205 results found
North T, Muxworthy A, Williams W, et al., 2024, The effect of stress on paleomagnetic signals: a micromagnetic study of magnetite's single-vortex response, Geophysical Research Letters, Vol: 51, ISSN: 0094-8276
In this study we use micromagnetic modeling to show that the magnetizations of magnetically single-vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single-domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single-vortex and equant single-domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single-vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity.
Bray VJ, Schenk PM, Melosh HJ, et al., 2024, Corrigendum to “Ganymede crater dimensions – Implications for central peak and central pit formation and development” [Icarus (2012) 115–129, (S0019103511003976), (10.1016/j.icarus.2011.10.004)], Icarus, Vol: 407, ISSN: 0019-1035
The authors regret that an important figure of Bray et al. (2012) included an incorrect topographic profile of a Ganymede crater, which failed to properly display a two-tiered peak. A tiered central peak (c.f. Bray et al., 2008, 2012) has a wider base compared to conical central peaks (also see Fig. 5C of Bray et al., 2008). Fig. 2 from Bray et al. (2012) shows a variety of topographic profiles and images of “transitional” crater morphologies on Ganymede. The examples include: (A) A 39 km crater with a pitted peak/summit-pit. (B) A 42 km crater with hummocky floor and the potential beginnings of a central pit. (C) An example of a tiered central peak in a 51 km diameter crater. (D) A flat-bottomed pit in a 77 km diameter crater. The topographic profile used for part C of Fig. 2 is incorrect, as it includes a profile from another crater, not the example shown in the corresponding image. Vitally, this is the profile provided by Bray et al. (2012) to illustrate the existence of tiered central peaks on Ganymede. Without the correct topographic profile, this important point is not demonstrated. In this corrigendum, we provide a correction to Fig. 2 of Bray et al., (2012). Fig. 1 shows the correct collection of topographic profiles that fit with their corresponding images. The tiered-peaks and ringed-pits, suggested by Bray et al. (2008; 2012) to be transitional morphologies produced by peak collapse and corresponding concentric flexure of the surrounding crater floor, are now visible and marked with arrows. The authors would like to apologise for any inconvenience caused. The authors would also like to draw the reader's attention to Bland and Bray (2023), which models the formation of tiered-peak and ringed-pit morphologies as a result of viscous relaxation, rather than a ‘transitional’ pristine crater morphology.
DeCoster ME, Luther R, Collins GS, et al., 2023, The relative effects of surface and subsurface morphology on the deflection efficiency of kinetic impactors-implications for the DART Mission, The Planetary Science Journal, ISSN: 2632-3338
The Double Asteroid Redirection Test (DART) mission impacted Dimorphos, the moonlet of the binary asteroid 65803 Didymos, on September 26, 2022, and successfully tested a kinetic impactor as an asteroid deflection technique. The success of the deflection was partly due to the momentum of the excavated ejecta material, which provided an extra push to changeDimorphos’ orbital period. Pre-impact images provided constraints on the surface, but not the subsurface morphology of Dimorphos. DART observations indicated that Dimorphos contained a boulder-strewn surface, with an impact site located between a cluster of largesurface boulders. In order to better understand the momentum enhancement factor (β) resulting from the impact, we performed impact simulations into two types of targets: idealized homogeneous targets with a single boulder of varying size and buried depth at the impact site, and an assembly of boulders at the impact site with subsurface layers. We investigated the relative effects of surface morphology to subsurface morphology to put constraints on the modeling phase space for DART following impact. We found that surface features created a 30-96% armoring effect on β, with large surface boulders measuring on the order of the spacecraft bus creating the largest effect. Subsurface effects were more subtle (3-23%), and resulted in an anti-armoring effect on β, even when layers/boulders were close to the surface. We also compared our 2D axisymmetric models to a 3D rectilinear model to understand the effects of grid geometry and dimension on deflection efficiency computational results.
