Reconstructing paleoenvironments—particularly aquatic ones—is essential for identifying potential habitats for life, both on early Earth and early Mars. Impact craters often serve as effective sediment traps that are relatively shielded from erosion. In aquatic settings—most commonly in shallow marine environments—where seafloor craters can form, the return flow of water during the early stages of crater modification can produce distinctive resurge deposits. Analyses of such deposits from drill cores at various marine-target impact structures, including the Decorah impact structure (Iowa, USA) examined in this study, reveal a direct correlation between average clast frequency per meter, impact event magnitude (i.e., projectile diameter), and the depth of the target water. If two of these parameters are known, the third can be inferred. In this study, we analyzed two drill cores obtained from the interior of the Decorah impact structure to gain insights into the paleoenvironment at the time of impact. Applying the aforementioned relationships yields an estimated target water depth of 40−90 m, thereby situating the Decorah impact structure paleoenvironment within a defined range of the ancient marine realm.

Asteroid (162173) Ryugu is a spinning-top shaped, rubble-pile C-type asteroid with a surface dominated by boulders spanning a broad size-range. Using Hayabusa2 ONC-T mosaics for mapping, we present the most extensive global boulder dataset to date, representing an eleven-fold increase over the earliest survey and greater completeness than later AI-based estimates. Crucially, this work provides the first global boulder orientation dataset. The cumulative size-frequency distribution follows a power-law slope of − 2.665 ± 0.066 (boulders ≥ 3 m), indicating its fragmented nature. Boulder density is lower along the equatorial ridge, consistent with regolith accumulation during earlier YORP-driven spin-up and poleward migration of blocks during the present spin-down phase. Orientation analyses reveal systematic hemispheric trends in what we define as slope-breaker zones (i.e., regions of high slope differentials), with NW–SE alignment in the northern hemisphere and NE–SW in the southern hemisphere, but absent at the equatorial ridge and poles. We interpret these as reorientations that developed during downslope boulder migration, as despite ongoing spin-down, the current spin rate remains high enough to drive such motion. In addition, fresh craters exhibit locally heightened boulder densities, recording ongoing resurfacing by impact events that exhume buried subsurface boulders and segregate them from finer regolith via seismic shaking induced granular convection. Together, these results yield new insights into rubble-pile surface evolution, rotational dynamics, and impact-driven resurfacing, with boulder orientations providing critical evidence of spin-related downslope transport and establish a framework for comparative asteroid studies.

The Tv & auml;ren structure in southeastern Sweden has been listed as a confirmed marine-target impact structure for decades. However, to date, no measurements and/or indexed data of planar deformation features in quartz grains from the structure have been published or any other unequivocal evidence of impact. Here, we present an investigation aimed at searching for shocked quartz in the 224 m deep Tv & auml;ren-2 drill core. We confirm that the rocks of this core contain, on average, about 5% of shocked quartz, either displaying up to 10 sets of planar deformation features, planar fractures, or both. Petrographic investigation resulted in a division of the core into four main stratigraphic units: (i) lithic impact breccia; (ii) coarse melt-bearing resurge deposit; (iii) finer melt-bearing resurge deposit; and (iv) post-impact deposit. Studying sedimentary facies and structures as well as using petrographic and textural characteristics of the material made it possible to recreate the process of crater formation. We describe a sequence of excavation stage-generated crystalline breccia overlain by early modification stage polymictic breccia with crystalline and limestone clasts formed when the collapse of the crater rim and walls had begun. This breccia is, in turn, overlain by a resurge deposit comprised of material brought into the crater as the water returned. Hence, studying macro- and microstructures is yet another approach to better understand the mechanisms involved in the formation of small impact craters and their associated deposits in marine environments.

Gypsophytes are plants that thrive on gypsum soils on Earth. They possess some adaptive traits that could constitute pre-adaptations to the conditions for potential cultivation in a controlled habitat on Mars. Martian agriculture should utilize substrates obtained directly from the planet itself. However, the detection of perchlorates in the soil of Mars raises doubts about this possibility. These molecules are distributed globally and in concentrations toxic to both humans and plants. The polar winds may preserve some Martian gypsum outcrops from the effects of perchlorates. If so, using this Martian gypsum as a growing substrate for gypsophytes may be a viable option. In the medium term, implementing gypsophyte adaptations on staple crops would also be possible using CRISPR-Cas9 and/or other gene-editing technologies. According to the literature reviewed, Gypsophila struthium subsp. struthium shows a high degree of colonization capacity and high resistance to drought. This taxon serves as an ecological facilitator for other species, and its germination appears to be favored by the presence of gypsum. Several experimental results suggest it would be worthwhile to test the cultivation of this and other plants on reliable simulants or Martian gypsum through sample return missions or on a mission that would perform the cultivation on Mars itself.

The Wetumpka impact structure, which has a NW-SE diameter of similar to 5 km and a NE-SW diameter of similar to 7.6 km, is located in central Alabama (USA), where it was formed in a shallow, nearshore marine environment during the Late Cretaceous. This impact structure has been studied previously through field investigations, shallow core drilling, and gravity modeling. In this paper, we build upon those studies by performing hydrocode modeling using iSALE-2D to investigate the transient crater evolution and the craterfilling sequence. The present study helps explain the unusual collapsed, southwestern, seaward-facing, quadrant of the rim, which is thought to have contributed substantially to the upper part of the crater-filling sequence. We chose a three-layer model to approximate the initial target layer morphology: water on top; sediments in the middle; and granite at the bottom. We performed compression and tensile strength tests on intact micaceous schist (approximated as granite in the model) collected from the crater rim, which were used to obtain values for cohesion in the iSALE-2D damage model. We performed simulations with different combinations of water depths (62.5-125 m), impact velocities (12-18 km/s), and sediment thicknesses (100-300 m) to assess five different impact scenarios. We observed that simulations involving a 400-m-diameter impactor, impacting at 12 km/s (vertical component) on a target with 62.5 m water depth and a 300-m-target sediment layer, resulted in a final crater model that best approximates what has been observed in the field as well as by drilling and gravity modeling. Finally, we compared the pressures predicted by iSALE-2D with previous studies of Wetumpka's shock petrography. Our numerical results show a relatively close correlation between both the geological relationships and shock levels observed within and among the craterfilling units. This study not only enhances our understanding of the Wetumpka impact structure but also demonstrates the potential of numerical modeling in reconstructing impact crater evolution, offering a foundation for future research in both terrestrial and planetary impact cratering.

