Publications
209 results found
Collins GS, Schwarz D, Wojcicka N, et al., 2022, BAYESIAN INVERSION OF IMPACTOR PARAMETERS FROM PROPERTIES OF CRATER CLUSTERS ON MARS, Publisher: WILEY, ISSN: 1086-9379
Raducan SD, Jutzi M, Davison TM, et al., 2022, IMPACT FORMATION MODELS OF METAL-RICH BODIES AND IMPLICATIONS FOR ASTEROID (16) PSYCHE, 85th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379
Davison TM, Baijal N, Collins GS, 2022, HIGH-RESOLUTION OBLIQUE IMPACT SIMULATIONS OF THE FORMATION OF THE SOUTH POLE-AITKEN, 85th Annual Meeting of the Meteoritical-Society, Publisher: WILEY, ISSN: 1086-9379
Ormö J, Raducan SD, Luther R, et al., 2022, Impact Induced Motion of Boulders and Their Effect on Ejecta Emplacement on Rubble-pile Targets 
<jats:p>&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt; Asteroids smaller than about 50 km in diameter are the result of the break-up of a larger parent body [1]. They are often considered to be rubble-pile objects, aggregates held together only by self-gravity or small cohesive forces [2, 3], and have highly heterogeneous surfaces. Recently, the artificial impact experiment (SCI) of JAXA&amp;#8217;s Hayabusa2 mission on the surface of asteroid Ryugu [4] created a relatively large crater (~14 m diameter) despite the presence of large boulders close to the impact location [5].&lt;/p&gt;&lt;p&gt;Post-impact images of the SCI impact site revealed that the boulders had different motion mechanisms depending on their size and initial position relative to the impact point. 1 m-sized boulders were ejected several metres outside of the crater, a 5 m boulder was moved about 3m, while a large, possibly deeply rooted boulder (&amp;#8220;Okamoto&amp;#8221;) was not moved [4]. Impact cratering on weak, heterogeneous targets is still poorly studied, both by means of laboratory experiments and numerical simulations. For example, it is not yet known how the boulders affect the crater size or how the boulders motion is affected by their mass, size, shape or initial location.&lt;/p&gt;&lt;p&gt;This is also important in context of NASA&amp;#8217;s Double Asteroid Redirection Test (DART) impact on the surface of Dimorphos (the secondary of the 65803 Didymos asteroid system) on the 26th of September 2022. The impact will demonstrate the controlled deflection capabilities of near-Earth asteroids by a kinetic impactor [6]. ESA&amp;#8217;s Hera mission [7] will arrive at Dimorphos several years after the DART impact and provide a detailed characterisation of the impact outcome.&lt;/p&gt;&lt;p&gt;Rece
Daubar IJ, Dundas CM, McEwen AS, et al., 2022, New craters on Mars: an updated catalog, Journal of Geophysical Research: Planets, Vol: 127, Pages: 1-21, ISSN: 2169-9097
We present a catalog of new impacts on Mars. These craters formed in the last few decades, constrained with repeat orbital imaging. Crater diameters range from 58 m down to <1 m. For each impact, we report whether it formed a single crater or a cluster (58% clusters); albedo features of the blast zone (88% halos; 64% linear rays; 10% arcuate rays; majority dark-toned; 4% light-toned; 14% dual-toned); and exposures of ice (4% definite; 2% possible). We find no trends in the occurrences of clusters with latitude, elevation, or impact size. Albedo features do not depend on atmospheric fragmentation. Halos are more prevalent at lower elevations, indicating an atmospheric pressure dependence; and around smaller impacts, which could be an observational bias. Linear rays are more likely to form from larger impacts into more consolidated material and may be enhanced by lower atmospheric pressure at higher elevations. Light- and dual-toned blast zones occur in specific regions and more commonly around larger impacts, indicating excavation of compositionally distinct material. Surfaces covered with bright dust lacking cohesion are favored to form detectable surface features. The slope of the cumulative size frequency distribution for this dataset is 2.2 for diameters >8 m (differential slope 2.9), significantly shallower than the slope of new lunar craters. We believe that no systematic biases exist in the martian dataset sufficient to explain the discrepancy. This catalog is complete at the time of writing, although observational biases exist, and new discoveries continue.
Collins GS, Newland EL, Schwarz D, et al., 2022, Meteoroid fragmentation in the martian atmosphere and the formation of crater clusters, Journal of Geophysical Research: Planets, Vol: 127, Pages: 1-22, ISSN: 2169-9097
The current rate of small impacts on Mars is informed by more than one thousand impact sites formed in the last twenty years, detected in images of the martian surface. More than half of these impacts produced a cluster of small craters formed by fragmentation of the meteoroid in the martian atmosphere. The spatial distributions, number and sizes of craters in these clusters provide valuable constraints on the properties of the impacting meteoroid population as well as the meteoroid fragmentation process. In this paper, we use a recently compiled database of crater cluster observations to calibrate a model of meteoroid fragmentation in Mars’ atmosphere and constrain key model parameters, including the lift coefficient and fragment separation velocity, as well as meteoroid property distributions. The model distribution of dynamic meteoroid strength that produces the best match to observations has a minimum strength of 10–90 kPa, a maximum strength of 3–6 MPa and a median strength of 0.2–0.5 MPa. An important feature of the model is that individual fragmentation events are able to produce fragments with a wide range of dynamic strengths as much as ten times stronger or weaker than the parent fragment. The calibrated model suggests that the rate of small impacts on Mars is 1.5–4 times higher than recent observation-based estimates. It also shows how impactor properties relevant to seismic wave generation, such as the total impact momentum, can be inferred from cluster characteristics.
