a new crater near insight implications for seismic impact detectability on mars a new 1 5 m diameter impact crater was discovered on mars only 40 km from the insight lander context camera images constrained its formation between 21 february and 6 april 2019 follow up high resolution imaging science experiment images resolved the crater during this time period three seismic events were identified in insight data we derive expected seismic signal characteristics and use them to evaluate each of the seismic events however none of them can definitively be associated with this source atmospheric perturbations are generally expected to be generated during impacts however in this case no signal could be identified as related to the known impact using scaling relationships based on the terrestrial and lunar analogs and numerical modeling we predict the amplitude peak frequency and duration of the seismic signal that would have emanated from this impact the predicted amplitude falls near the lowest levels of the measured seismometer noise for the predicted frequency hence it is not surprising this impact event was not positively identified in the seismic data finding this crater was a lucky event as its formation this close to insight has a probability of only 0 2 and the odds of capturing it in before and after images are extremely low we revisit impact seismic discriminators in light of real experience with a seismometer on the martian surface using measured noise of the instrument we revise our previous prediction of seismic impact detections downward from a few to tens to just 2 per earth year still with an order of magnitude uncertainty

a surface gravity traverse on mars indicates low bedrock density at gale crater gravimetry the precise measurement of gravitational fields can be used to probe the internal structure of earth and other planets the curiosity rover on mars carries accelerometers normally used for navigation and attitude determination we have recalibrated them to isolate the signature of the changing gravitational acceleration as the rover climbs through gale crater the subsurface rock density is inferred from the measured decrease in gravitational field strength with elevation the density of the sedimentary rocks in gale crater is 1680 180 kilograms per cubic meter this value is lower than expected indicating a high porosity and constraining maximum burial depths of the rocks over their history

the boycott effect in magma chambers 1 we investigate the plausibility of the stratified boycott effect as a source of layering in magma chambers crystal settling within the magma chamber will generate buoyant fluid near the sloping sidewalls whose vertical ascent may be limited by the ambient stratification associated with vertical gradients in sio2 the resulting flow may be marked by a layered structure each layer taking the form of a convection cell spanning the lateral extent of the magma chamber using parameters relevant to magma chambers we estimate that such convection cells would be established over a timescale of a month and have a depth on the order of 4m which is roughly consistent with field observations of strata within solidified chambers

subsurface imaging in south central egypt using low frequency radar bir safsaf revisited we present the capabilities of low frequency radar systems to sound the subsurface for a site located in south central egypt the bir safsaf region this site was already intensively studied since the sir a and sir b orbital radars revealed buried paleodrainage channels our approach is based on the coupling between two complementary radar techniques the orbital synthetic aperture radar sar in c and l bands 5 3 and 1 25 ghz for imaging large scale subsurface structures and the ground penetrating radar gpr at 500 and 900 mhz for sounding the soil at a local scale we show that the total backscattered power computed from l band sar and 900 mhz gpr profiles can be correlated and we combined both data to derive the geological structure of the subsurface gpr data provide information on the geometry of the buried scatterers and layers while the analysis of polarimetric sar data provides information on the distribution of rocks in the sedimentary layers and at the interface between these layers the analysis of 500 mhz gpr data revealed some deeper structures that should be detected by lower frequency sars such as a p band system

double diffusive convection in magma chambers single or multiple layers an approximate set of equations applicable to double diffusive convection in magma chambers has been solved in the steady state for a range of geologically relevant parameters no evidence for the steady state existence of layered convection for conditions appropriate to magma chambers has been found at large ratios of the thermal to chemical diffusivity lewis number le the heat transport is independent of the lewis number and equal to that found for thermal convection in a single component fluid the vertical upward transport of light component varies directly with both the rayleigh and lewis numbers nuc ra0 23 le0 37

evolutionary structures in double diffusive convection in magma chambers finite amplitude solutions to subcritical time dependent double diffusive convection d d c applicable for magma chambers are obtained by a two dimensional finite element method based on stream function temperature and compositional fields grid refinement is used for resolving the disparately scaled thermal and chemical boundary layers present for large ratios of the thermal to chemical diffusivity lewis number characteristic of magmas the occurrence of layered convection depends strongly on the initial conditions of the temperature and composition it is shown that in the infinite prandtl number limit a local transition from a diffusive to a finger like regime can take place for large enough lewis numbers this time dependent finding suggests that a strict categorization of d d c into the finger and diffusive regimes requires modification in geological applications

