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Rubble-pile asteroids may be the type of near-Earth object most likely to threaten Earth in a future collision event. Small-scale impact experiments and numerical simulations for large-scale impacts were conducted to clarify the size ratio of the boulder/projectile diameter effects on ejecta size–velocity distribution. A series of small-scale impact cratering experiments were performed on porous gypsum–basalt targets at velocities of 2.3 to 5.5 km·s−1. Three successive ejection processes were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient and cratering size were measured. A three-dimensional numerical model reflecting the random distribution of the interior boulders of the rubble-pile structure asteroid is established. The size ratio (length to diameter) of the boulder size inside the asteroid to the projectile diameter changed from 0.25 to 1.7. We conducted a smoothed particle hydrodynamics numerical simulation in the AUTODYN software to study the boulder size effect on the ejecta size–velocity distribution. Simulation results suggest that the microscopic porosity on regolith affects the propagation of shock waves and reduces the velocity of ejecta. Experiments and numerical simulation results suggest that both excavation flow and spalling ejection mechanism can eject boulders (0.12–0.72 m) out of the rubble-pile asteroid. These experiments and simulation results help us select the potential impact site in a planetary defense scenario and reduce deflection risk. are comprised primarily of boulders of a range of sizes. [ABSTRACT FROM AUTHOR]

It is generally hard to put robust constraints on progenitor masses of supernovae and supernova remnants (SNRs) observationally, while they offer tantalizing clues to understanding explosion mechanisms and mass distribution. Our recent study suggests that "shell merger," which is theoretically expected for stellar evolution, can appreciably affect the final yields of intermediate-mass elements (IMEs; such as Ne, Mg, and Si). In light of this, here we report the results of the X-ray spectral analysis of a Galactic SNR G359.0−0.9, whose abundance pattern may possibly be anomalous according to a previous study. Our spectroscopy using all the available data taken with XMM-Newton reveals that this remnant is classified as a Mg-rich SNR because of its high Mg-to-Ne ratio ( Z Mg / Z Ne = 1.90 − 0.19 + 0.27 ; mass ratio 0.66 − 0.07 + 0.09 ) and conclude that the result cannot be explained without the shell merger. By comparing the observation with theoretical calculations, we prefer the so-called Ne-burning shell intrusion and in this case, the progenitor mass M ZAMS is likely <15 M ⊙. We confirm the result also with our new molecular-line observations with the Nobeyama 45 m telescope: G359.0−0.9 is located in the Scutum–Centaurus arm (2.66–2.94 kpc) and in this case, the resultant total ejecta mass ∼6.8 M ⊙ is indeed consistent with the above estimate. Our method using mass ratios of IMEs presented in this paper will become useful to distinguish the type of shell merger, the Ne-burning shell intrusion, and the O-burning shell merger, for future SNR studies. [ABSTRACT FROM AUTHOR]

Satellites orbiting in low Earth orbits face potential threats from space debris. To mitigate this risk, a Whipple shield is employed to shield satellites from potential hyper-velocity impacts caused by debris of varying sizes and speeds. Typically, these protective systems use spaced aluminum plates affixed to the satellite's exterior. Ongoing advancements in this field include exploring alternative materials such as foam, cellular cores, and ceramics to replace aluminum in plate construction. This study introduces a hybrid configuration featuring a Newtonian fluid-filled, high-performance fiber-reinforced polymer core positioned between the aluminum alloy plates, aiming to enhance the Whipple shield's overall shielding effectiveness. The analysis of hyper-velocity impacts was performed numerically using ANSYS Autodyn® computational software. Spherical projectiles made of stainless steel, ranging in diameter from 2 mm to 4 mm, were selected for direct collision simulations with the Whipple shield at velocities of 5 km/s, 7 km/s, and 9 km/s. The front and rear plates, each 1 mm thick, were constructed using AA6061-T6. The core, measuring 10 mm in thickness, incorporated multiple plies of Kevlar fiber-reinforced polymer (KFRP), with interplay spacing between successive KFRP plies filled with a Newtonian fluid (water). It was observed that spherical projectiles made of stainless steel with diameter ≥ 3 mm penetrated the rear plate of the whipple shield at the lower velocity of 5 km/s, with enhanced damage as the initial velocity of the projectile was increased from 5 km/s to 9 km/s. The debris cloud was found to scatter the fluid droplets, rupture the successive KFRP layers, with the initial kinetic energy playing a significant role in the severity of the damage. • Hybrid Whipple shield configuration with a Newtonian fluid-filled, high-performance fiber-reinforced polymer core. • Computation of the HVI by spherical projectiles on the shield carried out using Ansys Autodyn®. • Simulations at 5, 7 and 9 km/s with emphasis on energy variation for the projectile and Whipple shield conducted. • Perforation and debris cloud propagation captured during the simulations. [ABSTRACT FROM AUTHOR]

A series of small-scale impact cratering experiments were performed on basalt at velocities of 3.5–6.0 km s−1. The formation and motion process of ejecta were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient values and cratering size were measured. Hydrodynamic simulations in 2D were carried out to replicate the impact conditions of the basalt and calibrate model parameters. The contribution of jet, central cratering, and spalling ejection to momentum enhancement was quantitatively analyzed by simulation. Simulation results show that: the mass and the momentum of the jet are less than 1 % of the projectile mass, and the initial momentum, can be ignored. For craters in small-sized basalt, the momentum enhancement mainly comes from the spall region ejecta. The formation mechanism of ejecta at different stages was analyzed based on the shock wave and jet theory. An analytical model is developed for estimating the velocity and motion of ejecta formation at different stages. The model calculation results of the speed of the ejecta formed in different stages are consistent with the numerical results. The maximum velocity of the ejecta formed in the jet and cratering stage depends on the initial impact velocity and the Hugoniot parameters of the projectile/target material. The minimum velocity of the spallation ejecta is linearly related to the spalling strength of the target. The model provides a fast and simple method to calculate the ejecta velocity and estimate the influence range of ejecta under different impact conditions. • The speed of the jet is greater than the initial impact speed. • The contribution of jet to momentum enhancement can be ignored. • For craters in small-sized, the momentum enhancement and mass mainly come from the spall region ejecta. • A model was developed for estimating the velocity and motion of ejecta. [ABSTRACT FROM AUTHOR]

Safe landings are imperative to accomplish NASA's Artemis goal to enable human exploration on the Moon, including sample collection missions. However, a process known as plume surface interaction (PSI) presents a significant hazard to lunar landings. PSI occurs when the engine exhaust of a lander interacts with the surface ejecting large amounts of regolith particles at high velocities that can interfere with the landing, disturb the surface, and damage hardware. To better understand PSI, the particle impact event (PIE) sensor is being developed to measure the kinetic energy and the flux of ejecta during landings, to quantify the potential damage, and to quantify the ejecta displaced. Multiple parameters were estimated to define the PIE instrument requirements. These estimates demonstrate that ejecta can travel at velocities of up to 800 m/s and impact the surrounding area with energies of up to 400 µJ. A significant amount of ejecta can be deposited several 10 s of meters away from the landing site, modifying the surface and causing dust-related challenges. The PIE sensor will be launched for the first time in an upcoming lunar lander. Then, PIE measurements will be used to improve PSI prediction capabilities and develop mitigation strategies to ensure safe landings. [ABSTRACT FROM AUTHOR]

