eruptions of the smaller so2 rich plumes likely contribute significantly to io s resurfacing rate whereas dust ejection is likely dominated by the tenuous giant plumes both types of plume deposits fade on time scales of months to years through burial and alteration episodic seepages of so2 at haemus montes zal montes dorian montes and the plateau to the north of pillan patera may have been triggered by activity at nearby volcanic centers

io meteorology how atmospheric pressure is controlled locally by volcanos and surface frosts the hydrodynamic model of a p ingersoll m e summers s g schilpf 1985 icarus 64 375 390 is modified to include the effects of nonuniform surface properties as revealed in recent observational studies the observations indicate that so 2 frost is concentrated in a band within 30 latitude of the equator covering 270 of longitude and that the darker surface at midlatitude is warmer than the frost at times of maximum insolation the approach to the hydrodynamics has been to make the model simpler and more versatile solutions are now obtained in closed analytic form we calculate atmospheric pressures horizontal winds sublimation rates and condensation rates for a wide variety of surface conditions patchy and continuous frost cover volcanic venting treated as a source of mass distributed over the plume area discontinuities of surface temperature subsurface cold trapping and insolation propagation into the frost the principal new concept is the horizontal averaging length l which is equal to 2 h where h is the atmospheric scale height and is the sticking coefficient if frost is present either on the surface or just below it then each area of dimension l of order 100 km determines its own atmospheric pressure away from the volcanic plumes the pressure follows the local vapor pressure inside the plumes the pressure is higher e g a volcanic source of 10 6 kg sec spread over an area 300 km in radius raises the local pressure by an amount equal to the vapor pressure of a frost at 124 k the key unknowns for io are the strength of the volcanic sources and the temperature of frost near the subsolar point if the frost is cold below 110 k then the only substantial atmospheres are beneath the plumes if the frost is warm e g 125 k then there is also a substantial atmosphere near the subsolar point the equatorial frost deposits are then losing net mass at a substantial rate e g 0 1 cm year for a subsolar frost temperature of 125 k

space weathering from mercury to the asteroid belt the variety of evidence bearing on the nature of space weathering is reviewed the effects of space weathering include spectral darkening reddening and subdued absorption bands and the distinctive magnetic electron spin resonance caused by single domain metallic iron particles ever since the apollo missions two paradigms have dominated the thinking of the planetary science community concerning space weathering 1 the optical effects are caused by impact vitrified glass in agglutinates and 2 the submicroscopic metallic iron results from the reduction of ferrous iron by the impact melting of minerals whose surfaces have been saturated with hydrogen from the solar wind however studies carried out since the apollo program showed that both of these paradigms are invalid a hypothesis first suggested by the author and his colleagues 26 years ago but not generally accepted at that time now appears to be essentially correct both the optical and magnetic effects are caused by metallic iron particles smaller than the wavelength in ubiquitous vapor deposited coatings on soil particle surfaces and inside agglutinates the vapor is generated by both solar wind sputtering and micrometeorite impact vaporization and injected preferentially downward into the porous regolith the iron is reduced by a physical process the selective loss of oxygen that occurs during deposition of the vapor and does not require heating melting or a reducing environment a mathematical theory that describes the optical effects of the submicroscopic iron quantitatively is derived and applied to the regoliths of the moon mercury and an s asteroid

recent tectonic stress field active faults and geothermal fields hot water type in china abstract it is quite probable that geothermal fields of the hot water type in china do not develop in the absence of recently active faults such active faults are all controlled by tectonic stress fields using the data of earthquake fault plane solutions active faults and surface thermal manifestations a map showing the recent tectonic stress field and the location of active faults and geothermal fields in china is presented data collected from 89 investigated prospects with geothermal manifestations indicate that the locations of geothermal fields are controlled by active faults and the recent tectonic stress field about 68 of the prospects are controlled by tensional or tensional shear faults the angle between these faults and the direction of maximum compressive stress is less than 45 and both tend to be parallel about 15 of the prospects are controlled by conjugate faults another 14 are controlled by compressive shear faults where the angle between these faults and the direction maximum compressive stress is greater than 45

