aeolian dune migration along the ceara coast north eastern brazil aeolian dune dimensions and migration rates are analysed along the ceara coast north east brazil dunes that are currently mobile along the ceara coast are composed of barchans and sand sheets the results show that barchans maintain an equilibrium form which can be characterized by values of dimensionless shape parameters h w and w l where h is the dune height w is the wing to wing width and l is the dune length dunes are highly mobile with average migration rates of 17 5 m year 1 for barchans and 10 m year 1 for sand sheets the calculated migration rates were found to depend strongly on dune dimensions for both barchans and sand sheets i e the larger the dune is the lower the migration rate will be this size dependence was associated with the existence of a representative common transport rate along the dune fields which induces a different dune migration rate dependent on dune size finally from the observed dune evolution an aggregated scale aeolian sediment transport was inferred this bulk transport rate of the order of 90 100 m3 m 1 year 1 is only valid for a timescale of years to decades which is the timescale used in dune evolution analysis

a near earth asteroid population estimate from the linear survey i estimate the size and shape of the near earth asteroid nea population using survey data from the lincoln near earth asteroid research linear project covering 375 000 square degrees of sky and including more than 1300 nea detections a simulation of detection probabilities for different values of orbital parameters and sizes combined with the detection statistics in a bayesian framework provides a correction for observational bias and yields the nea population distribution as a function of absolute magnitude semi major axis eccentricity and inclination the nea population is more highly inclined than previously estimated and the total number of kilometer sized neas is 1227 90 170 1

tracing a meteoric trajectory with infrasound 1 a bright bolide appeared over the netherlands on the evening of 2003 february 19 infrasound generated by this bolide was detected at two nearby infrasound arrays as two distinct events the origins of the infrasonic signals were located in the stratosphere at heights of 30 and 57 km the results were obtained independently of visual observations of the bolide but confirm the reported time of occurrence the ability to distinguish between a moving and static source is crucial for the application of infrasound as a monitoring technique this study also illustrates the dependence of the infrasound technique on signal coherency inter array distance and atmospheric knowledge

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

physical characteristics of near earth asteroids from thermal infrared spectrophotometry thermal infrared spectrophotometric observations of the near earth asteroids 433 eros 1980 tezcatlipoca and 3671 dionysus are presented and their implications for the physical characteristics of the objects discussed sizes and albedos are derived on the basis of published thermal models and comparison of the infrared data with optical observations the results for 433 eros are in very good agreement with radar and other earlier findings and demonstrate the accuracy achievable with one of the thermal models used the new data together with earlier results from the literature suggest the surface thermal inertia of 433 eros is no larger than three times that of the moon the derived effective diameter and optical albedo of 1980 tezcatlipoca around lightcurve maximum are d 6 7 1 0 km and pv 0 15 0 05 and for 3671 dionysus d 1 0 0 2 km and pv 0 40 0 15 these diameters are significantly different from previous estimates the thermal continua of tezcatlipoca and dionysus are indicative of high surface thermal inertias a near infrared spectrum of dionysus coupled with the high albedo suggests an m or e classification such taxonomic types are relatively rare amongst near earth asteroids

theoretical analysis of secondary cratering on mars and an image based study on the cerberus plains the issue of crater retention age estimates on planetary surfaces is discussed with an attempt to quantify the effect of overlapping primary and secondary impact crater populations in restricted crater diameter ranges the approach to this problem is illustrated with a simple model production function where the secondary crater input is artificially enhanced extrapolation of such a secondary crater model distribution to a global record results in extraordinarily high crater frequencies that do not exist on mars and implies the need of detailed studies of the size frequency distribution for remote secondary craters to date poorly known a key case the martian crater zunil and its secondary crater field illustrate that reasonable predictions for the secondary crater size frequency distribution at small 100 m crater diameters affected the standard model crater retention age for the cerberus plains less than the statistical uncertainty these observations show that age determination based on appropriate crater counting statistics is valid in a wide primary crater diameter range