moon meteoritic seismic hum steady state prediction 1 we use three different statistical models describing the frequency of meteoroid impacts on earth to estimate the seismic background noise due to impacts on the lunar surface because of diffraction seismic events on the moon are typically characterized by long codas lasting 1 h or more we find that the small but frequent impacts generate seismic signals whose codas overlap in time resulting in a permanent seismic noise that we term the lunar hum by analogy with the earth s continuous seismic background seismic hum we find that the apollo era impact detection rates and amplitudes are well explained by a model that parameterizes 1 the net seismic impulse due to the impactor and resulting ejecta and 2 the effects of diffraction and attenuation the formulation permits the calculation of a composite waveform at any point on the moon due to simulated impacts at any epicentral distance the root mean square amplitude of this waveform yields a background noise level that is about 100 times lower than the resolution of the apollo long period seismometers at 2 s periods this noise level is more than 1000 times lower than the low noise model prediction for earth s microseismic noise sufficiently sensitive seismometers will allow the future detection of several impacts per day at body wave frequencies

degassing of stratified magma by compositional convection abstract a new model is proposed for passive degassing from sub volcanic magma chambers the water content in stably stratified shallow magma chamber will be equated to its solubility at the upper boundary by convection water from a lower layer high in water content can enrich the contact zone of the upper layer and lead to further convective overturn of this boundary layer a complete set of equations describing convection with bubble formation and dissolution is reduced to a simplified form by assuming a small bubble content the development and pattern of flow driven by vesiculation is modeled numerically in a 2d magma chamber for relatively low raleigh numbers 5 105 bubbles rising from the magma will collect near the roof in a layer of 8 10 vol and then escape upward to fumaroles the stokes flux of bubbles escaping from an andesitic magma with viscosity 104 p and a top surface of about 500 500 m corresponds with observed total magmatic water fluxes of 35 kg s pressure within the chamber is buffered by elastic and local visco elastic deformations in the solid rocks bounding the chamber to the range between ambient and close to lithostatic values in a chamber closed to fresh magma inputs the decrease in volume due to such gentle volatile escape lowers the reference pressure bubbles flux from the lower layer induced by variation of the saturation level around stratification boundary may be efficient mechanism for the water transport between layers

overview of the mars science laboratory mission bradbury landing to yellowknife bay and beyond the mars science laboratory mission reached bradbury landing in august 2012 in its first 500 sols the rover curiosity was commissioned and began its investigation of the habitability of past and present environments within gale crater curiosity traversed eastward toward glenelg investigating a boulder with a highly alkaline basaltic composition encountering numerous exposures of outcropping pebble conglomerate and sampling aeolian sediment at rocknest and lacustrine mudstones at yellowknife bay on sol 324 the mission turned its focus southwest beginning a year long journey to the lower reaches of mt sharp with brief stops at the darwin and cooperstown waypoints the unprecedented complexity of the rover and payload systems posed challenges to science operations as did a number of anomalies operational processes were revised to include additional opportunities for advance planning by the science and engineering teams

changes in blast zone albedo patterns around new martian impact craters abstract blast zones bzs around new martian craters comprise various albedo features caused by the initial impact including diffuse halos extended linear and arcuate rays secondary craters ejecta patterns and dust avalanches we examined these features for changes in repeat images separated by up to four mars years here we present the first comprehensive survey of the qualitative and quantitative changes observed in impact blast zones over time such changes are most likely due to airfall of high albedo dust restoring darkened areas to their original albedo the albedo of adjacent non impacted surfaces although some sites show drastic changes over short timescales nearly half of the sites show no obvious changes over several mars years albedo changes are more likely to occur at higher latitude sites lower elevation sites and at sites with smaller central craters no correlation was seen between amount of change and dust cover index relative halo size or historical regional albedo changes quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features the average lifetime among sites with measurable fading is 15 mars years the median is 8 mars years for a linear brightening however at approximately half of sites with three or more repeat images a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior this would predict even longer lifetimes the predicted lifetimes of bzs are comparable to those of slope streaks and considered representative of fading by global atmospheric dust deposition they last significantly longer than dust devil or rover tracks albedo features that are erased by different processes these relatively long lifetimes indicate that the measurement of the current impact rate by daubar et al daubar i j et al 2013 icarus 225 506 516 http dx doi org 10 1016 j icarus 2013 04 009 does not suffer significantly from overall under sampling due to blast zones fading before new impact sites can be initially discovered however the prevalence of changes seen around smaller craters may explain in part their shallower size frequency distribution