Kinetic deflection is a planetary defense technique delivering spacecraft momentum to a small body to deviate its course from Earth. The deflection efficiency depends on the impactor and target. Among them, the contribution of global curvature was poorly understood. The ejecta plume created by NASA's Double Asteroid Redirection Test impact on its target asteroid, Dimorphos, exhibited an elliptical shape almost aligned along its north-south direction. Here, we identify that this elliptical ejecta plume resulted from the target's curvature, reducing the momentum transfer to 44 ± 10% along the orbit track compared to an equivalent impact on a flat target. We also find lower kinetic deflection of impacts on smaller near-Earth objects due to higher curvature. A solution to mitigate low deflection efficiency is to apply multiple low-energy impactors rather than a single high-energy impactor. Rapid reconnaissance to acquire a target's properties before deflection enables determining the proper locations and timing of impacts.

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft intentionally collided with Dimorphos, the moon of the binary asteroid system 65803 Didymos. This collision provided the first full-scale test of a kinetic impactor for planetary defense. Images from DART's DRACO camera revealed Dimorphos to be an oblate spheroid covered in boulders of varying sizes and shapes. Very little was known about Dimorphos prior to DART's impact, including its shape, structure, and material properties. Approach observations and those following the DART impact have provided crucial knowledge that narrows the parameter space relevant to modeling the impact into Dimorphos. Here we present the results of a suite of hydrocode simulations of the DART impact on Dimorphos. Despite remaining uncertainties, initial models of DART's kinetic impact provide important information about the results of DART (e.g., potential crater size and morphology, ejecta mass) and the properties of Dimorphos. Simulations here suggest that Dimorphos has near-surface strength ranging from a few Pascals to tens of kPa, which corresponds to crater sizes of similar to 40-60 m. Simulated crater sizes provide a crucial comparison metric for the European Space Agency Hera mission when it arrives at the Didymos system. Hera's measurement of crater size in combination with measurement of Dimorphos's mass will allow us to assess our simulations and provide the information needed to make the DART impact experiment both the first test of a planetary defense mitigation mission and the first full-scale planetary defense simulation validation exercise.

On 2022 September 26, the Double Asteroid Redirection Test (DART) spacecraft intentionally collided with Dimorphos, the moon of the binary asteroid system 65803 Didymos. This collision provided the first full-scale test of a kinetic impactor for planetary defense. Images from DART’s DRACO camera revealed Dimorphos to be an oblate spheroid covered in boulders of varying sizes and shapes. Very little was known about Dimorphos prior to DART’s impact, including its shape, structure, and material properties. Approach observations and those following the DART impact have provided crucial knowledge that narrows the parameter space relevant to modeling the impact into Dimorphos. Here we present the results of a suite of hydrocode simulations of the DART impact on Dimorphos. Despite remaining uncertainties, initial models of DART’s kinetic impact provide important information about the results of DART (e.g., potential crater size and morphology, ejecta mass) and the properties of Dimorphos. Simulations here suggest that Dimorphos has near-surface strength ranging from a few Pascals to tens of kPa, which corresponds to crater sizes of ∼40–60 m. Simulated crater sizes provide a crucial comparison metric for the European Space Agency Hera mission when it arrives at the Didymos system. Hera’s measurement of crater size in combination with measurement of Dimorphos’s mass will allow us to assess our simulations and provide the information needed to make the DART impact experiment both the first test of a planetary defense mitigation mission and the first full-scale planetary defense simulation validation exercise.

Abstract Hypervelocity impacts play a significant role in the evolution of asteroids, causing material to be ejected and partially reaccreted. However, the dynamics and evolution of ejected material in a binary asteroid system have never been observed directly. Observations of Double Asteroid Redirection Test (DART) impact on asteroid Dimorphos have revealed features on a scale of thousands of kilometers, including curved ejecta streams and a tail bifurcation originating from the Didymos system. Here we show that these features result naturally from the dynamical interaction of the ejecta with the binary system and solar radiation pressure. These mechanisms may be used to constrain the orbit of a secondary body, or to investigate the binary nature of an asteroid. Also, they may reveal breakup or fission events in active asteroids, and help determine the asteroid’s properties following an impact event. In the case of DART, our findings suggest that Dimorphos is a very weak, rubble-pile asteroid, with an ejecta mass estimated to be in the range of (1.1-5.5)×107 kg.