the record of miocene impacts in the argentine pampas argentine pampean sediments represent a nearly continuous record of deposition since the late miocene 10 ma previous studies described five localized concentrations of vesicular impact glasses from the holocene to late pliocene two more occurrences from the late miocene are reported here one near chasico ch with an 40ar 39ar age of 9 24 0 09 ma and the other near baha blanca bb with an age of 5 28 0 04 ma in contrast with andesitic and dacitic impact glasses from other localities in the pampas the ch and bb glasses are more mafic they also exhibit higher degrees of melting with relatively few xenoycrysts but extensive quench crystals in addition to evidence for extreme heating 1700 c shock features are observed e g planar deformation features pdfs and diaplectic quartz and feldspar in impact glasses from both deposits geochemical analyses reveal unusually high levels of ba 7700 ppm in some samples which is consistent with an interpretation that these impacts excavated marine sequences known to be at depth these two new impact glass occurrences raise to seven the number of late cenozoic impacts for which there is evidence preserved in the pampean sediments this seemingly high number of significant impacts over a 10 6 km 2 area in a time span of 10 myr is consistent with the number of bolides larger than 100 m expected to enter the atmosphere but is contrary to calculated survival rates following atmospheric disruption the pampean record suggests therefore that either atmospheric entry models need to be reconsidered or that the earth has received an enhanced flux of impactors during portions of the late cenozoic evidence for the resulting collisions may be best preserved and revealed in rare dissected regions of continuous low energy deposition such as the pampas additionally the rare earth element ree concentrations of the target sediments and impact melts associated with the chasic event resemble the hna k australites of similar age this suggests the possibility that those enigmatic tektites could have originated as high angle distal ejecta from an impact in argentina thereby accounting for their rarity and notable chemical and physical differences from other australasian impact glasses

a collision in 2009 as the origin of the debris trail of asteroid p 2010 a2 the peculiar object p 2010 a2 was discovered 1 in january 2010 and given a cometary designation because of the presence of a trail of material although there was no central condensation or coma the appearance of this object in an asteroidal orbit small eccentricity and inclination in the inner main asteroid belt attracted attention as a potential new member of the recently recognized 2 class of main belt comets if confirmed this new object would expand the range in heliocentric distance over which main belt comets are found here we report observations of p 2010 a2 by the rosetta spacecraft we conclude that the trail arose from a single event rather than a period of cometary activity in agreement with independent results 3 the trail is made up of relatively large particles of millimetre to centimetre size that remain close to the parent asteroid the shape of the trail can be explained by an initial impact ejecting large clumps of debris that disintegrated and dispersed almost immediately we determine that this was an asteroid collision that occurred around 10 february 2009

p waveform analysis for local subduction geometry south of puget sound washington the local subduction geometry at a site south of puget sound in western washington is investigated using teleseismicp waveforms recorded on a three component event triggered seismograph the data are processed using source equalization deconvolution in order to isolate locally convertedp to s arrivals and stacked to improve the signal to noise ratio stable arrivals in the radial component indicate an oceanic moho within the subducted slab at a depth of about 53 km beneath the station observed amplitude variations with azimuth in the radial data as well as qualitative aspects of the tangential data are used to establish a slab dip of 16 to the southeast our results are compatible with previous results from a site 60 km to the west and further confirm a substantial warp in the regional geometry of the subducted juan de fuca plate

the villalbeto de la pena meteorite fall i fireball energy meteorite recovery strewn field and petrography an impressive daylight fireball was observed from spain portugal and the south of france at 16h46m45s utc on january 4 2004 the meteoroid penetrated into the atmosphere generating shock waves that reached the ground and produced audible booms the associated airwave was recorded at a seismic station located 90 km north of the fireball trajectory in spain and at an infrasound station in france located 750 km north east of the fireball the absolute magnitude of the bolide has been determined to be 18 1 from a casual video record the energy released in the atmosphere determined from photometric seismic and infrasound data was about 0 02 kilotons kt a massive fragmentation occurred at a height of 28 0 2 km resulting in a meteorite strewn field of 20 6 km the first meteorite specimen was found on january 11 2004 near the village of villalbeto de la pena in northern palencia spain to date about 4 6 kg of meteorite mass have been recovered during several recovery campaigns the meteorite is a moderately shocked s4 l6 ordinary chondrite with a cosmic ray exposure age of 48 5 ma radioisotope analysis shows that the original body had a mass of 760 150 kg which is in agreement with the estimated mass obtained from photometric and seismic measurements