The Hyper Velocity Impact Experiments of prospective structural materials and shields are necessary to ensure the safety of satellites and spacecraft, particularly in lower earth orbits. The advancement of computational tools has made it simpler to reproduce the hyper velocity impact scenarios by facilitating the change in control parameters during simulations. Numerical models have been extensively used for the impact simulations of metallic target plates that possess isotropic behavior. However, due to the intricate nature of the material models, failure models, shock response, and fracture models, it is more challenging to simulate orthotropic target materials compared to isotropic materials. In this work, a numerical model has been adopted to predict the behavior of orthotropic materials during hyper velocity impact experiments involving spherical aluminum AA2017-T4 projectiles (1 mm in diameter). The orthotropic material comprises a 16-layered sequence of carbon fiber-reinforced epoxy plies in a quasi-isotropic arrangement. The numerical simulations were conducted on the ANSYS Autodyn® finite element software. On comparison of numerical and experimental results, it was observed that perforation diameter from the simulation was in close agreement with that of the experimental at both 2.5 km/s and 5.0 km/s. Additionally, the damage mechanisms (energy absorption) for different failure modes of the laminates were analyzed in detail. Fiber pullout and Fiber debonding were the dominant failure mechanisms contributing to more than 90% of the surface energy. • Multi-layered CFRP laminates subjected to hypervelocity impact (HVI). • Numerical model developed for orthotropic laminates. • HVI simulations at 2.5 km/s and 5 km/s with emphasis on debris propagation. • Katz model for identifying dominant energy absorption mechanism during HVI. [ABSTRACT FROM AUTHOR]

This work focuses on the effect of the interval between two shocks on the ejecta formation from the grooved aluminum (Al1100) surface by using smoothed particle hydrodynamics numerical simulation. Two unsupported shocks are obtained by the plate-impact between sample and two flyers at interval, with a peak pressure of approximately 30 GPa for each shock. When the shock interval varies from 2.11 to 7.67 times the groove depth, the bubble velocity reduces to a constant, and the micro jetting factor RJ from spike to bubble exhibits a non-monotonic change that decreases initially and then increases. At a shock interval of 3.6 times the groove depth, micro jetting factor RJ from spike to bubble reaches its minimum value of approximately 0.6. While, the micro jetting factor RF from spike to free surface decreases linearly at first, and stabilizes around 0.25 once the shock interval surpasses 4.18 times the groove depth. When the shock interval is less than 4.18 times the groove depth, the unloading wave generated by the breakout of the first shock wave is superimpose with the unloading part of the second shock wave to form a large tensile area.

The present work is part of a systematic mineralogical and petrographic characterization of mica-bearing xenoliths from Somma-Vesuvius volcano (Roman Magmatic Province, southern Italy). Skarns, composite skarns-marbles and cumulates from Pompeii Plinian eruption (AD 79), and skarns and syenite from Avellino eruption (3945 ± 10 cal yr BP) were investigated to define the crystal chemistry of the Somma-Vesuvius trioctahedral micas and to draw inferences on petrogenetic processes to which they were subjected. Xenoliths were characterized by means of polarized optical microscopy, scanning electron microscopy (SEM-EDS), X-ray powder diffraction (XRPD), and bulk-rock geochemical analyses. Mica crystals were studied using electron microprobe analysis (EMPA) and single-crystal X-ray diffraction (SCXRD). Micas from skarns are variably associated with Mg ± Ca silicates (clinopyroxene, vesuvianite, humite, clinohumite, chondrodite, forsterite, and garnet), other sporadic silicates (anorthite, sodalite, titanite, and britholite), apatite, calcite, various types of oxides, as well as rare sulfides and halides. In composite skarn-marble rocks, the mineral assemblages show some differences compared to skarns, as a lack of clinopyroxene and the presence of dolomite. Cumulate samples consist of mica and clinopyroxene, whereas syenite is mainly composed of mica, K-feldspar, feldspathoids, and clinopyroxene. Together with mica, apatite occurs in all the lithotypes. Trace element arrays are scattered for skarn and composite skarn-marble samples. The REE patterns have a general enrichment in light (La, Ce, Pr, Nd) and medium (Sm, Eu, Gd, Tb, Dy) rare earth elements, in some cases with slight positive Gd anomaly. Cumulate samples generally have low amounts of Ba, Sr, Zr, and Th, while syenite exhibits low concentrations of trace elements, except for Rb, Cs, and Tl. Mica crystals occurring in the studied xenoliths are phlogopite with different Al and Mg contents at the octahedral site, a negligible tetraferriphlogopite component and variable dehydrogenation degree. All samples belong to the 1M polytype (C2/m and C2 space group) and have a wide range of unit-cell parameters, especially of the c axis [5.3055(1) ≤ a ≤ 5.3218(1) Å, 9.1893(1) ≤ b ≤ 9.2188(4) Å, 10.1803(2) ≤ c ≤ 10.2951(2) Å]. The shortest c-cell parameter pertains to de-hydrogenated phlogopite from Avellino skarn, whereas OH-rich phlogopite from Pompeii composite skarns-marbles has a c-cell parameter that approximates that of the end-member phlogopite. Overall, it is observed that the crystal chemistry of the micas studied here extends the known range of the other Vesuvian micas from the literature. The Ti-depletion and the wide degree of dehydrogenation of phlogopites from skarns and composite skarns-marbles suggest that the studied samples originated under variable pressure conditions. In addition, the presence of humite in the mineral assemblage seems to indicate the occurrence of devolatilization reactions. The scarce mica occurrence in cumulate and mainly in syenite, instead, may depend on pressure conditions in the magma storage system exceeding the mica stability. [ABSTRACT FROM AUTHOR]

Rubble-pile asteroids may be the type of near-Earth object most likely to threaten Earth in a future collision event. Small-scale impact experiments and numerical simulations for large-scale impacts were conducted to clarify the size ratio of the boulder/projectile diameter effects on ejecta size–velocity distribution. A series of small-scale impact cratering experiments were performed on porous gypsum–basalt targets at velocities of 2.3 to 5.5 km·s−1. Three successive ejection processes were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient and cratering size were measured. A three-dimensional numerical model reflecting the random distribution of the interior boulders of the rubble-pile structure asteroid is established. The size ratio (length to diameter) of the boulder size inside the asteroid to the projectile diameter changed from 0.25 to 1.7. We conducted a smoothed particle hydrodynamics numerical simulation in the AUTODYN software to study the boulder size effect on the ejecta size–velocity distribution. Simulation results suggest that the microscopic porosity on regolith affects the propagation of shock waves and reduces the velocity of ejecta. Experiments and numerical simulation results suggest that both excavation flow and spalling ejection mechanism can eject boulders (0.12–0.72 m) out of the rubble-pile asteroid. These experiments and simulation results help us select the potential impact site in a planetary defense scenario and reduce deflection risk. are comprised primarily of boulders of a range of sizes.

