TRR 170: Late Accretion onto Terrestrial Planets

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The major theme of the collaborative research centre TRR 170 'Late Accretion onto Terrestrial Planets' is to understand the late growth history of the terrestrial planets, from the last giant collisions with Moon- to Mars-sized planetary embryos to the subsequent late bombardment with smaller objects. This period of planet formation is critically important for understanding the formation of the terrestrial planets and their chemical differentiation, and for constraining the parameters that controlled their subsequent evolution. To address these questions and improve our current understanding of the late growth history of the Earth, its Moon, and other terrestrial planets from 4.5 to 3.8 billion years ago, TRR 170 applies a multidisciplinary approach that combines expertise in geochemistry and petrology, remote sensing and planetary geology, and geodynamic and impact modelling. TRR 170's research programme will provide novel insights into the timing and rates, chemical budget, and geodynamic implications of late accretion and will constrain the physicochemical boundary conditions during this time interval. Specifically, we will (1) constrain the timing and distribution of basin-forming impacts on the Moon to improve basic parameters of the cratering chro-nology in the inner solar system, (2) quantify the mass, provenance and chemical composition of accreted materials between 4.5 and 3.8 billion years ago, (3) determine how the compositions of these materials were modified during accretionary impacts and magma degassing, (4) assess how accreted material was distrib-uted within the growing terrestrial planets and how it changed their subsequent evolution, and (5) develop quantitative models for the thermal evolution of the terrestrial planets, including the formation of and interac-tion between magma oceans, crust and early atmospheres in the relevant time interval. The combined results will refine our fragmentary understanding of several key processes during the early evolution of the terrestri-al planets, such as the role of giant impacts in volatile loss processes and core formation, the development and evolution of magma oceans, the transition to solid-state convection, homogenization of chemical and isotopic heterogeneities, and the cooling history of the terrestrial planets. Besides its scientific goals, TRR 170's dedicated integrated graduate programme will educate the next generation of planetary scientists, with a particular emphasis on the multidisciplinary character of modern planetary sciences.