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Large Impacts on the Early Earth

#2785


Large Impacts on the Early Earth: Computer and Laboratory Modeling of Physical Processes

Tech Area / Field

  • OBS-NAT/Natural Resources and Earth Sciences/Other Basic Sciences

Status
3 Approved without Funding

Registration date
06.06.2003

Leading Institute
Institute of Dynamics of the Geosphere, Russia, Moscow

Supporting institutes

  • VNIITF, Russia, Chelyabinsk reg., Snezhinsk

Collaborators

  • University of Arizona / Department of Planetary Science, USA, AZ, Tucson\nJohannes Gutenberg-Universitat Mainz / Institute of Nuclear Chemistry, Germany, Mainz\nCalifornia Institute of Technology / Seismological Laboratory, USA, CA, Los-Angeles\nHumboldt-University / Museum of Natural History / Institute for Mineralogy, Germany, Berlin\nPlanetary Science Institute, USA, AZ, Tucson

Project summary

Impacts of bodies with sizes 100 to 3000 km played a very important role in the Earth evolution. The evolution and state of the early Earth cannot be determined without comprehensive studies of these large impacts. We propose to study the processes accompanying these impacts mainly by means of computer and laboratory simulations. Obtained results will help elaborate models of the early Earth, which are developed by many scientists in the world. The project study will be focused on impactors about 3000 km in size because larger impacts on the Earth were, if any, unique, and the giant collision of the proto-Earth with approximately Mars-sized impactors (suggested as a cause for the formation of the Moon) has been intensely studied for about last three decades. On the other hand, impacts smaller than 100 km have been well studied recently through analysis of geological data, numerical modeling, and laboratory experiments. The range of impactor sizes under investigation corresponds to kinetic energies ranging within 5 orders of magnitude.

Scaling laws applicable to relatively small impacts are violated for impactors larger than 100 km because of the Earth’s spherical shape and shell structure, and other specific features of large impacts. It is suggested to investigate these poorly studied features, including shock wave propagation through the whole Earth to the antipodal point, reflection of the shock wave from the mantle/core boundary, deformation, displacement and subsequent oscillations of the core. As estimates show, huge waves propagating all over the Earth (with amplitudes up to several hundred km) may cause substantial deformation of the Earth’s surface, motion of the mantle substance, and disruption of the crust.

In the course of project implementation the evolution of crater ejecta will be studied. A substantial part of ejecta falls back onto the Earth. For the largest of the impactors under consideration the mass of the fallen back ejecta can be by three orders of magnitude bigger than the mass of the modern atmosphere and, therefore, these impacts strongly influenced the atmospheric evolution. Most of volatile substances replenished the atmosphere with composition quite different from the modern one. The least volatile part of the fallen back ejecta could form a global melted layer with an equivalent thickness as large as several tens kilometers for a 3000 km impactor.

Large impacts lead to displacement of the substance of the Earth’s interior from deep layers near the impact site to the upper layers in other regions and mixing of the Earth’s substance with that of the impactors. Appearance of magma ocean or melted pools under the impact site can be accompanied by extrusion of magma rising through gaps between blocks of the crust. Resulting volcanic activity influences the atmospheric chemical composition. A large amount of dust and greenhouse gases, which appear in the atmosphere, affects the cooling rates of the mantle and forming crust. Not all of these processes can be adequately simulated. In these cases it is planned to make estimates and simulations on the base of simplified models.

The Project is targeted for obtaining quantitative characteristics of the impacts, such as energy and mass partitioning, molten and evaporated masses, escaped masses, and masses ejected into Earth-bound orbits. The hydrodynamic and physical quantities associated with the large impacts have not been well determined yet and this is one of the main aims of the Project. The anticipated results will have fundamental importance for understanding the Earth’s evolution, for planetology, geology, geochemistry and geophysics. Computer and laboratory simulations and theoretical estimates are main techniques to solve the problem. Laboratory modeling experiments will be used to study volumetric heating and melting of meteoritic substance in a high-power microwave installation built in IDG. Other laboratory experiments will be carried out for the investigation of separation in mixture of immiscible liquids.

One of the project aims is development of reliable physical mathematical models, methods, and software, and also pursuance of direct numerical simulations of phenomena accompanying large hypervelocity impacts on the Earth. It is proposed to develop a 3D complex of codes to simulate the motion of medium with block structures, with account of compressibility of real media (in dynamic, shock processes), strength, viscosity and plasticity, and also distortions of the gravitational field during large impacts. 3D simulations will give the pattern of the processes and consequences of large-scale impacts typical for the period of heavy bombardment; scenarios of geodynamic relaxation will be elaborated.

The best use of models, methods and code complexes previously developed in RFNC-VNIITF and IDG RAS and the experience in simulations of physical processes in closely-related fields of physics will be made in the course of development of means for numerical simulations of hypervelocity collisions. New principles of mesh generation based on the results of the Ural School of Academician A.F. Sidorof will be used for direct numerical modeling.

Participants of the Project have great experience in the numerical simulations and laboratory modeling of hydrodynamic and physical processes. Some of these scientists have long experience in the studies of early Earth evolution and large impacts upon the Earth and other planets. The Project will provide the possibility for all the participants involved in the development and testing of nuclear weapons to reorientate their activity for peaceful and fundamental scientific goals. The interaction with collaborators will help adjust the course of investigations and to integrate weapon scientists into the world scientific community.


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