Sediments in southern Laos and eastern Thailand confirm that the Australasian tektite strewn field came from an extraterrestrial impact crater on the Bolaven Plateau of southern Laos. The principal evidence is the Bolaven diamicton, a pebbly to bouldery breccia that is thickest and coarsest on the plateau. Tektites, the melted target material strewn widely by the forces of the impact 789.0 ± 1.8 ka ago, lie either within the uppermost part of the diamicton or atop it. On the flanks of the plateau, the basal diamicton often contains clasts from preimpact lavas and gravels and sometimes mantles broken Mesozoic bedrock. Locally, its upper portions contain unweathered boulders of basalt or sandstone. Its sharp upper contact with a thick sandy silt implies that the two beds formed in rapid succession. These characteristics of the Bolaven diamicton show that it resulted primarily from the excavation, comminution, and launch of sandstone and weathered basaltic lavas from a crater on the Bolaven Plateau, and entrained other materials while in transit. [ABSTRACT FROM AUTHOR]

We report the discovery of a geocoronal solar wind charge exchange (SWCX) event corresponding to the well‐known 2006 December 13th coronal mass ejection (CME) event. Strong evidence for the charge exchange origin of this transient diffuse emission is provided by prominent non‐thermal emission lines at energies of O7+, Ne9+, Mg11+, Si12+, Si13+. Especially, a 0.53 keV emission line that most likely arises from the N5+ 1s15p1 → 1s2 transition is detected. Previously, the forecastability of SWCX occurrence with proton flares has been disputed. In this particular event, we found that the SWCX signal coincided with the arrival of the magnetic cloud inside CME, triggered with a time delay after the proton flux fluctuation as the CME shock front passed through the Earth. Moreover, a spacecraft orbital modulation in SWCX light curve suggests that the emission arises close to the Earth. The line of sight was found to always pass through the northern magnetospheric cusp. The SWCX intensity was high when the line of sight passed the dusk side of the cusp, suggesting an azimuthal anisotropy in the flow of solar‐wind ions inside the cusp. An axisymmetric SWCX emission model is found to underestimate the observed peak intensity by a factor of about 50. We suggest this discrepancy is related to the azimuthal anisotropy of the solar‐wind flow in the cusp. Plain Language Summary: We discovered compelling observational evidence of the coronal mass ejection (CME) interacting with Earth's magnetosphere by the Suzaku satellite. The signal arises from a process called charge exchange, in which heavily charged ions within the CME interact with neutral hydrogen within Earth's magnetosphere. This specific process, known as solar wind charge exchange (SWCX), was associated with the CME event occurred on 2006 December 13th during the solar minimum. This event provided us with a unique opportunity to gain insights into the interplanetary consequences of CMEs. Despite a delay relative to the shock wave associated with the CME, the SWCX coincided with the arrival of a magnetic cloud. This suggests that solar wind ions were guided along magnetic field lines into a region near Earth called the cusp, through a process known as magnetic reconnection. Additionally, we observed that SWCX emissions were most pronounced when the satellite's line of sight passed through the dusk region of the cusp. This indicates that the CME ejecta may have followed a path along the Parker spiral—a magnetic field pattern twisted by solar rotation—resulting in the solar wind arriving from a direction distinct from that of the Sun. Key Points: We discover a solar wind charge exchange event with Suzaku X‐ray satellite driven by the 2006‐December‐13th coronal mass ejectionThe solar wind charge exchange (SWCX) occurrence time coincides with the CME magnetic cloud arrival. It is a useful knowledge in space weather forecastingWe modeled the light curve variation of the SWCX. The result indicates that the solar‐wind flow is anisotropic in the cusp [ABSTRACT FROM AUTHOR]

We explore a possible explosion scenario resulting from core collapses of rotating massive stars that leave a black hole by performing radiation-viscous-hydrodynamics simulations in numerical relativity. We take moderately and rapidly rotating compact pre-collapse stellar models with zero-age main-sequence masses of 9 M ⊙ and 20 M ⊙ based on stellar evolution calculations as the initial conditions. We find that viscous heating in the disk formed around the central black hole is the power source for an outflow. The moderately rotating models predict a small ejecta mass of the order of 0.1 M ⊙ and an explosion energy of ≲1051 erg. Due to the small ejecta mass, these models may predict a short-timescale transient with a rise time of 3–5 days. This can lead to a bright (∼1044 erg s−1) transient, like superluminous supernovae in the presence of a dense massive circumstellar medium. For hypothetically rapidly rotating models that have a high mass-infall rate onto the disk, the explosion energy is ≳3 × 1051 erg, which is comparable to or larger than that of typical stripped-envelope supernovae, indicating that a fraction of such supernovae may be explosions powered by black hole accretion disks. The explosion energy is still increasing at the end of the simulations with a rate of >1050 erg s−1, and thus, it may reach ∼1052 erg. A nucleosynthesis calculation shows that the mass of 56Ni amounts to ≳0.1 M ⊙, which, together with the high explosion energy, may satisfy the required amount for broad-lined type Ic supernovae. Irrespective of the models, the lowest value of the electron fraction of the ejecta is ≳0.4; thus, synthesis of heavy r -process elements is not found in our models. [ABSTRACT FROM AUTHOR]

We present JWST NIRCam (F356W and F444W filters) and MIRI (F770W) images and NIRSpec Integral Field Unit (IFU) spectroscopy of the young Galactic supernova remnant Cassiopeia A (Cas A) to probe the physical conditions for molecular CO formation and destruction in supernova ejecta. We obtained the data as part of a JWST survey of Cas A. The NIRCam and MIRI images map the spatial distributions of synchrotron radiation, Ar-rich ejecta, and CO on both large and small scales, revealing remarkably complex structures. The CO emission is stronger at the outer layers than the Ar ejecta, which indicates the re-formation of CO molecules behind the reverse shock. NIRSpec-IFU spectra (3–5.5 μ m) were obtained toward two representative knots in the NE and S fields that show very different nucleosynthesis characteristics. Both regions are dominated by the bright fundamental rovibrational band of CO in the two R and P branches, with strong [Ar vi ] and relatively weaker, variable strength ejecta lines of [Si ix ], [Ca iv ], [Ca v ], and [Mg iv ]. The NIRSpec-IFU data resolve individual ejecta knots and filaments spatially and in velocity space. The fundamental CO band in the JWST spectra reveals unique shapes of CO, showing a few tens of sinusoidal patterns of rovibrational lines with pseudocontinuum underneath, which is attributed to the high-velocity widths of CO lines. Our results with LTE modeling of CO emission indicate a temperature of ∼1080 K and provide unique insight into the correlations between dust, molecules, and highly ionized ejecta in supernovae and have strong ramifications for modeling dust formation that is led by CO cooling in the early Universe.

Safe landings are imperative to accomplish NASA’s Artemis goal to enable human exploration on the Moon, including sample collection missions. However, a process known as plume surface interaction (PSI) presents a significant hazard to lunar landings. PSI occurs when the engine exhaust of a lander interacts with the surface ejecting large amounts of regolith particles at high velocities that can interfere with the landing, disturb the surface, and damage hardware. To better understand PSI, the particle impact event (PIE) sensor is being developed to measure the kinetic energy and the flux of ejecta during landings, to quantify the potential damage, and to quantify the ejecta displaced. Multiple parameters were estimated to define the PIE instrument requirements. These estimates demonstrate that ejecta can travel at velocities of up to 800 m/s and impact the surrounding area with energies of up to 400 µJ. A significant amount of ejecta can be deposited several 10 s of meters away from the landing site, modifying the surface and causing dust-related challenges. The PIE sensor will be launched for the first time in an upcoming lunar lander. Then, PIE measurements will be used to improve PSI prediction capabilities and develop mitigation strategies to ensure safe landings.

