Fragments Of Asteroids Research Articles

Shock melt in the Cold Bokkeveld CM2 carbonaceous chondrite and the response of C‐complex asteroids to hypervelocity impacts

AbstractMany of the CM carbonaceous chondrites are regolith breccias and so should have abundant evidence for collisional processing. The constituent clasts of these fragmental rocks frequently display compactional petrofabrics; yet, olivine microstructures show that most CMs are unshocked. To better understand the reasons for this contradiction, we have sought other evidence for hypervelocity impact processing of CM chondrites using the Cold Bokkeveld meteorite. We find that this regolith breccia contains rare particles of vesicular shock melt that are close in chemical composition to bulk CM chondrite. Transmission electron microscopy of a melt bead shows that it is composed of silicate glass with inclusions of pentlandite, pyrrhotite, and wüstite. Characterization of shards of another bead by atom probe tomography reveals nanoscale clusters of sulfur that represent sulfide inclusions arrested at an early stage of growth. These glass particles are mineralogically comparable to micrometeoroid impact melt described from the Cb‐type asteroid Ryugu and melt that has been experimentally produced by pulsed laser irradiation of CM targets. The glass could have formed by in situ shock‐melting, but petrographic evidence is more consistent with an origin as ballistic ejecta from a distal impact. The scarcity of melt in this meteorite, and CM chondrites more broadly, is consistent with the explosive fragmentation of hydrous asteroids following energetic collisions. Cold Bokkeveld's parent body is likely to be a second‐generation asteroid that was constructed from the debris of one or more earlier bodies, and only a small proportion of the reaccreted material had been highly shocked and melted.

Optical and acoustic ground effects simulations from terminal defense asteroid disruption via the PI method

Our simulations suggest that Pulverize It (PI), a NASA Phase II NIAC study, is an effective multi-modal approach for planetary defense that can operate in extremely short interdiction modes (with intercepts as short as hours prior to atmospheric entry) as well as long-interdiction time scales with months to years of warning. The basic process is complete disruption of the threat via fragmentation. In scenarios with sufficiently long warning time, the fragment cloud spreads enough to miss Earth, resulting in no ground effects. In “worst-case” scenarios with short warning times (“terminal” scenarios), the fragments (typically <10 m in diameter) will enter Earth’s atmosphere, where their energy is dissipated in a series of ground-level optical pulses and de-correlated shock waves, mitigating any significant damage. We investigate the optical and acoustic ground effects through a set of simulation codes that model the interaction of asteroid fragments with Earth’s atmosphere following terminal threat interception. Even in such cases where fragments enter the atmosphere, our simulations suggest that threats mitigated by PI produce vastly less damage on the ground when compared to an equivalent unfragmented case, yielding optical energy deposition below 200 kJ/m2 and shock wave over-pressures under 3 kPa. Our simulations support the proposition that threats like 2023 PDC, the hypothetical 800 m diameter asteroid from the 2023 Planetary Defense Conference impact exercise, can be effectively mitigated through fragmentation. We find that a terminal defense mitigation scenario that disrupts 2023 PDC into 1 million fragments with an intercept of 60 days before ground impact results in reasonable ground effects with minimal damage.

Acoustic ground effects simulations from asteroid disruption via the “Pulverize It” method

Our simulations show that PI (“Pulverize It”), a NASA Phase II NIAC study, is an effective multi-modal approach for planetary defense that can operate in extremely short interdiction modes (with intercepts as short as hours prior to atmospheric entry) as well as long interdiction time scales with months to years of warning. The basic process is complete disruption of the threat via fragmentation. In long warning time cases, the fragment cloud spreads enough to miss Earth, resulting in no ground effects. In cases where the warning time is short, the fragments (typically &amp;lt;10 m in diameter) will enter Earth’s atmosphere where their energy is dissipated in a series of ground-level optical pulses and de-correlated shock waves, mitigating any significant damage. We investigate the acoustic ground effects through a set of simulation codes that model the interaction of asteroid fragments with the Earth’s atmosphere following threat interception. Even in the short warning time cases where the fragments enter the atmosphere, our simulations show that threats mitigated by the PI method produce vastly less damage on the ground when compared to the same unfragmented case, yielding shock wave over-pressures under 3 kPa. Our simulations support the proposition that threats sized 20 m—1000 m in diameter can be effectively mitigated through fragmentation, resulting in acoustic ground effects that are below estimated damage thresholds and yield short- and long-term non-lethal effects.