Bray VJ, Hagerty JJ, Collins GS, 2022, "False peak" creation in the Flynn Creek marine target impact crater, Meteoritics and Planetary Science, Vol: 57, Pages: 1365-1386, ISSN: 1086-9379
Impacts into marine targets are known to create abnormal crater morphologies. We investigate the formation of the ~4 km diameter Flynn Creek marine target impact crater using the iSALE hydrocode. We compare simulation results to topographic profiles, mineral pressure indicators, and breccia sequencing from drill cores to determine the most likely sea depth at this location at the time of impact (~360 Ma, Tennessee, USA): 700–800 m. Both the peak shock pressure produced by the impact and the mechanism(s) of central peak formation differ with sea depth. The large central mound of Flynn Creek could have been produced in three distinct ways, all requiring the presence of an ocean: (1) a relatively cohesive rim collapse deposit that reached the crater center as part of a ground flow and came to rest on top of the existing crater stratigraphy; (2) chaotic resurge of ejecta with the returning ocean that deposited at the crater center; (3) large uplift facilitated by the removal of overburden pressure from a deep ocean. The first two of these mechanisms create “false peaks” in which high-shock uplifted material and original crater floor are buried beneath > 200 m of relatively low shock material. Our simulations suggest that drilling of marine impact sites might require deeper than expected drill cores, so that any high-pressure mineralogical indictors at depth can be accessed.
Raducan SD, Jutzi M, Davison TM, et al., 2022, Influence of the projectile geometry on the momentum transfer from a kinetic impactor and implications for the DART mission, International Journal of Impact Engineering, Vol: 162, Pages: 104147-104147, ISSN: 0734-743X
The DART spacecraft will impact Didymos’s secondary, Dimorphos, at the end of 2022 and cause a change in the orbital period of the secondary. For simplicity, most previous numerical simulations of the impact used a spherical projectile geometry to model the DART spacecraft. To investigate the effects of alternative, simple projectile geometries on the DART impact outcome we used the iSALE shock physics code in two and thee-dimensions to model vertical impacts of projectiles with a mass and speed equivalent to the nominal DART impact, into porous basalt targets. We found that the simple projectile geometries investigated here have minimal effects on the crater morphology and momentum enhancement. Projectile geometries modelled in two-dimensions that have similar surface areas at the point of impact, affect the crater radius and the crater volume by less than 5%. In the case of a more extreme projectile geometry (i.e., a rod, modelled in three-dimensions), the crater was elliptical and 50% shallower compared to the crater produced by a spherical projectile of the same momentum. The momentum enhancement factor in these test cases, commonly referred to as , was within 7% for the 2D simulations and within 10% for the 3D simulations, of the value obtained for a uniform spherical projectile. The most prominent effects of projectile geometry are seen in the ejection velocity as a function of launch position and ejection angle of the fast ejecta that resides in the so-called ‘coupling zone’. These results will inform the LICIACube ejecta cone analysis.
Raducan SD, Davison TM, Collins GS, 2022, Ejecta distribution and momentum transfer from oblique impacts on asteroid surfaces, Icarus, Vol: 374, Pages: 1-16, ISSN: 0019-1035
NASA’s Double Asteroid Redirection Test (DART) mission will impact its target asteroid, Dimorphos, at anoblique angle that will not be known prior to the impact. We computed iSALE-3D simulations of DARTlike impacts on asteroid surfaces at different impact angles and found that the vertical momentum transferefficiency, 𝛽, is similar for different impact angles, however, the imparted momentum is reduced as the impactangle decreases. It is expected that the momentum imparted from a 45◦impact is reduced by up to 50%compared to a vertical impact. The direction of the ejected momentum is not normal to the surface, howeverit is observed to ‘straighten up’ with crater growth. iSALE-2D simulations of vertical impacts provide contextfor the iSALE-3D simulation results and show that the ejection angle varies with both target properties andwith crater growth. While the ejection angle is relatively insensitive to the target porosity, it varies by upto 30◦ with target coefficient of internal friction. The simulation results presented in this paper can helpconstrain target properties from the DART crater ejecta cone, which will be imaged by the LICIACube. Theresults presented here represent the basis for an empirical scaling relationship for oblique impacts and canbe used as a framework to determine an analytical approximation of the vertical component of the ejectamomentum, 𝛽 − 1, given known target properties.
