40 research outputs found
Insight into the Distribution of High-pressure Shock Metamorphism in Rubble-pile Asteroids
Funding Information: This work was supported by the Academy of Finland, project Nos. 293975 and 335595, the European Regional Development Fund, the Mobilitas Pluss programme (grant No. MOBJD639), and the NASA Solar System Exploration Research Virtual Institute Center for Lunar and Asteroid Surface Science, and it was conducted within institutional support RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences. R.L. appreciates funding from the European Union’s Horizon 2020 research and innovation program, NEO-MAPP, grant agreement No. 870377. Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.Shock metamorphism in ordinary chondrites allows for reconstructing impact events between asteroids in the main asteroid belt. Shock-darkening of ordinary chondrites occurs at the onset of complete shock melting of the rock (>70 GPa) or injection of sulfide and metal melt into the cracks within solid silicates (∼50 GPa). Darkening of ordinary chondrites masks diagnostic silicate features observed in the reflectance spectrum of S-complex asteroids so they appear similar to C/X-complex asteroids. In this work, we investigate the shock pressure and associated metamorphism pattern in rubble-pile asteroids at impact velocities of 4–10 km s−1. We use the iSALE shock physics code and implement two-dimensional models with simplified properties in order to quantify the influence of the following parameters on shock-darkening efficiency: impact velocity, porosity within the asteroid, impactor size, and ejection efficiency. We observe that, in rubble-pile asteroids, the velocity and size of the impactor are the constraining parameters in recording high-grade shock metamorphism. Yet, the recorded fraction of higher shock stages remains low (<0.2). Varying the porosity of the boulders from 10% to 30% does not significantly affect the distribution of pressure and fraction of shock-darkened material. The pressure distribution in rubble-pile asteroids is very similar to that of monolithic asteroids with the same porosity. Thus, producing significant volumes of high-degree shocked ordinary chondrites requires strong collision events (impact velocities above 8 km s−1 and/or large sizes of impactors). A large amount of asteroid material escapes during an impact event (up to 90%); however, only a small portion of the escaping material is shock-darkened (6%).Peer reviewe
Pressure-temperature evolution of primordial solar system solids during impact-induced compaction
Prior to becoming chondritic meteorites, primordial solids were a poorly consolidated mix of mm-scale igneous inclusions (chondrules) and high-porosity sub-μm dust (matrix). We used high-resolution numerical simulations to track the effect of impact-induced compaction on these materials. Here we show that impact velocities as low as 1.5 km s−1 were capable of heating the matrix to >1,000 K, with pressure–temperature varying by >10 GPa and >1,000 K over ~100 μm. Chondrules were unaffected, acting as heat-sinks: matrix temperature excursions were brief. As impact-induced compaction was a primary and ubiquitous process, our new understanding of its effects requires that key aspects of the chondrite record be re-evaluated: palaeomagnetism, petrography and variability in shock level across meteorite groups. Our data suggest a lithification mechanism for meteorites, and provide a ‘speed limit’ constraint on major compressive impacts that is inconsistent with recent models of solar system orbital architecture that require an early, rapid phase of main-belt collisional evolution
Quantifying the Release of Climate-Active Gases by Large Meteorite Impacts With a Case Study of Chicxulub
Assessing the survivability of biomarkers within terrestrial material impacting the lunar surface
The history of organic and biological markers (biomarkers) on the Earth is effectively non-existent in the
geological record >3.8 Ga ago. Here, we investigate the potential for terrestrial material (i.e., terrestrial meteorites) to be
transferred to the Moon by a large impact on Earth and subsequently survive impact with the lunar surface, using the
iSALE shock physics code. Three-dimensional impact simulations show that a typical basin-forming impact on Earth can
eject solid fragments equivalent to ~10–3 of an impactor mass at speeds sufficient to transfer from Earth to the Moon.