Compositional characterization of a primordial S-type asteroid family of the inner main belt

Context. Recently, a primordial family of moderate-albedo asteroid fragments was discovered in the inner main belt. Its age was estimated to be 4.4 ± 1.7 Gyr. However, there is a lack of compositional characterization, which is important to the study of the earliest collisions in the main belt. Aims. In addition to the previously identified members and the parameters that define the family’s borders (V shape), we expanded the list of family members to include asteroids located within the central region of the V shape. These additional potential members were selected based on their diameter (larger than 7 km) and their geometric visible albedo (greater than or equal to 12%). Subsequently, we conducted a spectroscopic survey to determine the dominant taxonomy and composition of this family. This allowed us to further refine the list of family members by removing interlopers. Methods. From an initial list of 263 asteroids that are considered to be potential members of the aforementioned primordial family, we retrieved their spectra in the visible and near-infrared range from the literature and from the Gala DR3 spectral catalog of Solar System objects. For asteroids with no or poor signal-to-noise ratio spectra in the literature, we carried out new ground-based observations. We obtained new spectra for 33 members of the family using the 1.82 m Asiago Telescope for the visible spectroscopy, while for near-infrared spectroscopy, we used the 3.58 m Telescopio Nazionale Galileo (TNG) and the 4.30 m Lowell Discovery Telescope (LDT). Results. In total, we collected spectra for 261 potential members of the primordial S-type family out of 263. We determined their spectral taxonomy and properties, such as spectral slopes and absorption band parameters, when existing. Using the taxonomical characterization and the orbital space parameters, we identified and removed 71 interlopers from the potential members list. The final list of the primordial S-type family members includes 190 asteroids. The family is dominated by S-complex (~71%) asteroids with a mineralogy similar to ordinary chondrites and pyroxene-rich minerals. The family also contains members classified as L-types and V-types. (~15% and ~9%, respectively). Conclusions. The mean albedo of the family is ~23%, and its largest probable remnant is the asteroid (30) Urania. The estimated size of the family parent body ranges between 110 and 210 km. This size range is compatible with the progenitor of H and L chondrites.

Identification of a 4.3 billion year old asteroid family and planetesimal population in the Inner Main Belt

Context. Understanding the conditions that lead to the formation of planetesimals – the building blocks of planets - and their initial size distribution is a central problem of modern planetology. While most of these original planetesimals were accreted onto the terrestrial planets and the cores of the giant planets, some were also stranded in the main belt, where 4.5 Gyr of collisional evolution broke most of them into families of collisional asteroid fragments. However, some planetesimals survived, and are still hidden amongst asteroid fragments in the main belt. Aims. We make use of astronomical data to identify these leftover planetesimals amongst all other asteroids. Our search is based on separating planetesimal survivors from families of asteroids generated by collisions. Namely, we aim to identify and “clean” the main belt of collisional family members: by doing so, we would be left with the surviving members of the original planetesimals. Methods. We focus here on the inner portion of the main belt for asteroids with intermediate to high albedo. It is known that current asteroid family catalogs are not suitable for the aforementioned cleaning; they are conservative and only one-quarter of the known asteroids are associated with the approximately 120 distinct asteroid families. We therefore developed methods to inclusively link asteroids to known collisional families in order to better capture their extent. Namely, we apply a hierarchical clustering method (HCM) on asteroids filtered according to the V-shape of the Yarkovsky drift of each family in order to reassess family membership (V-shape-constrained HCM). The identified families were removed and the remaining background population was searched for previously undetected collisional families. Results. We succeed in using our V-shape-constrained HCM to link family “halos” to their cores. After removing these reassessed families from the asteroid population, our V-shape search reveals a previously unknown collisional family of S-type asteroids in the inner main belt with an age of 4.3 ± 1.7 Gyr and a significance level of 3.4σ. When this ancient collisional family is removed, 34 planetesimals are identified and their size-frequency distribution is presented. Conclusions. The asteroid belt has two components: planetesimals and collisional fragments. The cumulative size-frequency distribution of planetesimals has a steep power-law index for bodies larger than 100 km in diameter and a much smaller power-law index for planetesimals smaller than 100 km.