The potential effects of soil liquefaction at level ground sites should be evaluated through examining soil element responses of the individual soil layers and system responses of the soil deposits they form. The cyclic responses and postliquefaction volumetric strain of uniform clean sand, sandy gravel, nonplastic silty sand, and nonplastic silt at the element level can be captured in a unified manner using relative density or the state parameter. The depositional environment should be characterized because geologic details, such as soil fabric, which can be discerned through detailed logging of high-quality continuous sampling, are important in evaluating liquefaction effects. Effective stress analysis enables soil system responses that govern the effects of liquefaction, including the formation of ejecta, to be investigated. A calibrated cone penetration test (CPT) procedure employing the liquefaction ejecta demand parameter captures key aspects of system response and provides an estimate of ejecta-induced building settlement. A probabilistic CPT-based procedure for estimating postliquefaction ground settlement is developed using laboratory and field case history databases. Correlations are developed to estimate Dr or ψo to enable use of the laboratory-based volumetric strain models. Adjustment factors enable the procedure to capture field observations of postliquefaction ground settlement. The proposed ground settlement procedure is combined with shear and ejecta-induced settlement procedures to estimate liquefaction-induced building settlement. [ABSTRACT FROM AUTHOR]

Very few impact craters on Earth have preserved proximal ejecta (ejecta blanket), which when present help us to better understand the cratering processes when asteroid hits Earth. The 458 Ma old Lockne impact structure consists of a 7.5‐km wide nested crater in the crystalline basement surrounded by an approximately 3‐km wide brim developed in the upper sedimentary target. The asteroid struck a marine environment with 500 m sea water, 50‐m lithified limestone, and 30 m of Cambrian clay covering a peneplainized crystalline basement. The transient crater that developed in rock and water obtained a "soup‐plate" shape and reached about 7 km from the impact crater center, the farthest on the down‐range side. The brim of the soup‐plate was partially stripped of Ordovician limestone and water before the emplacement of inner impact crater ejecta. Most of the ejecta rest upon the Cambrian clay (today shale). The asteroid struck obliquely from the east, which is reflected in the ejecta distribution. The proximal ejecta field is divided into two crescent‐shaped areas to the northwest and southwest of the nested crater and covers 26 km2. Resistivity profiles, mapping, and core drilling show that the thickness of the ejecta masses range between 30 and 50 m with a total volume of about 1 km3. They were not re‐worked by the resurge. They represent roughly 26 vol% of the calculated excavated volume of crystalline rocks. Thus, it can be concluded that the Lockne impact crater has a well‐preserved ejecta blanket. Plain Language Summary: Very few terrestrial impact structures have preserved ejecta blankets. Generally, the strong erosion affecting Earth's surface, and the often frail character of the ejected material, hampers their preservation. Despite its high age of 458 million years, the Lockne impact structure is a rare exception due to a combination of a target with 500 m of seawater, 80 m of limestone, and 30 m of clay resting on a flat granitic basement, and rapid burial by subsequent marine sedimentation. The seawater was expelled outward, and the expanding crater reached deep into the basement. Limestone surrounding the basement crater was blasted off like a carpet. The impact structure obtained a "soup‐plate" shape with a 7.5 km wide nested crater in the basement surrounded by a 3.5‐km wide, shallow "brim." The more difficultly mobilized clay and exposed basement rock of the brim got bombarded by granitic ejecta forming a blanket. After less than 2 min, the 2 km high water wall collapsed and water rushed back to flood the dry impact crater, leaving only larger ejecta fragments and more consolidated parts of the ejecta blanket. This sequence of events only occurs in marine and stratified target settings, such as at Lockne. Key Points: The Lockne marine impact structure uniquely preserves its proximal ejecta blanketThe well‐preserved proximal ejecta represents roughly 26 vol% of the calculated excavated volume of crystalline rocksThe structure and its ejecta reveal the sequence of events that take place when an asteroid hits a marine, sediment, and crystalline target [ABSTRACT FROM AUTHOR]

It is generally hard to put robust constraints on progenitor masses of supernovae and supernova remnants (SNRs) observationally, while they offer tantalizing clues to understanding explosion mechanisms and mass distribution. Our recent study suggests that “shell merger,” which is theoretically expected for stellar evolution, can appreciably affect the final yields of intermediate-mass elements (IMEs; such as Ne, Mg, and Si). In light of this, here we report the results of the X-ray spectral analysis of a Galactic SNR G359.0−0.9, whose abundance pattern may possibly be anomalous according to a previous study. Our spectroscopy using all the available data taken with XMM-Newton reveals that this remnant is classified as a Mg-rich SNR because of its high Mg-to-Ne ratio ( ${Z}_{\mathrm{Mg}}/{Z}_{\mathrm{Ne}}={1.90}_{-0.19}^{+0.27};$ mass ratio ${0.66}_{-0.07}^{+0.09}$ ) and conclude that the result cannot be explained without the shell merger. By comparing the observation with theoretical calculations, we prefer the so-called Ne-burning shell intrusion and in this case, the progenitor mass M _ZAMS is likely

The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H , G _1 , G _2 parameterization.

Impact-derived ejecta covers most of the lunar surface, originating from recent impacts through to the beginning of the geologic record. Despite how common ejecta is, accurate measurements of ejecta thickness are difficult to obtain, and existing estimates of ejecta thickness vary widely. This study uses excavation by meter-scale impacts on the fresh ejecta blankets of larger, kilometer-scale impacts to make point measurements of ejecta thickness. We estimate ejecta thickness at the rims of 73 lunar craters (0.1–4.8 km diameter) and create isopach maps of ejecta thickness for three craters. We derive an equation for ejecta thickness, $t=0.14\pm 0.062{R}^{(0.77\pm 0.080)}{\left(r/R\right)}^{(-B)}$ , where r is the horizontal distance from the center of the crater, R is the center-to-rim crater radius, and B describes the rate at which ejecta thickness decays with radial distance. Our average value for B (2.8 ± 0.1) is similar to previous work, though we observe that B can vary significantly within an ejecta blanket.

Supernova (SN) 1987A offers a unique opportunity to study how a spatially resolved SN evolves into a young SN remnant. We present and analyze Hubble Space Telescope (HST) imaging observations of SN 1987A obtained in 2022 and compare them with HST observations from 2009 to 2021. These observations allow us to follow the evolution of the equatorial ring (ER), the rapidly expanding ejecta, and emission from the center over a wide range in wavelength from 2000 to 11,000 Å. The ER has continued to fade since it reached its maximum ∼8200 days after the explosion. In contrast, the ejecta brightened until day ∼11,000 before their emission levelled off; the west side brightened more than the east side, which we attribute to the stronger X-ray emission by the ER on that side. The asymmetric ejecta expand homologously in all filters, which are dominated by various emission lines from hydrogen, calcium, and iron. From this overall similarity, we infer the ejecta are chemically well mixed on large scales. The exception is the diffuse morphology observed in the UV filters dominated by emission from the Mg ii resonance lines that get scattered before escaping. The 2022 observations do not show any sign of the compact object that was inferred from highly ionized emission near the remnant’s center observed with JWST. We determine an upper limit on the flux from a compact central source in the [O iii ] HST image. The nondetection of this line indicates that the S and Ar lines observed with JWST originate from the O free inner Si–S–Ar-rich zone and/or that the observed [O iii ] flux is strongly affected by dust scattering.