Burchell MJ, Collins GC, Vasile M, 2023, Impact Earth! Protecting the UK and further afield from impacts by Near-Earth objects, Astronomy and Geophysics, Vol: 64, Pages: 6.34-6.39, ISSN: 0035-8738
Mark Burchell, Gareth Collins and Massimiliano Vasile report on an RAS Specialist Discussion Meeting dedicated to investigating the effects of potentially hazardous objects colliding with the Earth
Daubar IJ, Fernando BA, Garcia RF, et al., 2023, Two seismic events from InSight confirmed as new impacts on Mars, The Planetary Science Journal, Vol: 4, ISSN: 2632-3338
We report confirmed impact sources for two seismic events on Mars detected by the NASA InSight mission. These events have been positively associated with fresh impact craters identified from orbital images, which match predicted locations and sizes to within a factor of three, and have formation time constraints consistent with the seismic event dates. They are both of the Very High Frequency family of seismic events and present with chirps (dispersed infrasound/acoustic waves). This brings the total number of confirmed martian impact-related seismic events to eight thus far. All seismic events with chirp signals have now been confirmed as having been caused by impact cratering events. This includes all seismic activity within 100 km of the lander, and two out of the four events with source locations between 100-300 km distance.
Zenhäusern G, Wójcicka N, Stähler S, et al., 2023, What Marsquakes Tell Us About Impact Rates on Mars
<jats:p>The current Martian cratering rate has been determined either from&#160;repeated orbital imaging (e.g.), or using lunar rates&#160;extended to Mars in combination with crater counting . Eight seismic events detected by the NASA InSight seismometer have been confirmed as impacts by orbital imaging . Six of those events are part of the Very High Frequency (VF) group of marsquakes, which consists of 70 events in total. The impact signals are very similar to other VF events, suggesting that more or all VF events could be impact related. The unique characteristics of VF events, such as a long seismic coda interpreted as a result of shallow source in a strongly scattering near-surface layer  and their temporal and spatial distributions, are consistent with impact origin.Assuming all high quality VF events are impacts allows us to place a novel constraint on the impact rate on Mars, independent of the formation of easy-to-spot large blast zones, necessary to identify fresh craters in orbital images. We test the compatibility with the existing cratering rate estimates by using two approaches to derive a first seismically constrained impact rate for Mars. First, we use the Gutenberg-Richter law to determine the slope of the VF event magnitude-frequency distribution. The impact rate is derived by applying a relationship between seismic moment and crater diameter . We refine our estimates by extrapolating the detectability of each event using a semi-empirical relationship between crater size and seismic amplitude . We find that both approaches give similar rates, varying slightly depending on the detectability conditions assumed by each method. The cumulative rates N(D&#8805;8m) = 1-4x10-6 /km2/yr are higher than those from previous imaging studies, but consistent with isochron rates .The discrepancy with imaging-based rates could indicate that there are impacts which are missed in imagery due to absent blast zones
Steele SC, Fu R, Volk MWR, et al., 2023, Paleomagnetic evidence for a long-lived, potentially reversing martian dynamo at ~3.9 Ga, Science Advances, Vol: 9, Pages: 1-13, ISSN: 2375-2548
The 4.1-billion-year-old meteorite Allan Hills 84001 (ALH 84001) may preserve a magnetic record of the extinct martian dynamo. However, previous paleomagnetic studies have reported heterogeneous, nonunidirectional magnetization in the meteorite at submillimeter scales, calling into question whether it records a dynamo field. We use the quantum diamond microscope to analyze igneous Fe-sulfides in ALH 84001 that may carry remanence as old as 4.1 billion years (Ga). We find that individual, 100-μm-scale ferromagnetic mineral assemblages are strongly magnetized in two nearly antipodal directions. This suggests that the meteorite recorded strong fields following impact heating at 4.1 to 3.95 Ga, after which at least one further impact heterogeneously remagnetized the meteorite in a nearly antipodal local field. These observations are most simply explained by a reversing martian dynamo that was active until 3.9 Ga, thereby implying a late cessation for the martian dynamo and potentially documenting reversing behavior in a nonterrestrial planetary dynamo.