in situ optical measurements of chang e 3 landing site in mare imbrium 1 mineral abundances inferred from spectral reflectance the visible and near infrared imaging spectrometer on board the yutu rover of chinese chang e 3 mission measured the lunar surface reflectance at a close distance similar to 1m and collected four spectra at four different sites these in situ lunar spectra have revealed less mature features than that measured remotely by spaceborne sensors such as the moon mineralogy mapper instrument on board the chandrayaan 1 mission and the spectral profiler on board the kaguya over the same region mineral composition analysis using a spectral lookup table populated with a radiative transfer mixing model has shown that the regolith at the landing site contains high abundance of olivine themineral abundance results are consistent with that inferred from the compound measurement made by the on board alpha particle x ray spectrometer

volcanic resurfacing of io post repair hst imaging abstract in march 1994 we used the newly refurbished hubble space telescope hst to obtain global imaging of io at five wavelengths between 0 34 and 1 02 m with a spatial resolution of 160 km the images provided the clearest view of io since voyager and the first systematic observations in the wavelength range 0 7 1 0 m we have produced absolutely calibrated global mosaics of io s reflectance in all our five wavelengths the near infrared images reveal that the 0 55 to 0 7 m absorption edge seen in io s disk integrated spectrum has a very different spatial distribution from the better known 0 40 to 0 50 m absorption edge studied by voyager and must be generated by a different chemical species the 0 55 to 0 7 m absorption edge is strongly concentrated in the pyroclastic ejecta blanket of the volcano pele at a few much smaller discrete spots and probably also in the polar regions the pele ejecta spectrum is consistent with the idea that s 2 o partially decomposed to s 4 and probably s 3 may be the species responsible for the 0 55 to 0 7 m absorption edge at pele and elsewhere on io though s 4 generated by other processes may also be a possibility s 2 o can be produced by high temperature decomposition of so 2 gas and the high temperature of the pele volcano may account for its concentration there spectral anomalies of comparable size and prominence are not seen around the other pele type volcanos surt and aten a s mcewen and l a soderblom 1983 icarus 55 191 217 suggesting that these volcanos if chemically similar to pele are much less active the spectrum of high latitude regions is similar to that of quenched red sulfur glass and if this similarity is not coincidental the glass may be preserved here by the low polar surface temperatures alternatively the low polar temperatures may preserve sulfur that has been reddened by radiation there are many changes in albedo patterns in the 15 years between voyager and these hst observations but these are generally subtle at hst resolution and are not strongly concentrated in longitude however there was a major brightening of a 400 km diameter region centered on ra patera between march 1994 and repeat hst observations in july 1995 which was a larger albedo change than any seen in the previous 15 years this was presumably due to a large eruption at ra patera as confirmed by galileo images long exposure eclipse images of io at 1 02 m on march 6 1994 place strong limits on the area of exposed silicate magma on io at the time of the observations

orogeny and relative plate motions example of the japanese islands abstract the paleogeography of the eastern margin of asia near japan for the past 250 ma has been reconstructed on the basis of the relative motions between the oceanic plates and the eurasian plate engebretson et al 1982 and on land geology the relationships between the plate kinematics and orogeny are as follows calc alkaline magmatism is related to the presence of subduction when a plate boundary is a transform fault there is no volcanism very slow convergence rates do not give rise to magmatism migration of rft type triple junctions or ridge subduction produces forearc volcanism near the trench and also a wider volcanic zone uplift of low p t type regional metamorphic belts is related to collision episodes the uplift of the high p t blueschist belts on the contrary is not contemporaneous with them they appear to be related to the start of the subduction of a young plate after the migration of an rft type triple junction because the formation of a voluminous accretionary complex is contemporaneous with this and thrusting of this young accretionary complex beneath the uplifted metamorphic belt is often observed the underplating of the young accretionary complex beneath the older accretionary complex would be the cause of the uplift of the high p t type metamorphic belt the subduction of a young plate would thus be an important factor causing these orogenic events highly oblique convergence also results in formation of a serpentinite melange zone with fragments of blueschists presumably along a mechanical plate boundary in the forearc

