We measure ejecta mass as a function of azimuthal and impact angle for 104 m/s oblique impacts into sand. We find that the ejecta mass distribution is strongly sensitive to azimuthal angle, with as high as eight times more mass in ejecta on the downrange side compared to the uprange side. Crater radii, measured from the impact point, are measured at different impact and azimuthal angles. Crater ejecta scaling laws are modified to depend on azimuthal and impact angle. We find that crater radii are sensitive to both impact and azimuthal angle, but the ejecta mass as a function of both angles can be estimated from the cube of the crater radius without an additional angular dependent function. The ejecta distributions are relevant for processes that depend upon the integrated properties of approximately 100 m/s impacts occurring in the outer solar system and possibly during planetesimal formation.
Accurate dating of Martian meteorites is crucial for understanding key events in the planet's evolution. However, not all Martian meteorites are amenable to dating techniques currently in use for these rocks. The priority of sample preservation precludes mineral separation methods for low-volume specimens, whereas the less destructive in situ SIMS U-Pb method depends on the availability of U-bearing accessory minerals. Micromilling allows for spatially guided sampling of target phases down to the sub-mm scale, therefore enabling chromatography-based analysis while preserving the overall specimen. This study presents an evaluation of micromill sampling for extracting individual mineral fractions in situ from shergottites, the most common group of Martian meteorites, for Rb-Sr and Sm-Nd geochronology. Based on trace element content in major minerals in shergottites (pyroxene, plagioclase, olivine, and merrillite) and assuming that a minimum load size of 0.25 ng Sr and 1 ng Nd is required to achieve baseline isotopic precision (2σ of ~240 ppm on 87Sr/86Sr and ~100 ppm on 143Nd/144Nd), the minimum required sample volume ranges in the orders of 105–107 μm3 for one Sr isotopic analysis and 105–109 μm3 for one Nd isotopic analysis. Considering the need for sample purity, significant limitations exist in the maximum sampling resolution of the micromill instrument (~40 μm for the conical carbide drill bit chosen for this study) with respect to shergottite petrography. Insufficient grain size, irregular morphology, and the presence of small inclusions may reduce the area that can be drilled per grain. Shock-induced fractures, which sometimes act as pathways for terrestrial alteration, are pervasive in shergottites and create additional challenges for effective high-purity sampling of the target phase. In addition, variation in trace element content in the target phases may result in the realistically required drilling volumes being orders of magnitude greater than the minimum estimates. Lastly, estimated drilling time per fraction may reach over 5 h for pyroxene (Sr, Nd), plagioclase (Nd), and olivine (Sr, Nd), increasing the susceptibility to a larger procedural blank as well as requiring constant, labor-intensive monitoring for long durations. Based on these technical and physical constraints, we do not consider micromill sampling to be currently compatible with Sr isotopic analysis of olivine and Nd isotopic analysis of pyroxene, plagioclase, and olivine in shergottites. The feasibility of geochronology applications may be improved with future advances in analytical development, such as increasing the micromill sampling resolution and reducing the load size required for isotopic analysis.
Meteorites are easily contaminated at the Earth's surface by microbial activity. Here, DNA extracts from two meteorite specimens and samples from curation laboratory surfaces are analyzed with amplicon sequencing, to understand microbial communities that contaminate meteorites and that may be resident in curation facilities. In addition, two different DNA extraction kits, the PowerSoil DNA Isolation Kit and the QIAamp UCP Pathogen Mini Kit, are utilized to determine if certain kits are more favorable for low biomass studies of meteorites. We find that, regardless of the type of kit used, the majority of microbial taxa that dominate meteorite and meteorite curation environments include those that are prevalent in soils or in the human microbiome. Our results have implications for advanced curation methods to protect the intrinsic properties of meteorites, such as extraterrestrial organics and minerals, from microbes. Preserving meteorites in pristine states and understanding the complex relationship between meteorites and terrestrial microbes can inform our search for the origin of life or life elsewhere in the universe.
Chondrules are one of the oldest objects in our solar system. Therefore, they play an important role as messengers, offering new insights into the early stage of the solar system processes and potential understanding of formation. Therefore, the investigation of all detailed structures, especially not well-known inversely zoned chondrules (IZ chondrules), is crucial. In this paper, we describe the chemical as well as the structural composition of inversely zoned chondrules with EDX, light microscopy, BSE, and Raman spectroscopy, which reveal a new process in the early solar system. Inversely zoned chondrules consist of a pyroxene core surrounded by an olivine rim. The olivines have a higher Fe content (Fa, 39%–41%) compared to those found in most other chondrules. The core displays a radial pyroxene chondrule with sometimes olivines (Fa34). These IZ chondrules have originated during the early stages of our solar system and do not show the typical known forming process of chondrules. Minor fluctuations in the SiO₂ content of chondritic melts can lead to SiO₂ depletion of the residual melt at a constant temperature due to crystallization of pyroxene, which shifts the phase equilibrium in favor of fayalite-enriched olivine, which forms a rim.
