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In the early stage of its evolution, Mars has experienced many very large meteorite impacts that left craters or basins as visible surface structures. These structures are often also associated with gravity and magnetic anomalies and identifiable on global maps. However, information derived from these data is ambiguous, but other geophysical methods, e.g., seismics and electromagnetic imaging has not yet been applied to such a target. In this study, we revisit the results from numerical mantle convection models that were coupled with a petrological model of the martian mantle and attempt to calculate electrical conductivity and seismic bulk velocity distributions. We discuss the potential of electromagnetic and seismic observations for detecting or ascertaining impact structures, for clarifying the properties of their subsurface, and for the general characterization of the deep interior of Mars. The InSight seismometer and magnetometer may offer opportunities to test some of the predictions.

Fully dynamical convection models of the martian mantle coupled with a mineralogical model and a parameterized representation of a large meteorite impact are used to derive geophysical observables, in particular synthetic density/gravity, seismic velocities, electrical conductivity, and heat flow, which are of interest with respect to the ongoing InSight mission.

Most studies of the effect of basin-forming impacts on mantle convection include only a single impact. The actual evolution of planets, however, is shaped by a multitude of impacts, many of which occur in relatively close succession and proximity to each other, and so interactions between them are expected. We follow up on some earlier studies that considered the potential cumulative effects of successive impacts and investigate the extent of mutual interaction between two or more impacts as a function of spatial and temporal separation with a series of numerical mantle convection models.

Energy sources involved in the early stages of planetary formation can cause partial or even complete melting of the mantle of terrestrial bodies leading to the formation of magma oceans. Upon planetary cooling, solidification is expected to take place from the bottom upwards because of the steeper slope of the liquid adiabat with respect to the liquidus (Elkins-Tanton, 2012; Solomatov, 2015). Fractional solidification, in particular, can lead to the formation of a compositional layering that can play a fundamental role for the subsequent long-term dynamics and evolution of the interior (Tosi et al., 2013; Plesa et al., 2014). In order to assess to what extent primordial compositional heterogeneities generated upon magma ocean solidification can be preserved, we investigate the cooling and solidification of a whole-mantle magma ocean along with the conditions that allow solid-state convection to start mixing the mantle before solidification has completed. To this end, we run 2-D numerical simulations in cylindrical geometry using the finite-volume code GAIA (Hüttig et al., 2013). We treat the liquid magma ocean in a parametrized fashion while we self-consistently solve the conservation equations of thermochemical convection in the growing solid mantle accounting for pressure-, temperature- and melt-dependent rheology. We consider two end-member cases: fractional crystallization, where melt is instantaneously extracted into the overlying liquid leaving beneath a differentiated mantle, and batch crystallization where melt remains in contact with the silicate matrix throughout solidification causing no differentiation. By testing the effects of different cooling rates and Rayleigh numbers, we show that for a lifetime of the liquid magma ocean between 1 and 10 Myr (Lebrun et al., 2013), the onset of solid state convection prior to complete mantle crystallization is possible and that part or even all of the compositional heterogeneities generated upon fractionation can be erased by efficient mantle stirring (Figure 1). We discuss the consequences of our findings in relation to the early and long-term evolution of compositional heterogeneities generated via fractional crystallization of magma oceans in terrestrial bodies with emphasis on Mars' thermochemical history.

A number of numerical mantle convection studies from the past two decades have investigated the effects of very large meteorite impacts on mantle dynamics in terrestrial planets, especially Mars. On the grounds that most observed craters seem to have been produced by collisionally evolved bodies, probably main-belt asteroids, the impactors were generally assumed to be rocky and have material parameters similar to those of the target. However, the statistical analysis does not imply that all craters derive from an S-type asteroid, as there is a significant fraction of impactors whose properties differ substantially from those of the target, and the dynamical effects in the interior may be quite different even if the final crater is similar; candidate alternative impactors include C- and X-type asteroids, comets, and TNO-type bodies. It is generally not possible to deduce the nature of the impactor from the final crater, because the remnants of the impactor are rarely preserved. We show by analyzing scaling laws how different impactors may result in the same final crater on a given planet ("isocrater impacts") and investigate some dynamical effects for different impactor types for the bodies in the inner Solar System. The analysis shows how strongly the sizes of impactors of different types must differ in isocrater impacts for any combination of density and velocity. For the dynamics of the interior, it is the subsurface features of an impact rather than the crater that are of primary interest, but their geometry and properties are more difficult to study and less well described in terms of an analytical model. We extend the analysis of existing scaling laws to investigate the differences in penetration depth and size of shocked volume for different impactor types in isocrater impacts. Apart from the geometrical relations, there are also semi-empirical relations between impactor parameters and the amount of melt produced in an impact. The differences in melt production might allow to resolve the non-uniqueness of the impactor type. We also carry out numerical mantle convection simulations with a modified version of STAGYY in which the impact is represented as an instantaneous thermal anomaly. The models show that the effects on the interior of isocrater impacts by impactors of different types can vary considerably, especially between rocky impactors with low to intermediate velocities and fast, ice-rich impactors.