Introduction: The NASA Double Asteroid Redirection Test (DART) impact [1], was the first space mission that successfully demonstrated the kinetic impactor technique for planetary defense. It was at the same instant, on 26th September 2022, when ASI/Light Italian Cubesat for Imaging of Asteroids (LICIACube) [2] was the first Cubesat to image the plume coming from Dimorphos, the smaller body of the binary asteroid (65803) Didymos. The DART impact into Dimorphos [3] caused ejecta plume propagation with high velocity and very filamentary structure, composed of dust particles from μm to cm sizes in size [4]. The large aperture and observed spikes did not prevent propagation of larger excavated material, namely, boulders up to ~2 m [5]. Far-field observations such as HST clearly showed dust tail formed from the low-speed ejecta dust due to solar radiation pressure (SRP) [4].The scientific objectives: The estimation of the size distribution and velocity distribution of the plume in close vicinity to Dimorphos, captured in the LICIACube images is still an unanswered question. While the long-term monitoring of the tail can reveal the size distribution up to tens of cm in size, the impact simulations can constrain the initial velocity of the excavated material. Near and mid – field simulations considering different dynamical properties at local scale can address the complex collimated but inhomogeneous distribution of the dust within the plume. Here, we discuss some of the dynamical properties of the plume using the available observational DART and LICIACube data of the plume propagation. We try to constrain the particle sizes within the collimated plume structures.The model: We apply the 3D+t model – LIMARDE [6,7] constrained with laboratory observations [8], impact simulations and near- and far- field observations such as the LICIACube [9] images and HST [2] dust observations, respectively. The model computes single particle trajectories, the dust rotational frequencies and velocity as well as the particle orientation at any time and distance. We compute the dust velocity distribution based on the physical properties (size, mass and shape) derived from the LICIACube observations. The results are useful to check what is the role of the fragmentation of the particles and to constrain the physical properties based on the dynamical properties of the ejected dust in the near- and mid- environment.Fig. 1. The dust speed and rotation frequency of particles with different shapes as constitutes of the dust clumps shown in the observations of ASI/LICIACube/LUKE, 2022-09-26T23:17:04.Discussion: The LICIACube observations suggest that we have the locations of accumulation of different particles along the collimated plume streamers. The latter may contain particles of the same density and shape but with different velocity and rotation due to the initial ejected position and form not-linear motion within the collimated filament – like structures. In Fig. 1 we show LIMARDE simulations with particles of different shapes that result with different velocities suggesting a scenario where the dusty clumps could occur at the same location due to motion of particles with different shapes. The study discusses what is the probability that these dust clumps are formed owing to fragmentation, or their location is a result of their motion history of the ejected particles.Acknowledgements: This research was supported by the Italian Space Agency (ASI) within the LICIACube (ASI-INAF agreement AC n. 2019-31-HH.0).References: [1] Rivkin, A.S. et al. 2021, PSJ, 2, 24pp; [2] Dotto, E. et al. 2021, PSS 199, [3] Daly, R.T. et al. (2023) Nature. [4] Li, J.-Y., et al. (2023) Nature. [5] Farnham et al. LPSC abs. [6] Ivanovski et al. 2023, u.rev.; [7] Fahnestock et al. 2022, PSJ; [8] Ormo et al. 2022, E&PSL [9] Dotto et al. 2023, Nature

The Lockne Crater and its smaller companion Målingen form the yet only confirmed impact structure from a binary, most likely of “rubble-pile” configuration, asteroid on Earth [1]. Both craters formed simultaneously in a shallow sea that allowed them to become very well preserved with most of the crater filling and near-field ejecta remaining. This provides a unique opportunity to explore the crater morphology as it was directly after the cratering and early modification. The marine target setting with seawater and sedimentary strata covering a flat and near-horizontal crystalline peneplain can be seen as an extreme case of target layers of different density and strength, which is known to impose a certain concentric shape of the resulting crater. We are investigating how the concentricity may be enhanced by the oblique, rubble-pile (pancake-shape after atmospheric entry) impact.IntroductionAt Lockne, the inner, nested, crater of about 7.5 km width is surrounded by a shallow, approximately 14 km wide, outer crater visible in the sedimentary rock. The oblique impact caused a downrange offset of the outer crater [2]. At Målingen, the nested crater in the basement is only about 0.7 km wide (Fig. 1).Both craters formed simultaneously (Fig. 2) by the impact of a binary asteroid at 458 Ma [1,3]. The Lockne/Målingen asteroid was generated in a massive collision in the asteroid belt at ~470 Ma, the so-called Middle Ordovician breakup event [4,5]. Not all fragments from a break-up event are massive and monolithic. After a catastrophic breakup of asteroids, smaller fragments can re-accumulate relatively fast (order of weeks) by gravitational attraction into larger objects, so-called “rubble-piles”. It is known that if an asteroid is binary, like in the case for Lockne-Målingen, it is a good indication that it is a rubble-pile.Geologically constrained, advanced 3-D numerical simulations of the Lockne impact have so far been done for a monolithic impactor [e.g., 6]. A best fit between the crater dimensions and the projectile for an impact of the most common configuration, i.e. 45° impact angle in an East to West direction, and 15 km/s impact velocity, gave a projectile size of about 600 m in diameter and a target water depth of slightly less than the projectile diameter. Likewise, based on numerical simulation of small marine target impacts [7], Ormö et al. [3] estimated the Målingen projectile to have been about 150 m in diameter if assumed a massive body. However, a rubble-pile asteroid of the dimensions of the Lockne and Målingen projectiles will separate upon entry into the atmosphere, but maintain their trajectory causing a “pancake-like” cluster, or debris-jet of projectiles [8]. The effect on the target area can, much simplified, be compared to that of a shotgun blast rather than a single rifle bullet, i.e. a shallow, widespread, but still coherent crater. The effect is enhanced in targets with weaker material covering a more massive substrate, as porous, wide projectiles tend to release their energy nearer to the target surface, i.e., in the here also more easily excavated upper layer. The diameter of the pancake-shaped cluster may exceed that of the initial projectile body by an order of magnitude [8]. Obliquity of impact is intensifying the breakup effect, the near-surface release of energy, and also the downrange extent and offset of the shallow outer crater [2].Ongoing and planned activitiesOur geological investigations of the Lockne- Målingen doublet crater serve as basis for numerical simulations [9], but also experiments to be carried out in the Experimental Projectile Impact Chamber (EPIC) at the Centro de Astrobiología in Spain. The simulations will increase our understanding of the subsurface morphology of the otherwise well-documented craters, e.g., the shape of true crater floor, the existence of a central uplift, and dimensions of the damaged zone around the crater. The experiments will focus on:a) The influence of a layered target on both vertical and oblique impacts. Some initial studies have already been successfully performed [2,10]. The experiments are carried out as projectile shots into granular targets with layers of different properties.b) The effects of a clustered projectile (”rubble-pile”) vs. a massive projectile of the same material and mass. The special design of the EPIC cannon allows the use of a great variety of projectiles. The shots will be made into single and dual layer granular targets.c) A repetition of the shots in points ”a” and ”b” above, but in aquatic targets with various water layer thicknesses.The definition of the deep subsurface morphology of especially the Lockne crater, combined with its already exceptionally well-known surface geology, will add the Lockne-Målingen doublet to the best-studied craters in the world as well as provide a unique opportunity for the analysis (geological and/or numerical) of the effects of an impact from a binary, “rubble-pile” asteroid into a layered target.