An X-Ray Burst Associated with FRB 200428 from a Magnetar-asteroid Impact

Fast radio bursts (FRBs) are extragalactic radio transients with millisecond duration and brightness temperature. An FRB-associated X-ray burst (XRB) was recently found to arise from the Galactic magnetar SGR J1935+2154. Following the model of Dai, in which an FRB may originate from a magnetar encountering an asteroid, we focus on explaining the spectrum of the XRB associated with FRB 200428 from SGR J1935+2154. Collisions between asteroidal fragments and the magnetar surface produce a fireball, which further expands relativistically. Due to the velocity difference among some shells in the fireball, internal shocks would form far away from the magnetar, and further emit X-ray emission. We propose that the FRB-associated XRB can be produced by synchrotron emission from the internal shocks, and then constrain the physical parameters by the observed XRB spectrum.

Elemental and triple oxygen isotope geochemistry of new Northwest Africa (NWA) ordinary chondrites (L5, L6): Implications for onion-shell to rubble-pile OC parent body structure

The new L-type ordinary chondrites (OCs) are characterized by fayalite (25.7–26.1 mol%) and ferrosillite (21.5–22.2 mol%) contents in olivine and low-Ca pyroxene, respectively. The Fe/Mg and Fe/Mn ratios in olivine, as well as oxygen isotope compositions in bulk samples, compared to those of other impact-related brecciated OCs (e.g., NWA 869, L3-6, Ghubara, L5) and olivine from Itokawa dust particles. The data demonstrate a correlation between Fe/Mg and Fe/Mn ratios in olivine, and comparability in oxygen isotope compositions between the newly analyzed L-type meteorites and various clasts of NWA 869 used as a proxy for rubble-pile asteroid. Furthermore, these ratios from bulk and olivine of equilibrated ordinary chondrites (EOC) derived from the literature data fall close to the co-variation line (1:1). However, the ratios of different fractions in unequilibrated ordinary chondrites (UOC) such as chondrules, clasts, and matrix, do not fall close to the co-variation line. The coupled anti-correlation trend observed between the bulk and olivine ratios in EOC (i.e., H, L, and LL) is primarily due to variations in the total Fe content caused by redox reactions of silicate to metal in the nebula and metal to silicate in the parent body. The proposed scenario for the formation and evolution of larger asteroids in the early solar system suggests that the they accreted and evolved as an onion-shell structure, and over time, they may have undergone internal heating due to radioactive decay. The internal heating may have caused metal-silicate segregation and thermal metamorphism. Eventually, catastrophic impacts may have caused the fragmentation of the asteroid into smaller pieces. Later, gravitational collapse reassembled the parent asteroid's fragments into several daughter asteroids that resembled rubble-piles, with the H-chondrites representing the deepest part and the L- and LL-chondrites representing the outer parts of the larger asteroid(s). Additionally, the oxygen isotope compositions of new L-chondrites are similar to those of the impact-related clasts in brecciated chondrites NWA 869, indicating that they have a shared L-type parent asteroid that was once part of a larger asteroid.

