The early bombardment history of Mars may have drastically shaped its crustal evolution. Impact-induced melting of crustal and mantle materials leads to the formation of local and regional melt ...ponds, and the cumulative effects of the impact flux could result in widespread melting of the crust. To quantify impact-melt production, its provenance and final distribution as a function of impact conditions, we carried out a systematic parameter study using the iSALE shock physics code. In contrast to simplified scaling laws for estimating the amount of melt generated by shock compression, we take the planet's thermal state at the time of impact into account. In addition, we consider decompression melting as a consequence of lithostatic uplift of initially deep-seated material. We find that the geothermal profile has a strong effect on melt production, and that melt volumes are significantly increased by up to a factor of seven in comparison to existing analytical estimates. Enhanced melting occurs at impactor sizes (and velocities) that deposit most of their energy at a depth close to the base of the lithosphere. Impactors larger than 10 km penetrate through the lithosphere and can generate a significant amount of melt by decompression due to lithostatic uplift, which can make up to 40% of the total melt volume. In some cases, the total melt volume exceeds the volume of the transient (and final) crater and the surface expression of these collisions may resemble large igneous provinces rather than typical craters.
•Melt production on early hot Mars is increased by up to 7× compared to scaling laws.•Decompression can notably contribute to melting in large impacts on early Mars.•Paucity of large carters on Mars may explained by craters drowning in their melt.•Classical scaling laws fail to estimate melt production by large impactors (> 10 km).
•We develop scaling laws for the impact-induced heat distribution and melt shape.•We perform more than 100 smoothed particle hydrodynamic (SPH) simulations.•Our model reproduces the mantle heat ...distribution calculated by SPH generally well.•The pressure at the base of a melt pool is higher than that of a global magma ocean.•Our model is publicly available through GitHub.
Growing protoplanets experience a number of impacts during the accretion stage. A large impactor hits the surface of a protoplanet and produces impact-induced melt, where the impactor's iron emulsifies and experiences metal-silicate equilibration with the mantle of the protoplanet while it descends towards the base of the melt. This process repeatedly occurs and determines the chemical compositions of both mantle and core. The partitioning is controlled by parameters such as the equilibration pressure and temperature, which are often assumed to be proportional to the pressure and temperature at the base of the melt. The pressure and temperature depend on both the depth and shape of the impact-induced melt region. A spatially confined melt region, namely a melt pool, can have a larger equilibrium pressure than a radially uniform (global) magma ocean even if their melt volumes are the same. Here, we develop scaling laws for (1) the distribution of impact-induced heat within the mantle and (2) shape of the impact-induced melt based on more than 100 smoothed particle hydrodynamic (SPH) simulations. We use Legendre polynomials to describe these scaling laws and determine their coefficients by linear regression, minimizing the error between our model and SPH simulations. The input parameters are the impact angle θ (0∘,30∘,60∘, and 90∘), total mass MT (1MMars−53MMars, where MMars is the mass of Mars), impact velocity vimp (vesc−2vesc, where vesc is the mutual escape velocity), and impactor-to-total mass ratio γ (0.03−0.5). We find that the equilibrium pressure at the base of a melt pool can be higher (up to ≈80%) than those of radially-uniform global magma ocean models. This could have a significant impact on element partitioning. These melt scaling laws are publicly available on GitHub (https://github.com/mikinakajima/MeltScalingLaw).
Melting and vaporization of rocks in impact cratering is mostly attributed to be a consequence of shock compression. However, other mechanism such as plastic work and decompression by structural ...uplift also contribute to melt production. In this study we expand the commonly used method to determine shock‐induced melting in numerical models from the peak shock pressure by a new approach to account for additional heating due plastic work and internal friction. We compare our new approach with the straight‐forward method to simply quantify melting from the temperature relative to the solidus temperature at any arbitrary point in time in the course of crater formation. This much simpler method does account for plastic work but suffers from reduced accuracy due to numerical diffusion inherent to ongoing advection in impact crater formation models. We demonstrate that our new approach is more accurate than previous methods in particular for quantitative determination of impact melt distribution in final crater structures. In addition, we assess the contribution of plastic work to the overall melt volume and find, that melting is dominated by plastic work for impacts at velocities smaller than 7.5–12.5 km/s in rocks, depending on the material strength. At higher impact velocities shock compression is the dominating mechanism for melting. Here, the conventional peak shock pressure method provides similar results compared with our new model. Our method serves as a powerful tool to accurately determine impact‐induced heating in particular at relatively low‐velocity impacts.