Sierra Gorda 013 (SG 013) is an unusual CBa-like chondrite containing two texturally different, isotopically identical lithologies—chondritic (L1) and achondritic (L2), which should have a common origin. The metal globules of the L1 metal preserved the magmatic pattern of the siderophile element distribution that indicates they had a fractionated precursor. In this work, the trace element metal composition of lithology 2 was studied, and the revisited LA-ICP-MS data on the L1 metal was presented. Lithologies 1 and 2 have Ni and Co in the range of CB chondrites. The Ni-Co distribution in L1 and depletion in Cr of both lithologies with a negative Cr-Ni correlation are similar to that of the magmatic irons. Highly refractory siderophile element (HRSE) (W, Re, Os, Ir, Pt, Ru, Rh, and Mo) compositions of the L1 metal are highly fractionated relative to CI, but the L2 metal has a nearly uniform HRSE distribution similar to the depleted patterns of some HRSE-poor L1 metal compositions. Metal from both lithologies is depleted in volatile siderophile elements. In the L1 metal globules, the metal composition shows definite linear correlations of the HRSE elements versus Ni similar to those observed in many magmatic iron meteorites, distinct from those of the CH/CBb-zoned metal. Meanwhile, the L2 metal compositions are systematically plotted as limited clusters in the middle of the L1 trends. Based on a fractional crystallization (FC) model of the CR-like metal composition, it was shown that the distribution of siderophile elements in the metal globules of L1 can cover the full range of the fractional crystallization products of a metallic (Fe-Ni-S) liquid from the core of a differentiated body at S content 13 wt%. In contrast, the metal from L2 corresponds to a more limited range of fractional crystallization products and indicates a mixture of the fractionated metal with the primitive metal from the chondritic colliding body. Our results suggest that during a catastrophic impact event when the metallic core of a differentiated body was disrupted, the L1 lithology was quickly cooled in the impact plume, more reduced than that of CB chondrites and avoided equilibration with plume gas and preserved its fractionated HRSE patterns. The distribution of siderophile volatile elements and Au was likely overprinted by high-temperature processes of volatilization and recondensation to different degrees in the impact plume under disequilibrium conditions. The L2 metal probably avoided equilibration with the plume gas and was affected by thermal metamorphism up to 900°C in the SG 013 parent body, which possibly resulted in the higher W abundance compared to the L1 metal with a magmatic Ir-W trend due to the redox reactions with silicates under reducing conditions.
Oxygen isotopic compositions of minerals in three Ca-Al-rich inclusions (CAIs), one amoeboid olivine aggregate (AOA) and one Al-rich chondrule (ARC) from the pristine ungrouped carbonaceous chondrite Acfer 094 were analyzed by secondary ion mass spectrometry (SIMS), including conventional spot analyses and O-isotope imaging. Most of the ARC minerals analyzed in this study are 16O-poor (Δ17O ≥ −5.4‰), with one outlier in high-Ca pyroxene (Δ17O = −10.6 ± 2.8‰), indicating that if the ARC precursors formed initially in an 16O-rich setting, isotopic compositions were mostly reset during chondrule melting in an 16O-poor environment. The CAIs and AOA analyzed are dominated by 16O-rich compositions, consistent with previous work, but partial isotopic resetting to 16O-poor compositions has been identified. Melilite with a moderately 16O-depleted composition (Δ17O = −15.7 ± 3.0‰) was identified in an AOA, and 16O-poor diopside (Δ17O = −1.9 ± 2.5‰) was identified as the outermost layer of a Wark–Lovering-like rim of an 16O-rich CAI (Δ17O ranges from −18 to −22 ± 2.5‰). The diopside layer is bounded by an inner rim of anorthite replacing melilite, which is in turn bounded by the grossite-hibonite-perovskite-spinel-bearing core of the CAI. Isotopic imaging shows that the diopside/anorthite boundary coincides with a steep gradient in O isotopic composition. Based on modeling of O diffusion in the temperature range of 1400–1500 K, thermal events that formed the diopside and anorthite rim layers were limited to durations of no more than approximately 100 days and were probably much shorter. Given the weak metamorphic alteration of Acfer 094, the partial to nearly complete O-isotope resetting of AOA, CAI, and ARC minerals analyzed in this study occurred by short-term thermal events in the solar nebula prior to the formation of the Acfer 094 parent body. Therefore, the isotopic variations identified in this study show that at least some refractory materials were transported from 16O-rich environments, where initial crystallization took place, to 16O-poor environments in the solar nebula, where subsequent crystallization and/or isotopic resetting occurred.