Introduction: The Lockne impact structure, located in central Sweden, is a well-preserved marine-target crater that was formed ~470 million years ago in the epicontinental sea that covered great part of the Baltoscandia [1][2]. The water depth at the time of the impact is interpreted to approximately have been 500 meters, or possibly more [3]. The nearly horizontal target rocks were comprised of, from top to bottom, ~50m of limestone, ~30m of dark, organic rich, shale, and Proterozoic crystalline basement [1]. The Locke structure consists of a concentric 7.5 km wide nested crater, in the basement, surrounded by a 14 km wide outer crater, where most of the sediment material was excavated [2]. Core drilling in the interior of the nested inner crater revealed crater-fill breccias composed mostly by sedimentary material, interfingered with crystalline breccia lens (Tandsbyn breccia) and resurge deposits (Lockne breccia and Loftarsone). Lockne-Målingen crater doublet has been hypothesized to have formed by a rubber-pile “pancake” shaped impactor [4]. This study aims to understand, through numerical simulations, the crater formation based on different asteroid parameters such as density, shape, and velocity.Methodology: The formation of Lockne is being simulated by iSALE, an extension of the SALE hydrocode developed to model impact crater formation [5,6,7,8]. Current study focuses on iSALE-2D simulations with an axisymmetric approximation of the original impact problem and a resolution of 20, 30 and 60 CPPR (cells per projectile radius), depending on the simulation. The main question to be explored is the influence of the impactor parameters on crater development.In the 60 CPPR simulations, we consider a four-layer target represented by different equations of estate (EoS): (1) crystalline basement as granite, (2) 30 meters of mudstone as wet tuff, (3) 50 meters of limestone as calcite, and (4) 500 meter of sea water. In this case we set a 600-meter wide massive asteroid traveling at 20km/sec.For the 30 CPPR simulations the model comprises a three-layer target: (1) crystalline basement, (2) ~80 meters of limestone, and (3) 500 m of sea water. In the first set of 30 CPPR, we consider a massive 600-meter wide asteroid with velocity of 20 km/sec, and also a 7km/sec simulation where, in order to keep the same kinetic energy released by the impact, the asteroid diameter was expanded to 1200 m. To compensate the doubled volume, we set damage value to the maximum of 1, suggesting less cohesive, and more fragmented, material.The 20 CPPR simulations consider a “pancake” shaped asteroid based on the original and doubled asteroid size. We kept the original volume of the asteroid and calculated the new diameter/height in an approximately 8:1 ratio. For these simulations, we consider the three-layer target (similar to 30 CPPR simulations), asteroid damage set to 1, and impact velocity of 7 km/sec.Results and Discussion: Cratering processes were observed mostly in 30 CPPR simulations, which have reached up to ~900 seconds. Simulations show a maximum transient crater at approximately 15 seconds, and the ejecta curtain starts to collapse over the water layer around 25-30 seconds, forming a tsunami wave that moves outwards. Some amount of water is kept in the crater interior without being ejected and then, at 52 seconds, the sea water starts to move back into the crater, gradually filling the structure, bringing ejecta sediments and crystalline material. At about 650 seconds the water layer is stable and covering the entire 8km wide structure.In the 30 CPPR simulations, the higher velocity simulation revealed a pressure peak of ~90GPa at 0.1 seconds (same was observed for 60 CPPR), whereas the lower velocity simulations show a peak of ~50GPa, even with the enlarged projectile. Temperature peaks are also higher for faster impact, being ~8000K for 20km/sec (similar in 60 CPPR) and 1850K for 12km/sec. The amount of kinetic energy on both cases is similar but the velocity itself seems to play an import role in pressure and temperature conditions. If not, these significant differences can be attributed to different asteroid damage values. New simulations, with similar asteroid damage values, are being prepared to better understand the influence of damage on crater formation. Other differences are related to volume of excavated material. Higher speed simulations show a maximum transient crater with 8km in diameter and 2.0km in depth, whereas lower speed impact show a 7 km wide crater with 2km in depth.The 20 CPPR simulations with a “pancake” shaped asteroid were performed keeping exactly the same parameters as previous 30 CPPR simulations, just changing the asteroid shape. Peak pressure and temperature were lower for spherical asteroids (Table 1), being the difference in temperature more significant than the difference in pressure.As future work, we intend to perform simulations where the asteroid density is decreased by addition of porosity properties to the material. Also, to perfom different combinations in order to explore the actual role of projectile velocity and damage.Peak Spherical projectile Ellipsoid projectile Pressure 45 GPa 52 GPa Temperature 1850 K 11500 K Table 1. Peak pressure and temperature for two identical simulations except for the projectile shape. Speed: 7km/sec, Damage=1References: [1] Lindström et al. (2005) Impact Studies, Springer 357-388 [2] Ormö et al. (2007) Meteoritics & Planet. Sci. 42, 1929-1943 [3] Ormö et al. (2002) JGR, 107, 31-39 [4] Sturkell E. and Ormö J., EPSC abstracts 2020, EPSC2020-956. [5] Melosh H.J. et al. (1992) JGR 97, no. E9, 14735-14759. [6] Ivanov B.A. et al. (1997) Int. J. Impact Eng. 20, 411-430. [7] Collins G. et al. (2004) MAPS 39, 217-231. [8] Wunnemann K. et al. (2006) Icarus 180, 514-527.Acknowledgements: The authors are grateful to the CSIC financial support for international cooperation: I-LINK project LINKA20203 “Development of a combined capacity of numerical and experimental simulation of cosmic impacts with special focus on effects of marine targets”.