Convection in planetary mantles is driven by buoyancy that results from density variations, which may have thermal or compositional causes. We study the relative importance of the thermal and compositional buoyancy of melt-induced density heterogeneities in Mars by coupling dynamical 2D convection models with a model of the mineralogy and material properties of martian rock. For the purely thermally driven models, the compositional contribution was suppressed by forcing the density to remain at the value of undepleted mantle. The main focus lies on the anomalies created by giant impacts, which lead to particularly intense melting that may reach deeper than the regular asthenospheric melting zone. The impacts are represented as instantaneous thermal anomalies. As we model them after existing martian craters, we deduce impact parameters such as the impactor size from observed final crater diameters D using empirical scaling laws. Impacts of three different sizes (D: 470-3380 km), all occurring at 4 Ga, are considered. Most models assumed a bulk water content of 36 ppm by mass, but with respect to the ongoing discussion concerning the water content of the martian mantle, we also ran some models with the fourfold initial concentration; the principal effect of this parameter concerns mantle viscosity. In models with both thermal and compositional buoyancy, the strongly depleted compositional anomaly from the impact spreads beneath the lithosphere and remains there as a stable layer, which is progressively incorporated into the growing thermal lithosphere. By contrast, the compositional anomaly in the purely thermal models is mixed back into the mantle and leaves no coherent trace that survives to the present. The thermal anomaly decays by diffusion within a few tens of millions of years in both cases. The crustal thickness at the impact site results from the combination of additional melting, crater excavation, and ejecta deposition. The results suggest that it can be locally overestimated by up to 4-8 km if impact-induced density anomalies in the mantle are neglected. The different behavior displayed by the two model variants is due to the additional density deficit caused by compositional changes of the melting rock. It suggests that the signature of an impact-generated compositional anomaly may be detectable by gravimetry, but a detection by seismics would not be expected with instrumentation whose deployment on Mars can be expected within the next decades.

With the recent increase in Gold (Au) wire cost Copper (Cu) wire becomes an attractive way to manage overall package cost. On the other hand, Copper wire bonding introduces much higher mechanical impact to underlying BEoL structures and actives because of the higher stiffness and lower ductility of Copper compared to Gold. These trends are accompanied by the application of new porous or nano-particle filled materials like low-k and ultra low-k materials for Back-end of Line (BEoL) layers of advanced CMOS technologies. As a result, higher delamination and cracking risks in BEoL structures underneath bonded areas represent an increasing challenge for the thermo-mechanical reliability requirements. To overcome the related reliability issues the authors performed a two level nonlinear FEM-simulation approach. Initially nonlinear axi-symmetric modeling and simulation of the copper bonding process are coupled with a spatial simulation model of the whole BeoL and bond pad structure. Cracking and delamination risks are estimated by a surface based cohesive contact approach and the utilization of a crushing foam constitutive material model for ultra low-k materials.

©2015. American Geophysical Union The upcoming InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) mission, to be launched in 2016, will carry out the first in situ Martian heat flux measurement, thereby providing an important baseline to constrain the present‐day heat budget of the planet and, in turn, the thermal and chemical evolution of its interior. The surface heat flux can be used to constrain the amount of heat‐producing elements present in the interior if the Urey ratio (Ur)—the planet's heat production rate divided by heat loss—is known. We used numerical simulations of mantle convection to model the thermal evolution of Mars and determine the present‐day Urey ratio for a variety of models and parameters. We found that Ur is mainly sensitive to the efficiency of mantle cooling, which is associated with the temperature dependence of the viscosity (thermostat effect), and to the abundance of long‐lived radiogenic isotopes. If the thermostat effect is efficient, as expected for the Martian mantle, assuming typical solar system values for the thorium‐uranium ratio and a bulk thorium concentration, simulations show that the present‐day Urey ratio is approximately constant, independent of model parameters. Together with an estimate of the average surface heat flux as determined by InSight, models of the amount of heat‐producing elements present in the primitive mantle can be constrained.

A new thermal infrared instrumentation to observe Io combined with the unique capabilities of PEL will provide new insights into the evolution of Io.

BMC Pulmonary Medicine 15, 7 Seiten (2015). doi:10.1186/1471-2466-15-5, Published by BioMed Central, London