Coronal mass ejections (CMEs) are large-scale eruptions with a typical radial size at 1 au of 0.21 au but their angular width in interplanetary space is still mostly unknown, especially for the magnetic ejecta (ME) part of the CME. We take advantage of STEREO-A angular separation of 20°–60° from the Sun–Earth line from 2020 October to 2022 August, and perform a two-part study to constrain the angular width of MEs in the ecliptic plane: (a) we study all CMEs that are observed remotely to propagate between the Sun–STEREO-A and the Sun–Earth lines and determine how many impact one or both spacecraft in situ, and (b) we investigate all in situ measurements at STEREO-A or at L1 of CMEs during the same time period to quantify how many are measured by the two spacecraft. A key finding is that out of 21 CMEs propagating within 30° of either spacecraft only four impacted both spacecraft and none provided clean magnetic cloud-like signatures at both spacecraft. Combining the two approaches, we conclude that the typical angular width of an ME at 1 au is ∼20°–30°, or 2–3 times less than often assumed and consistent with a 2:1 elliptical cross section of an ellipsoidal ME. We discuss the consequences of this finding for future multi-spacecraft mission designs and for the coherence of CMEs.

With the increasing number of binary asteroid systems being discovered, ejecta studies must expand from solely investigating single-body systems to modeling more complex multiple-body systems. For example, the Double Asteroid Redirection Test provides an opportunity to study the dynamics of a debris cloud around Didymos and Dimorphos, a near-Earth binary asteroid system. Here we simulate 72 variations on the Didymos system in order to categorize types of ejecta outcomes and analyze the influence of the varying system parameters on each outcome. We have varied five parameters: the system separation, the mass ratio between the two bodies, the impact location, the target-body shape, and the target-body rotation period. The resulting provenance maps of the final ejecta distributions were blindly sorted into five categories, while the resulting cumulative distribution functions (CDFs), describing the rate at which particles hit the surface, were blindly sorted into eight categories. We count the occurrences of the parameter values in each of the categories and apply a Cramer’s V statistical test to evaluate the significance of the association between each varied effect and the overall grouping of the provenance maps and CDFs. We conclude that more dominant effects, such as a small rotation period, produce notably similar ejecta distributions that result in being assigned to the same category. Less dominant effects, such as target-body location, are sorted into several categories due to the larger influence of varying dominant effects.

The paper presents the results of model calculations of impact craters ejecta thickness variations in the south polar region of the Moon from the south pole to 70° S for craters of Nectarian, Imbrian, Eratosthenian, and Copernican ages. This work does not consider pre-Nectarian craters since younger deposits often hide the boundaries of their ejecta. Housen, Sharpton and Fassett models were chosen to estimate the power. The first was used for craters larger than 45 km in diameter, the second for smaller craters (from 3 to 45 km), and the third for the Mare Orientale basin. During estimation, the mixing factor of ejecta with the underlying regolith (factor μ) was considered. As a result, maps of ejecta thicknesses were produced for the Moon's south polar region. They provide an opportunity for quantitative estimation of the various aged impact events' contribution to the formation of polar regolith and, accordingly, to determine the dominant source (sources) of material in a particular area, not least in the proposed landing sites. [ABSTRACT FROM AUTHOR]

When a spacecraft fires its thrusters near the surface of a celestial body, objects on the surface of the body are scattered in the vertical direction and adhere to the cameras and ranging instruments mounted on the spacecraft, degrading their performance. In order to establish a future spacecraft design theory that is less sensitive to the scattering of surface objects, we first investigate the scattering factors and scattering tendencies of surface objects. We predict that celestial surface objects are scattered according to the wall angle of the crater created by the thruster plume. The relationship between the crater shape and the object dispersal angle is not fully understood. Mechanisms of crater formation include viscous erosion, which creates craters with a small wall angle, and bearing capacity failure, which creates craters with a large wall angle. Here, we experimentally clarify the transition point between the two crater formation mechanisms when the thruster plume penetrates soil with various shear strength values. We find that the objects disperse along the crater wall for both mechanisms. Based on the results, we examine measures for preventing the spacecraft from being hit by scattered surface objects. [ABSTRACT FROM AUTHOR]

Kinetic impacts on a binary asteroid will produce ejecta debris as well as causing a disturbance to the spin-orbit motion of the binary components. Understanding the complex interactions between the ejecta and the binary system can be crucial to both theoretical study and mission design. In this paper, we develop a detailed model for the dynamical evolution of ejecta within a binary asteroid system, in which we combined various perturbations on the ejecta and considered the collisional process with the asteroid. Taking an example scenario like the DART impact, we calculated the fate of ejecta from size 0.01 mm to 10 m and analyzed the distribution of their final deposition locations. The results show that ejecta with diameter less than 0.1 mm escape quickly under the influence of solar radiation pressure, while ejecta of larger size survive longer, i.e., a few cycles in the binary system for more than 400 days. We analyzed the influence of the coefficient of restitution between ejecta and asteroid, and found more damped collisions would allow the ejecta to survive longer in orbit. We also studied the effect of the tumbling rotation of the secondary on the distribution of ejecta on the surface of the secondary, the results suggest that a tumbling rotational state causes obvious changes in Dimorphos' surface slope, which, however, are not sufficient for triggering surface landslides. In addition, the influence of the internal structure of the primary on the evolution of the ejecta is studied, and we show it has little effect on the evolution of the ejecta but does affect the distribution of ejecta on the surface of the primary. This is due to the change of the distribution of relative acceleration on the surface of the primary, which changes the regions where the ejecta can remain. [ABSTRACT FROM AUTHOR]

This study identifies 140 distal impact melt features with definitive flow morphology and determines them to originate from Tycho crater. The furthest of these impact melt deposits are located ∼450 km from Tycho (approximately ten crater radii). The impact melt deposits that we report in this study exhibit definitive melt flow features such as surface cracks, ridges, and block-rich margins. We typically found melt features with these morphologies on steep, Tycho-facing slopes. However, this population does not represent the full extent of distal melt that is likely to have been produced in the Tycho impact. Pond and veneer morphologies on nearby shallow slopes often suggest the presence of additional melt without either elevated Lunar Reconnaissance Orbiter Diviner instrument Rock Abundance fractions or distinctive melt flow morphologies in high-resolution imagery. We propose that topography is a controlling factor for the development of definitive melt flow morphologies in distal impact melts. The melt features that we identified in this work highlight the capacity for a single, large cratering event to resurface terrains at great distances from the crater. Modeling the production and distribution of distal impact melts, therefore, is an important next step in understanding the role that they play in the resurfacing history of airless bodies like the Moon. • Identifies 140 distal Tycho impact melt features with definitive flow morphologies. • Most distal melt flow features detected on steep, Tycho-facing slopes. • Distal impact melt is more difficult to detect when located on shallow slopes. • There is potentially much more distal impact melt than is currently detected. [ABSTRACT FROM AUTHOR]