Collins GS, Newland EL, Schwarz D, et al., 2021, Meteoroid Fragmentation in the Martian Atmosphere and the Formation of Crater Clusters
Fernando B, Wójcicka N, Han Z, et al., 2021, Questions to Heaven, Astronomy and Geophysics, Vol: 62, Pages: 622-625, ISSN: 1366-8781
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Rajšić A, Miljković K, Wójcicka N, et al., 2021, Numerical simulations of the Apollo S-IVB artificial impacts on the moon, Earth and Space Science, Vol: 8, ISSN: 2333-5084
The third stage of the Saturn IV rocket used in the five Apollo missions made craters on the Moon ∼30 m in diameter. Their initial impact conditions were known, so they can be considered controlled impacts. Here, we used the iSALE-2D shock physics code to numerically simulate the formation of these craters, and to calculate the vertical component of seismic moment (∼4 × 1010 Nm) and seismic efficiency (∼10−6) associated with these impacts. The irregular booster shape likely caused the irregular crater morphology observed. To investigate this, we modeled six projectile geometries, with footprint area between 3 and 105 m2, keeping the mass and velocity of the impactor constant. We showed that the crater depth and diameter decreased as the footprint area increased. The central mound observed in lunar impact sites could be a result of layering of the target and/or low density of the projectile. Understanding seismic signatures from impact events is important for planetary seismology. Calculating seismic parameters and validating them against controlled experiments in a planetary setting will help us understand the seismic data received, not only from the Moon, but also from the InSight Mission on Mars and future seismic missions.
Fernando B, Wójcicka N, Maguire R, et al., 2021, Seismic constraints from a Mars impact experiment using InSight and Perseverance, Nature Astronomy, Vol: 6, Pages: 59-64, ISSN: 2397-3366
NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy).
Johnson BC, Milliken RE, Lewis KW, et al., 2021, Impact generated porosity in Gale crater and implications for the density of sedimentary rocks in lower Aeolis Mons, Icarus, Vol: 366, Pages: 1-11, ISSN: 0019-1035
Sedimentary rocks in Gale crater record important information about the climatic history and evolution of Mars. Recent gravity measurements and modeling indicate strata encountered by the Curiosity rover have a very low density (1680 ± 180 kg m−3) and thus unusually high porosity. Missing in these models, however, is the role of deeper crustal porosity on the observed gravity signatures. Here we simulate the impact formation of Gale crater and find that impact generated porosity results in a negative gravity anomaly that decreases in magnitude with distance from the basin center. Incorporating this expected post-impact gravity signature into models for the bulk density of strata in lower Mt. Sharp, we find a best-fit density of 2300 ± 130 kg m−3 for an impact into a target with no pre-impact porosity. Models incorporating pre-impact porosity result in densities that are up to 200 kg/m3 lower. These revised densities increase the maximum potential burial depth of rocks along the rover traverse, allowing for the possibility Gale crater may once have been filled with sediment.
Rajšić A, Miljković K, Wojcicka N, et al., 2021, Numerical modelling of the artificial impacts on the Moon
<jats:p>&lt;div&gt;&lt;p&gt;&lt;strong&gt;Introduction: &lt;/strong&gt;A possible source of seismic activity on Mars is meteoroid impacts [5]. Nevertheless, in the first Martian year of the the NASA InSight Mission [2] no signal has been unambiguously associated with an impact event [4]. This calls for further investigation of meteorite strikes and the relationship between impact conditions and the seismic signals they generate. One of the ways to understand the seismic signature of meteoroid impacts is to analyze already existing data from other planetary bodies.&lt;/p&gt;&lt;p&gt;During the Apollo era, over one thousand seismic signals were recorded on the Moon [e.g. 12]. Part of the Apollo seismic experiments were artificial impacts of Lunar modules (LM) and Saturn booster drops (S-IVB). Artificial impacts are considered large scale controlled experiments, because the exact position of the crater and the impactor parameters that made it are known. In this work, we model S-IVB artificial impacts on the Moon, using the iSALE-2D shock physics hydrocode [e.g., 1, 3, 21]. We simulated both the crater formation and the pressure wave propagation and attenuation. We examined size of the crater, cratering efficiency, impact momentum transferred to the target and two seismic parameters: seismic efficiency and seismic moment, and compared these measurements to the existing data [e.g., 10, 8, 7].&lt;/p&gt;&lt;p&gt;One challenge with modelling the S-IVB artificial impacts is the realistic presentation of the projectile. The Apollo S-IVB boosters were hollow aluminum cylinders, with a very low bulk density of 23 gcm&lt;em&gt;&lt;sup&gt;&amp;#8722;&lt;/sup&gt;&lt;/em&gt;&lt;sup&gt;3&lt;/sup&gt; and mass of 14 t. The booster was 17.8 m long and
Ormö J, Raducan SD, Luther R, et al., 2021, Influence of Layering and Boulder Inclusions in a Granular Target on Crater Formation: Insight from Laboratory and Numerical Studies. &#160;