the flux of small near earth objects colliding with the earth asteroids with diameters smaller than approximately 50 100 m that collide with the earth usually do not hit the ground as a single body rather they detonate in the atmosphere these small objects can still cause considerable damage such as occurred near tunguska siberia in 1908 the flux of small bodies is poorly constrained however in part because ground based observational searches pursue strategies that lead them preferentially to find larger objects a tunguska class event the energy of which we take to be equivalent to 10 megatons of tnt was previously estimated to occur every 200 300 years with the largest annual airburst calculated to be approximately 20 kilotons kton tnt equivalent ref 4 here we report satellite records of bolide detonations in the atmosphere over the past 8 5 years we find that the flux of objects in the 1 10 m size range has the same power law distribution as bodies with diameters 50 m from this we estimate that the earth is hit on average annually by an object with approximately 5 kton equivalent energy and that tunguska like events occur about once every 1 000 years

the mixing of lunar regolith vital updates to a canonical model abstract in this work we update the regolith mixing model presented by gault et al 1974 including new input values and reworking key parameters much as gault et al did we present a way to calculate the rate at which lunar regolith is overturned at depth the model describes a mixing front that proceeds downward from the surface following a power law function of time our most important update is the inclusion of secondary impacts our calculations show that secondaries are necessary to produce the reworking rate inferred from the depth distribution of surface correlated material in apollo cores fruchter et al 1977 morris 1978 blanford 1980 from the rate at which splotches rework the top 3 cm of regolith speyerer et al 2016 and from the rate at which diviner cold spots bandfield et al 2014 and crater rays pieters et al 1985 hawke et al 2004 werner and medvedev 2010 are reworked into background regolith overturn calculations that only consider the impact of primaries fail to describe observed reworking rates at all depths and timescales we conclude that secondary impacts dominate mixing in the top meter of lunar regolith

critical crater diameter and asteroid impact seismology if impact stress reverberation is the primary gradational process on an asteroid at global scales then the largest undegraded crater records an asteroid s seismological response the critical crater diameter dcrit is defined as the smallest crater whose formation disrupts all previous craters globally up to its size it is solved for by combining relationships for crater growth and for stress attenuation the computation for dcrit gives a simple explanation for the curious observation that small asteroids have only modest undegraded craters in comparison to their size whereas large asteroids have giant undegraded craters dcrit can even exceed the asteroid diameter in which case all craters are local and the asteroid becomes crowded with giant craters dcrit is the most recent crater to have formed on a blank slate when it is equated to the measured diameter of the largest undegraded crater on known asteroids peak particle velocities are found to attenuate with the 1 2 1 3 power of distance less attenuative than strong shocks and more characteristic of powerful seismic disturbances this is to be expected since global degradation can result from seismic cm s 1 particle velocities on small asteroids attenuation as modeled appears to be higher on asteroids known to be porous although these are also bodies for which different crater scaling rules might apply

the fall of the st robert meteorite the st robert quebec canada meteorite shower occurred on 1994 june 15 at 0h02m ut accompanied by detonations audible for 200 km from the fireball endpoint the fireball was recorded by visual observers in vermont new york state new hampshire quebec and ontario as well as by optical and infrared sensors in earth orbit penetration to an altitude of 36 km occurred 60 km to the northeast of montreal where the bolide experienced several episodes of fragmentation a total of 20 fragments of this h5 chondrite comprising a total mass of 25 4 kg were recovered in an ellipse measuring 8 3 5 km one fragment of the shower partially penetrated the aluminum roof of a shed interpretation of the visual and satellite data suggests that the fireball traveled from south southwest to north northeast with a slope from the horizontal of 55 61 a statistical evaluation of the likely heliocentric orbits for the body prior to collision with the earth coupled with theoretical modeling of the entry suggests an entry velocity in the range of 12 7 13 3 km s the meteoroid had moved in a low inclination orbit with orbital perihelion located extremely close to the earth s orbit from satellite optical data it is found that the photometric mass consumed during the largest detonation is 1200 kg estimation of the amplitude of the acoustic signal detected by the most distant observer yields a source energy near 0 5 kt tnt equivalent energy which corresponds to a mass of order 10 metric tonnes this measure is uncertain to approximately one order of magnitude theoretical modeling of the entry of the object suggests a mass near 1600 kg cosmogenic radionuclide activities constrain the lower initial mass to be 700 kg with an upper limit near 4000 kg seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground the total mass estimated to have reached the ground is 100 kg in material comprising 55 g fragments while the preatmospheric mass is found to be most probably in the range of 1200 2000 kg