the current martian cratering rate abstract the discovery of 248 dated impact sites known to have formed within the last few decades allows us to refine the current cratering rate and slope of the production function at mars we use a subset of 44 of these new craters that were imaged before and after impact by mars reconnaissance orbiter s context camera a thoroughly searched data set that minimizes biases from variable image resolutions we find the current impact rate is 1 65 10 6 craters with an effective diameter 3 9 m km2 yr with a differential slope power law exponent of 2 45 0 36 this results in model ages that are factors of three to five below the hartmann hartmann w k 2005 icarus 174 294 320 and neukum et al neukum g ivanov b a hartmann w k 2001 space sci rev 96 55 86 ivanov ivanov b a 2001 space sci rev 96 87 104 model production functions where they overlap in diameter the best fit production function we measure has a shallower slope than model functions at these sizes but model function slopes are within the statistical errors more than half of the impacts in this size range form clusters which is another reason to use caution when estimating surface ages using craters smaller than 50 m in diameter

overturn and evolution of a crystallized magma ocean a numerical parameter study for mars 1 early in the history of terrestrial planets the fractional crystallization of a magma ocean can lead to a mantle stratification characterized by a progressive enrichment in heavy elements from the core mantle boundary to the surface such configuration is gravitationally unstable it causes mantle overturn and the formation of a stable chemical layering using simulations of thermo chemical convection we analyzed the consequences of overturn and subsequent layering on mantle dynamics assuming mars scaling parameters we found that the time needed to achieve chemical homogenization via convective mixing scales exponentially with the buoyancy ratio inline image which measures the relative importance of chemical to thermal buoyancy in addition when using a strongly temperature dependent viscosity the formation of a stagnant lid prevents the uppermost crystallized layers from sinking into the mantle in order to obtain their subduction an yielding mechanism must be invoked 2 in the context of mars evolution our results suggest that complete chemical mixing is unlikely to take place within time scales comparable with the planet s age magma ocean freezing could be thus responsible for the long term preservation of compositional heterogeneities as required by meteoritic evidence the lack of a surface highly enriched in incompatible elements and of a high density lid is difficult to reconcile with a stagnant lid regime operating throughout mars history an episode of surface mobilization induced by compositional overturn can resolve this difficulty provided that inline image is large enough too large buoyancy ratios however tend to suppress convective heat transport rendering it problematic to explain the late volcanic history of mars

experimental ejection angles for oblique impacts implications for the subsurface flow field a simple analytical solution for subsurface particle motions during impact cratering is useful for tracking the evolution of the transient crater shape at late times a specific example of such an analytical solution is maxwells z model which is based on a point source assumption here the parameters for this model are constrained using measured ejection angles from both vertical and oblique experimental impacts at the nasa ames vertical gun range data from experiments reveal that impacts at angles as high as 45 to the targets surface generate subsurface flow fields that are significantly different from those created by vertical impacts the initial momentum of the projectile induces a subsurface momentum driven flow field that evolves in three dimensions of space and in time to an excavation flow field during both vertical and oblique impacts a single stationary pointsource model specifically maxwells z model however is found inadequate to explain this detailed evolution of the subsurface flow field during oblique impacts because 45 is the most likely impact angle on planetary surfaces a new analytical model based on a migrating point source could prove quite useful such a model must address the effects of the subsurface flow field evolution on crater excavation ejecta deposition and transient crater morphometry

nonlinear physics of double diffusive convection in geological systems double diffusive convection d d c is a nonlinear fluid dynamical phenomenon driven by thermal and compositional effects on the density we discuss the nature of subcritical finite amplitude double diffusive convection for infinite prandtl number and large lewis number le which have applications in magma chambers and at the d layer at the core mantle boundary cmb numerical solutions by two dimensional finite element method are presented to portray the nature of time dependent d d c in both the diffusive and the finger regimes the compositional heterogeneities at the cmb are far more complex than the local thermal structure because of the largele and may have important implications for the scattering of seismic waves off the cmb the effects of increasing the buoyancy ratior are to suppress time dependent d d c even at highra in narrow slots shear heating instabilities can be triggered in the finger regime by the abrupt overturn of the compositional interface this phenomenon may occur in tall magma chambers with low dissipation numbers of of order 0 0 01