Sarah is a Professor at Arizona State University's School of Earth and Space Exploration. Before this, she was tenured faculty at both the University of California, Davis, and Harvard University. Her academic journey began at Harvard, where she earned two A.B. degrees in Astrophysics and Physics in 1995. Sarah then pursued a Ph.D. in Planetary Science from Caltech under the supervision of Tom Ahrens, completing her degree in 2002. Later, she held a G. K. Gilbert postdoctoral fellowship at the Carnegie Institution of Washington. This foundation equipped Sarah with the skills and deep understanding necessary for her groundbreaking work.
Sarah's achievements are numerous. Beyond the Barringer Medal we celebrate today, Sarah has received a MacArthur “Genius” Fellowship, the Urey Prize, and a Presidential Early Career Award for Scientists and Engineers. She is a Fellow of the American Association for the Advancement of Science and the American Physical Society. She has advised and mentored a dozen graduate students, nine postdoctoral fellows, and many undergraduates. Sarah cares about the people who do research, in addition to research itself. She has also led or co-led over 20 grants from NASA, the Army Research Office, the Department of Energy, and the National Science Foundation.
Sarah's work is best known for two things: her fiendishly complicated shock physics experiments and her mastery of numerical impact modeling. This marriage of methods sets her apart from most other people who study planetary cratering. And this dual approach is part of the secret sauce that empowers Sarah and her group to make such meaningful contributions. For example, numerical impact models struggle with the limited quality of equations of state and constitutive models, which describe how materials behave under extreme conditions. Sarah tackles this limitation head-on. When gas gun experiments cannot reach the needed pressures and temperatures, she turns to Z machine experiments. Sarah and her team analyze these innovative shock physics experiments to derive new equations of state. These revisions aren't just minor tweaks; these new equations of state fundamentally advance our knowledge of material behavior. Her research group then takes these improved equations of state and meticulously integrates them into numerical impact models. This blend of shock experiments and numerical modeling has transformed how we think about, for example, melting and vaporization during planet formation.
Some of Sarah's highest-impact work centers on the Earth-Moon system. In 2012, she and Matija Cuk published a pivotal paper in Science. They proposed that the Moon formed via a giant impact into a fast-spinning Earth, followed by a period of resonant despinning. This scenario successfully explains the isotopic similarities between the Earth and Moon, though other scenarios have been proposed. Since then, Sarah's group has modeled the aftermath of the Moon-forming impact
Meteorites arriving on Earth possess indigenous organic, isotopic, mineralogic, and magnetic properties that reveal conditions and processes from their formation. However, these properties can rapidly change when exposed to the Earth's environment. Asteroids, which formed nearly 4.5 billion years ago, inhabit the ultrahigh vacuum of interplanetary space, with a pressure of around 1.3 × 10−11 Pa, equivalent to only a few tens of atoms per cubic centimeter. Fragments of these asteroids, which land on Earth as meteorites, immediately adsorb atmospheric gases into their pore spaces, which can subsequently adsorb into and onto the minerals. In this study, we show that adsorption of atmospheric water can significantly increase the mass of the smectite-rich Tarda (C2-ung) meteorite, with mass gains reaching around 30 wt% at 100% relative humidity (RH) and between 5 and 10 wt% under typical laboratory conditions (up to ~50% RH). In contrast, the serpentine-rich Aguas Zarcas meteorite gains approximately 11 wt% at 100% RH and around 2 wt% at ~50% RH. This water adsorption leads to observable mass fluctuations in clay-rich carbonaceous chondrites (CCs), especially those with high smectite content, which undergo a “breathing-like” process. This process involves the uptake and release of water, influenced by atmospheric humidity. Although this mass change is reversible in the short term, prolonged “breathing” can alter the mineral composition and physical properties of these materials, complicating our understanding of their origins and evolution. For instance, gypsum forms in Tarda after 10 min of exposure to 100% RH at room temperature, while the Aguas Zarcas meteorite forms significant gypsum within 24 h under similar conditions. In addition, mass changes for Tarda are measured with thermal gravimetry in a He atmosphere, by heating the sample at 100°C in a high vacuum, and after curation under an ultradry atmosphere. These experiments show that samples exposed to the atmosphere rapidly adsorb significant water that is not removed by curation under dry N2. Our findings indicate that this “breathing” process can profoundly and rapidly affect the properties of astromaterials, including samples returned from asteroids Ryugu and Bennu. Maintaining these materials in a stable, low-humidity environment can help prevent such changes and preserve their indigenous properties.
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