Schmelzen, Impakte und der Volatilgehalt des Inneren und der Atmosphären von Mars und Venus
Zusammenfassung der Projektergebnisse
The purpose of this project was to investigate, mostly by numerical modeling, various phenomena and processes related to meteorite impacts and their effects in regard to melting in the interiors of terrestrial planets – in particular Mars and Venus – and to the relations between impacts, melting, and the evolution of planetary atmospheres, which are thought to be at least partly derived from volatile components such as water and carbon dioxide from the interior or from impactors. In one subproject, a former project was revisited and extended to derive models of the spatial patterns of density, bulk sound speed (as a measure of seismic wave velocity), and electrical conductivity of the interior of Mars. All of these variables are to some extent sensitive towards variations in the amount of water dissolved in rock-forming minerals and to the presence of melts, and all of them can in principle be measured with established geophysical methods. Average radial profiles of the density, bulk sound speed, and electrical conductivity of the present-day martian mantle were derived and compare fairly well with independent results from modeling, experiments, and observations. It was also investigated to which extent seismic or electromagnetic sounding could be used to clarify the nature of ancient basins potentially formed by very large impacts, and it was found that a dedicated experiment could help answer that question if the melts generated during the impact are extracted from their source regions efficiently; alternatively, measurements in a confirmed basin could put constraints on the extent of melt extraction in large impacts. The models encourage the use of magnetotelluric methods in missions to other planets as an additional means to probe their interiors, especially with regard to the presence of melt and their water content. Impactors modify the volatile content of a planet in several ways. If they are too small to traverse the atmosphere, they only release their own volatiles into it while also eroding the atmosphere to some degree; it depends on the properties of the atmosphere and the impactor as well as the impact parameters whether this interaction results in a net loss or gain of atmospheric mass. If the impactor reaches the ground and produces a crater, additional processes occur: material ejected during crater formation can enhance atmospheric erosion, and a part of the target is heated beyond the melting point by the shock; furthermore, crater excavation and longer-term geodynamical processes triggered by the thermal anomaly that was caused by the impact may result in magmatic activity that transports melts towards the surface. All these melts may contain volatiles that existed in the target as trace components and will exchange them with the atmosphere, thus modifying the composition of the atmosphere and the interior. As part of this project, numerical models were being developed that implemented these processes as parts of a mass balance to track the evolution of the atmosphere. Preliminary results indicate that its evolution is mostly shaped by a small number of large impactors because of the sheer absolute magnitude of the effects they cause, even though smaller impactors are more efficient if their effects are measured in terms of their own size. Melt generation in the target is by itself a complex process to which shock heating, decompression melting during the uplift stage of crater formation as well as during the longer-term geodynamical evolution, and frictional heating contribute in ways that depend on the parameters of the impact as well as on the structure and properties of the target. In this project, we build simple evolution models of generic terrestrial planets of different sizes and with different core-to-mantle ratios and investigate the effects impacts of different magnitudes produce in them at different times of their evolution, which yield different internal structures. The goal is to identify certain patterns or regularities in the amount and distribution of melt produced, but results obtained so far suggest that nonlinear behavior occurs that precludes simple interpolation between some endmember cases. This work is still in progress. Apart from these principal topics, there were some opportunities to participate in other work with some relation to the objectives of this project. Most prominent at this point is the development of a petrological melting model of martian mantle rock by Max Collinet and collaborators that is capable of closely reproducing the melting processes that generated various types of rocks from Mars.
Projektbezogene Publikationen (Auswahl)
- (2019): Dynamical effects of multiple impacts: Large impacts on a Mars-like planet. Phys. Earth Planet. Inter. 287, 76-92
Ruedas, T.; Breuer, D.
(Siehe online unter https://doi.org/10.1016/j.pepi.2019.01.003) - (2019): The habitability of stagnant-lid Earths around dwarf stars. Astron. Astrophys. 625(5), A12
Godolt, M.; Tosi, N.; Stracke, B.; Grenfell, J. L.; Ruedas, T.; Spohn, T.; Rauer, H.
(Siehe online unter https://doi.org/10.1051/0004-6361/201834658) - (2021): Electrical and seismological structure of the martian mantle and the detectability of impact-generated anomalies. Icarus 358, 114176
Ruedas, T.; Breuer, D.
(Siehe online unter https://doi.org/10.1016/j.icarus.2020.114176) - (2021): MAGMARS: A melting model for the martian mantle and FeO-rich peridotite. J. Geophys. Res. 126(12)
Collinet, M.; Plesa, A.-C.; Grove, T. L.; Schwinger, S.; Ruedas, T.; Breuer, D.
(Siehe online unter https://doi.org/10.1029/2021JE006985)