geodesy constraints on the interior structure and composition of mars abstract knowledge of the interior structure of mars is of fundamental importance to the understanding of its past and present state as well as its future evolution the most prominent interior structure properties are the state of the core solid or liquid its radius and its composition in terms of light elements the thickness of the mantle its composition the presence of a lower mantle and the density of the crust in the absence of seismic sounding only geodesy data allow reliably constraining the deep interior of mars those data are the mass moment of inertia and tides they are related to mars composition to its internal mass distribution and to its deformational response to principally the tidal forcing of the sun here we use the most recent estimates of the moment of inertia and tidal love number k2 in order to infer knowledge about the interior structure of the mars we have built precise models of the interior structure of mars that are parameterized by the crust density and thickness the volume fractions of upper mantle mineral phases the bulk mantle iron concentration and the size and the sulfur concentration of the core from the bulk mantle iron concentration and from the volume fractions of the upper mantle mineral phases the depth dependent mineralogy is deduced by using experimentally determined phase diagrams the thermoelastic properties at each depth inside the mantle are calculated by using equations of state since it is difficult to determine the temperature inside the mantle of mars we here use two end member temperature profiles that have been deduced from studies dedicated to the thermal evolution of mars we calculate the pressure and temperature dependent thermoelastic properties of the core constituents by using equations state and recent data about reference thermoelastic properties of liquid iron liquid iron sulfur and solid iron to determine the size of a possible inner core we use recent data on the melting temperature of iron sulfur within our model assumptions the geodesy data imply that mars has no solid inner core and that the liquid core contains a large fraction of sulfur the absence of a solid inner is in agreement with the absence of a global magnetic field we estimate the radius of the core to be 1794 65 km and its core sulfur concentration to be 16 2 wt we also show that it is possible for mars to have a thin layer of perovskite at the bottom of the mantle if it has a hot mantle temperature moreover a chondritic fe si ratio is shown to be consistent with the geodesy data although significantly different value are also possible our results demonstrate that geodesy data alone even if a mantle temperature is assumed can almost not constrain the mineralogy of the mantle and the crust in order to obtain stronger constraints on the mantle mineralogy bulk properties like a fixed fe si ratio have to be assumed

seismic observations of meteors coupling theory and observations to date coupling of acoustic waves directly with the earth s surface represents the bulk of the observed meteor related seismic signals while precursory and impact related seismic waves remain an observational rarity with proliferation of infrasound and seismic monitoring systems new opportunities exist to explore the relationship between earth s atmosphere andsurface continued studyofmeteorseismologywillleadto new methods to constrain energies sizes and fluxes for moderately cm to m sized meteoroids on earth and potentially on mars

quantifying crater production and regolith overturn on the moon with temporal imaging random bombardment by comets asteroids and associated fragments form and alter the lunar regolith and other rocky surfaces the accumulation of impact craters over time is of fundamental use in evaluating the relative ages of geologic units crater counts and radiometric ages from returned samples provide constraints with which to derive absolute model ages for unsampled units on the moon and other solar system objects however although studies of existing craters and returned samples offer insight into the process of crater formation and the past cratering rate questions still remain about the present rate of crater production the effect of early stage jetting during impacts and the influence that distal ejecta have on the regolith here we use lunar reconnaissance orbiter camera lroc narrow angle camera nac temporal before and after image pairs to quantify the contemporary rate of crater production on the moon to reveal previously unknown details of impact induced jetting and to identify a secondary impact process that is rapidly churning the regolith from this temporal dataset we detected 222 new impact craters and found 33 per cent more craters with diameters of at least ten metres than predicted by the standard neukum production and chronology functions for the moon we identified broad reflectance zones associated with the new craters that we interpret as evidence of a surface bound jetting process we also observe a secondary cratering process that we estimate churns the top two centimetres of regolith on a timescale of 81 000 years more than a hundred times faster than previous models estimated from meteoritic impacts ten million years

quantitative analysis of impact induced seismic signals by numerical modeling we quantify the seismicity of impact events using a combined numerical and experimental approach the objectives of this work are 1 the calibration of the numerical model by utilizing real time measurements of the elastic wave velocity and pressure amplitudes in laboratory impact experiments 2 the determination of seismic parameters such as quality factor q and seismic efficiency k for materials of different porosity and water saturation by a systematic parameter study employing the calibrated numerical model by means of numerical experiments we found that the seismic efficiency k decreases slightly with porosity from k 3 4 10 3 for nonporous quartzite to k 2 6 10 3 for 25 porous sandstone if pores are completely or partly filled with water we determined a seismic efficiency of k 8 2 10 5 which is approximately two orders of magnitude lower than in the nonporous case by measuring the attenuation of the seismic wave with distance in our numerical experiments we determined the seismic quality factor q to range between 35 for the solid quartzite and 80 for the porous dry targets for water saturated target materials q is much lower 10 the obtained values are in the range of literature values translating the seismic efficiency into seismic magnitudes we show that the seismic magnitude of an impact event is about one order of magnitude smaller considering a water saturated target in comparison to a solid or porous target obtained seismic magnitudes decrease linearly with distance to the point of impact and are consistent with empirical data for distances closer to the point of impact the seismic magnitude decreases more rapidly with distance for a water saturated material compared to a dry material