<jats:p>&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt; NASA&amp;#8217;s Double Asteroid Redirection Test (DART) will impact the smaller component of the 65803 Didymos asteroid system, Dimorphos, and alter its orbital period around the primary, thus demonstrating the controlled deflection capabilities of near-Earth asteroids by a kinetic impactor [1, 2]. ESA&amp;#8217;s Hera mission [2] will arrive at Dimorphos several years after the DART impact and provide a detailed characterization of the impact outcome, including the morphometry and morphology of the crater. Recent impact experiments and numerical studies [3&amp;#8211;5] have shown that the kinetic impact efficiency depends strongly on the target properties and structure, and is non-unique (i.e., a number of target property configurations, such as different cohesion-porosity combinations, can result in the same deflection and a measure of the deflection alone can be interpreted in different ways depending on the target and impact properties). Therefore, for a successful interpretation of the DART impact outcome it is important to understand the influence of asteroid properties on the cratering process. Moreover, the DART impact outcome analysis will be based on numerical models, which require extensive and accurate prior validation.&lt;/p&gt;&lt;p&gt;Most previous impact experiments and the subsequent validation work of numerical models have focused on homogeneous targets [e.g., 6, 7]. However, it is unlikely that Dimorphos is homogeneous at the scale of DART impact. Here we present preliminary results from impact experiments and numerical simulations specifically designed to mimic asteroid surface materials and structures (e.g., layered targets, rubble piles). The experiments are performed at the Experimental Projectile Impact Chamber (EPIC) at Centro de Astrobiolog&amp;#237;a CSIC-INTA, Sp
Neidhart T, Miljković K, Sansom EK, et al., 2021, Updated statistics for crater clusters on Mars
<jats:p>&lt;p&gt;An increasing number of newly formed impact craters on Mars have been detected in the last 15 years. These small craters are normally identified via dark spots in lower resolution images that formed during the impact process, presumably through the removal or disturbance of bright surface material [1]. Later higher resolution images revealed single craters or crater clusters, which form when impactors fragment in the atmosphere, within those halos [1,2]. Due to this detection method, most of the new impact sites found are in dusty regions, which imposes an observational bias [3]. Newly formed clusters consist of two to thousands of individual craters and can be tightly clustered or spread out over hundreds of meters [2]. Since the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed on Mars in 2018 [4], the search for newly formed impact craters has become even more important, because identifying impacts in seismic signals could provide further constraints on both the atmospheric and solid-body effects of impact cratering process on Mars, as well as help place further constraints on the properties of the uppermost layer of the crust. As one of InSight&amp;#8217;s mission goals is to estimate the current impact rate on Mars, the seismic detection of impacts is also crucial [4].&lt;/p&gt;&lt;p&gt;The aim of this new study is to describe the properties of the complete catalog of known newly formed craters on Mars and examine correlations between different crater cluster properties. We investigated 559 crater clusters and 493 single craters detected between 2008 and 2020 using 25 cm/px HiRISE images. The locations and diameters were noted for each single crater, as well as for every individual crater within a cluster down to 1 m diameter. This was done using ArcMap (ArcGIS) software with the three-point method of the CraterTools add-in [5]. We
Miljkovic K, Rajsic A, Neidhart T, et al., 2021, Numerical modelling of recent impacts on Mars and contribution to InSight mission science
<jats:p>&lt;p&gt;The crust on Mars has been structurally affected by various geologic processes such as impacts, volcanism, mantle flow and erosion. Previous observations and modelling point to a dynamically active interior in early Martian history, that for some reason was followed by a rapid drop in heat transport. Such a change has significantly influenced the geological, geophysical and geochemical evolution of the planet, including the history of water and climate. Impact-induced seismic signature is dependent on the target properties (conditions in the planetary crust and interior) at the time of crater formation; Thus, we can use simulations of impact cratering mechanics as a tool to probe the interior properties of a planet.&lt;/p&gt;&lt;p&gt;Contrary to large impacts happening in Mars&amp;#8217; early geologic history, the present-day impact bombardment is limited to small meter-size crater-forming impacts (in the atmosphere and on the ground), which are also natural seismic sources (Daubar et al., 2018, 2020; Neidhart et al., 2020). Impact simulations, in tandem with NASA InSight seismic observations (Benerdt et al., 2020, Giardini et al., 2020), can help understand the crustal properties over the course of Mars&amp;#8217; evolution, including the state of Mars&amp;#8217; crust today. Our most recent numerical investigations include: estimating the seismic efficiency and moment from small meter-size impact events, tracking pressure propagation from the impact point into far field, transfer of impact energy into seismic energy, etc (Rajsic et al., 2020, Wojcicka et al., 2020). Understanding coupling between impact crater formation process with the generation and progression of seismic energy can help identify small impact everts in seismic data on Mars. We also looked at the same process on the Earth (Neidhart et al., 2020) and the Moon (Rajsic, et al., this issue).&lt;/p&