Kinetic deflection is a planetary defense technique that delivers spacecraft momentum to a small body to deviate its course from Earth. The deflection efficiency depends strongly on the impactor and target. Among them, the contribution of global curvature was poorly understood. The ejecta plume created by NASA's DART impact on its target asteroid, Dimorphos, exhibited an elliptical shape almost aligned along its north-south direction. Here, we identify that this elliptical ejecta plume resulted from the target’s curvature, reducing the momentum transfer to 44±10% along the orbit track compared to an equivalent impact on a flat target. We also find lower kinetic deflection of impacts on smaller Near-Earth objects (NEOs) due to higher curvature. A solution to mitigate low deflection efficiency is to apply multiple low-energy impactors rather than a single high-energy impactor. Rapid reconnaissance to acquire a target's properties before deflection enables determining the proper locations and timing of impacts.

Introduction: Reconstruction of paleoenvironments, especially aquatic, is important in search for potential Life habitats, e.g. on Mars. Remote sensing, preferably combined with rovers, give information on telltale geochemistry and landforms. However, this may be hampered by extensive surface erosion. Impact craters offer efficient sediment traps relatively protected from erosion. In aquatic (“marine”) environments, water may rush back into the crater during early modification generating “resurge deposits” [1]. Resurge deposits in drill cores from several impact craters show a direct relation between average clast frequency per meter (‹N›), event magnitude (i.e., projectile diameter, d) and target water depth (H) as ‹N›=-15(d/H) +100 for a “low” (e.g. moat) location, or ‹N›=-13(d/H) +150 for a “high”, more turbulent position (e.g., near rim) [2;3]. This implies that any of these factors can be calculated if the other two are known. This was applied on Rochechouart impact structure that was debated if marine-target or not due to lack of marine sediments in the area [4]. Here, we study drill cores from the interior of the today burried Decorah crater, Iowa (43°18′ 49″N, 91°46′19″W), to learn more about its paleoenvironment.The 5.6km Decorah crater seemingly lacks a central uplift expected for its size and target, and is suggested to be marine-target [5]. Target rocks were Upper Cambrian and Lower Ordovician sandstones and dolomite [5;6]. Earliest post-impact infill by marine Winneshiek Shale places the impact in Darriwilian[7]. Decorah is extensively drilled, but only two yielded cores useful for this study; the ~33m “H2” core (0.32km inside the eastern rim), and the ~28m “CS1” core (approx. halfway between south-western rim and crater center) [cf. 5].Methods: We log the polymict breccias of the 5cm in diameter H2 and CS1 cores as their observed grading [5] suggests resurge deposits [cf. 1]. At the time of writing, only H2 is fully logged and interpreted. CS1 will be presented at the conference. The logged section of H2 spans 9.6m from the bottom of the core until the clasts sizes become to small (98%. Size sorting calculates as the standard deviation of the clast size per length unit (here half a meter). Roundness is estimated with a grain shape comparator [cf. 12]. Matrix- or clast support of each clast is based on contact with adjacent clasts and plotted as a ratio per length unit. Alltogether, plotted values show relative variations indicating trends, not absolute values. In addition, clast colors and textures were noted to enable an association with the target stratigraphy [e.g., 4; 8]Results and discussion: A selection of the 416 clasts examined in H2 is shown in Fig 1. The plots in Fig. 2 support the normally graded appearance of the breccia as noted by [5]. When comparing with logs from aforementioned craters, where cores have reached through resurge deposits into underlying slump and avalance breccias, it is evident that H2 ends within resurge deposits. Nevertheless, the cored interval shows similar trends as several of the other craters. We primarily compare with Rochechouart. There, the sequence is subdivided into 6 intervals [see fig. 4 in 4]. Especially intervals 3–6 in Rochechouart show similarities to H2, whereas intervals 1-2 likely were not cored at Decorah, but would be expected as they represent the inevitable initial stages of the resurge. Intervals 3 and 4 at Rochechouart (“outwards passage of anti-resurge” followed by development of “body of standing water”) are characterized by slight upwards increase in clast frequency (until 32m in H2) followed by slight decrease (until 30.25m in H2). In the same interval at Rochechouart, the clast size and size sorting remained stable (up to 30.25m in H2), but accompanied by an increase in clast angularity (up to 30.25m in H2). With interval 5 at Rochechouart, a new pulse in transport energy caused a strong increase in clast size and drop in size sorting, as well as slight increase in roundness (29.25–30.25m in H2). This is then in Rochechouart followed by interval 6 that includes an increase in clast frequency and size sorting, and a generally normal grading towards the top (29.2m and upwards in H2). There is also a general upwards decrease in roundness similar to H2. This interval is interpreted to represent settling of material in a now almost water-filled crater, with seiches causing minor repeated beds (e.g., at 26m and 27m in H2)H2 shows an obvious change in clast lithologies at interval 29.25–30.25m (Fig. 2). The “white” and“dark green” fragments are followed by “dark brown-red”, “dark grey” and “light brown”, whereas “terracotta colored”, “light tan-grey” and “light grey” appear throughout the logged sequence, possibly as the basement clasts do at Rochechouart. Two stratigraphic intervals can be correlated with clast types; The Upper Cambrian Lone Rock Formation, which contains glauconitic and feldspathic sandstone with some beds of dolomite and green-gray shale, and the Lower Ordovician Oneota and Shakopee formations, which include beds that have been stained red owing to their relationship to the truncating, inter-regional unconformity at the base of directly overlying St. Peter Sandstone [6]. These two intervals produce the more easily traceable greenish and reddish clasts.The calculated ‹N› = 43. The online "Earth impact effects program" calculator gives a 350m projectile diameter (d) for a final crater diameter of 5.8km. This results in 92m target water depth (H). This seems reasonable considering that resurge must have been able to overcome the elevated rim [cf. 1]. Likewise, certain benthic fossils in the Winneshiek Shale indicate a deposition within the photic zone (i.e.,