Insights into the formation and evolution of extraterrestrial amino acids from the asteroid Ryugu

All life on Earth contains amino acids and carbonaceous chondrite meteorites have been suggested as their source at the origin of life on Earth. While many meteoritic amino acids are considered indigenous, deciphering the extent of terrestrial contamination remains an issue. The Ryugu asteroid fragments (JAXA Hayabusa2 mission), represent the most uncontaminated primitive extraterrestrial material available. Here, the concentrations of amino acids from two particles from different touchdown sites (TD1 and TD2) are reported. The concentrations show that N,N-dimethylglycine (DMG) is the most abundant amino acid in the TD1 particle, but below detection limit in the other. The TD1 particle mineral components indicate it experienced more aqueous alteration. Furthermore, the relationships between the amino acids and the geochemistry suggest that DMG formed on the Ryugu progenitor body during aqueous alteration. The findings highlight the importance of aqueous chemistry for defining the ultimate concentrations of amino acids in primitive extraterrestrial samples.

Fragment Dynamics in Active Asteroid 331P/Gibbs

We present a dynamical analysis of the fragmented active asteroid 331P/Gibbs. Using archival images taken by the Hubble Space Telescope from 2015 to 2018, we measured the astrometry of the primary and the three brightest (presumably the largest) components. Conventional orbit determination revealed a high degree of orbital similarity between the components. We then applied a fragmentation model to fit the astrometry, obtaining key parameters including the fragmentation epochs and separation velocities. Our best-fit models show that Fragment B separated from the primary body at a speed of ∼1 cm s−1 between 2011 April and May, whereas two plausible scenarios were identified for Fragments A and C. The former split either from the primary or from Fragment B, in 2011 mid June at a speed of ∼8 cm s−1, and the latter split from Fragment B either in late 2011 or between late 2013 and early 2014, at a speed of ∼0.7–0.8 cm s−1. The results are consistent with rotational disruption as the mechanism causing the cascading fragmentation of the asteroid, as suggested by the rapid rotation of the primary. The fragments constitute the youngest known asteroid cluster, providing us with a great opportunity to study asteroid fragmentation and formation of asteroid clusters.

Data on 824 fireballs observed by the digital cameras of the European Fireball Network in 2017–2018

Meteoroids impacting the Earth on a daily basis are fragments of asteroids and comets. By studying fireballs produced during their disintegration in the atmosphere, we can gain information about their source regions and the properties of their parent bodies. In this work, data on 824 fireballs presented in an accompanying paper and catalog are used. We propose a new empirical parameter for the classification of the physical properties of meteoroids, based on the maximum dynamic pressure suffered by the meteoroid in the atmosphere. We then compare the physical and orbital properties of meteoroids. We find that aphelion distance is a better indicator of asteroidal origin than the Tisserand parameter. Meteoroids with aphelia lower than 4.9 AU are mostly asteroidal, with the exception of the Taurids and α Capricornids associated with the comets 2P/Encke and 169P/NEAT, respectively. We found another population of strong meteoroids of probably asteroidal origin on orbits with either high eccentricities or high inclinations, and aphelia up to χ 7 AU. Among the meteoroid streams, the Geminids and η Virginids are the strongest, and Leonids and α Capricornids the weakest. We found fine orbital structures within the Geminid and Perseid streams. Four minor meteoroid streams from the working list of the International Astronomical Union were confirmed. No meteoroid with perihelion distance lower than 0.07 AU was detected. Spectra are available for some of the fireballs, and they enabled us to identify several iron meteoroids and meteoroids deficient in sodium. Recognition and frequency of fireballs leading to meteorite falls is also discussed.

Athor asteroid family as the source of the EL enstatite meteorites

The identification of meteorite parent bodies provides the context for understanding planetesimal formation and evolution as well as the key Solar System events they have witnessed. However, identifying such links has proven challenging and some appear ambiguous. Here, we identify that the family of asteroid fragments whose largest member is (161) Athor is the unique source of the rare EL enstatite chondrite meteorites, the closest meteorites to Earth in terms of their isotopic ratios. The Athor family was created by the collisional fragmentation of a parent body 3 Gyr ago in the inner main belt. We calculate that the diameter of the Athor family progenitor was 64 km in diameter, much smaller than the putative size of the EL original planetesimal. Therefore, we deduce that the EL planetesimal that accreted in the terrestrial planet region underwent a first catastrophic collision in that region, and one of its fragments suffered a more recent catastrophic collision in the main belt, generating the current source of the EL meteorites.