Luther R, Raducan SD, Jutzi M, et al., 2021, Simulating the Momentum Enhancement with iSALE and SPH: An AIDA Benchmark & Validation Study
<jats:p>&lt;p&gt;&lt;strong&gt;1. Introduction&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The AIDA international collaboration, which includes the DART (NASA) and Hera (ESA) missions, aims to test the technology of deflection by a kinetic impactor and to enhance our understanding of small bodies in general. In the context of these missions, a spacecraft, DART, will impact the secondary of the 65803 Didymos system, Dimorphos, at the end of October 2022 [1]. The impact will eject asteroid material from the target surface, leading to a measurable change in the orbital period of the binary. A second, follow-up spacecraft, Hera, will arrive at the system several years after the impact to characterize the system and the impact consequences [2].&lt;/p&gt;&lt;p&gt;The objective of this study, which is conducted in the context of the NEO-MAPP project, is to model the collision of the kinetic impactor with Dimorphos and to predict the outcome of the impact with respect to parameters that are measurable by spaceborne and in-situ instrumentation provided by the Hera mission. We model the impact using two different numerical schemes: a continuum approach using iSALE-2D/-3D &amp; a smooth particle approach using Bern SPH. Although all codes solve similar forms of conservation equations and use similar constitutive models, different numerical schemes can produce systematically different results. Hence, as a first step, accurate validation tests against laboratory experiments are conducted to improve the reliability of results from numerical modelling.&lt;br /&gt;&lt;br /&gt;&lt;strong&gt;2. Method&lt;/strong&gt;&lt;br /&gt;iSALE-2D/-3D [3, 4] is a grid-based arbitrary Eulerian Lagrangian (ALE) code and is best suited to study crater formation and the propagation of shock waves from a high
Fernando B, Wójcicka N, Froment M, et al., 2021, Listening for the landing: seismic detections of perseverance's arrival at Mars with InSight, Earth and Space Science, Vol: 8, Pages: 1-21, ISSN: 2333-5084
The entry, descent, and landing (EDL) sequence of NASA's Mars 2020 Perseverance Rover will act as a seismic source of known temporal and spatial localization. We evaluate whether the signals produced by this event will be detectable by the InSight lander (3,452 km away), comparing expected signal amplitudes to noise levels at the instrument. Modeling is undertaken to predict the propagation of the acoustic signal (purely in the atmosphere), the seismoacoustic signal (atmosphere-to-ground coupled), and the elastodynamic seismic signal (in the ground only). Our results suggest that the acoustic and seismoacoustic signals, produced by the atmospheric shock wave from the EDL, are unlikely to be detectable due to the pattern of winds in the martian atmosphere and the weak air-to-ground coupling, respectively. However, the elastodynamic seismic signal produced by the impact of the spacecraft's cruise balance masses on the surface may be detected by InSight. The upper and lower bounds on predicted ground velocity at InSight are 2.0 × 10−14 and 1.3 × 10−10 m s−1. The upper value is above the noise floor at the time of landing 40% of the time on average. The large range of possible values reflects uncertainties in the current understanding of impact-generated seismic waves and their subsequent propagation and attenuation through Mars. Uncertainty in the detectability also stems from the indeterminate instrument noise level at the time of this future event. A positive detection would be of enormous value in constraining the seismic properties of Mars, and in improving our understanding of impact-generated seismic waves.
Rajšić A, Miljković K, Collins GS, et al., 2021, Seismic efficiency for simple crater formation in the Martian top crust analogue, Journal of Geophysical Research: Planets, Vol: 126, Pages: 1-12, ISSN: 2169-9097
The first seismometer operating on the surface of another planet was deployed by the NASA InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission to Mars. It gives us an opportunity to investigate the seismicity of Mars, including any seismic activity caused by small meteorite bombardment. Detectability of impact generated seismic signals is closely related to the seismic efficiency, defined as the fraction of the impactor's kinetic energy transferred into the seismic energy in a target medium. This work investigated the seismic efficiency of the Martian near surface associated with small meteorite impacts on Mars. We used the iSALE‐2D (Impact‐Simplified Arbitrary Lagrangian Eulerian) shock physics code to simulate the formation of the meter‐size impact craters, and we used a recently formed 1.5 m diameter crater as a case study. The Martian crust was simulated as unfractured nonporous bedrock, fractured bedrock with 25% porosity, and highly porous regolith with 44% and 65% porosity. We used appropriate strength and porosity models defined in previous works, and we identified that the seismic efficiency is very sensitive to the speed of sound and elastic threshold in the target medium. We constrained the value of the impact‐related seismic efficiency to be between the order of ∼10‐7 to 10‐6 for the regolith and ∼10‐4 to 10‐3 for the bedrock. For new impacts occurring on Mars, this work can help understand the near‐surface properties of the Martian crust, and it contributes to the understanding of impact detectability via seismic signals as a function of the target media.
