Dynamical and chemical evolution of Mars- and Venus-like Planets
Final Report Abstract
This project has addressed topics in the thermochemical evolution of the mantles of terrestrial planets, with a focus on the interactions between large, basin-forming meteorite impacts and convection and melting in the Martian mantle. Two-dimensional numerical models that combine the fluid dynamics of mantle convection with a mineralogical model of mantle rock properties and a simplified description of meteorite impacts were developed to simulate planetary evolution over the course of the past 4.4 billion years. This research led to two major results. First, it was demonstrated that large impacts cause extensive compositional mantle anomalies as a consequence of impact-related melt production. These anomalies rise due to their thermal and chemical buoyancy and tend to integrate themselves into the lithosphere, where they may be preserved for billions of years if the lithosphere itself remains stable, as it does in Mars as well as in the Moon and Mercury but not in Venus. If such lithospheric domains are later sampled by other processes, they could reveal themselves in the form of chemical deviations from other parts of the planet. Second, it was shown how very different meteorites can result in impact craters of the same size in a given planet, but may nonetheless produce quite different effects in the deeper interior. In any given set of impacts with the same resulting crater, asteroidal impactors generally have weaker effects and produce smaller anomalies than non-asteroidal ones. On the basis of the mantle convection models and the mineralogical model, it is also possible to derive various geophysical and geochemical quantities that can be observed by spacecraft or be inferred from such observations. This possibility assists the interpretation of observations and permits a comparison with, and validation of, numerical simulations. In the framework of this project, the focus was put on deriving predictions of the density distribution of the interiors, which shapes the gravity field of a planet that is routinely mapped by orbiting spacecraft, and of seismic velocities, which are available for the Moon and are expected to become available for Mars in the near future. As far as impact-generated mantle anomalies are concerned, it was found that their gravity signature may be detectable if a good crust model is available as a constraint, but that seismological observations will only be possible with a targeted regional seismic network. Distinguishing between different impactor types is expected to be very difficult even with good gravity data.
Publications
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(2017): Globally smooth approximations for shock pressure decay in impacts. Icarus 289, 22–33
Ruedas, T.
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(2017): Impact-induced changes in source depth and volume of magmatism on Mercury and their observational signatures; Nat. Comm.
Padovan, S., Tosi, N., Plesa, A.-C., Ruedas, T.
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(2017): Interior responses to impacts by different impactor types. 48th Lunar and Planetary Science Conference, The Woodlands, TX, 2017 (Abstract 2321)
Ruedas, T., Breuer, D.
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(2017): On the relative importance of thermal and chemical buoyancy in regular and impact-induced melting in a Mars-like planet; J. Geophys. Res. – Planets, 122(7), 1554–1579
Ruedas, T., Breuer, D.
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(2017): Radioactive heat production of six geologically important nuclides; Geochem. Geophys. Geosyst., 18(9), 3530–3541
Ruedas, T.
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(2017): The habitability of a stagnant-lid Earth; Astron. Astrophys., 605, A71
Tosi, N., Godolt, M., Stracke, B., Ruedas, T., Grenfell, L., Höning, D., Nikolaou, A., Plesa, A.-C., Breuer, D., Spohn, T.