Previous modelling of meteorite survivability has relied heavily upon the assumption that peak-shock pressures can be
used as a proxy for gauging survival of projectiles and their possible biomarker constituents. Here, we show the
importance of considering both pressure and temperature within the projectile, and the inclusion of both shock and shear
heating, in assessing biomarker survival. Assuming that they survive launch from Earth, we show that some biomarker
molecules within terrestrial meteorites are likely to survive impact with the Moon, especially at the lower end of the range
of typical impact velocities for terrestrial meteorites (2.5 km s-1). The survival of larger biomarkers (e.g., microfossils) is
also assessed, and we find limited, but significant, survival for low impact velocity and high target porosity scenarios.
Thermal degradation of biomarkers shortly after impact depends heavily upon where the projectile material lands, whether
it is buried or remains on the surface, and the related cooling timescales. Comparing sandstone and limestone projectiles
shows similar temperature and pressure profiles for the same impact velocities, with limestone providing slightly more
favourable conditions for biomarker survival
Numerische Modellierung impaktinduzierter Stoß- und elastischer Wellenausbreitung sowie Kraterbildung in heterogenem Material
Impact processes have shaped the development and evolution of the planetary
bodies in our solar system. Despite the importance of this fundamental
geological process, the consequences of impact events for targets with varying
properties have not been sufficiently quantified. Thus, this thesis
investigates the effect of target properties on impact-induced shock and
elastic wave propagation and the crater formation using numerical simulations.
This approach aims to offer a better understanding of impact processes on
heterogeneous targets, which is key for quantitatively assessing of the role
of impact and collision processes in the formation of the solar system and the
evolution of planetary surfaces. For this study, the iSALE shock physics code
has been used to conduct numerical simulations of impact processes within the
Multidisciplinary Experimental and Modeling Impact Research Network (MEMIN).
The usage of numerical models first requires rigorous validation and
calibration of numerical parametrizations of the thermodynamic and mechanical
response of material upon impact (so-called material models) against
experimental observations. Then, the study focuses on the simulation of
laboratory impact experiments in quartzite and in dry and water-saturated
sandstone. Finally, the numerical data are applied to impact cratering in
nature. To investigate the entire cratering process in detail, the first thing
needed is an understanding of the propagation of the shock wave and how the
target material responds to shock loading as a function of petrophysical
properties is needed. To provide detailed quantitative insights, mesoscale
models, where single pores and grains are resolved, have been developed and
analyzed in this thesis to gain a detailed understanding of shock wave-induced
pore collapse. Pore collapse results in localized pressure amplifications,
which can be up to four times greater than the average shock pressure in a
porous sample. Mesoscale simulations, therefore, can explain the observed
localized high shock pressure phases that appear next to more or less
unshocked grains in impactites and meteorites; they can also explain the
occurrence of shock effects such as the formation of diaplectic quartz glass
in experiments in the low-pressure range. In addition to the investigation of
the shock wave, the elastic wave, which eventually evolves from the initial
shock wave, has been recorded and analyzed using numerical sensors in iSALE. A
systematic modeling study of impacts into targets with varying properties and
the analysis of recorded seismic signals resulted in the determination of the
so-called seismic efficiency k, which relates the seismic energy to the impact
energy. According to our results, k decreases slightly with porosity and is
approximately two orders of magnitude lower for water-saturated materials than
for dry nonporous material. The seismic quality factor Q, which quantifies how
fast the wave attenuates, ranges between 35 and 80 for “dry” materials and is
much lower (<10) for “wet” materials. The seismic magnitude of an impact event
is about one order of magnitude larger for a solid or porous target than for a
water-saturated target, showing that the seismic consequences are
significantly dependent on target properties, and less seismic energy is
induced if targets contain water. Finally, the numerical results obtained at
the laboratory scale were then extrapolated to natural crater dimensions.