discovery of hotspots on io using disk resolved infrared imaging active tidally driven volcanism on jupiter s satellite io1 2 was discovered in voyager images in 1979 voyager also detected the thermal emission from the volcanoes3 4 and this emission has since been monitored from earth using a variety of techniques employing single element infrared detectors5 10 because of io s small angular size no more than 1 2 arcsec however it has normally been possible to resolve and locate only the brightest individual hotspot loki although additional hotspots can be located at five year intervals during occultations of io by the other galilean satellites11 12 here we present first results using two new techniques for ground based observation of io s hotspots first use of an infrared array camera allowed us to exploit the mauna kea observatory s excellent atmospheric stability to obtain direct infrared images of io with resolution better than 0 5 arcsec this allowed us to see more than one hotspot on io in jupiter eclipse in jupiter s shadow second we used the camera to make the first observations of the jupiter occultation disappearance behind jupiter of the hotspots these new techniques have revealed and located at least three hotspots and will now permit routine ground based monitoring of the locations temperatures and sizes of multiple hotspots on io

active volcanism on io as seen by galileo ssi abstract active volcanism on io has been monitored during the nominal galileo satellite tour from mid 1996 through late 1997 the solid state imaging ssi experiment was able to observe many manifestations of this active volcanism including 1 changes in the color and albedo of the surface 2 active airborne plumes and 3 glowing vents seen in eclipse about 30 large scale tens of kilometers surface changes are obvious from comparison of the ssi images to those acquired by voyager in 1979 these include new pyroclastic deposits of several colors bright and dark flows and caldera floor materials there have also been significant surface changes on io during the galileo mission itself such as a new 400 km diameter dark pyroclastic deposit around pillan patera while these surface changes are impressive the number of large scale changes observed in the four months between the voyager 1 and voyager 2 flybys in 1979 suggested that over 17 years the cumulative changes would have been much more impressive there are two reasons why this was not actually the case first it appears that the most widespread plume deposits are ephemeral and seem to disappear within a few years second it appears that a large fraction of the volcanic activity is confined to repeated resurfacing of dark calderas and flow fields that cover only a few percent of io s surface the plume monitoring has revealed 10 active plumes comparable to the 9 plumes observed by voyager one of these plumes was visible only in the first orbit and three became active in the later orbits only the prometheus plume has been consistently active and easy to detect observations of the pele plume have been particularly intriguing since it was detected only once by ssi despite repeated attempts but has been detected several times by the hubble space telescope at 255 nm pele s plume is much taller 460 km than during voyager 1 300 km and much fainter at visible wavelengths prometheus type plumes 50 150 km high long lived associated with high temperature hot spots may result from silicate lava flows or shallow intrusions interacting with near surface so2 a major and surprising result is that 30 of io s volcanic vents glow in the dark at the short wavelengths of ssi these are probably due to thermal emission from surfaces hotter than 700 k with most hotter than 1000 k well above the temperature of pure sulfur volcanism active silicate volcanism appears ubiquitous there are also widespread diffuse glows seen in eclipse related to the interaction of energetic particles with the atmosphere these diffuse glows are closely associated with the most active volcanic vents supporting suggestions that io s atmopshere is dominated by volcanic outgassing globally volcanic centers are rather evenly distributed however 14 of the 15 active plumes seen by voyager and or galileo are within 30 of the equator and there are concentrations of glows seen in eclipse at both the sub and antijovian points these patterns might be related to asthenospheric tidal heating or tidal stresses io will continue to be observed during the galileo europa mission which will climax with two close flybys of io in late 1999

