Publications
195 results found
Daly RT, Ernst CM, Barnouin OS, et al., 2023, Successful Kinetic Impact into an Asteroid for Planetary Defense., Nature
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.
Cheng AF, Agrusa HF, Barbee BW, et al., 2023, Momentum Transfer from the DART Mission Kinetic Impact on Asteroid Dimorphos., Nature
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.
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
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
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, 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
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
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, Newland EL, Schwarz D, et al., 2022, Meteoroid fragmentation in the martian atmosphere and the formation of crater clusters, Journal of Geophysical Research: Planets, Vol: 127, Pages: 1-22, ISSN: 2169-9097
The current rate of small impacts on Mars is informed by more than one thousand impact sites formed in the last twenty years, detected in images of the martian surface. More than half of these impacts produced a cluster of small craters formed by fragmentation of the meteoroid in the martian atmosphere. The spatial distributions, number and sizes of craters in these clusters provide valuable constraints on the properties of the impacting meteoroid population as well as the meteoroid fragmentation process. In this paper, we use a recently compiled database of crater cluster observations to calibrate a model of meteoroid fragmentation in Mars’ atmosphere and constrain key model parameters, including the lift coefficient and fragment separation velocity, as well as meteoroid property distributions. The model distribution of dynamic meteoroid strength that produces the best match to observations has a minimum strength of 10–90 kPa, a maximum strength of 3–6 MPa and a median strength of 0.2–0.5 MPa. An important feature of the model is that individual fragmentation events are able to produce fragments with a wide range of dynamic strengths as much as ten times stronger or weaker than the parent fragment. The calibrated model suggests that the rate of small impacts on Mars is 1.5–4 times higher than recent observation-based estimates. It also shows how impactor properties relevant to seismic wave generation, such as the total impact momentum, can be inferred from cluster characteristics.
Daubar IJ, Dundas CM, McEwen AS, et al., 2022, New craters on Mars: an updated catalog, Journal of Geophysical Research: Planets, Vol: 127, Pages: 1-21, ISSN: 2169-9097
We present a catalog of new impacts on Mars. These craters formed in the last few decades, constrained with repeat orbital imaging. Crater diameters range from 58 m down to <1 m. For each impact, we report whether it formed a single crater or a cluster (58% clusters); albedo features of the blast zone (88% halos; 64% linear rays; 10% arcuate rays; majority dark-toned; 4% light-toned; 14% dual-toned); and exposures of ice (4% definite; 2% possible). We find no trends in the occurrences of clusters with latitude, elevation, or impact size. Albedo features do not depend on atmospheric fragmentation. Halos are more prevalent at lower elevations, indicating an atmospheric pressure dependence; and around smaller impacts, which could be an observational bias. Linear rays are more likely to form from larger impacts into more consolidated material and may be enhanced by lower atmospheric pressure at higher elevations. Light- and dual-toned blast zones occur in specific regions and more commonly around larger impacts, indicating excavation of compositionally distinct material. Surfaces covered with bright dust lacking cohesion are favored to form detectable surface features. The slope of the cumulative size frequency distribution for this dataset is 2.2 for diameters >8 m (differential slope 2.9), significantly shallower than the slope of new lunar craters. We believe that no systematic biases exist in the martian dataset sufficient to explain the discrepancy. This catalog is complete at the time of writing, although observational biases exist, and new discoveries continue.
Bray VJ, Hagerty JJ, Collins GS, 2022, "False peak" creation in the Flynn Creek marine target impact crater, Meteoritics and Planetary Science, Vol: 57, Pages: 1365-1386, ISSN: 1086-9379
Impacts into marine targets are known to create abnormal crater morphologies. We investigate the formation of the ~4 km diameter Flynn Creek marine target impact crater using the iSALE hydrocode. We compare simulation results to topographic profiles, mineral pressure indicators, and breccia sequencing from drill cores to determine the most likely sea depth at this location at the time of impact (~360 Ma, Tennessee, USA): 700–800 m. Both the peak shock pressure produced by the impact and the mechanism(s) of central peak formation differ with sea depth. The large central mound of Flynn Creek could have been produced in three distinct ways, all requiring the presence of an ocean: (1) a relatively cohesive rim collapse deposit that reached the crater center as part of a ground flow and came to rest on top of the existing crater stratigraphy; (2) chaotic resurge of ejecta with the returning ocean that deposited at the crater center; (3) large uplift facilitated by the removal of overburden pressure from a deep ocean. The first two of these mechanisms create “false peaks” in which high-shock uplifted material and original crater floor are buried beneath > 200 m of relatively low shock material. Our simulations suggest that drilling of marine impact sites might require deeper than expected drill cores, so that any high-pressure mineralogical indictors at depth can be accessed.