Introduction: The Wetumpka impact structure is a Late Cretaceous marine-target crater located in central Alabama, USA [1][2]. The target region was comprised of weathered crystalline rock of the Piedmont metamorphic terrane, which was overlain by poorly consolidated sediments from the Upper Cretaceous Tuscaloosa Group and Eutaw Formation. The water depth is interpreted to have been approximately 35-100 m [1][3]. The current crater is heavily eroded and exhibits asymmetric rims, due to collapse of the southwest section, reaching a maximum NE-SW diameter of 7.6 km [1][3]. Wetumpka’s surficial geology consists of a deformed, semi-circular, crystalline-rim, and a relatively lower relief area, composed by deformed sediments and mega-blocks from sedimentary and crystalline target rocks, as well as resurge chalk deposits [4]. Not unlike other marine-target craters, the layer of sea water may have played an important role on Wetumpka’s crater unique features, such as the collapsed rim and the distinctive moat-filling sequence. The water may influence since early stages of crater formation, as transient crater depth and diameter, until late formation stages, as tsunami-influenced sediment transport and an aqueous-dominated, moat-filling sequence. This study aims to understand the effect of water depth, tsunami formation, and mechanical parameters of target materials, on crater development and final morphology. Methodology: The formation of Wetumpka was simulated using iSALE-2D, an extension of the SALE hydrocode developed to model impact crater formation [5][6][7][8]. The current study focuses on an axisymmetric approximation of the original impact problem and a resolution of 32 CPPR (cells per projectile radius). A lower resolution simulation (9 CPPR) was also used to obtain a rough but faster estimate of the visible processes during the crater evolution. The main questions to be explored in this study are the influences of impact velocity, water layer, and target properties on crater formation. The target consisted of three layers: (1) metamorphic bedrock as granite; (2) a layer of sediment as either wet tuff or quartzite; and (3) the topmost sea water layer. A spherical impactor of 400m diameter traveling at 12 and 20km/sec was considered. Simulations were achieved using different water depths (60m and 125m), different sediment material (quartzite and wet tuff) and thicknesses (100, 200, or 300m), while maintaining the impactor and target properties. Samples were collected from the crystalline rim for split-Brazilian and compressive tests as per ASTM standards to obtain better estimate of material parameters. Results and Discussion: Three main processes were identified in 9 CPPR simulations: (1) crystalline rim collapse, (2) sedimentary rim collapse, and (3) tsunami resurge. For 32 CPPR simulations, a total of 24 distinct simulations were performed with different combinations of initial water depth scenarios (60m and 125m), impact speed (12km/sec and 20km/sec), sediment layer thickness (100, 200, and 300m), and EoS used for sediment (wet tuff and quartzite). Tensile and compressive strength values, obtained by split-Brazilian and compressive tests, were used to estimate cohesion (17.12 MPa) and friction angle (0.373) of metamorphic bedrock. These values were then used to set more realist input parameters for the 32 CPPR simulations. While the simulations are ongoing, results are presented for approximately 70 seconds after the impact. The main differences observed between the simulations are connected to the impact velocity and sediment layer thickness. The higher velocity impact shows a maximum diameter of the transient crater developed by about 13 seconds, with an approximate 6 km diameter and 1.8 km depth. For the lower velocity impact, the maximum transient crater size was attained at about 10 seconds, with an approximate 5 km diameter and 1.5 km depth. In both cases, the rim started to collapse at about 25 seconds, and the ejecta curtain started to fall on top of the water layer, creating tsunami waves that move outwards. This turbulent flow carried sea floor sediments and blocks of the impacted target rocks, which are more abundant in the proximities of the crater. Simulations with different sediment layer thickness show differences in the composition of the crater rim and upper crater wall. According to our simulations, the crater rim was composed mostly by sedimentary material that can extend to the upper crater walls. Thicker initial sediment layer result in greater areas of crater wall composed of sedimentary material. Higher velocity simulations also show higher peak pressure and temperature, reaching about 47GPa and 7700K at 0.1 seconds, whereas lower velocity impacts produce peaks of about 42 GPa and 4500K. Temperature peaks act on a greatly small volume of rock on lower speed simulations. This could lead us to relate the lack of melt fragments in the crater area with the lower velocity impact. References: [1] King D.T. Jr. et al. (2002) EPSL 202, 541-549. [2] Wartho J.-A. et al. (2012) MAPS 47, 1243-1255. [3] King and Ormö (2011) GSA SP 483, 287-300. [4] King D. T. Jr. et al. (2006) MAPS 41, 1625–1631. [5] Melosh H.J. et al. (1992) JGR 97, no. E9, 14735-14759. [6] Ivanov B.A. et al. (1997) Int. J. Impact Eng. 20, 411-430. [7] Collins G. et al. (2004) MAPS 39, 217-231. [8] Wunnemann K. et al. (2006) Icarus 180, 514-527. Acknowledgements: The authors are grateful to the CSIC financial support for international cooperation: I-LINK project LINKA20203 “Development of a combined capacity of numerical and experimental simulation of cosmic impacts with special focus on effects of marine targets”.