a slippery problem with explosive consequences water has remarkable effects on the properties of geochemical materials such as magma the result is that a small change in water concentration can make the difference between explosive volcanic eruptions and less violent ones in his perspective spera discusses results reported in the same issue by ochs and lange on new measurements of the amount of water in molten silicates the findings will add new insight to the atomic structure of these materials as well as the effects of water on them

the production of small primary craters on mars and the moon abstract we model the primary crater production of small d d 10 20 cm well below the downturn observed in the distribution of fresh craters detected by the mars global surveyor mgs mars orbiter camera moc or the mars reconnaissance orbiter mro context camera ctx crater counts are conducted on the ejecta blanket of zunil crater and the interior of pangboche crater on mars and north ray and cone craters on the moon our model isochrons produce a similar slope and age estimate for the formation of zunil crater as the hartmann production function 1 ma we derive an age of 35 1 ma for pangboche when accounting for the higher elevation 20 km higher than zunil a factor 2 younger than estimated using the hartmann production function which assumes 6 mbar surface pressure we estimate ages of 52 3 ma and 23 9 ma for north ray and cone crater respectively consistent with cosmic ray exposure ages from apollo samples our results indicate that the average cratering rate has been constant on these bodies over these time periods since our monte carlo simulations demonstrate that the existing crater chronology systems can be applied to date young surfaces using small craters on the moon and mars we conclude that the signal from secondary craters in the isochrons must be relatively small at these locations as our monte carlo model only generates primary craters

oxygen isotope study of the long valley magma system california isotope thermometry and convection in large silicic magma bodies products of voluminous pyroclastic eruptions with eruptive draw down of several kilometers provide a snap shot view of batholith scale magma chambers and quench pre eruptive isotopic fractionations i e temperatures between minerals we report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite pyroxene and zircon from individual pumice clasts of ignimbrite and fall units of caldera forming 0 76 ma bishop tuff bt pre caldera glass mountain 2 1 0 78 ma and post caldera rhyolites 0 65 0 04 ma to characterize the long lived batholith scale magma chamber beneath long valley caldera in california values of 18o show a subtle 1 decrease from the oldest glass mountain lavas to the youngest post caldera rhyolites older glass mountain lavas exhibit larger 1 variability of 18o quartz the youngest domes of glass mountain are similar to bt in 18o quartz values and reflect convective homogenization during formation of bt magma chamber surrounded by extremely heterogeneous country rocks ranging from 2 to 29 oxygen isotope thermometry of bt confirms a temperature gradient between late 815 c and early 715 c bt the 18o quartz values of early and late bt are 8 33 and 8 21 consistent with a constant 18o melt 7 8 0 1 and 100 c temperature difference zircon melt saturation equilibria gives a similar temperature range values of 18o quartz for different stratigraphic units of bt and in pumice clasts ranging in pre eruptive depths from 6 to 11 km based on melt inclusions and document vertical and lateral homogeneity of 18o melt worldwide five other large volume rhyolites lava creek lower bandelier fish canyon cerro galan and toba exhibit equal 18o melt values of earlier and later erupted portions in each of the these climactic caldera forming eruptions we interpret the large scale 18o homogeneity of bt and other large magma chambers as evidence of their longevity 105 years and convection however remaining isotopic zoning in some quartz phenocrysts trace element gradients in feldspars and quartz and zircon crystal size distributions are more consistent with far shorter timescales 102 104 years we propose a sidewall crystallization model that promotes convective homogenization roofward accumulation of more evolved and stagnant volatile rich liquid and develops compositional and temperature gradients in pre climactic magma chamber crystal melt gas bubbles mush near chamber walls of variable 18o gets periodically remobilized in response to chamber refill by new hotter magmas one such episode of chamber refill by high ti sr ba zr and volatile richer magma happened 103 104 years prior to the 0 76 ma caldera collapse that caused magma mixing at the base mush thawing near the roof and walls and downward settling of phenocrysts into this hybrid melt