Cheng AF, Agrusa HF, Barbee BW, et al., 2023, Momentum transfer from the DART mission kinetic impact on asteroid dimorphos, Nature, Vol: 616, Pages: 457-460, ISSN: 0028-0836
The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on September 26, 2022 as a planetary defense test1. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defense, intended to validate kinetic impact as a means of asteroid deflection. Here we report the first determination of the momentum transferred to an asteroid by kinetic impact. Based on the change in the binary orbit period2, we find an instantaneous reduction in Dimorphos's along-track orbital velocity component of 2.70 ± 0.10 mm s-1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. For a Dimorphos bulk density range of 1,500 to 3,300 kg m-3, we find that the expected value of the momentum enhancement factor, [Formula: see text], ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m-3, [Formula: see text]. These [Formula: see text] values indicate that significantly more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos.
Daly RT, Ernst CM, Barnouin OS, et al., 2023, Successful kinetic impact into an asteroid for planetary defense, Nature, Vol: 616, Pages: 443-447, ISSN: 0028-0836
While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1-3. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact4. While past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.
Neidhart T, Sansom EK, Miljković K, et al., 2023, Diversity of new martian crater clusters informs meteoroid atmospheric interactions, Journal of Geophysical Research: Planets, Vol: 128, Pages: 1-16, ISSN: 2169-9097
We investigated 634 crater clusters on Mars detected between 2007 and 2021, which represent more than half of all impacts discovered in this period. Crater clusters form when meteoroids in the 10 kg–10 ton mass range break up in Mars' atmosphere to produce a few to a few hundred fragments that hit the ground. The properties of the clusters can inform our understanding of meteoroid properties and the processes that govern their fragmentation. We mapped individual craters >1 m within each cluster and defined a range of cluster properties based on the spatial and size distributions of the craters. The large data set, with over eight times more cluster observations than previous work, provides a more robust statistical investigation of crater cluster parameters and their correlations. Trends in size, dispersion, and large crater fraction with elevation support weak atmospheric filtering of material. The diversity in the number of individual craters within a cluster, and their size-frequency distributions, may reflect either a diversity in fragmentation style, fragility, or internal particle sizes.
Rajšić A, Miljković K, Wójcicka N, et al., 2023, Seismic efficiency and seismic moment for small craters on mars formed in the layered uppermost crust, Journal of Geophysical Research: Planets, Vol: 128, Pages: 1-15, ISSN: 2169-9097
Seismic activity generated by impacts depends on impact conditions and properties of the impact site. Here, we combined mapping of the regolith thickness with numerical impact simulations to better estimate the seismic efficiency and seismic moment generated in small impact events in the uppermost crust on Mars. We used mapping of crater morphology to determine the regolith thickness that craters formed in. We found that local regolith thickness in the late Amazonian units is between 4 and 9 m. Combined with previous estimates for the NASA InSight landing site, we composed a more realistic uppermost crust analog and implemented it in numerical impact simulations. We estimated the seismic efficiency and seismic moment for small craters on Mars impacting a non-porous or fractured bedrock overlaid by 5, 10, or 15 m thick regolith. Seismic energy showed more dependence on target properties. Three orders of magnitude more energy were produced in stronger targets. The seismic moment does not depend on target properties, and we confirm that seismic moment is almost proportional to impact momentum. The resulting seismic moment is in agreement up to a factor of 4 between different target types. We improved the scaling relationships developed from numerical simulations used in seismic moment approximations by constraining its dependence on more realistic target properties.
Dundas CM, Mellon MT, Posiolova LV, et al., 2023, A large new grater exposes the limits of water ice on Mars, Geophysical Research Letters, Vol: 50, Pages: 1-9, ISSN: 0094-8276
Water ice in the Martian mid-latitudes has advanced and retreated in response to variations in the planet's orbit, obliquity, and climate. A 150 m-diameter new impact crater near 35°N provides the lowest-latitude impact exposure of subsurface ice on Mars. This is the largest known ice-exposing crater and provides key constraints on Martian climate history. This crater indicates a regional, relatively pure ice deposit that is unstable and has nearly vanished. In the past, this deposit may have been tens of meters thick and extended equatorward of 35°N. We infer that it is overlain by pore ice emplaced during temporary stable intervals, due to recent climate variability. The marginal survival of ice here suggests that it is near the edge of shallow ice that regularly exchanges with the atmosphere.