mass wasting features on the moon how active is the lunar surface abstract mass wasting features have long been noticed on the moon but there has been no systematic studies for their morphological geometrical or distribution characteristics the effect of mass wasting on topographic evolution and surface erosion on the moon is not fully understood using high resolution image and topography data obtained from the lunar reconnaissance orbiter spacecraft we found that mass wasting has been globally and continuously occurring on the moon meteor impacts and moonquakes are the two major triggering mechanisms in forming lunar mass wasting features we selected over 300 examples of lunar mass wasting features and classified them as falls flows slides slumps and creeps after studying their morphology potential mode of emplacement and sizes of displaced materials the slope and age distributions for their host terrains are studied to estimate the topographic evolutionary sequence of the lunar surface under the effect of mass wasting due to continuous reshaping by mass wasting surface topographies on the moon tend to become smoother with time with fewer mass wasting events occurring on older surfaces pre nectarian surfaces may represent the final stage of surface topographic evolution on slope angles regarding the effect of mass wasting crater densities on lunar surfaces vary with slope angles because the surface erosion rate and regolith production rate on slopes are larger than those on flat areas

complexities in pyroxene compositions derived from absorption band centers examples from apollo samples hed meteorites synthetic pure pyroxenes and remote sensing data we reexamine the relationship between pyroxene composition and near infrared absorption bands integrating measurements of diverse natural and synthetic samples we test an algorithm plc involving a two part linear continuum removal and parabolic fits to the 1 and 2 m bands a computationally simple approach which can easily be automated and applied to remote sensing data employing a suite of synthetic pure pyroxenes the plc technique is shown to derive similar band centers to the modified gaussian model plc analyses are extended to natural pyroxene bearing materials including 1 bulk lunar basalts and pyroxene separates 2 diverse lunar soils and 3 hed meteorites for natural pyroxenes the relationship between composition and absorption band center differs from that of synthetic pyroxenes these differences arise from complexities inherent in natural materials such as exsolution zoning mixing and space weathering for these reasons band center measurements of natural pyroxene bearing materials are compositionally nonunique and could represent three distinct scenarios 1 pyroxene with a narrow compositional range 2 complexly zoned pyroxene grains or 3 a mixture of multiple pyroxene or nonpyroxene components therefore a universal quantitative relationship between band centers and pyroxene composition cannot be uniquely derived for natural pyroxene bearing materials without additional geologic context nevertheless useful relative relationships between composition and band center persist in most cases these relationships are used to interpret m3 data from the humboldtianum basin four distinct compositional units are identified 1 mare humboldtianum basalts 2 distinct outer basalts 3 low ca pyroxene bearing materials and 4 feldspathic materials

optical effects of space weathering the role of the finest fraction the optical properties of lunar softs are different than those of rocks from which they are derived as a consequence of lunar space weathering soils are darker and exhibit a distinctive red sloped continuum and weaker mineral absorption bands the accumulation of dark glass welded aggregates agglutinates has been thought to account for these optical effects of space weathering on lunar soils spectroscopic analyses of agglutinate separates and size fractions for a suite of lunar softs presented here indicate that the agglutinate paradigm is insufficient to fully account for lunar optical alteration it is the finest fraction of lunar soils 25 gm which constitute 25 wt that dominates the optical properties of the bulk soil unlike size fractions of most silicates for which the finest fraction is the brightest the lunar soil size fractions all have comparable albedos in the short wavelength visible in the near infrared however it is the finest fraction that exhibits the steep red continuum and weak absorption bands the properties of the finest fraction cannot be duplicated by preparing a fine fraction by grinding larger agglutinate rich soil particles these results suggest space weathering on airless bodies is dominated by surface correlated processes perhaps associated with the development of fine grained fe o on or near the surface of grains and the accumulation of the larger agglutinates is not necessarily required to account for lunar optical alteration