Impacts into layered targets may generate "concentric craters" where a wider outer crater in the top layer surrounds a smaller, nested crater in the basement, which itself may be complex or simple. The influence of target on cratering depends on the ratio of target strength to lithostatic stress, which, in turn, is affected by gravity, target density, and crater diameter. When this ratio is large, the crater size is primarily determined by target strength, whereas gravitational forces dominate when the ratio is small. In two-layer targets, strength may dominate in one or both layers, whereby the outer crater develops in the weaker top layer and the nested crater in the stronger substrate. However, large natural craters that should be gravity-dominated in both cover strata and substrate may be concentric, the reasons for which are not yet fully understood. We performed qualitative impact experiments at 10-502 G and 1.8 km/s with the Boeing Corp. Hypervelocity centrifuge gun, and at 1 G and 0.4 km/s with the CAB CSIC-INTA gas gun into layered sand targets of different compositions and grain densities but similar granulometry to analyze gravity-dominated cratering. The results are compared with iSALE-2D numerical simulations and natural craters on Earth and Mars. We show that target layering also affects the excavation process and concentric crater formation in gravity-dominated impacts. The most important factors are the density and internal friction of each target layer, respectively. We propose that this is also valid for natural craters of sizes that should make their formation gravity-dominated. Concentric impact craters show a "soup-plate" or "inverted sombrero" shape that forms on planetary surfaces with distinct subsurface layers. Generally, a deep inner crater forms in the substrate and a shallower, broader outer crater forms in the upper layer. The shape is obtained either from extensive post-impact collapse of the upper, often weaker layer, or already during crater excavation, which is the focus of this study. The ratio of outer to inner diameter in the latter craters can be used to probe the depth of the upper layer and the contrast in material properties to the substrate. However, the controls on the relative size of the inner and outer craters are not well understood. While the formation of natural concentric craters is often attributed to a change in cohesive strength between the upper and lower layers, we show through impact experiments and numerical simulations that concentric craters can also form in cohesionless targets with a contrast in both density and friction coefficient between the layers. This provides an additional mechanism for concentric crater formation that may explain the development of some large, gravity-dominated, naturally occurring concentric craters on Earth, Mars and elsewhere. Concentric craters are not only due to strength differences between layers but also observed in cohesionless, gravity-dominated targets This may explain the occurrence of large gravity-dominated concentric craters on Earth, Mars and elsewhere Key factors affecting the concentric growth in these cases are the density and internal friction of each target layer, respectively

On September 26, 2022, NASA's Double Asteroid Redirection Test (DART) mission successfully impacted Dimorphos, the natural satellite of the binary near-Earth asteroid (65803) Didymos. Numerical simulations of the impact provide a means to explore target surface material properties and structures, consistent with the observed momentum deflection efficiency, ejecta cone geometry, and ejected mass. Our simulation, which best matches observations, indicates that Dimorphos is weak, with a cohesive strength of less than a few pascals (Pa), similar to asteroids (162173) Ryugu and (101955) Bennu. We find that a bulk density of Dimorphos, rhoB, lower than 2400 kg/m3, and a low volume fraction of boulders (<40 vol%) on the surface and in the shallow subsurface, are consistent with measured data from the DART experiment. These findings suggest Dimorphos is a rubble pile that might have formed through rotational mass shedding and re-accumulation from Didymos. Our simulations indicate that the DART impact caused global deformation and resurfacing of Dimorphos. ESA's upcoming Hera mission may find a re-shaped asteroid, rather than a well-defined crater.

NASA's Double Asteroid Redirection Test (DART) mission was the first to demonstrate asteroid deflection, and the mission's Level 1 requirements guided its planetary defense investigations. Here, we summarize DART's achievement of those requirements. On 2022 September 26, the DART spacecraft impacted Dimorphos, the secondary member of the Didymos near-Earth asteroid binary system, demonstrating an autonomously navigated kinetic impact into an asteroid with limited prior knowledge for planetary defense. Months of subsequent Earth-based observations showed that the binary orbital period was changed by –33.24 minutes, with two independent analysis methods each reporting a 1 σ uncertainty of 1.4 s. Dynamical models determined that the momentum enhancement factor, β , resulting from DART's kinetic impact test is between 2.4 and 4.9, depending on the mass of Dimorphos, which remains the largest source of uncertainty. Over five dozen telescopes across the globe and in space, along with the Light Italian CubeSat for Imaging of Asteroids, have contributed to DART's investigations. These combined investigations have addressed topics related to the ejecta, dynamics, impact event, and properties of both asteroids in the binary system. A year following DART's successful impact into Dimorphos, the mission has achieved its planetary defense requirements, although work to further understand DART's kinetic impact test and the Didymos system will continue. In particular, ESA's Hera mission is planned to perform extensive measurements in 2027 during its rendezvous with the Didymos–Dimorphos system, building on DART to advance our knowledge and continue the ongoing international collaboration for planetary defense.