Understanding the mechanisms governing the interaction of high-velocity projectiles and sand targets is important for numerous applications and industries. The high-velocity penetration of sand targets is known to be controlled by micromechanical phenomena; however, our quantification of these phenomena and our understanding of water saturation effects on target response is presently limited. To help improve our understanding of these phenomena, we performed impact experiments on wet and dry sand with in-situ and post-mortem analysis in a two-stage gas gun with varying impact chamber pressures. For in-situ analysis, we developed and used a novel experimental method for measuring projectile depth and three-dimensional displacement fields from orthogonal flash X-ray images acquired during the penetration process. We also employed in-situ high-speed imaging of ejecta. For post-mortem analysis, we examined final depths of penetration, particle size distributions, and permanent penetrator deformation. We found that impacts into wet sand targets featured enhanced sand displacements around projectiles, enhanced ejecta, and enhanced intermediate and final depths of penetration as compared to impacts into dry targets. We also found that impacts into wet targets led to less particle breakage than impacts into dry targets. Target chamber pressure was found to significantly influence final depth of penetration, likely through a fluidization process as air and fluid escaped the sample's pores to equilibrate with the surrounding chamber pressure after initial impact. We discuss our findings in the context of existing literature and discuss the hypothesized origin of several of our observations with support from modeling efforts described elsewhere. • Projectiles penetrate deeper into wet sand than they do in dry sand. • Dry sand features more breakage and flow around projectiles than wet sand. • Impact chamber pressure significantly affects intermediate and final depths of penetration. • Two flash X-ray images can be used to reconstruct 3D flow fields during penetration. [ABSTRACT FROM AUTHOR]

NGC 6302 (The Butterfly Nebula) is an extremely energetic and rapidly expanding bipolar planetary nebula (PN). If the central source is a single star, then its apparent location in an H-R diagram places it among the most massive, hottest, and presumably rapidly evolving of all central stars of PNe. Our proper motion study of NGC 6302, based on Hubble Space Telescope WFC3 images spanning 11 yr, has uncovered at least four different pairs of uniformly expanding internal lobes ejected at various times and orientations over the past two millennia at speeds ranging from 10–600 km s ^−1 . In addition, we find a pair of collimated off-axis flows in constant motion at ∼770 ± 100 km s ^−1 within which bright [Fe ii ] feathers are conspicuous. Combining our results with those previously published, we find that the ensemble of flows has an ionized mass >0.1 M _⊙ and its kinetic energy, between 10 ^46 and 10 ^48 erg, lies at the upper end of gravity-powered PNe ejection processes such as stellar mergers or mass accretion. We assemble our results into a plausible historical timeline of ejections from the nucleus and suggest that the ejections are powered by gravitational infall.

We explore a possible explosion scenario resulting from core collapses of rotating massive stars that leave a black hole by performing radiation-viscous-hydrodynamics simulations in numerical relativity. We take moderately and rapidly rotating compact pre-collapse stellar models with zero-age main-sequence masses of 9 M _⊙ and 20 M _⊙ based on stellar evolution calculations as the initial conditions. We find that viscous heating in the disk formed around the central black hole is the power source for an outflow. The moderately rotating models predict a small ejecta mass of the order of 0.1 M _⊙ and an explosion energy of ≲10 ^51 erg. Due to the small ejecta mass, these models may predict a short-timescale transient with a rise time of 3–5 days. This can lead to a bright (∼10 ^44 erg s ^−1 ) transient, like superluminous supernovae in the presence of a dense massive circumstellar medium. For hypothetically rapidly rotating models that have a high mass-infall rate onto the disk, the explosion energy is ≳3 × 10 ^51 erg, which is comparable to or larger than that of typical stripped-envelope supernovae, indicating that a fraction of such supernovae may be explosions powered by black hole accretion disks. The explosion energy is still increasing at the end of the simulations with a rate of >10 ^50 erg s ^−1 , and thus, it may reach ∼10 ^52 erg. A nucleosynthesis calculation shows that the mass of ^56 Ni amounts to ≳0.1 M _⊙ , which, together with the high explosion energy, may satisfy the required amount for broad-lined type Ic supernovae. Irrespective of the models, the lowest value of the electron fraction of the ejecta is ≳0.4; thus, synthesis of heavy r -process elements is not found in our models.

We model the observed charge states of the elements C, O, Mg, Si, and Fe in the ejecta of coronal mass ejections (CMEs). We concentrate on “halo” CMEs observed in situ by the Advanced Composition Explorer/Solar Wind Ion Composition Spectrometer to measure ion charge states, and also remotely by the Solar Terrestrial Relations Observatory when in near quadrature with the Earth, so that the CME expansion can be accurately specified. Within this observed expansion, we integrate equations for the CME ejecta ionization balance, including electron heating parameterized as a fraction of the kinetic and gravitational energy gain of the CME. We also include the effects of non-Maxwellian electron distributions, characterized as a κ function. Focusing first on the 2010 April 3 CME, we find a somewhat better match to the observed charge states with κ close to the theoretical minimum value of κ = 3/2, implying a hard spectrum of nonthermal electrons. Similar but more significant results come from the 2011 February 15 event, although it is quite different in terms of its evolution. We discuss the implications of these values, and of the heating required, in terms of the magnetic reconnection Lundquist number and anomalous resistivity associated with CME evolution close to the Sun.

We present optical, radio, and X-ray observations of a rapidly evolving transient SN2019wxt (PS19hgw), discovered during the search for an electromagnetic counterpart to the gravitational-wave (GW) trigger S191213g. Although S191213g was not confirmed as a significant GW event in the off-line analysis of LIGO-Virgo data, SN2019wxt remained an interesting transient due to its peculiar nature. The optical/near-infrared (NIR) light curve of SN2019wxt displayed a double-peaked structure evolving rapidly in a manner analogous to currently known ultrastripped supernovae (USSNe) candidates. This double-peaked structure suggests the presence of an extended envelope around the progenitor, best modeled with two components: (i) early-time shock-cooling emission and (ii) late-time radioactive ^56 Ni decay. We constrain the ejecta mass of SN2019wxt at M _ej ≈ 0.20 M _⊙ , which indicates a significantly stripped progenitor that was possibly in a binary system. We also followed up SN2019wxt with long-term Chandra and Jansky Very Large Array observations spanning ∼260 days. We detected no definitive counterparts at the location of SN2019wxt in these long-term X-ray and radio observational campaigns. We establish the X-ray upper limit at 9.93 × 10 ^−17 erg cm ^−2 s ^−1 and detect an excess radio emission from the region of SN2019wxt. However, there is little evidence for SN1993J- or GW170817-like variability of the radio flux over the course of our observations. A substantial host-galaxy contribution to the measured radio flux is likely. The discovery and early-time peak capture of SN2019wxt in optical/NIR observations during EMGW follow-up observations highlight the need for dedicated early, multiband photometric observations to identify USSNe.

A cone penetration test (CPT)-based procedure to estimate liquefaction-induced ejecta severity is developed. The liquefaction ejecta demand parameter (LD) captures the amount of upward seepage pressure that can produce artesian flow due to elevated excess hydraulic head, and the crust layer resistance parameter (CR) captures the strength and thickness of the nonliquefiable crust layer. The procedure is examined using 176 well-documented field case histories consisting of thick, clean sand, and stratified silty soil sites in Christchurch. LD tends to increase systematically as ejecta severity increases at the thick, clean sand sites, and low LD values are estimated at stratified soil sites that did not produce ejecta, which resolves the apparent overestimation by other liquefaction indices at stratified soil sites. CR improves the reliability of the procedure by differentiating the performance of sites with and without a competent crust layer overlying a thick liquefiable layer with a high LD value. The proposed LD–CR liquefaction ejecta severity chart separates cases with severe or extreme ejecta, which have high LD and low CR values, from cases with minor or no ejecta, which have low LD and high CR values. [ABSTRACT FROM AUTHOR]