Plain Language Summary
During the collision of cosmic bodies such as planets and asteroids on various scales, the involved material is heated such that melting or vaporization can occur. The vast amount of heat is considered to be generated during shock compression, however recent studies found that plastic deformation during decompression also contribute to the heating process. In this study, we introduce a new approach to quantify impact‐induced melting more accurately under consideration of the latter heating mechanisms. We demonstrate that our approach is more accurate than previous attempts and quantify the contribution from plastic work on impact‐induced melting. We systematically study the effect of impact velocity and material strength on melt production and find, that it is dominated by plastic work for impact velocities up to 7.5–12.5 km/s in rocks, depending on the material strength.
Key Points
We propose an improved method to quantify impact‐induced melt production for rocks
We quantify impact‐induced melt production and separate between heating due to shock compression and plastic work
Melting due to frictional heating (plastic work) dominates over shock melting for impact velocities below 7–13 km/s depending on strength
•The settling of impact-delivered metal in a terrestrial magma ocean is studied.•The settling history of metal droplets depends on the target latitude of the impact.•Fast settling at poles, slower ...settling at lower latitudes due to planetary rotation.•Low degree of mixing and metal-silicate equilibration for impacts near to the poles.•Larger degree of dispersion and equilibration for impacts at lower latitudes.
Impacts on Earth crucially influenced core formation and the subsequent evolution of Earth's mantle and may have contributed to late accretion of material. However, to what extent the present-day geochemical signature of Earth's mantle reflects the processes of core formation and late accretion, and how much of material delivered by giant impacts and by impacts of smaller projectiles during late accretion was incorporated into the core remains unclear. To improve the insight into these processes, it is of key importance to comprehend how impact-delivered metal droplets are dispersed and subsequently settle in a terrestrial magma ocean. Settling and mixing are potentially strongly influenced by the convective and rotational state of the magma ocean.
Therefore, by means of numerical experiments in spherical geometry, we study how the convective state of the magma ocean and the potentially strong planetary rotation affect the settling of impact-delivered material in a deep global magma ocean. We reveal crucial differences in metal dispersion and in settling history depending on the impactor's target latitude. For an impact at either pole, the metal dispersion within the magma ocean is spatially limited while the metal droplets settle fast. Impacts at lower latitudes allow for a higher degree of dispersion, being accompanied by a slower metal settling. Consequently, metal-silicate equilibration may differ depending on the target latitude, being limited to certain localized domains of the magma ocean. We further demonstrate that the volume fraction undergoing metal-silicate equilibration seems to depend linearly on the impactor's diameter and may be largely underestimated in previous studies. Overall, we present a possible mechanism for heterogeneous metal-silicate equilibration and the generation of chemical heterogeneities and isotopic anomalies in Earth's mantle due to the influence of planetary rotation, potentially shaping the geochemical signatures that are observed today.
Differently aged impact melt in lunar samples is key to unveiling the early bombardment history of the Moon. Due to the mixing of melt products ejected from distant craters, the interpretations of ...the origin of lunar samples are difficult. We use numerical modeling for a better quantitative understanding of the production of impact‐induced melt and in particular its distribution in ejecta blankets for lunar craters with sizes ranging from 1.5 to 50 km. We approximate the lunar stratigraphy with a porosity gradient, which represents the gradual transition from upper regolith via megaregolith to the solid crustal material. For this lunar setting, we quantify the melt production relative to crater volume and derive parameters describing its increasing trend with increasing transient crater size. We found that about 30%–40% of the produced melt is ejected from the crater. The melt concentration in the ejecta blanket increases almost linearly with distance from the crater center, while the thickness of the ejecta blanket decreases following a power law. Our study demonstrates that if in lunar samples the concentration of a melt with a certain age is interpreted to be of a nonlocal origin, these melts could be the impact products of a large crater (>10 km) located hundreds of kilometers away.
Plain Language Summary
Lunar samples contain abundant impact‐induced melt that crystallized at different ages. The melt ages record the formation time of its source craters and are key for a better understanding of the lunar bombardment history. In samples, there is not only the melt derived from the sampling region but also some that originate far away by being entrained in the ejecta of distant craters. Recognizing the distant‐derived melt is essential for the more credible sample interpretation, which requires knowledge of the melt distribution in the ejecta. We use numerical modeling to quantify the production of impact‐induced melt and in particular its distribution in ejecta blankets for lunar craters. We found that the melt concentration in the ejecta blanket increases with distance from the crater center. If the concentration of distant‐derived melt of a certain age in lunar samples is rather high (>30%), it could originate from large craters (>10 km) located hundreds of kilometers away.