Makna “Bintang Sebagai Alat Pelempar Setan” dalam al-Mulk ayat 5: Studi Interkonektif Tafsir dan Data Astronomis

This paper aims to further explore the meaning of "stars as a tool/weapon throwing demons" contained in several verses of the al-Quran, including al-Mulk verse five. The need for further study of this verse is motivated by the potential contradiction between the meaning of the verse and modern scientific knowledge that is developing today, especially with the science of astronomy. The translation of the word star and its function of throwing demons, is a textual meaning that is not in accordance with the astronomical interpretation of the phenomenon of falling celestial bodies. Because what falls astronomically is not a star, but a meteoroid which is an asteroid debris where this fragment can come from planetary debris or the rest of planet-forming material and sometimes not only from planetary debris but also from satellites and comets. So the question is what is meant by the star in the verse? And what is meant by the demon thrower. In the process, the researcher uses interconnection theory to examine the existing data. With the interconnection theory, it is possible for data that is naqli (religious proposition) to be linked with other data internally -such as the Prophet's hadith, the aṡar of friends of the scholars' opinions-, as well as externally, such as astronomical data regarding the history of meteors and comets. The results of this study indicate that, in terms of the vocabulary used in the verses of the al-Quran, najm, kawkab, and other vocabularies can indeed be interpreted not only as stars in the present sense, but also other celestial bodies, such as meteors and planets. So that only interpreting the vocabulary in stars results in reducing the scope of meaning of the vocabulary itself. In addition, various hadiths that explain al-Mulk verse 5 show that what is meant by a large planet is not the material thrown by the jinn who tap the sky news, but meteoroids which are asteroid fragments. The use of the word najm is precisely to refute the ignorant myth about meteor showers. So, it is precisely the use of the vocabulary in the verse to expand the Arabic imagination when it comes to celestial bodies. Finally, epistemologically it is necessary to admit that astronomy does not allow to reveal the full meaning of the sentence, because the phenomena of celestial bodies in the Qur'an have several functions, including functions that cannot be understood by human reason.

GENGA. II. GPU Planetary N-body Simulations with Non-Newtonian Forces and High Number of Particles

We present recent updates and improvements of the graphical processing unit (GPU) N-body code GENGA. Modern state-of-the-art simulations of planet formation require the use of a very high number of particles to accurately resolve planetary growth and to quantify the effect of dynamical friction. At present the practical upper limit is in the range of 30,000–60,000 fully interactive particles; possibly a little more on the latest GPU devices. While the original hybrid symplectic integration method has difficulties to scale up to these numbers, we have improved the integration method by (i) introducing higher level changeover functions and (ii) code improvements to better use the most recent GPU hardware efficiently for such large simulations. We added treatments of non-Newtonian forces such as general relativity, tidal interaction, rotational deformation, the Yarkovsky effect, and Poynting–Robertson drag, as well as a new model to treat virtual collisions of small bodies in the solar system. We added new tools to GENGA, such as semi-active test particles that feel more massive bodies but not each other, a more accurate collision handling and a real-time openGL visualization. We present example simulations, including a 1.5 billion year terrestrial planet formation simulation that initially started with 65,536 particles, a 3.5 billion year simulation without gas giants starting with 32,768 particles, the evolution of asteroid fragments in the solar system, and the planetesimal accretion of a growing Jupiter simulation. GENGA runs on modern NVIDIA and AMD GPUs.

Tracing the Primordial Chemical Life of Glycine: A Review from Quantum Chemical Simulations.