Halim SH, Crawford IA, Collins GS, et al., 2021, Assessing the survivability of biomarkers within terrestrial material impacting the lunar surface, Icarus, Vol: 354, Pages: 1-15, ISSN: 0019-1035
The history of organic and biological markers (biomarkers) on the Earth is effectively non-existent in the geological record >3.8 Ga ago. Here, we investigate the potential for terrestrial material (i.e., terrestrial meteorites) to be transferred to the Moon by a large impact on Earth and subsequently survive impact with the lunar surface, using the iSALE shock physics code. Three-dimensional impact simulations show that a typical basin-forming impact on Earth can eject solid fragments equivalent to ~10−3 of an impactor mass at speeds sufficient to transfer from Earth to the Moon. Previous modelling of meteorite survivability has relied heavily upon the assumption that peak-shock pressures can be used as a proxy for gauging survival of projectiles and their possible biomarker constituents. Here, we show the importance of considering both pressure and temperature within the projectile, and the inclusion of both shock and shear heating, in assessing biomarker survival. Assuming that they survive launch from Earth, we show that some biomarker molecules within terrestrial meteorites are likely to survive impact with the Moon, especially at the lower end of the range of typical impact velocities for terrestrial meteorites (2.5 km s−1). The survival of larger biomarkers (e.g., microfossils) is also assessed, and we find limited, but significant, survival for low impact velocity and high target porosity scenarios. Thermal degradation of biomarkers shortly after impact depends heavily upon where the projectile material lands, whether it is buried or remains on the surface, and the related cooling timescales. Comparing sandstone and limestone projectiles shows similar temperature and pressure profiles for the same impact velocities, with limestone providing slightly more favourable conditions for biomarker survival.
Devillepoix HAR, Cupák M, Bland PA, et al., 2020, A global fireball observatory, Planetary and Space Science, Vol: 191, Pages: 1-10, ISSN: 0032-0633
The world’s meteorite collections contain a very rich picture of what the early Solar System would have been made of, however the lack of spatial context with respect to their parent population for these samples is an issue. The asteroid population is equally as rich in surface mineralogies, and mapping these two populations (meteorites and asteroids) together is a major challenge for planetary science. Directly probing asteroids achieves this at a high cost. Observing meteorite falls and calculating their pre-atmospheric orbit on the other hand, is a cheaper way to approach the problem. The Global Fireball Observatory (GFO) collaboration was established in 2017 and brings together multiple institutions (from Australia, USA, Canada, Morocco, Saudi Arabia, the UK, and Argentina) to maximise the area for fireball observation time and therefore meteorite recoveries. The members have a choice to operate independently, but they can also choose to work in a fully collaborative manner with other GFO partners. This efficient approach leverages the experience gained from the Desert Fireball Network (DFN) pathfinder project in Australia. The state-of-the art technology (DFN camera systems and data reduction) and experience of the support teams is shared between all partners, freeing up time for science investigations and meteorite searching. With all networks combined together, the GFO collaboration already covers 0.6% of the Earth’s surface for meteorite recovery as of mid-2019, and aims to reach 2% in the early 2020s. We estimate that after 5 years of operation, the GFO will have observed a fireball from virtually every meteorite type. This combined effort will bring new, fresh, extra-terrestrial material to the labs, yielding new insights about the formation of the Solar System.
Rowe J, Daly L, McMullan S, et al., 2020, Using incompatible fireball camera systems to find meteorites &#8211; towards a data exchange standard
<jats:p>&lt;p&gt;In the UK there are five meteor camera networks using four different camera and software systems that are aiming to recover meteorites. Utilising all observations of a fireball event from each network is crucial to constrain a precise orbit and fall position. However, the various camera systems generate a diversity of data outputs that are not compatible with each other. As a result, when a potentially meteorite-dropping fireball event occurs it is currently challenging to exchange calibrated observations between networks, which creates obstacles to response time and rapid meteorite recovery.&lt;/p&gt;&lt;p&gt;If recorded by at least two observatories, the fireball&amp;#8217;s trajectory, pre-arrival orbit, final mass, and (in combination with a &amp;#8216;dark flight&amp;#8217; model) the final fall position of any surviving meteorite can also be calculated. For this, the minimum useful data set from each camera consists of (a) the location of the observatory, and (b) a set of timed direction vectors representing each point at which the meteor was observed. While the inclusion of additional data are recommended, this is the minimum required dataset for a fireball observation from a single camera, that can be exchanged between cooperating fireball networks to provide for accurate triangulation.&lt;/p&gt;&lt;p&gt;Camera systems currently used in the UK or considered as candidates for adoption as a data exchange standard are:&lt;/p&gt;&lt;ul&gt;&lt;li&gt;&lt;strong&gt;UFOAnalyzer.&lt;/strong&gt; Used by UK Meteor Observation Network and the NEMETODE network, UFOAnalyzer&amp;#8217;s &amp;#8220;A.XML&amp;#8221; file contains the essential and recommended data in XML format.&amp;#160; UFOAnalyzer is widely used by amateurs in the UK, We
Rajsic A, Miljković K, Collins G, et al., 2020, Seismic efficiency of Martian upper crust simulant.