composition of amazonian volcanic materials in tharsis and elysium mars from mro crism reflectance spectra abstract compositions of the amazonian aged tharsis and elysium volcanic provinces of mars have been largely obscured in mars orbital remote sensing data by windblown dust fresh impact craters formed within the last few years have disturbed surface dust providing unique windows to explore these regions relatively dust free mineralogic compositions such fresh craters plus other small exposures of less dusty materials are resolved spatially in high resolution targeted observations of visible short wave infrared spectral reflectance by the compact reconnaissance imaging spectrometer for mars crism analysis of crism observations of small relatively dust free locations in the tharsis and elysium regions shows that these provinces are dominated by high ca pyroxene and olivine similar to volcanic materials of hesperian age thus the mafic mineral compositions of hesperian and amazonian volcanic materials appear similar to each other but distinct from the olivine and low ca pyroxene rich compositions that dominate noachian rocks in the core regions of both provinces where thermal infrared data indicate the thickest dust cover the dust is sufficiently thick that few fresh craters penetrate to expose the underlying volcanics these results may be consistent with low si contents of surface materials in elysium and western tharsis measured by gamma ray spectroscopy resulting from a thick cover of dust depleted in si rich phases possibly due to eolian sorting

rock types of south pole aitken basin and extent of basaltic volcanism the enormous pre nectarian south pole aitken spa basin represents a geophysically and compositionally unique region on the moon we present and analyze the mineralogical diversity across this basin and discuss the implications for basin evolution rock types are derived from clementine multispectral data based on diagnostic characteristics of ferrous absorptions in fresh materials individual areas are characterized as noritic dominated by low ca pyroxene gabbroic basaltic dominated by high ca pyroxene feldspathic 3 6 feo and olivine gabbro dominated by high ca pyroxene and olivine the anorthositic crust has effectively been removed from the interior of the basin the style of volcanism within the basin extends over several 100 myr and includes mare basalt and pyroclastic deposits several areas of ancient pre orientale volcanism or cryptomaria have also been identified the nonmare mafic lithology that occurs across the basin is shown to be noritic in composition and is pervasive laterally and vertically we interpret this to represent impact melt breccia deposits derived from the lower crust a few localized areas are identified within the basin that contain more diverse lithologies gabbro olivine gabbro some of which may represent material from the deepest part of the lower crust and perhaps uppermost mantle involved in the spa event

the character of south pole aitken basin patterns of surface and subsurface composition using moon mineralogy mapper data we characterize surface diversity across the enormous south pole aitken basin spa by evaluating the abundance and composition of pyroxenes which are overwhelmingly the most abundant mafic mineral in the region although spa exhibits significant complexity due to billions of years of geologic processes subsequent to formation the basin has retained regular patterns of compositional heterogeneity across its structure four distinct roughly concentric zones are defined 1 a central spa compositional anomaly spaca which exhibits a pervasive elevated ca fe rich pyroxene abundance 2 a mg pyroxene annulus which is dominated by abundant mg rich pyroxenes 3 a heterogeneous annulus which exhibits localized pyroxene rich areas spatially mixed with feldspathic materials and 4 the spa exterior which is primarily feldspathic pyroxene compositions in the heterogeneous annulus are similar to those in the mg pyroxene annulus and mg rich pyroxenes also underlie the more ca fe rich pyroxene surface material across spaca the establishment of these four distinct compositional zones across spa constrains future basin evolution models serves to guide potential sample return and other science targets

mineral maps of the moon 1 global maps of the distribution of plagioclase orthopyroxene clinopyroxene and olivine on the moon were derived from radiative transfer analysis of 400 000 clementine uvvis spectra plagioclase inversely correlates with iron while clinopyroxene positively correlates with iron showing these are the major carriers of aluminum and iron respectively the distribution of olivine in the maria agrees with previous studies in the highlands the abundance of olivine is low but ubiquitous at a few percent except within the south pole aitken basin where it is only present in very small exposures in the very anorthositic farside highlands olivine is often the sole mafic mineral the abundance of orthopyroxene is generally low excepting elevated abundances in the nearside highlands and in areas near and within south pole aitken basin mare units with elevated abundances of orthopyroxene are found in some mare and cryptomare deposits distant from the sample return sites