Glycine (Gly), NH2CH2COOH, is the simplest amino acid. Although it has not been directly detected in the interstellar gas-phase medium, it has been identified in comets and meteorites, and its synthesis in these environments has been simulated in terrestrial laboratory experiments. Likewise, condensation of Gly to form peptides in scenarios resembling those present in a primordial Earth has been demonstrated experimentally. Thus, Gly is a paradigmatic system for biomolecular building blocks to investigate how they can be synthesized in astrophysical environments, transported and delivered by fragments of asteroids (meteorites, once they land on Earth) and comets (interplanetary dust particles that land on Earth) to the primitive Earth, and there react to form biopolymers as a step towards the emergence of life. Quantum chemical investigations addressing these Gly-related events have been performed, providing fundamental atomic-scale information and quantitative energetic data. However, they are spread in the literature and difficult to harmonize in a consistent way due to different computational chemistry methodologies and model systems. This review aims to collect the work done so far to characterize, at a quantum mechanical level, the chemical life of Gly, i.e., from its synthesis in the interstellar medium up to its polymerization on Earth.

On the cooling rate evolution of asteroid fragments

Recent observations of rapid cooling rates at high temperatures in several ordinary chondrite and primitive achondrite meteorite groups suggest the fragmentation of their parent bodies near peak temperatures. We use analytic models for conductive cooling of collisional fragments to show that the actively cooling part of a fragment experiences similar cooling rates over a large range of temperatures. This characteristic cooling rate decays inversely with time and the larger a fragment the longer this decay continues. Measurements of high temperature cooling rates therefore place a lower bound on the cooling time and size of collisional fragments. Applying this model to the cooling rates in H chondrites, which vary from 101 to 10−2 °C/yr at temperatures between 700 to 850 °C, we estimate cooling times of at least 101 and 104 years in fragments at least 102 to 103 m in radius.

On the Stability of Spinning Asteroids

Most asteroids with a diameter larger than sim 300 {mathrm{m}} are rubble piles, i.e., consisting of more than one solid object. All asteroids are rotating but almost all asteroids larger than sim 300 mathrm{m} rotate with a period longer than 2.3 {text{hours}}, which is the critical period where the centrifugal force equals the gravitational force. This indicates that there are nearly no adhesive interaction forces between the asteroid fragments. We show that this is due to the surface roughness of the asteroid particles which reduces the van der Waals interaction between the particles by a factor of 100 for micrometer sized particles and even more for larger particles. We show that surface roughness results in an interaction force which is independent of the size of the particles, in contrast to the linear size dependency expected for particles with smooth surfaces. Thus, two stone fragments of size 100 {mathrm{nm}} attract each other with the same non-gravitational force as two fragments of size 10 {mathrm{m}}.

Spectral diversity of the inner belt primitive asteroid background population

We present new near-infrared spectra of 55 objects observed using the NASA InfraRed Telescope Facility and the Telescopio Nazionale Galileo, along with visible spectra of 21 objects obtained from the SMASS and S3OS2 surveys, to explore the differences in spectral slope and curvature between the background and the families and to show that the background is a possible source for both Bennu and Ryugu. Within the background population there is spectral diversity in taxonomy, spectral slope, and absorption band parameters. Our sample of asteroids shows that the background looks spectrally similar to the families in the same region, i.e., the background and families may have originated from the same or similar composition parent bodies. Average band center (0.69 ± 0.02 μm, depth: 2.3 ± 0.9%) of an ~0.7 μm absorption feature attributed to aqueous alteration is present in 30% of our primitive background asteroid sample, similar to abundances observed in other primitive inner belt asteroid families. Both near-Earth asteroid sample return mission targets, (101955) Bennu and (162173) Ryugu, are thought to have originated from primitive asteroid populations in the inner main belt, specifically from the low inclination asteroid families. A population that has not been explored spectrally but is dynamically able to deliver asteroid fragments to near-Earth space is the background population, i.e., asteroids that do not cluster into families. Based on our spectral comparisons, the primordial background is a possible source for (162173) Ryugu, but not for (101955) Bennu.