Therefore, numerical models were used to investigate crater formation beyond
the scale of laboratory impact experiments, where crater size is controlled by
the yield strength of the target material. It is well known that on the scale
of natural impact craters, crater size is primarily controlled by gravity. In
the current study, scaling parameters have been determined for cohesive
materials, whereby the dynamic strength of the materials was accounted for.Impaktprozesse haben wesentlich zur Entwicklung und Evolution von planetaren
Körpern in unserem Sonnensystem beigetragen. Auch wenn die Bedeutung dieses
fundamentalen Prozesses allgemein bekannt ist, wurden die Konsequenzen von
Impaktereignissen unter der Berücksichtigung von Targeteigenschaften bisher
nicht ausreichend quantifiziert. Diese Arbeit beschäftigt sich mit der
Untersuchung des Einflusses von Targeteigenschaften auf die impaktinduzierte
Stoßwellenausbreitung, die elastische Wellenausbreitung und auf die
Kraterbildung unter Verwendung von numerischen Simulationen. Dieser Ansatz hat
das Ziel, ein besseres Verständnis von Kraterprozessen in heterogenen
Targetmaterialien zu erlangen. Dies ist Voraussetzung für eine quantitative
Bewertung, welche Rolle Impakt- und Kollisionsprozesse in der Entwicklung
unseres Sonnensystems und der Evolution von planetaren Oberflächen spielen.
Der iSALE shock physics code wird benutzt um numerische Simulationen von
Kraterprozessen im Rahmen des "Multidisciplinary Experimental and Modelling
Impact research Network” (MEMIN) auszuführen. Die Verwendung von numerischen
Modellen setzt eine komplexe Validierung und Kalibrierung von numerischen
Parametrizierungen des thermodynamischen und mechanischen Verhaltens des
Materials (sogenannter Materialmodelle), basierend auf experimentelle
Beobachtungen, während eines Impaktes voraus. Die Studie konzentriert sich
vorwiegend auf die Modellierung von Impaktexperimenten in Quarzit und in
trockenen und wassergesättigten Sandstein. Letztendlich werden die
numerischen Daten auf Impaktkrater in der Natur angewendet. Um den gesamten
Kraterprozess im Detail zu untersuchen, ist es zunächst nötig ein gutes
Verständnis über die Ausbreitung der Stoßwelle und wie das Targetmaterial
als Funktion seiner petrophysikalischen Eigenschaften auf die Stoßwelle
reagiert, zu erlangen. Mesoskalige Modelle, in denen einzelne Poren und
Kornstrukturen aufgelöst werden, wurden entwickelt und analysiert um einem
detaillierten Verständnis über stoßwelleninduzierten Porenkollaps gerecht zu
werden. Porenkollaps führt zu lokalen Druckerhöhungen, die das Vierfache der
gemittelten Stoßwellendrücke in einem porösen Material erreichen können.
Mesoskalige Modelle können so das Auftreten von beobachteten lokalen
Stoßwelleneffekten direkt neben ungeschockten Körnern in Impaktiten und
Meteroriten sowie die Bildung von diaplaktischem Quarzglas in Experimenten im
Niedrigdruckbereich erklären. Zusätzlich zu der Untersuchung der Stoßwellen,
wurden elastische Wellen mit Hilfe von numerischen Sensoren aufgezeichnet und
ausgewertet. Eine systematische Modellierungsstudie von Impakten in
Zielgesteinen unterschiedlicher Eigenschaften und die Analyse aufgenommener
seismischer Signale führt zur Bestimmung der sogenannten seismischen
Effizienz k, welche die seismische Energie mit der Impaktenergie in Relation
setzt. Laut der ausgeführten Studie nimmt k mit Zunahme der Porosität leicht
ab und ist ungefähr zwei Größenordnungen kleiner für wassergesättigte
Materialien als für Festgesteine ohne Wasseranteil. Der sogenannte seismische
Qualitätsfaktor Q quantifiziert das Abklingverhalten der elastischen Welle in
einem bestimmten Material, und liegt zwischen Werten von 35 und 80 für
trockenes Material und ist signifikant kleiner (<10) für nasse Materialien.