Boulder falls are an archives of recent surface activity on Mars, however, determining how recently they fell remains elusive. Our multitemporal HiRISE image analysis shows that new tracks are characterized by a herringbone‐like ejecta pattern at each boulder bounce that we call boulder fall ejecta (BFE). First systematic survey of BFE revealed ∼4,500 tracks whose total integrated track length is ∼900 km. Our BFE longevity analysis reveals that these tracks likely formed in the last few decades. From few examples we also observed slope streaks originating from BFE tracks, providing additional evidence favoring a dry origin theory. BFE fade in as little as ∼2 to 4 Mars years, whereas, others can persist >6 Mars years suggesting differential weathering. Nearly 30% of BFE are observed in the Cerberus Fossae region, which suggests it is one of the most seismically active regions. Thus, BFE can be used to recognize very recent surface processes on planetary surfaces. Plain Language Summary: High‐resolution images of Mars have revealed numerous boulder falls on the surface. Here, we systematically surveyed images from 2006 to 2020 to find recent boulder falls which have ejecta. The images of the same place taken at different times, revealed that all new boulder falls have ejecta which we call boulder fall ejecta (BFE). We searched all the images and found BFE present in large numbers suggesting recent falls are common and widespread. Our results revealed that on Mars it takes ∼2 to 4 Mars years (4–8 Earth years) for BFE to disappear, whereas on Earth BFE are rarely preserved. We found that the Cerberus Fossae region adjacent to NASA's InSight lander landing site hosts nearly 30% of BFE, suggesting it is a currently active regions on Mars. Key Points: Comprehensive multitemporal HiRISE image analysis revealed all new boulder falls have ejecta along the track termed as boulder fall ejecta (BFE)Approximately 4,500 tracks with total integrated length of ∼900 km formed in last few decades, 30% BFE located in Cerberus Fossae suggests active regionSome BFE fade within 2–4 Mars year and few persist >6 Mars year, evidence for slope streaks originating from BFE tracks support dry theory [ABSTRACT FROM AUTHOR]

We use gravity data from NASA's GRAIL mission to characterize the porosity structure of the upper lunar crust. We analyze the gravitational anomalies produced by the porosity of craters with diameters D between 10 and 30 km. We find that the gravitational signature of craters changes significantly at D=16.4−0.6+1.4 $D=16.{4}_{-0.6}^{+1.4}$ km, which is related to a discrete change in porosity at a depth ∼3–5 km. We propose that this discrete porosity change reveals the location of the boundary between large‐scale basin ejecta and the deeper less porous portion of the megaregolith, known as the structurally disturbed crust. The ejecta thickness can help constrain models of material transport and mixing on the Moon and, because the ejecta layer acts as an insulating blanket, models of heat flow and magmatism. Plain Language Summary: The amount of porosity, in a planet or Moon's crust controls how magma and heat are transferred through it. We use gravity data from NASA's GRAIL mission to determine the vertical distribution of porosity in the upper lunar crust, shedding light on the thermal and magmatic history of the Moon. We analyzed the gravitational signature of lunar craters because their gravity signature depends on the density of the target material, which depends on the crustal composition and porosity. We consider lunar craters 10–30 km in diameter as these craters are most sensitive to the shallow depths that we are investigating. We find that the gravitational signature of craters changes significantly at diameters of around 16 km. Relating the size of the craters to the depth of the porosity induced by the impact, we find a porosity boundary at a depth of 3–5 km in the lunar crust. This boundary is most likely the predicted boundary between two of the most broken‐up layers in the upper lunar crust. This is the first time this boundary has been observed with global gravity data helping us understand the origin and evolution of porosity in the lunar crust. Key Points: We detect a significant change in the trend between Residual Bouguer Anomaly (RBA) and crater diameter for craters in the range 10–30 kmThe change in RBA trend implies the existence of a porosity boundary at 3–5 km depth, revealing the thickness of large‐scale basin ejectaThe newly inferred global thickness of the ejecta layer provides constraints on mixing, heat flow, and magmatism models of the Moon [ABSTRACT FROM AUTHOR]

At sufficiently high velocities, a microparticle impacting a metal substrate can cause ejection of material from the substrate and impact-induced melting, both of which can result in erosion. Here, we directly image the impact of individual hard steel microparticles on soft tin substrates, at controlled impact velocities in the range of ~100 to 1000 m/s. By using scanning electron and laser scanning confocal microscopy, we characterize the surface morphology, depth, and volume of each impact crater. We observe a gradual onset of impact-induced melting in the craters, as well as the production of increasing amounts of ejecta from the target metal. By comparing measurements of impact and rebound velocity to an elastic-plastic model, we observe that at a high enough impact velocity, melting and ejection begin to consume additional kinetic energy beyond that expected by plastic deformation of the target material alone. By calculating the excess energy dissipation using this elastic-plastic model, we show that although this divergent behavior is associated with the onset of melting, the majority of the ejected volume must be solid rather than liquid. [ABSTRACT FROM AUTHOR]

The prototype for investigations of formation mechanisms and related geological effects of large impact basins on planetary bodies has been the Orientale basin on the Moon. Its widespread secondaries, light plains, and near-rim melt flows have been well mapped in previous studies. Flow features are also widely associated with secondaries on planetary bodies, but their physical properties are not well constrained. The nature of flow features associated with large impact basins are critically important to understand the emplacement process of basin ejecta, which is one of the most fundamental processes in shaping the shallow crusts of planetary bodies. Here we use multisource remote sensing data to constrain the physical properties of flow features formed by the secondaries of the Orientale basin. The results suggest that such flows are dominated by centimeter-scale fine debris fines; larger boulders are not abundant. The shattering of target materials during the excavation of the Orientale basin, landing impact of ejecta that formed the secondaries, and grain comminution within the flows have substantially reduced particle sizes, forming the fine flows. The discovery of global-wide fine debris flows formed by large impact basins has profound implications to the interpretation of both previously-returned samples and remote sensing data.

The deeply eroded Acraman structure in the Mesoproterozoic Gawler Range Volcanics, Gawler Craton, South Australia, ranks among the world's largest known impact structures, with a transient crater ∼40 km in diameter and a ∼90 km-diameter collapse crater. An impact age of ca 590 Ma is suggested by Rb–Sr shale dating of Ediacaran strata hosting a related ejecta band of volcanic fragments in the Adelaide Rift Complex and Officer Basin, and ca 580 Ma by chemostratigraphy. Ascertaining an accurate and precise impact age would greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. However, numerous attempts to date the impact, using material from exposures at Acraman and the ejecta band, have been unsuccessful. U–Pb dating of zircons from shattered dacite basement, melt rock and ejecta by three laboratories gave ages related to the 1592 Ma Yardea Dacite. K/Ar and 40Ar/39Ar dating of end-member K-feldspar in melt rock by two laboratories provided early Paleozoic ages, indicating later fluid movement. Although 80% of terrestrial impact structures ≥40 km in diameter have been drilled, Acraman has not. Deep drilling of the 'hot shock' zone of the unexposed central uplift is required to obtain zircons with U–Pb ratios that were likely reset by the impact. High-resolution aeromagnetic data for Acraman reveal an elliptical magnetic low measuring 19.5 × 18.3 km, with NNE–SSW-trending major axis and a high-amplitude dipolar anomaly of the central uplift that is offset to the SSW. The magnetic signature suggests oblique impact from the SSW. The source of the dipolar magnetic anomaly, centred ∼1 km below the Lake Acraman salina and with a remanence direction concordant with that of the melt rock, marks the 'hot shock' zone and a potential target for drilling. The scientific rewards of such drilling could be substantial. Acraman in the Mesoproterozoic Gawler Range Volcanics, South Australia, is one of the world's largest known impact structures, with a related ejecta band of volcanic fragments hosted by Ediacaran (ca 590–580 Ma) strata in the Adelaide Rift Complex and Officer Basin at unfolded distances from 250 km up to 550 km from the impact site. Numerous attempts at U–Pb dating of zircons from shattered volcanic basement and melt rock at Acraman, and zircons from the ejecta, gave un-reset basement ages, and K/Ar and 40Ar/39Ar dating of melt rock gave early Paleozoic ages related to later fluid movement. An accurate and precise age for the impact would provide a reliable age for the ejecta-hosting Ediacaran strata and greatly benefit Ediacaran biostratigraphic, biogeochemical and magnetostratigraphic global correlations. Deep drilling of the 'hot shock' zone of Acraman's central uplift, inferred to be the source of a high-amplitude dipolar aeromagnetic anomaly centred ∼1 km below the Lake Acraman salina, is required to obtain zircons with U–Pb ratios most likely to have been reset by the impact. [ABSTRACT FROM AUTHOR]