implications of using broadband photometry for compositional remote sensing of icy objects water ice has such a low absorption coefficient at visual wavelengths 0 01 cm 1 that a very small amount of particulate material can significantly darken an icy surface a variety of ice plus particle mixtures were studied to show that particulate contaminations of 1 by weight even 0 1 or less in some cases in ice or frosts result in reflectance levels close to that of the contaminants in a very clear ice no bubbles it is plausible to have a reflectance 0 05 for particulate contaminations 10 7 by weight for submicron dark particles such as carbon lampblack scattering conditions compete for domination with contaminants for control of visual reflectance implying that the apparent reflectivity level and color of a surface is a poor indicator of ice content a dark surface e g albedo 0 05 does not necessarily imply that there us very little water ice present infrared jhk colors of water ice and other minerals including ice mineral mixtures show that some orthopyroxenes can have jhk colors very similar to fine grained water frosts in general it is possible that the jhk colors of an ice plus particulate mixture can fall anywhere in the classical j h versus h k diagram thus the diagram cannot be used to distinguish a predominately rock surface from one which is predominantely ice for one specific case an important exception is the case where both the j h and h k colors are 0 2 it appears that such colors indicate a relatively pure icy surface in some cases the diagram might be used as a statistical tool to distinguish between the compositions of surfaces within a class of objects but the validity of such comparisons decreases for different classes such as the main belt asteroids when compared to outer solar system satellites where water ice is more stable

radiometric performance of the voyager cameras the voyager imaging experiment provided high quality data of jupiter and the galilean satellites with the two flyby trajectories in march and july of 1979 moderately accurate radio metric measurements have been made using these data this paper evaluates the radiometric results and describes the inflight and ground geometric and radiometric correction factors the radiometric quantities of intensity i and geometric albedo i f are derived and scaling factors for each of the filters are tabulated for correcting the calibrated data from the image processing laboratory at jpl in addition the key characteristics of both voyager 1 and voyager 2 cameras are tabulated

chang e 4 initial spectroscopic identification of lunar far side mantle derived materials over 60 years of spacecraft exploration has revealed that the earth s moon is characterized by a lunar crust1 dominated by the mineral plagioclase overlying a more mafic richer in iron and magnesium mantle of uncertain composition both crust and mantle formed during the earliest stages of lunar evolution when late stage accretional energy caused a molten rock magma ocean flotation of the light plagioclase sinking of the denser iron rich minerals such as olivine and pyroxene and eventually solidification2 very large impact craters can potentially penetrate through the crust and sample the lunar mantle the largest of these craters is the approximately 2 500 kilometre diameter south pole aitken spa basin3 on the lunar far side evidence obtained from orbiting spacecraft shows that the floor of the spa basin is rich in mafic minerals4 but their mantle origin is controversial and their in situ geologic settings are poorly known china s chang e 4 lunar far side lander recently touched down in the von karman crater5 6 to explore the floor of the huge spa basin and deployed its rover yutu 2 here we report on the initial spectral observations of the visible and near infrared spectrometer vnis 7 onboard yutu 2 which we interpret to represent the presence of low calcium ortho pyroxene and olivine materials that may originate from the lunar mantle geological context6 suggests that these materials were excavated from below the spa floor by the nearby 72 km diameter finsen impact crater event and transported to the landing site continued exploration by yutu 2 will target these materials on the floor of the von karman crater to understand their geologic context origin and abundance and to assess the possibility of sample return scenarios initial spectral observations by china s chang e 4 far side lunar rover suggest the presence of materials that may originate from the moon s mantle