a crater and its ejecta an interpretation of deep impact we apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the deep impact event an important question is whether the cratering event was gravity or strength dominated the answer gives important clues about the properties of the surface material of tempel 1 gravity scaling was assumed in pre event calculations and has been asserted in initial studies of the mission results because the gravity field of tempel 1 is extremely weak a gravity dominated event necessarily implies a surface with essentially zero strength the conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution we address that feature here and conclude that even strength dominated craters would result in a plume that appeared to remain attached to the surface we then calculate the plume characteristics from scaling laws for a variety of material types and for gravity and strength dominated cases we find that no model of cratering alone can match the reported observation of plume mass and brightness history instead comet like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few hour time frame with such mechanisms and to within the large uncertainties either gravity or strength craters can provide the levels of estimated observed mass thus the observations are unlikely to answer the questions about the mechanical nature of the tempel 1 surface

apollo lunar seismic experiment final summary processing and initial analysis of the entire set of apollo lunar seismic data collected continuously from 1969 through 1977 have now been completed recent results include 1 better defined deep moonquake locations which appear to be bounded rather sharply between about 800 km and 1000 km depths with concentrations near both boundaries and 2 middle mantle 500 to 1000 km depth seismic velocities of vp 8 3 0 4 km sec and vs 4 6 0 2 km sec which are significantly higher than previous estimates and represent an increase of velocities from the upper mantle as opposed to a decrease in previous estimates

predicted detection rates of regional scale meteorite impacts on mars with the insight short period seismometer abstract in 2016 nasa will launch the insight discovery class mission which aims to study the detailed internal structure of mars for the first time short and long period seismometers form a major component of insight s payload and have the potential to detect seismic waves generated by meteorite impacts large globally detectable impact events producing craters with diameters of 100 m have been investigated previously and are likely to be rare teanby n a wookey j 2011 phys earth planet int 186 70 80 but smaller impacts producing craters in the 0 5 20 m range are more numerous and potentially occur sufficiently often to be detectable on regional scales 1000 km at these distances seismic waves will have significant high frequency content and will be suited to detection with insight s short period seismometer seis sp in this paper i estimate the current martian crater production function from observations of new craters malin m c et al 2006 science 314 1573 1577 daubar i j et al 2013 icarus 225 506 516 model results williams j p pathare a v aharonson o 2014 icarus 235 23 36 and standard isochrons hartmann w k 2005 icarus 174 294 320 these impact rates are combined with an empirical relation between impact energy source receiver distance and peak seismogram amplitude derived from a compilation of seismic recordings of terrestrial and lunar impacts chemical explosions and nuclear tests the resulting peak seismogram amplitude scaling law contains significant uncertainty but can be used to predict impact detection rates i estimate that for a short period instrument with a noise spectral density of 10 8 ms 2 hz 1 2 in the 1 16 hz frequency band approximately 0 1 30 regional impacts per year should be detectable with a nominal value of 1 3 impacts per year therefore small regional impacts are likely to be a viable source of seismic energy for probing mars crustal and upper mantle structure this is particularly appealing as such impacts should be easily located with orbital imagery increasing their scientific value compared to other types of events with unknown origins finally comparison of the empirical results presented here with the modelling study of teanby and wookey teanby n a wookey j 2011 phys earth planet int 186 70 80 provides constraints on the seismic efficiency suggesting that values of 5 10 4 may be appropriate for impact generated seismic waves comparing explosion and impact datasets indicate that buried explosions are 10 times more efficient at generating seismic waves than impacts

present day impact cratering rate and contemporary gully activity on mars the mars global surveyor mars orbiter camera has acquired data that establish the present day impact cratering rate and document new deposits formed by downslope movement of material in mid latitude gullies on mars twenty impacts created craters 2 to 150 meters in diameter within an area of 21 5 106 square kilometers between may 1999 and march 2006 the values predicted by models that scale the lunar cratering rate to mars are close to the observed rate implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating the new gully deposits formed since august 1999 are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water relatively long extended digitate distal and marginal branches diversion around obstacles and low relief the observations suggest that liquid water flowed on the surface of mars during the past decade