Raducan SD, Jutzi M, Davison TM, et al., 2022, Influence of the projectile geometry on the momentum transfer from a kinetic impactor and implications for the DART mission, International Journal of Impact Engineering, Vol: 162, Pages: 104147-104147, ISSN: 0734-743X
The DART spacecraft will impact Didymos’s secondary, Dimorphos, at the end of 2022 and cause a change in the orbital period of the secondary. For simplicity, most previous numerical simulations of the impact used a spherical projectile geometry to model the DART spacecraft. To investigate the effects of alternative, simple projectile geometries on the DART impact outcome we used the iSALE shock physics code in two and thee-dimensions to model vertical impacts of projectiles with a mass and speed equivalent to the nominal DART impact, into porous basalt targets. We found that the simple projectile geometries investigated here have minimal effects on the crater morphology and momentum enhancement. Projectile geometries modelled in two-dimensions that have similar surface areas at the point of impact, affect the crater radius and the crater volume by less than 5%. In the case of a more extreme projectile geometry (i.e., a rod, modelled in three-dimensions), the crater was elliptical and 50% shallower compared to the crater produced by a spherical projectile of the same momentum. The momentum enhancement factor in these test cases, commonly referred to as , was within 7% for the 2D simulations and within 10% for the 3D simulations, of the value obtained for a uniform spherical projectile. The most prominent effects of projectile geometry are seen in the ejection velocity as a function of launch position and ejection angle of the fast ejecta that resides in the so-called ‘coupling zone’. These results will inform the LICIACube ejecta cone analysis.
Raducan SD, Davison TM, Collins GS, 2022, Ejecta distribution and momentum transfer from oblique impacts on asteroid surfaces, Icarus, Vol: 374, Pages: 1-16, ISSN: 0019-1035
NASA’s Double Asteroid Redirection Test (DART) mission will impact its target asteroid, Dimorphos, at anoblique angle that will not be known prior to the impact. We computed iSALE-3D simulations of DARTlike impacts on asteroid surfaces at different impact angles and found that the vertical momentum transferefficiency, 𝛽, is similar for different impact angles, however, the imparted momentum is reduced as the impactangle decreases. It is expected that the momentum imparted from a 45◦impact is reduced by up to 50%compared to a vertical impact. The direction of the ejected momentum is not normal to the surface, howeverit is observed to ‘straighten up’ with crater growth. iSALE-2D simulations of vertical impacts provide contextfor the iSALE-3D simulation results and show that the ejection angle varies with both target properties andwith crater growth. While the ejection angle is relatively insensitive to the target porosity, it varies by upto 30◦ with target coefficient of internal friction. The simulation results presented in this paper can helpconstrain target properties from the DART crater ejecta cone, which will be imaged by the LICIACube. Theresults presented here represent the basis for an empirical scaling relationship for oblique impacts and canbe used as a framework to determine an analytical approximation of the vertical component of the ejectamomentum, 𝛽 − 1, given known target properties.
Collins GS, Newland EL, Schwarz D, et al., 2021, Meteoroid Fragmentation in the Martian Atmosphere and the Formation of Crater Clusters
Fernando B, Wójcicka N, Han Z, et al., 2021, Questions to Heaven, Astronomy and Geophysics, Vol: 62, Pages: 622-625, ISSN: 1366-8781
Rajšić A, Miljković K, Wójcicka N, et al., 2021, Numerical simulations of the Apollo S-IVB artificial impacts on the moon, Earth and Space Science, Vol: 8, ISSN: 2333-5084
The third stage of the Saturn IV rocket used in the five Apollo missions made craters on the Moon ∼30 m in diameter. Their initial impact conditions were known, so they can be considered controlled impacts. Here, we used the iSALE-2D shock physics code to numerically simulate the formation of these craters, and to calculate the vertical component of seismic moment (∼4 × 1010 Nm) and seismic efficiency (∼10−6) associated with these impacts. The irregular booster shape likely caused the irregular crater morphology observed. To investigate this, we modeled six projectile geometries, with footprint area between 3 and 105 m2, keeping the mass and velocity of the impactor constant. We showed that the crater depth and diameter decreased as the footprint area increased. The central mound observed in lunar impact sites could be a result of layering of the target and/or low density of the projectile. Understanding seismic signatures from impact events is important for planetary seismology. Calculating seismic parameters and validating them against controlled experiments in a planetary setting will help us understand the seismic data received, not only from the Moon, but also from the InSight Mission on Mars and future seismic missions.