a large spectral survey of small lunar craters implications for the composition of the lunar mantle a global spectral survey of 4506 immature craters with diameters 1 km was carried out using near ir data from the kaguya spectral profiler to characterize the composition of the lunar megaregolith on the basis of band minima and radiative transfer mixing models small crater spectra fall into three groups 1 mare basalts with strong absorptions at relatively long wavelengths indicating high ratios of high to low ca pyroxene 2 norites containing about 50 plagioclase and with pyroxene assemblages dominated by low ca pyroxene that occur within the south pole aitken basin spa near apollo 14 and other locations near imbrium basin and three major cryptomaria deposits and 3 noritic anorthosites occurring within the feldspathic highlands terrane containing about 20 wt pyroxene with a pyroxene assemblage containing exclusively very low ca pyroxene very few pure anorthosites are present in this survey and there are no occurrences of pyroxene poor olivine rich assemblages models of the composition of basin ejecta incorporate large amounts of mantle material and the spectral results require that that the sampled mantle is orthopyroxenite basin depth diameter ratios used in the models required to match the measured composition are consistent with prior estimates for the largest basins the composition found in the spa and imbrium regions are consistent with mafic impact melt breccias or basaltic impact melts of basin origin for spa we model this composition and find it requires an extremely low impact angle while this is consistent with prior work on an oblique impact for the spa event a more robust solution invokes the production of norite in impact melt seas

so2 rich equatorial basins and epeirogeny of io abstract the most concentrated deposits of so 2 frost on io occur within a series of large equatorial basins about 30 of the surface is covered by so 2 outside of the basins increasing to more than 50 within the basins this pattern is poorly expressed in the region from longitude 240 to 360 where bright areas are frequently buried by the fallout from the large pele type plumes the fourfold pattern of alternating basins and swells in io s equatorial region is similar to the heat flow pattern predicted from tidal heating in a thin partially molten asthenosphere however the topographic pattern is offset from the predicted heat flow pattern thus it is unclear whether topographic highs correspond to regions of higher or lower predicted heat flow these two possibilities imply two very different models for io s highlands a thermal uplift model or a continental crust model in the thermal uplift model the regions of enhanced asthenospheric heating cause lithospheric thinning and isostatic uplift perhaps accompanied by uplift due to penetrative magmatism or basaltic underplating in the continental crust model continents of differentiated crust float on low density roots the crust and lithosphere are approximately one and the same and basal melting controls its thickness although both models are plausible the thermal uplift model best explains the so 2 distribution cold trapping must be important for concentrating so 2 frost in optically thick patches thus either cold traps are preferentially initiated over large basin areas or they are preferentially removed from the highlands the patchy distribution and approximately 30 so 2 coverage of the highlands show that cold traps are abundant here but not extensive thus the so 2 must be preferentially removed and or buried higher heat flows in the highlands should lead to increased volatilization of so 2 frost and a greater frequency of relatively so 2 poor volcanism should tend to bury frost patches this model links asthenospheric tidal heating large scale heat flow and topography volcanic activity and the global distribution of surface so 2 and it leads to several specific predictions for future observations

olivine rich exposures in the south pole aitken basin abstract the distribution and the geological context of the olivine rich exposures in the south pole aitken spa basin on the moon were investigated based on the spectral data obtained from the spectral profiler sp and multiband imager mi onboard the japanese lunar explorer kaguya selene the olivine rich exposures are found only in the peak rings or central peaks of the schrodinger basin and zeeman crater which are located in the outer region of the spa basin and not in the center region on a localized scale the olivine rich materials are exposed on landslide features on the crater walls or sloped wall of the central peaks or the peak rings another observational finding is the co existence of olivine rich and plagioclase rich materials on a kilometer scale spanning most of the olivine rich sites in the schrodinger basin pyroxene rich materials are found in fresh craters outside the peak rings or the central peaks with olivine rich materials based on these results the following scenario are proposed 1 the impact to form the spa basin melted a large amount of the lunar upper mantle and crust and distributed the melted materials to the outer region 2 local differentiation of melted materials hid the olivine rich materials in the center region of the spa basin 3 later impacts that formed the schrodinger and zeeman craters excavated and exposed the olivine rich materials to the surface again and 4 space weathering and regolith gardening obscured the olivine rich spectra at the exposure sites but recent small scale impacts or landslides on the sloped wall exposed fresh olivine rich materials allowing the identification of the olivine rich exposures by spectral remote sensing this suggests that several different scale events play an important role in forming the surface distributions of originally deep seated materials on the moon as well as on other planetary bodies