large impacts detected by the apollo seismometers impactor mass and source cutoff frequency estimations abstract meteoroid impacts are important seismic sources on the moon as they continuously impact the moon they are a significant contribution to the lunar micro seismic background noise they also were associated with the most powerful seismic sources recorded by the apollo seismic network we study in this paper the largest impacts we show that their masses can be estimated with a rather simple modeling technique and that high frequency seismic signals have reduced amplitudes due to a relatively low about 1 s corner frequency resulting from the duration of the impact process and the crater formation if synthetic seismograms computed for a spherical model of the moon are unable to match the waveforms of the observations they nevertheless provide an approximate measure of the energy of seismic waves in the coda the latter can then be used for an estimation of the mass of the impactors when the velocity of the impactor is known this method for the artificial impacts of the lm and sivb apollo upper stages allows us to retrieve the mass within 20 of relative error the estimated mass of the largest impacts observed during the 7 years of activity of the apollo seismic network provides an explanation for the non detection of surface waves on the seismograms the specifications of future moon seismometers in order to provide the detection of surface waves are given in conclusion

the seismic signatures of recently formed impact craters on mars we investigated the seismic signatures of recent impact crater clusters on mars that would be recorded by the interior exploration using seismic investigations geodesy and heat transport insight seismometers we used a database of 77 measured and dated impact sites with craters with diameters between 2 1 and 33 8 m along with inferred impact angle bolide trajectory and varying target material properties to empirically scale for the momentum expected seismic source function and radiation pattern of impacts the impact source is simulated in a local 3 d finite difference wave propagation code and coupled to teleseismic distances by scaling the spectra of 1 d global synthetic seismograms we use the insight seismometer noise floors to estimate detectability of impact s across azimuth and distance our experiments reveal that impact clusters have a higher peak corner frequency resulting from energy contributed by smaller craters to the power spectrum we also find that the time separation between individual impacts in a cluster is small 100 hz to resolve individual impacts within the cluster two of the clusters in our database 20 m effective diameter would have been detectable by insight with the assumptions that the martian background noise and seismic attenuation are both low joint detection of surface changes from newly formed crater s in images and by insight will provide precise source locations that are crucial for constraining the internal structure of mars

seismic detection of meteorite impacts on mars abstract meteorite impacts provide a potentially important seismic source for probing mars interior it has recently been shown that new craters can be detected from orbit using high resolution imaging which means the location of any impact related seismic event could be accurately determined thus improving the constraints that could be placed on internal structure using a single seismic station this is not true of other seismic sources on mars such as sub surface faulting which require location using multiple seismic stations this study aims to determine the seismic detectability of meteorite impacts and assess whether they are a viable means of probing deep internal structure first we derive a relation between crater diameter and equivalent seismic moment based on observational data compiled from impact tests controlled explosions and earthquake seismology second this relation was combined with updated cratering rates based on newly observed craters to derive the impact induced seismicity on mars which we estimate to total 10 13 10 14 n m per year finally seismic waveform modelling was used to determine the detectability of these impacts based on reasonable assumptions about likely seismometer performance and background noise levels for our nominal noise instrument case we find that detectable impacts at teleseismic distances source receiver offsets greater than 60 are very rare and occur approximately once every 10 years for our most optimistic noise instrument case approximately one such event occurs each year this suggests that using solely meteorite impacts is not a reliable way of probing the martian interior although local impacts are more frequently detectable and could provide important constraints on near surface seismic properties

impact cutoff frequency momentum scaling law inverted from apollo seismic data abstract we perform the analysis of both long and short period data for 40 large meteoroid impacts event gathered by the apollo lunar seismic network we extract the linear momentum released by the impact and the cutoff frequency of the recorded seismic spectrum related to the radiation process of the shock wave generated by the impact by using a proxy to the local porosity based on the density of surface craters and well correlated to the most recent grail observations we demonstrate that the seismic cutoff frequencies for 40 selected impacts correlate with this proxy and therefore likely with the porosity at the impacted areas our finding shows that lunar seismic records of meteoroid impacts represent unique geophysical data documenting medium to high energy 0 1 1 kt tnt yield impact processes including the interaction of shock waves with porous media this work can be applied to the analysis of the seismic data to be obtained by the insight mission in 2016 and the investigation of the lateral variations in the martian regolith

the morphology of small fresh craters on mars and the moon the depth diameter ratio for new meter to decameter scale martian craters formed in the last 20 years averages 0 23 only slightly deeper than that expected for simple primary craters on rocky surfaces large variations in depth diameter d d between impact sites indicate that differences between the sites such as target material properties impact velocity angle and physical state of the bolide s are important in determining the depth of small craters in the strength regime on the moon the d d of random fresh small craters with similar diameters averages only 0 10 indicating that either the majority of them are unrecognized secondaries or some proportion are degraded primaries older craters such as these may be shallower due to erosional infilling which is probably not linear over time but more effective over recently disturbed and steeper surfaces processes that are not yet acting on the new martian craters brand new meter to decameter scale craters such as the martian ones studied here are statistically easily distinguishable as primaries but the origins of older craters of the same size such as the lunar ones in this study are ambiguous