Die seismische Magnitude eines Impaktereignisses ist ungefähr eine Magnitude
größer in einem Festgestein ohne Wasser als in einem Gestein welches Wasser
enthält. Dies führt zu dem Schluss, dass seismische Konsequenzen signifikant
von den Eigenschaften des Zielgesteins abhängig sind und weniger seismische
Energie in wassergesättigte Gesteine induziert wird. Die numerischen
Ergebnisse auf der Skala von Laborexperimenten konnten letztendlich auf
natürliche Kraterdimensionen hochskaliert werden. Dafür wurden numerische
Modelle verwendet um den Kraterbildungsprozess nicht nur auf der Skala von
Laborexperimenten, wo die Kratergröße durch die Festigkeit des Zielgesteins
dominiert wird, zu untersuchen. Auf der Skala von natürlichen Impaktkratern
wird die Kratergröße hauptsächlich durch die Schwerkraft kontrolliert. Beim
Hochskalieren der numerischen Ergebnisse wurde die dynamische Festigkeit des
Materials berücksichtigt und Skalierungsparameter für Festgesteine bestimmt
Insight into the Distribution of High-pressure Shock Metamorphism in Rubble-pile Asteroids
Funding Information: This work was supported by the Academy of Finland, project Nos. 293975 and 335595, the European Regional Development Fund, the Mobilitas Pluss programme (grant No. MOBJD639), and the NASA Solar System Exploration Research Virtual Institute Center for Lunar and Asteroid Surface Science, and it was conducted within institutional support RVO 67985831 of the Institute of Geology of the Czech Academy of Sciences. R.L. appreciates funding from the European Union’s Horizon 2020 research and innovation program, NEO-MAPP, grant agreement No. 870377. Publisher Copyright: © 2022. The Author(s). Published by the American Astronomical Society.Shock metamorphism in ordinary chondrites allows for reconstructing impact events between asteroids in the main asteroid belt. Shock-darkening of ordinary chondrites occurs at the onset of complete shock melting of the rock (>70 GPa) or injection of sulfide and metal melt into the cracks within solid silicates (∼50 GPa). Darkening of ordinary chondrites masks diagnostic silicate features observed in the reflectance spectrum of S-complex asteroids so they appear similar to C/X-complex asteroids. In this work, we investigate the shock pressure and associated metamorphism pattern in rubble-pile asteroids at impact velocities of 4–10 km s−1. We use the iSALE shock physics code and implement two-dimensional models with simplified properties in order to quantify the influence of the following parameters on shock-darkening efficiency: impact velocity, porosity within the asteroid, impactor size, and ejection efficiency. We observe that, in rubble-pile asteroids, the velocity and size of the impactor are the constraining parameters in recording high-grade shock metamorphism. Yet, the recorded fraction of higher shock stages remains low (<0.2). Varying the porosity of the boulders from 10% to 30% does not significantly affect the distribution of pressure and fraction of shock-darkened material. The pressure distribution in rubble-pile asteroids is very similar to that of monolithic asteroids with the same porosity. Thus, producing significant volumes of high-degree shocked ordinary chondrites requires strong collision events (impact velocities above 8 km s−1 and/or large sizes of impactors). A large amount of asteroid material escapes during an impact event (up to 90%); however, only a small portion of the escaping material is shock-darkened (6%).Peer reviewe
Effect of target properties and impact velocity on ejection dynamics and ejecta deposition
Impact craters are formed by the displacement and ejection of target material. Ejection angles and speeds during the excavation process depend on specific target properties. In order to quantify the influence of the constitutive properties of the target and impact velocity on ejection trajectories, we present the results of a systematic numerical parameter study. We have carried out a suite of numerical simulations of impact scenarios with different coefficients of friction (0.0–1.0), porosities (0–42%), and cohesions (0–150 MPa). Furthermore, simulations with varying pairs of impact velocity (1–20 km s−1) and projectile mass yielding craters of approximately equal volume are examined. We record ejection speed, ejection angle, and the mass of ejected material to determine parameters in scaling relationships, and to calculate the thickness of deposited ejecta by assuming analytical parabolic trajectories under Earth gravity. For the resulting deposits, we parameterize the thickness as a function of radial distance by a power law. We find that strength—that is, the coefficient of friction and target cohesion—has the strongest effect on the distribution of ejecta. In contrast, ejecta thickness as a function of distance is very similar for different target porosities and for varying impact velocities larger than ~6 km s−1. We compare the derived ejecta deposits with observations from natural craters and experiments