North TL, Collins G, Davison T, et al., 2023, The heterogeneous response of Martian meteorite Allan Hills 84001 to planar shock, Icarus, Vol: 390, ISSN: 0019-1035
Impact-generated shock waves can change the physical properties of meteorites and their constituent minerals. Accounting for these effects is key to recovering information about the early solar system from meteorite observations. ALH 84001 is a rare ancient sample from the Martian crust, providing a unique window into the thermal and metamorphic evolution of Mars. A well-studied meteorite, past geochemical and petrologic investigations have attempted to deduce its thermal and impact history with some contradictory results. By simulating the passage of a planar shock wave through a synthetic analog for samples of ALH 84001 using the iSALE-2D shock physics code we have determined the meteorite’s likely thermodynamic and physical response during an impact. Our simulations show that heterogeneous shear heating, induced by the planar shock wave, can produce strong thermal gradients on the sub-millimeter ‘mesoscale’ throughout the meteorite, even in relatively weak shock waves (5 GPa). We are able to place new constraints on deformation events experienced by the meteorite during its time on the parent body, including the maximum pressure ALH 84001 has experienced since it acquired its remanent magnetization and its subsequent ejection from Mars.
Genge MJ, Alesbrook L, Almeida NV, et al., 2023, The fusion crust of the Winchcombe meteorite: A preserved record of atmospheric entry processes, METEORITICS & PLANETARY SCIENCE, ISSN: 1086-9379
On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures.
King AJ, Daly L, Rowe J, et al., 2022, The Winchcombe meteorite, a unique and pristine witness from the outer solar system., Science of Advanced Materials, Vol: 8, Pages: 1-17, ISSN: 1947-2935
Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water.
Davison TM, Collins GS, 2022, Complex crater formation by oblique impacts on the Earth and Moon, Geophysical Research Letters, Vol: 49, Pages: 1-9, ISSN: 0094-8276
Almost all meteorite impacts occur at oblique incidence angles, but the effect of impact angle on crater size is not well understood, especially for large craters. To improve oblique impact crater scaling, we present a suite of simulations of complex crater formation on Earth and the Moon over a range of impact angles, velocities and impactor sizes. We show that crater diameter is larger than predicted by existing scaling relationships for oblique impacts; there is little dependence on obliquity for impacts steeper than 45° from the horizontal. Crater depth, volume and diameter depend on impact angle in different ways—relatively shallower craters are formed by more oblique impacts. Our simulation results have implications for how crater populations are determined from impactor populations and vice-versa. They suggest that existing approaches to account for impact obliquity may underestimate the number of complex craters larger than a given size by as much as one-third.
Stickle AM, DeCoster ME, Burger C, et al., 2022, Effects of impact and target parameters on the results of a kinetic impactor: predictions for the double asteroid redirection test (DART) mission, The Planetary Science Journal, Vol: 3, Pages: 248-248, ISSN: 2632-3338
The Double Asteroid Redirection Test (DART) spacecraft will impact into the asteroid Dimorphos on 2022 September 26 as a test of the kinetic impactor technique for planetary defense. The efficiency of the deflection following a kinetic impactor can be represented using the momentum enhancement factor, β, which is dependent on factors such as impact geometry and the specific target material properties. Currently, very little is known about Dimorphos and its material properties, which introduces uncertainty in the results of the deflection efficiency observables, including crater formation, ejecta distribution, and β. The DART Impact Modeling Working Group (IWG) is responsible for using impact simulations to better understand the results of the DART impact. Pre-impact simulation studies also provide considerable insight into how different properties and impact scenarios affect momentum enhancement following a kinetic impact. This insight provides a basis for predicting the effects of the DART impact and the first understanding of how to interpret results following the encounter. Following the DART impact, the knowledge gained from these studies will inform the initial simulations that will recreate the impact conditions, including providing estimates for potential material properties of Dimorphos and β resulting from DART's impact. This paper summarizes, at a high level, what has been learned from the IWG simulations and experiments in preparation for the DART impact. While unknown, estimates for reasonable potential material properties of Dimorphos provide predictions for β of 1–5, depending on end-member cases in the strength regime.