<jats:p>&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt; Meteoroid bombardment is one of the sources of seismic activity on planetary bodies. The very first seismometer operating on the surface of another planet was successfully deployed by the NASA InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission to Mars. It gives us an opportunity to investigate the seismicity of Mars, including impact-induced seismic activity. This work investigated the seismic efficiency associated with small meteorite impacts on Mars, using numerical methods in targets analogue to the Martian surface. The Martian crust was simulated as non-porous bedrock (0% porosity) or regolith with different porosities (25%, 44% and 65%)&lt;/p&gt;&lt;p&gt;The seismic efficiency, k, is presented as a portion of impact energy that is transferred into seismic energy. It has been suspected that consolidated (bedrock) and non-consolidated (regolith) materials will have different values of seismic efficiency. Estimates of seismic efficiency range from k=10&lt;sup&gt;-2&lt;/sup&gt; to 10&lt;sup&gt;-6&lt;/sup&gt; (Schultz and Gault, 1975; Daubar et al., 2018; McGarr et al., 1969; Hoerth et al., 2014; Richardson &amp; Kedar, 2013; G&amp;#252;ldemeister &amp; W&amp;#252;nnemann, 2017). High seismic efficiency is typical in bedrock or highly consolidated materials (k&gt;10&lt;sup&gt;-3&lt;/sup&gt;). Low seismic efficiency is typical for sediments or unconsolidated sands and soils (k&lt;10&lt;sup&gt;-5&lt;/sup&gt;) (e.g., Patton and Walter 1993). In this work, we used a simplified approach (e.g. G&amp;#252;ldemeister &amp; W&amp;#252;nnemann, 2017) that defines the seismic efficiency as:&am
Raducan SD, Davison TM, Collins GS, 2020, Momentum transfer from oblique impacts
<jats:p>&lt;p lang=&quot;en-US&quot;&gt;&lt;strong&gt;Introduction:&lt;/strong&gt;&lt;/p&gt;&lt;p lang=&quot;en-US&quot;&gt;Earth is continuously impacted by space debris and small asteroids, and, while large asteroid impacts are very rare, they have the potential to cause severe damage. NASA's Double Asteroid Redirection Test (DART) aims to be the first mission to test a controlled deflection of a Near-Earth binary asteroid [1, 2], by impacting the smaller component of the 65803 Didymos asteroid system, Dimorphos. The impact will thereby alter the binary orbit period by an amount detectable from Earth [3].&lt;/p&gt;&lt;p lang=&quot;en-US&quot;&gt;ESA's Hera mission [3, 4], that will arrive at Dimorphos several years after the DART impact. It will rendezvous with the asteroid system and perform detailed characterisation of Dimorphos's volume and surface properties, as well as measure the DART impact outcome, such as change in the binary system orbit and the volume and morphology of the DART impact crater.&lt;/p&gt;&lt;p lang=&quot;en-US&quot;&gt;In high velocity impacts on an asteroid the change in momentum of the asteroid &lt;em&gt;&amp;#916;&lt;/em&gt;&lt;em&gt;P&lt;/em&gt; can be amplified by the momentum of crater ejecta that exceeds the escape velocity, which is often expressed in terms of the parameter &lt;em&gt;&amp;#946;&lt;/em&gt;&lt;em&gt;=&lt;/em&gt;&lt;em&gt;&amp;#916;&lt;/em&gt;&lt;em&gt;P/mU,&lt;/em&gt; where &lt;em&gt;mU&lt;/em&gt; is the impactor momentum [5]. The amount by which crater ejecta enh
Daly L, McMullan S, Rowe J, et al., 2020, The UK Fireball Alliance (UKFAll); combining and integrating the diversity of UK camera networks to aim to recover the first UK meteorite fall for 30 years
<jats:p>&lt;p&gt;&lt;strong&gt;Main text&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;The UK has a long history of meteorite falls (where the meteorite fireball is witnessed, and the stone recovered, dating back to 1623 (MetBull, 2020). But the last meteorite fall in the UK was nearly 30 years ago when the Glatton stone, an L6 ordinary chondrite was recovered in 1991 (Hutchinson et al., 1991). Meteorite falls are important samples as they are usually recovered within days of the fireball event.&amp;#160; As such, they have not experienced the deleterious effects terrestrial weathering that can change their extraterrestrial mineralogy, chemistry and isotopic composition (Bland et al., 2006). In exceptional circumstances rapidly recovered falls may have avoided rainfall so that soluble extraterrestrial minerals such as salts may be preserved (Chan et al., 2018). Therefore, meteorite falls represent much more pristine extraterrestrial material than their find counterparts within the same group, and consequently, characterisation of their texture and chemical signatures provides a clearer window into solar system processes. However, even falls are limited in their interpretive power as the geological context of the stone (i.e. where in the solar system it originated from) is unknown.&lt;/p&gt;&lt;p&gt;To derive this contextual information requires the imaging of the fireball event from multiple geographical positions (Devillepoix et al., 2020). This data provides two vital pieces of information; the initial orbit of the meteoroid can be calculated and the final fall position can be predicted with increased accuracy (Devillepoix et al., 2020). As such, dedicated fireball camera networks (Bowden, 2006) are entering &amp;#8216;a golden age&amp;#8217; with improvements in hardware and software capabilities as well as a reduction in production cos