The occurrence of sand boils or ejecta following earthquakes can cause considerable ground settlement. This study aims to investigate how soil properties influence ejecta-induced settlement by conducting experimental tests that simulate the sand boil process. Three materials, namely coarse C306 sand, fine C778 sand, and non-plastic silt, were used to examine the effects of grain size, fines content, and density on the amount of sand boil and resulting settlement. The test results indicate that loose specimens with low density experience more ejecta-induced settlement, while specimens with higher amounts of coarse grains or fines exhibit less settlement even at similar void ratios or relative densities. However, the amount of ejecta produced is directly proportional to the duration of high pore water pressure (H-PWP), which is influenced by both PWP supplies and dissipation. The differences in permeability and one-dimensional stiffness among materials explain the varying H-PWP duration across the tests. Therefore, when estimating the ejecta amount, it is crucial to account for the varying stiffness and permeability during liquefaction and post-liquefaction consolidation to accurately assess the H-PWP duration. • The effects of density, grain size, and fines on ejecta amounts are investigated. • The amount of ejecta is proportional to the high pore water pressure duration. • Loose specimens experience more ejecta amount Coarser or finer materials exhibit less settlement at the same relative densities. • Lower consolidation coefficient leads to longer high pore water pressure duration. [ABSTRACT FROM AUTHOR]

A database of detailed liquefaction ejecta case histories for the 2010–2011 Canterbury earthquakes is interrogated. More than 50 mm of ejecta-induced settlement occurred at thick, clean sand sites shaken by PGA 6.1 = 0.35–0.70 g (wherein PGA 6.1 is the peak ground acceleration for a M w 6.1 earthquake), whereas ejecta-induced settlement at highly stratified silty soil sites did not exceed 10 mm even when PGA 6.1 exceeded 0.45 g. Cone penetration test-based liquefaction-induced damage indices that do not consider soil-system response effects, such as post-shaking hydraulic mechanisms, overestimate the severity of ejecta at stratified silty soil sites. Considering post-shaking hydraulic mechanisms captures the lack of ejecta at stratified silty soil sites. It also improves the estimation of ejecta severity at clean sand sites with severe-to-extreme ejecta. Strongly shaken clean sand sites that did not produce ejecta typically had thick strata with high tip resistances, thick non-liquefiable crusts, or deeper non-liquefiable strata overlying liquefiable strata. Ejecta-induced fissures formed in the non-liquefiable crust during the Feb 2011 earthquake which liquefied soil at depth could exploit to produce ejecta during the Jun 2011 earthquake. When significant ejecta formed on the roads, elevated adjacent ground with houses typically had negligible ejecta. • Severe-to-extreme ejecta occurred predominantly at thick, clean sand sites. • Strongly shaken highly stratified silty soil sites produced negligible ejecta. • Most liquefaction indices overestimated ground failure at stratified silty sites. • Ejecta-induced land damage enhanced ejecta formation during later earthquakes. • Ground elevated above adjacent roads filled with ejecta often had negligible ejecta. [ABSTRACT FROM AUTHOR]

Abstract We report 40Ar‐39Ar step‐heating ages of Paleocene‐Eocene (P‐E) boundary impact spherules from Atlantic Margin coastal plain and open ocean sites. We test the hypothesis that the P‐E spherules are reworked from an earlier event (e.g., K‐Pg impact at ~66 Ma), which predicts a cooling age discordant from their depositional age of 55.93 ± 0.05 Ma at the P‐E boundary. Isochrons from the step‐heating analysis yield 40Ar‐36Ar intercepts in excess of the modern in most cases, indicating that the spherules have excess radiogenic Ar (40Ar*), typical of impact glasses incompletely degassed before solidification. The weighted mean of the isochron‐corrected plateau age is 54.2 ± 2.5 Ma (1σ), and their isochron age is 55.4 ± 4.0 Ma, both indistinguishable from their P‐E depositional age, not supporting the K‐Pg reworking hypothesis. This is consistent with all other stratigraphic and geochemical evidence for an impact at the P‐E boundary and ejecta distribution by air fall.

Radargrams obtained by the Yutu‐2 rover reveal that the post‐mare deposits at the Chang'E‐4 landing site are ∼45 m thick, consistent with estimations based on orbital observations. Besides obvious ejecta from Finsen, polarized interpretations exist on whether or not the Alder crater is another contributor to the post‐mare deposits, although predicted thicknesses of ejecta from all potential source craters are not adequately large compared to observations. We recognize that the rover has been exploring along a shared crater wall of two secondaries from Finsen. Mechanics of secondary impacts suggests that the discontinuous layers of coarse and fine materials observed in the radargram are older than Finsen. Cross‐cutting relationships and crater density comparisons show that Alder is older than the mare basalts, and the Orientale basin was the major source for the post‐mare materials. Lower‐crust materials excavated by Orientale constituted a substantial portion of the surface regolith detected by the rover. Plain Language Summary: Understanding surface processes at the lunar farside and revealing potential compositions related with SPA are two scientific targets of the Chang'E‐4 mission. Orbital observations and radargrams obtained by the rover show that the mare basalts at the landing area are covered by > 30 m thick deposits. Finsen has delivered bright rays to this area, but whether or not Alder is another source has been debated. Considering all potential sources that even include Alder, predicted thickness of post‐mare materials is substantially less than observations. We recognize that Yutu‐2 is exploring along the shared wall of two secondaries from Finsen, and subsurface materials are older than Finsen. Orientale's secondaries are traceable on top of Alder. The crater density on Orientale's ejecta deposits is comparable with that of the mare surface at the landing site, and morphological comparison of secondaries indicates that substantial ejecta had been deposited in Von Kármán before the volcanism in Leibnitz was ceased. The limited time window suggests that Orientale's ejecta were the only suitable source for the post‐mare materials, forming the discontinuous layers of coarse and fine materials revealed in radargrams. Surface regolith examined by Yutu‐2 should contain lower‐crust materials that were excavated by Orientale. Key Points: The Yutu‐2 rover has been exploring along the rim of Finsen's secondaries, and pre‐Finsen materials dominate the subsurfaceCrater density comparisons reveal that Orientale is a major source of the post‐mare ejecta, explaining the radargram obtainedSurface regolith detected by Yutu‐2 is dominated by lower‐crust materials ejected by Orientale, not related with SPA [ABSTRACT FROM AUTHOR]