Posiolova LV, Lognonné P, Banerdt WB, et al., 2022, Largest recent impact craters on Mars: Orbital imaging and surface seismic co-investigation., Science, Vol: 378, Pages: 412-417, ISSN: 0036-8075
Two >130-meter-diameter impact craters formed on Mars during the later half of 2021. These are the two largest fresh impact craters discovered by the Mars Reconnaissance Orbiter since operations started 16 years ago. The impacts created two of the largest seismic events (magnitudes greater than 4) recorded by InSight during its 3-year mission. The combination of orbital imagery and seismic ground motion enables the investigation of subsurface and atmospheric energy partitioning of the impact process on a planet with a thin atmosphere and the first direct test of martian deep-interior seismic models with known event distances. The impact at 35°N excavated blocks of water ice, which is the lowest latitude at which ice has been directly observed on Mars.
Luther R, Raducan S, Burger C, et al., 2022, Momentum enhancement during kinetic impacts in the low-intermediate-strength regime: benchmarking & validation of impact shock physics codes, The Planetary Science Journal, Vol: 3, Pages: 1-14, ISSN: 2632-3338
In September 2022, the DART spacecraft (NASA’s contribution to the Asteroid Impact & Deflection Assessment collaboration, AIDA) will impact the asteroid Dimorphos, the secondary in the Didymos system. The crater formation and material ejection will affect the orbital period. In 2027, Hera (ESA’s contribution to AIDA) will investigate the system, observe the crater caused by DART, and characterise Dimorphos. Before Hera’s arrival, the target properties are not well constrained. The relationships between observed orbital change and specific target properties are not unique, but Hera’s observations will add additional constraints for the analysis of the impact event, which will narrow the range of feasible target properties. In this study, we use three different shock physics codes to simulate momentum transfer from impactor to target and investigate the agreement between the results from the codes for well defined target materials. In contrast to previous studies, care is taken to use consistent crushing behaviour (e.g., distension as a function of pressure) for a given porosity for all codes. First, we validate the codes against impact experiments into a regolith simulant. Second, webenchmark the codes at the DART impact scale for a range of target material parameters (10-50% porosity, 1.4 - 100 kPa cohesion). Aligning the crushing behaviour improves theconsistency of the derived momentum enhancement between the three codes to within +/- 5%for most materials used. Based on the derived mass-velocity distributions from all three codes, we derive scaling parameters that can be used for studies of the ejecta curtain.
Garcia RF, Daubar IJ, Beucler É, et al., 2022, Newly formed craters on Mars located using seismic and acoustic wave data from InSight, Nature Geoscience, Vol: 15, Pages: 774-780, ISSN: 1752-0894
Rae ASP, Kenkmann T, Collins GS, et al., 2022, Dynamic strength, fragmentation, and the impact cratering process
<jats:p>&lt;p&gt;&lt;strong&gt;Introduction:&lt;/strong&gt;&amp;#160; During impact cratering, target materials are subjected to extreme deformation conditions. Brittle deformation under these conditions, where strain rates can exceed 10&lt;sup&gt;1&lt;/sup&gt; to 10&lt;sup&gt;2&lt;/sup&gt; s&lt;sup&gt;&amp;#173;&amp;#173;&lt;/sup&gt;&lt;sup&gt;-&lt;/sup&gt;&lt;sup&gt;1&lt;/sup&gt;, is rate-sensitive. Typically, rocks are stronger when deformed at high strain-rate conditions . This occurs because fracture propagation has a limited velocity; at high loading rates, the weakest flaws in a material are not able to cause failure before other, increasingly strong flaws are activated. This results in significant changes to mechanical properties and causes fragmentation of the target material [2, 3]. Dynamic compressive strength and fragmentation in brittle materials is not currently implemented in numerical impact simulations.&lt;/p&gt;&lt;p&gt;In this study, we present results of high strain rate mechanical tests to determine the characteristic strain rate for rate-dependent brittle failure and dynamic strength increase, and the fragment size and shape distributions that result from failure at these conditions. We investigated a variety of rock types and considered whether the fragment characteristics can be used as diagnostic indicators of loading conditions during brittle failure. In addition, we use numerical impact simulations to assess the significance of dynamic strength increase and compressive fragmentation during impact cratering at a variety of scales.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;Mechanical data and samp