Ormö J, Raducan SD, Luther R, et al., 2020, Effects of target heterogeneity on impact cratering processes in the light of the Hera mission: combined experimental and numerical approach
<jats:p>&lt;p&gt;&lt;strong&gt;The Double Asteroid Redirection Test (DART) plans to impact the smaller component of the 65803 Didymos asteroid system [1], Dimorphos, and alter the binary orbit period of the system [2]. The experiment aims to demonstrate the controlled deflection capabilities of a near-Earth asteroid. ESA&amp;#8217;s Hera mission [1,2] will arrive at Dimorphos four years after the DART impact and provides a detailed characterization of the impact. For a successful analysis it is important to know the influence of various parameters known to affect the cratering. Here we present some preliminary results as well as planned experiments at the Experimental Projectile Impact Chamber (EPIC) at Centro de Astrobiolog&amp;#237;a CSIC-INTA, Spain, carried out in concert with observations of natural craters and numerical simulations for mutual verification of the methods and a first analysis of the effects of factors such as heterogeneities in a granular (i.e. &amp;#8216;rubble-pile&amp;#8217;) target.&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Introduction, aim and methods&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;As shown by previous impact experiments and numerical simulations [3,4,5], the amount by which the target asteroid can be deflected is highly dependent on the target properties and structure, and non-unique. Thus, the knowledge of the final crater as observed by Hera is important to assess the target properties of Dimorphos [6]. However, such an analysis based on numerical models requires accurate validation of the applied numerical codes [7,8]. Previous validation work has focused on impacts into homogeneous targets [e.g. 9,10]. However, it is unlikely that asteroids are as homogeneous at this scale [cf. 11] as on the scale of previous laboratory experiments. Therefore, there
Wojcicka N, Collins G, Bastow I, et al., 2020, The seismic moment and seismic efficiency of small impacts on Mars, Journal of Geophysical Research: Planets, Vol: 125, Pages: 1-20, ISSN: 2169-9097
Since landing in late 2018, the InSight lander has been recording seismic signals on the surface of Mars. Despite nominal pre-landing estimates of 1–3 meteorite impacts detected per Earth year, none have yet been identified seismically. To inform revised detectability estimates, we simulated numerically a suite of small impacts onto Martian regolith and characterized their seismic source properties. For the impactor size and velocity range most relevant for InSight, crater diameters are 1-30 m. We found that in this range scalar seismic moment is 106−1010Nm and increases almost linearly with impact momentum. The ratio of horizontal to vertical seismic moment tensor components is∼1, implying an almost isotropic P-wave source, for vertical impacts. Seismic efficiencies are ∼10−6, dependent on the target crushing strength and impact velocity. Our predictions of relatively low seismic efficiency and seismic moment suggest that meteorite impact de-tectability on Mars is lower than previously assumed. Detection chances are best for impacts forming craters of diameter>10m.
Raducan S, 2020, Impact ejecta and crater formation on asteroid surfaces
Asteroids in the Solar System are numerous and have varied composition. Analysis of impact crater sizes and morphologies on asteroids can provide a direct diagnosis of the surface material properties and near-surface structures. This thesis describes numerical simulations of impacts into low-gravity asteroid surfaces using the iSALE shock physics code to inform this diagnosis. Asteroids may pose a future catastrophic threat to Earth and to avoid it, the incoming asteroid can be deflected by a spacecraft impact. However, the efficiency of the deflection is determined by target properties. This work considered different target scenarios to determine the sensitivity of crater morphology, ejecta mass-velocity distribution and momentum transferred, to asteroid surface properties and shallow structures. For homogeneous targets, the surface cohesion, initial porosity, and internal friction were found to greatly influence ejecta mass/velocity distributions and the amount an asteroid can be deflected. In a two-layer target scenario, the presence of a less porous, stronger lower layer can cause both amplification and reduction of ejected mass and momentum relative to the homogeneous case. Impacts into targets with decreasing porosity with depth only produced an enhancement in the ejected momentum for sharp exponential decreases in porosity. Using reasonable estimates for the material properties of the Double Asteroid Redirection Test (DART) asteroid target, the simulations show that the ejecta produced from the impact can enhance the deflection 2 to 4 times. Simulations of impacts into possible target structures on Psyche show large diversity in possible crater morphologies that the ‘Psyche’ mission could encounter. If Psyche’s interior is homogeneous, then the mission will find simple bowl-shaped craters, with a depth-diameter ratio diagnostic of rock or iron. If Psyche has a layered structure, the spacecraft could find craters with more complex morphologie
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