the formation and evolution of layered structures in porous media horizontally layered structures can develop in porous or partially molten environments such as magma chambers the early earth s mantle and hydrothermal systems we have studied the generation and evolution of these horizontally layered structures in a rigid porous medium by heating a compositionally stably stratified fluid from below growth of a convective layer through entrainment the formation of a vertical density interface on top of this layer and destabilization of the next layer are closely coupled it is shown that the growth of the first convective layer stops once the thermal equilibrium is reached since heat solute transfer across the thin density interfaces becomes purely diffusive dispersive the separately convecting layers can persist on a compositionally dispersive timescale while the number of layers that develop is determined by the magnitude of the thermal rayleigh number the final height of a newly formed layer is inversely proportional to the buoyancy ratio two dynamical mechanisms which lead to sudden interface disappearance determine the vertical layer scales rather than the initial evolution toward the thermal equilibrium finally the results are discussed with respect to the above mentioned geophysical scenarios

high spatial resolution models of time dependent layered mantle convection summary the degree of geochemical mixing that occurred during the mantle s early evolution is dependent on the history of convective motions in the mantle we present time dependent tnodels of mantle convection that show for certain conditions in the newly formed earth s mantle a transient phase of layered convection results during which geochemical differences between the upper and lower mantle could have been preserved the basic model assumes that the initial temperature profile for subsolidus mantle convection is strongly superadiabatic the mantle is represented by a constant viscosity boussinesq fluid in a 2 d cartesian box heated from the bottom the models have considerably greater spatial resolution 90 x 90 uniformly spaced grid points than our previous work parameters that have been vaned include the rayleigh number ra lo5 lo8 the aspect ratio 1 4 9 the buoyancy of the initial temperature profde and the maximum temperatures allowed for subsolidus convection the models support our previous assertion that there is a critical value of ra above which superadiabatic initial conditions result in a burst of convection that inverts the temperature gradient in the bulk of the mantle sufficiently to temporarily prohibit a single layer of convection instead two layers result this critical value is about ra lo6 for a mantle with the maximum amount of buoyancy for less buoyant initial conditions this critical value is somewhat higher the layering lasts on the order of lo9 yr for ra lo6 10 considering that ra for the early mantle was certainly much larger than lo6 this suggests that a transient phase of multiple layering may have prevented vigorous convection from geochemically homogenizing the early mantle however if a less buoyant initial condition prevailed or one where supersolidus convection controls the maximum temperature of the upper mantle the transient layering could not have taken place

the size isotopic evolution connection among layered mafic intrusions clues from a sr nd isotopic study of a small complex several theoretical and experimental works have focused on the processes occurring in continental mafic magma chambers in contrast systematic isotopic studies of natural remnants of these latter remain scarce although they can give fundamental constraints for theoretical studies this is especially true if different layered complex with contrasting characteristics e g different size are compared for this reason we present the results of a sr nd isotopic profile across a small layered mafic intrusion of permian age exposed near fozzano sw corsica in the main zone of the layered section decreasing 87sr 86sri and increasing 143nd 144ndi are observed from less evolved bottom to more evolved top rocks this peculiar pattern precludes assimilation and fractional crystallization afc as a dominant mechanism in the petrogenesis of this body instead we interpret this trend as reflecting the dilution of an early stage contaminated magma by several reinjections of fresh basalt in the chamber in agreement with mineralogical and structural data every cyclic unit is interpreted as a new magmatic input on the basis of rough refill and fractional crystallization rfc calculations the average volume for each reinjection is estimated to have been about 0 04 km3 the cumulative volume of these injections would amount to about 75 of the total volume of the layered complex this implies that reinjections were accompanied by an important increase of the volume of the chamber or by magma withdrawal by surface eruptions the rfc mechanism documented within this small layered body contrasts with the isotopic pattern observed between several intrusions at the regional scale in sw corsica and within large continental mafic magma chambers elsewhere in these cases the isotopic evolution is dominated by afc processes and there is no clear isotopic evidence for reinjections unless major influx of fresh magma occurred it is suggested that there is a close relationship between the assimilation rate and the magma chamber volume small magma chambers are quickly isolated from their country rocks and better preserve the subtle isotopic signature of reinjection processes