paleogeographic reconstruction and origin of the philippine sea abstract our reconstruction of the philippine sea suggests that it formed by two distinct episodes of back arc spreading each of which resulted from seaward retreat of the trench in the first episode the protoizu bonin trench retreated northward and the west philippine basin formed behind the northern half of the palau kyushu ridge in the second episode the izu mariana trench retreated eastward and the shikoku and parece vela basins formed behind it during the last 17 ma the philippine sea basin has been moving northwestward with respect to eurasia shifting the ttt triple junction off central japan westward by about 50 km the motion of the philippine sea with respect to eurasia at the triple junction changed from north northwestward to west northwestward 10 5 ma ago for the period before 17 ma ago we construct two models retreating trench model and anchored slab model the izu bonin trench migrated from south to northeast rotating in a clock wise sense since 48 ma ago in the retreating trench model in the anchored slab model the trench has been fixed with respect to eurasian margin since 43 ma ago we prefer the retreating trench model because the deformation of the plate boundary along the eastern margin of eurasia during 30 17 ma ago is much simpler for this model than for the anchored slab model furthermore rotations of the bonin mariana islands are consistent with those predicted from the retreating trench model the 48 ma ages of the northern part of the palau kyushu ridge and of chichi jima of the bonin islands indicate that there was subduction beneath the northern half of the ridge beginning at least 48 ma ago from this and the subparallelism in trend between the northern part of the palau kyushu ridge and the central basin ridge we propose that the major part of the west philippine basin formed by back arc spreading in a n s direction behind the northern part of the palau kyushu ridge the pacific plate was moving northward with respect to hot spots from 48 to 43 ma ago which implies that the pacific plate is not likely to have been subducting beneath the west philippine basin during this time we speculate that another plate existed south of the pacific plate and thai it was subducting beneath both tile west philippine basin and australia the annihilation of this plate might he a cause for the sudden change of the pacific plate motion at 43 ma ago

geological characteristics of von karman crater northwestern south pole aitken basin chang e 4 landing site region von karman crater diameter 186 km lying in the northwestern south pole aitken spa basin was formed in the pre nectarian the von karman crater floor was subsequently flooded with one or several generations of mare basalts during the imbrian period numerous subsequent impact craters in the surrounding region delivered ejecta to the floor together forming a rich sample of the spa basin and farside geologic history we studied in details the targeted landing region 45 0 46 0 s 176 4 178 8 e of the 2018 chinese lunar mission chang e 4 within the von karman crater the topography of the landing region is generally flat at a baseline of 60 m secondary craters and ejecta materials have covered most of the mare unit and can be traced back to at least four source craters finsen von karman l von karman l and antoniadi based on preferential spatial orientations and crosscutting relationships extensive sinuous ridges and troughs are identified spatially related to ba jie crater diameter 4 km reflectance spectral variations due to difference in both composition and physical properties are observed among the ejecta from various sized craters on the mare unit the composition trends were used together with crater scaling relationships and estimates of regolith thickness to reconstruct the subsurface stratigraphy the results reveal a complex geological history of the landing region and set the framework for the in situ measurements of the ce 4 mission which will provide unique insights into the compositions of farside mare basalt spa compositional zone including spa compositional anomaly and mg pyroxene annulus regolith evolution and the lunar space environment