Key Points
The melt concentration in the ejecta blanket increases almost linearly with distance from the crater center
Near‐surface porosity causes an increase in melt production. Due to decreasing porosity with depth, it is more prominent at small craters
The melt concentration in distal ejecta of crater of 10's km is rather high (>30%)
Here, we develop scaling laws for (1) the distribution of impact-induced heat within the mantle and (2) shape of the impact-induced melt based on more than 100 smoothed particle hydrodynamic (SPH) ...simulations. We use Legendre polynomials to describe these scaling laws and determine their coefficients by linear regression, minimizing the error between our model and SPH simulations. The input parameters are the impact angle \(\theta\) (\(0^{\circ}, 30^{\circ}, 60^{\circ}\), and \(90^{\circ}\)), total mass \(M_T\) (\(1M_{\rm Mars}-53M_{\rm Mars}\), where \(M_{\rm Mars}\) is the mass of Mars), impact velocity \(v_{\rm imp}\) (\(v_{\rm esc} - 2v_{\rm esc}\), where \(v_{\rm esc}\) is the mutual escape velocity), and impactor-to-total mass ratio \(\gamma\) (\(0.03-0.5\)). We find that the equilibrium pressure at the base of a melt pool can be higher (up to \(\approx 80 \%\)) than those of radially-uniform global magma ocean models. This could have a significant impact on element partitioning. These melt scaling laws are publicly available on GitHub (\(\href{https://github.com/mikinakajima/MeltScalingLaw}{https://github.com/mikinakajima/MeltScalingLaw}\)).
Recent studies have emphasized the importance of impurity scattering for the optical Higgs response of superconductors. In the dirty limit, an additional paramagnetic coupling of light to ...superconducting condensate arises, which drastically enhances excitation. So far, most work concentrated on the periodic driving with light, where the third-harmonic generation (THG) response of the Higgs mode was shown to be enhanced. In this paper, we extend this analysis by calculating full temperature and frequency dependence of THG to better compare the theory with current experimental setups. We additionally calculate the time-resolved optical conductivity of single- and two-band superconductors in a two-pulse quench-probe setup, where we find good agreement with existing experimental results. We use the Mattis-Bardeen approach to incorporate impurity scattering and calculate explicitly the time-evolution of the system. In contrast to previous work we calculate the response not only within a time-dependent density-matrix formalism but also in a diagrammatic picture derived from an effective action formalism, which gives a deeper insight into the microscopic processes.
In high-energy physics, the Higgs field couples to gauge bosons and fermions and gives mass to their elementary excitations. Experimentally, such couplings can be inferred from the decay product of ...the Higgs boson, i.e., the scalar (amplitude) excitation of the Higgs field. In superconductors, Cooper pairs bear a close analogy to the Higgs field. Interaction between the Cooper pairs and other degrees of freedom provides dissipation channels for the amplitude mode, which may reveal important information about the microscopic pairing mechanism. To this end, we investigate the Higgs (amplitude) mode of several cuprate thin films using phase-resolved terahertz third harmonic generation (THG). In addition to the heavily damped Higgs mode itself, we observe a universal jump in the phase of the driven Higgs oscillation as well as a non-vanishing THG above T
. These findings indicate coupling of the Higgs mode to other collective modes and potentially a nonzero pairing amplitude above T
.
Cuprate high-T
superconductors are known for their intertwined interactions and the coexistence of competing orders. Uncovering experimental signatures of these interactions is often the first step ...in understanding their complex relations. A typical spectroscopic signature of the interaction between a discrete mode and a continuum of excitations is the Fano resonance/interference, characterized by the asymmetric light-scattering amplitude of the discrete mode as a function of the electromagnetic driving frequency. In this study, we report a new type of Fano resonance manifested by the nonlinear terahertz response of cuprate high-T
superconductors, where we resolve both the amplitude and phase signatures of the Fano resonance. Our extensive hole-doping and magnetic field dependent investigation suggests that the Fano resonance may arise from an interplay between the superconducting fluctuations and the charge density wave fluctuations, prompting future studies to look more closely into their dynamical interactions.
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