The major theme of the collaborative research centre TRR 170 'Late Accretion onto Terrestrial Planets' was to understand the late growth history of the terrestrial planets, from the last giant collisions of Moon- or 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, their early chemical differentiation, and for constraining the parameters that controlled the subsequent evolution of planetary mantles, crusts and atmospheres. To improve our fragmentary understanding of these topics, TRR 170 applied a multidisciplinary approach that combines expertise in geochemistry and petrology, remote sensing and planetary geology, and geodynamic and impact modelling. TRR 170's research program provided novel insights into the timing and rates, chemical budget, and geodynamic implications of late accretion and constrained the physicochemical boundary conditions during the relevant time interval. In addition, some projects developed new approaches to study the early evolution of planetary building materials in the early protoplanetary disk from which the planets formed. Specifically, we (1) constrained the timing and distribution of basin-forming impacts on the Moon to improve basic parameters of the cratering chronology in the inner solar system, (2) quantified the mass, provenance and chemical composition of materials accreted to Earth and Moon between 4.57 and 3.8 billion years ago, (3) determined how the compositions of Earth, Moon and Mars were modified during accretionary impacts and volatile loss processes, (4) assessed how elements with different chemical properties were distributed within the growing terrestrial planets and how this changed their subsequent evolution, and (5) developed quantitative models for the thermal evolution of the early mantle, crust and atmospheres of the terrestrial planets, including the formation of and interaction between magma ocean, crust and early atmosphere in the relevant time interval. The combined results refined our understanding of several key processes during the early evolution of the terrestrial 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.

Contact: Prof. Harry Becker

AB Geochemistry Projects in TRR 170 (Funding period 2016 to 2024):

• Subproject A01 “Chronometric investigations of ancient lunar impact rocks”, PI w. E. Scherer
• Subproject A03 "Ancient bombardment of the inner solar system – reinvestigating the “fingerprints” of different impactor populations” PI w. T. Kneissl
• Subproject B01 “Origin of the depletion of volatile metals in lunar rocks”, PI
• Subproject B02 "Stable isotope fractionation of S, Te and Pd and the rolesof core formation and late accretion on siderophile volatile elements in the Earth” PI w. M. Fischer-Gödde and T. Kleine
• Subproject B08 “Is the depletion of the moderately volatile elements in the Earth inherited from nebular processes?”, PI w. T. John
• Subproject INF “TRR 170 data management - building a planetary data portal“, PI