Ormö J, Raducan SD, Jutzi M, et al., 2022, Boulder exhumation and segregation by impacts on rubble-pile asteroids, Earth and Planetary Science Letters, Vol: 594, Pages: 1-12, ISSN: 0012-821X
Small asteroids are often considered to be rubble-pile objects, and such asteroids may be the most likely type of Near Earth Objects (NEOs) to pose a threat to Earth. However, impact cratering on such bodies is complex and not yet understood. We perform three low-velocity (≈ 400 m/s) impact experiments in granular targets with and without projectile-size boulders. We conducted SPH simulations that closely reproduced the impact experiments.Our results suggest that cratering on heterogeneous targets displaces and ejects boulders, rather than fragmenting them, unless directly hit. We also see indications that as long as the energy required to disrupt the boulder is small compared to the kinetic energy of the impact, the disruption of boulders directly hit by the projectile may have minimal effect on the crater size.The presence of boulders within the target causes ejecta curtains with higher ejection angles compared to homogeneous targets. At the same time, there is a segregation of the fine ejecta from the boulders, resulting in boulders landing at larger distances than the surrounding fine grained material. However, boulders located in the target near the maximum extent of the expanding excavation cavity are merely exhumed and distributed radially around the crater rim, forming ring patterns similar to the ones observed on asteroids Itokawa, Ryugu and Bennu. Altogether, on rubble-pile asteroids this process will redistribute boulders and finer-grained material heterogeneously, both areally around the crater and vertically in the regolith. In the context of a kinetic impactor on a rubble-pile asteroid and the DART mission, our results indicate that the presence of boulders will reduce the momentum transfer compared to a homogeneous, fine-grained target.
Wiggins SE, Johnson BC, Collins GS, et al., 2022, Widespread impact-generated porosity in early planetary crusts., Nature Communications, Vol: 13, Pages: 1-6, ISSN: 2041-1723
NASA's Gravity Recovery and Interior Laboratory (GRAIL) spacecraft revealed the crust of the Moon is highly porous, with ~4% porosity at 20 km deep. The deep lying porosity discovered by GRAIL has been difficult to explain, with most current models only able to explain high porosity near the lunar surface (first few kilometers) or inside complex craters. Using hydrocode routines we simulated fracturing and generation of porosity by large impacts in lunar, martian, and Earth crust. Our simulations indicate impacts that produce 100-1000 km scale basins alone are capable of producing all observed porosity within the lunar crust. Simulations under the higher surface gravity of Mars and Earth suggest basin forming impacts can be a primary source of porosity and fracturing of ancient planetary crusts. Thus, we show that impacts could have supported widespread crustal fluid circulation, with important implications for subsurface habitable environments on early Earth and Mars.
North TL, Muxworthy AR, Collins GS, et al., 2022, THERMOREMANENT MAGNETISATION RECORDED DURING IMPACT-INDUCED COMPACTION EXPERIMENTS ON SYNTHETIC CHONDRITIC METEORITES, LSPC, Publisher: WILEY, ISSN: 1086-9379
Genge MJ, Alesbrook LS, Almeida NV, et al., 2022, THE FUSION CRUST OF THE WINCHCOMBE METEORITE: VIGOROUS DEGASSING DURING ATMOSPHERIC ENTRY., Publisher: WILEY, ISSN: 1086-9379
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&#160;
<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 . 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  created a relatively large crater (~14 m diameter) despite the presence of large boulders close to the impact location .&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 . 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 . ESA&amp;#8217;s Hera mission  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
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