Fragmentation model and strewn field estimation for meteoroids entry

Everyday thousands of meteoroids enter the Earth's atmosphere. The vast majority burn up harmlessly during the descent, but the larger objects survive, occasionally experiencing intense fragmentation events, and reach the ground. These events can pose a threat for a village or a small city; therefore, models of asteroid fragmentation, along with accurate post-breakup trajectory and strewn field estimation, are needed to enable a reliable risk assessment. In this work, a methodology to describe meteoroids entry, fragmentation, descent, and strewn field is presented by means of a continuum approach. At breakup, a modified version of the NASA Standard Breakup Model is used to generate the distribution of the fragments in terms of their area-to-mass ratio and ejection velocity. This distribution, combined with the meteoroid state, is directly propagated using the continuity equation coupled with the non-linear entry dynamics. At each time step, the probability density evolution of the fragments is reconstructed using GMM interpolation. Using this information is then possible to estimate the meteoroid's ground impact probability. This approach departs from the current state-of-the-art models: it has the flexibility to include large fragmentation events while maintaining a continuum formulation for a better physical representation of the phenomenon. The methodology is also characterised by a modular structure, so that updated asteroids fragmentation models can be readily integrated into the framework, allowing a continuously improving prediction of re-entry and fragmentation events. The propagation of the fragments' density and its reconstruction, currently considering only one fragmentation point, is first compared against Monte Carlo simulations, and then against real observations. Both deceleration due to atmospheric drag and ablation due to aerothermodynamics effects have been considered.

Origin of hydrogen isotopic variations in chondritic water and organics

Chondrites are rocky fragments of asteroids that formed at different times and heliocentric distances in the early solar system. Most chondrite groups contain water-bearing minerals, attesting that both water-ice and dust were accreted on their parent asteroids. Nonetheless, the hydrogen isotopic composition (D/H) of water in the different chondrite groups remains poorly constrained, due to the intimate mixture of hydrated minerals and organic compounds, the other main H-bearing phase in chondrites. Building on our recent works using in situ secondary ion mass spectrometry analyses, we determined the H isotopic composition of water in a large set of chondritic samples (CI, CM, CO, CR, and C-ungrouped carbonaceous chondrites) and report that water in each group shows a distinct and unique D/H signature. Based on a comparison with literature data on bulk chondrites and their water and organics, our data do not support a preponderant role of parent-body processes in controlling the D/H variations among chondrites. Instead, we propose that the water and organic D/H signatures were mostly shaped by interactions between the protoplanetary disk and the molecular cloud that episodically fed the disk over several million years. Because the preservation of D-rich interstellar water and/or organics in chondritic materials is only possible below their respective sublimation temperatures (160 and 350–450 K), the H isotopic signatures of chondritic materials depend on both the timing and location at which their parent body formed.

Experimental Simulations of Hypervelocity Impact Penetration of Asteroids Into the Terrestrial Ocean and Benthic Cratering

AbstractSeafloor cratering is an important process that records the impact history of the Earth, affects projectile survivability, and determines the mass of ejecta from benthic rock that is transported to the atmosphere. We report experimental hypervelocity impacts of chondrite and other projectiles (olivine, stainless‐steel, polycarbonate) on a water‐covered iron target to derive a scaling relationship for benthic cratering. In situ observations of 5‐km/s impacts quantify the deceleration of projectiles in the water column by shock‐induced deformation and fragmentation. The minimum water depths at which multiple craters appeared on the benthic target were two and four times the projectile diameter for chondrite and stainless steel, respectively. Based on the observed deceleration of projectiles in water, the cratering efficiency of a benthic target for a given impact velocity is predicted to follow an exponential decay law in terms of water depth normalized by projectile diameter (H/d), given by πv ∝ exp(−(H/d)/κ), when a projectile of original mass collides with the target. Comparing the volume of the largest crater in the experiments and that derived from the scaling relation, mass ratios of the largest projectile fragment to original projectile in the 5‐km/s impact were calculated to be 0.1–0.3 (H/d = 2–6) and 1.0 ± 0.3 (H/d = 5.5) for chondrite and stainless steel, respectively. Using the scaling relationship, the volume of the transient crater on oceanic crust by an asteroid impact is estimated to be smaller than previously predicted by hydrocode simulation when the asteroid fragmentation in the water column controls seafloor cratering.