Fernando B, Wójcicka N, Maguire R, et al., 2021, Seismic constraints from a Mars impact experiment using InSight and Perseverance, Nature Astronomy, Vol: 6, Pages: 59-64, ISSN: 2397-3366
NASA’s InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission has operated a sophisticated suite of seismology and geophysics instruments on the surface of Mars since its arrival in 2018. On 18 February 2021, we attempted to detect the seismic and acoustic waves produced by the entry, descent and landing of the Perseverance rover using the sensors onboard the InSight lander. Similar observations have been made on Earth using data from both crewed1,2 and uncrewed3,4 spacecraft, and on the Moon during the Apollo era5, but never before on Mars or another planet. This was the only seismic event to occur on Mars since InSight began operations that had an a priori known and independently constrained timing and location. It therefore had the potential to be used as a calibration for other marsquakes recorded by InSight. Here we report that no signal from Perseverance’s entry, descent and landing is identifiable in the InSight data. Nonetheless, measurements made during the landing window enable us to place constraints on the distance–amplitude relationships used to predict the amplitude of seismic waves produced by planetary impacts and place in situ constraints on Martian impact seismic efficiency (the fraction of the impactor kinetic energy converted into seismic energy).
Johnson BC, Milliken RE, Lewis KW, et al., 2021, Impact generated porosity in Gale crater and implications for the density of sedimentary rocks in lower Aeolis Mons, Icarus, Vol: 366, Pages: 1-11, ISSN: 0019-1035
Sedimentary rocks in Gale crater record important information about the climatic history and evolution of Mars. Recent gravity measurements and modeling indicate strata encountered by the Curiosity rover have a very low density (1680 ± 180 kg m−3) and thus unusually high porosity. Missing in these models, however, is the role of deeper crustal porosity on the observed gravity signatures. Here we simulate the impact formation of Gale crater and find that impact generated porosity results in a negative gravity anomaly that decreases in magnitude with distance from the basin center. Incorporating this expected post-impact gravity signature into models for the bulk density of strata in lower Mt. Sharp, we find a best-fit density of 2300 ± 130 kg m−3 for an impact into a target with no pre-impact porosity. Models incorporating pre-impact porosity result in densities that are up to 200 kg/m3 lower. These revised densities increase the maximum potential burial depth of rocks along the rover traverse, allowing for the possibility Gale crater may once have been filled with sediment.
Fernando B, Wójcicka N, Froment M, et al., 2021, Listening for the landing: seismic detections of perseverance's arrival at Mars with InSight, Earth and Space Science, Vol: 8, Pages: 1-21, ISSN: 2333-5084
The entry, descent, and landing (EDL) sequence of NASA's Mars 2020 Perseverance Rover will act as a seismic source of known temporal and spatial localization. We evaluate whether the signals produced by this event will be detectable by the InSight lander (3,452 km away), comparing expected signal amplitudes to noise levels at the instrument. Modeling is undertaken to predict the propagation of the acoustic signal (purely in the atmosphere), the seismoacoustic signal (atmosphere-to-ground coupled), and the elastodynamic seismic signal (in the ground only). Our results suggest that the acoustic and seismoacoustic signals, produced by the atmospheric shock wave from the EDL, are unlikely to be detectable due to the pattern of winds in the martian atmosphere and the weak air-to-ground coupling, respectively. However, the elastodynamic seismic signal produced by the impact of the spacecraft's cruise balance masses on the surface may be detected by InSight. The upper and lower bounds on predicted ground velocity at InSight are 2.0 × 10−14 and 1.3 × 10−10 m s−1. The upper value is above the noise floor at the time of landing 40% of the time on average. The large range of possible values reflects uncertainties in the current understanding of impact-generated seismic waves and their subsequent propagation and attenuation through Mars. Uncertainty in the detectability also stems from the indeterminate instrument noise level at the time of this future event. A positive detection would be of enormous value in constraining the seismic properties of Mars, and in improving our understanding of impact-generated seismic waves.
Rajšić A, Miljković K, Collins GS, et al., 2021, Seismic efficiency for simple crater formation in the Martian top crust analogue, Journal of Geophysical Research: Planets, Vol: 126, Pages: 1-12, ISSN: 2169-9097
The first seismometer operating on the surface of another planet was deployed by the NASA InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission to Mars. It gives us an opportunity to investigate the seismicity of Mars, including any seismic activity caused by small meteorite bombardment. Detectability of impact generated seismic signals is closely related to the seismic efficiency, defined as the fraction of the impactor's kinetic energy transferred into the seismic energy in a target medium. This work investigated the seismic efficiency of the Martian near surface associated with small meteorite impacts on Mars. We used the iSALE‐2D (Impact‐Simplified Arbitrary Lagrangian Eulerian) shock physics code to simulate the formation of the meter‐size impact craters, and we used a recently formed 1.5 m diameter crater as a case study. The Martian crust was simulated as unfractured nonporous bedrock, fractured bedrock with 25% porosity, and highly porous regolith with 44% and 65% porosity. We used appropriate strength and porosity models defined in previous works, and we identified that the seismic efficiency is very sensitive to the speed of sound and elastic threshold in the target medium. We constrained the value of the impact‐related seismic efficiency to be between the order of ∼10‐7 to 10‐6 for the regolith and ∼10‐4 to 10‐3 for the bedrock. For new impacts occurring on Mars, this work can help understand the near‐surface properties of the Martian crust, and it contributes to the understanding of impact detectability via seismic signals as a function of the target media.
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