. IntroductionThe launch of the Hera mission is scheduled for October 2024 [1]. The target of the mission is the binary Didymos system, especially the secondary Dimorphos, which was impacted by the DART mission on 27th September 2022 at 01:15 am (CEST) [2]. The mission shall provide a detailed characterisation of the two bodies and discover what happened to Dimorphos after the impact. To better understand the cratering process, numerical impact simulations have been conducted to analyse the effects of various target properties, (e.g. as strength and porosity), interior structures and exterior boulders, on the outcome of the cratering event [e.g. 3-5]. Nevertheless, these shock physics codes need to be validated against laboratory experiments [e.g. 6-8]. In this study, we explore the effects of curvature of the asteroid strength (cohesion, crush resistance), porosity, and density of boulders on the cratering process in laboratory experiments at the EPIC facility in CAB, and we use these experiments to validate numerical codes. 2. MethodImpact experiments are performed using the EPIC accelerator, which is a 20 mm calibre compressed N2 (300 bar) cannon that launches projectiles at velocities up to ≈420 m/s. The experiments, half- or quarter-space, can be recorded with two high-speed cameras. In the experiments presented here we have kept the impact velocity constant at approximately 380 m/s and used 20 mm spherical delrin projectiles. We used motion tracking sensors with a 100 Hz sampling rate to measure the seismic signal that is generated by the impact. For the first experiment, approximating the surface curvature of an asteroid, we used a target of quartz sand piled in the shape of a half-frustum of ~17 cm height (quarter-space). For the target properties-studies we used two unconsolidated targets of projectile-sized boulders of different strength (cohesion, crush resistance) in quarter-space configuration. The weaker boulder material is made from a blend of sand and gypsum with a lower crush-strength than the porous ceramic boulders in the other experiment. The material of the sand/gypsum boulders was also tested in a homogeneous cylinder impact setup (half-space).To simulate these experiments, we use the iSALE shock physics code [9-11], applying different strength models and the ε-α-porosity compaction model: For sand parameters, we refer to [6].3. ResultsThe crater in the frustum target (Figure 1, top) reaches a transient stage after ~85 ms. The crater is larger than a crater in a flat sand target (Figure 1, bottom). First models of the frustum experiment yield a similar crater diameter (+16%).Figure 1: Frustum. Top: Images of the original target (left half) and the final crater (right half). Colours denote: Blue – 26.7 cm crater width at pre-impact surface level when the maximum depth (8.2 cm, red) is reached (49 ms). Green – 27.3 cm crater width of final crater. Bottom: Simulation of frustum (left) and flat sand target (right) after 70.5 ms. The dashed line indicates the shape of the frustum.The crater in a cohesive homogeneous target of low strength (Figure 2) resembles typical craters in competent rock with fractures and spall pieces.Figure 2: Homogeneous weak (but cohesive) material buried in sand. The cylindric material is 20 cm in diameter and 20 cm in depth. The crater is ~7.1 ± 0.5 cm in diameter.The experiments with targets made of boulders of two different strengths produce craters of different characteristics (Figure 3). While the diameters are similar, the depth of the crater with weaker boulders is much deeper than in the case of stronger boulders, yielding a depth-diameter ratio of ~0.56 instead of ~0.19. In both cases, impact generated dust is injected into the pore space in the target. In the weak target, more boulders are crushed, and fragments are ejected. In the stronger case, ejection is mostly suppressed.Figure 3: Craters in unconsolidated targets of strong (top) and weak (bottom) cohesive, projectile-size boulders. The diameters (green) are 20 cm & 17.7 cm, respectively, and the depth (orange) is 3.8 cm & 9.9 cm.4. Conclusion and DiscussionOur experiments serve as validation scenarios for shock physics codes. First simulations can reproduce the resulting crater shape and diameter (Figure 1), but further modelling is ongoing.The experiments show that surface curvature plays an important role for the cratering event if a large fraction of the crater growths beyond the flat surface. In our case, the flat top diameter of the frustum is about the size of the crater radius in a flat target, i.e. about half of the cratering is ongoing beyond the flat surface. In contrast to a flat target, the release of the pressure and the resulting pressure gradients are not vertical (i.e. there is a horizontal component influencing material movement), and a larger lateral growth of the crater occurs.The experiments with targets of homogeneous projectile-sized particles (“boulders”) show some transition of the cratering regime from typical crater shapes to deep craters and funnels [cf. 12, 13]. Besides impact velocity or the projectile-target density ratio, the transition seems to depend on the strength and crushing behaviour of the target.AcknowledgementsWe gratefully acknowledge the developers of iSALE (www.isale-code.de). The work by J.O. and S.D.R. was supported by grant PID2021-125883NB-C22 by the Spanish Ministry of Science and Innovation/State Agency of Research MCIN/AEI/ 10.13039/501100011033 and by “ERDF A way of making Europe”. R.L., J.O., I.H. S.D.R., M.J., and K.W. were supported by the Spanish Research Council (CSIC) support for international cooperation: I-LINK project ILINK22061.References[1] Michel P. et al., PlanSciJour,3,160,2022.[2] Daly R. T. et al., Nature,616,443-447,2023.[3] Stickle A. M. et al., PlanSciJour,3,248,2022.[4] Raducan S. D. et al., Nature Astronomy,8,445-455,2024.[5] DeCoster M. E. et al., PlanSciJour,5,21,2024.[6] Ormö J. et al., M&PS, 50(12),2067-2086,2015.[7] Luther R. et al., PlanSciJour,3,227,2022.[8] Ormö J. et al., EPSL,594,117713,2022.[9] Amsden A. et al., LANL,LA-8095,101,1980.[10] Wünnemann, K. et al.,Icarus,180,514-527, 2006.[11] Collins, G. S. et al., Int.Journ.Imp.Eng.38,434-439,2011.[12] Kadono T., PSS,47,305-318,1999.[13] Luther R. et al., M&PS,58(12),1832-1847, 2023.