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

an entry model for the tagish lake fireball using seismic satellite and infrasound records we present instrumental observations of the tagish lake fireball and interpret the observed characteristics in the context of two different models of ablation from these models we estimate the pre atmospheric mass of the tagish lake meteoroid to be 56 tonnes and its porosity to be between 37 and 58 with the lowest part of this range most probable these models further suggest that some 1300 kg of gram sized or larger tagish lake material survived ablation to reach the earth s surface representing an ablation loss of 97 for the fireball satellite recordings of the tagish lake fireball indicate that 1 1 1012 j of optical energy were emitted by the fireball during the last 4 s of its flight the fraction of the total kinetic energy converted to light in the satellite pass band is found to be 16 infrasonic observations of the airwave associated with the fireball establish a total energy for the event of 1 66 0 70 kt tnt equivalent energy the fraction of this total energy converted to acoustic signal energy is found to be between 0 10 and 0 23 examination of the seismic recordings of the airwave from tagish lake have established that the acoustic energy near the sub terminal point is converted to seismic body waves in the upper most portion of the earth s crust the acoustic energy to seismic energy coupling efficiency is found to be near 10 6 for the tagish lake fireball the resulting energy estimate is near 1 7 kt corresponding to a meteoroid 4 m in diameter the seismic record indicates extensive nearly continuous fragmentation of the body over the height intervals from 50 to 32 km seismic and infrasound energy estimates are in close agreement with the pre atmospheric mass of 56 tonnes established from the modeling the observed flight characteristics of the tagish lake fireball indicate that the bulk compressive strength of the pre atmospheric tagish lake meteoroid was near 0 25 mpa while the material compressive strength most appropriate to the recovered meteorites was closer to 0 7 mpa these are much lower than values found for fireballs of ordinary chondritic composition the behavior of the tagish lake fireball suggests that it represents the lowest end of the strength spectrum of carbonaceous chondrites or the high end of cometary meteoroids the bulk density and porosity results for the tagish lake meteoroid suggest that the low bulk densities measured for some small primitive bodies in the solar system may reflect physical structure dominated by microporosity rather than macroporosity and rubble pile assemblages

the moravka meteorite fall 3 meteoroid initial size history structure and composition the properties and history of the parent meteoroid of the mora vka h5 6 ordinary chondrites have been studied by a combination of various methods the pre atmospheric mass of the meteoroid was computed from fireball radiation infrasound seismic signal and the content of noble gases in the meteorites all methods gave consistent results the best estimate of the pre atmospheric mass is 1500 500 kg the fireball integral bolometric luminous efficiency was 9 and the acoustic efficiency was 0 14 the meteoroid cosmic ray exposure age was determined to be 6 7 1 0 10 6 yr the meteorite shows a clear deficit of helium both 3 he and 4 he this deficit can be explained by solar heating numerical backward integration of the meteoroid orbit determined in a previous paper from video records of the fireball shows that the perihelion distance was probably lower than 0 5 au and possibly as low as 0 1 au 5 ma ago the collision which excavated mora vka probably occurred while the parent body was on a near earth orbit as opposed to being confined entirely to the main asteroid belt an overview of meteorite macroscopic properties petrology mineralogy and chemical composition is given the meteorites show all mineralogical features of h chondrites the shock level is s2 minor deviations from other h chondrites in abundances of trace elements la ce cs and rb were found the ablation crust is enriched with siderophile elements