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The evolution of planets is driven by the composition, structure, and thermal state of their internal core, mantle, lithosphere, crust, and by interactions with possible ocean and atmosphere. The Interuniversity Attraction Pole (IAP) ‘PLANET TOPERS’ addresses the fundamental understanding of the relationships and interactions between those different planetary reservoirs and their evolution through time. It brings further insight into the origin and sustainability of life on planets, including Earth.

The proposed interdisciplinary approach applied in this project goes beyond that of current studies in Earth-System and Planetary Sciences and/or Astronomy by
• Encompassing the entire planet from the upper atmosphere to the deep interior in the frame of the study of its habitability;
• Including, beside the Earth, a whole range of rocky bodies in the Solar System: such as Earth-like planets, natural satellites, and undifferentiated asteroids.

Particular attention is devoted to Mars, but also to planets and satellites possessing an atmosphere (Earth, Mars, Venus and Titan) or a subsurface ocean (e.g., Europa), because those are the best candidates for hosting life. The Interuniversity Attraction Pole (IAP) ‘PLANET TOPERS’ (Planets: Tracing the Transfer, Origin, Preservation, and Evolution of their ReservoirS) addresses four main themes: (1) the interaction between the interior and the atmosphere, (2) the interaction between the atmosphere and space, (3) the identification of preserved life tracers and interaction of life with planetary evolution, and (4) accretion and evolution of planets. The four themes are integrated into a comparative history of habitability conditions for Mars, Earth, and Venus.

The research program builds on, refines, and couples models of the individual reservoirs developed by the different partners. It also integrates new results of planetary geodesy – probing the deep interior, and of atmosphere remote sensing, laboratory studies of meteorite samples, and observations of traces of life in past and present extreme conditions. The search for biomarkers and traces of life on early Earth serves as a case study to refine techniques allowing to detect potential habitats and possible life on other planets. A strong emphasis is also placed on impact processes, an obvious shaper of planetary evolution, and on meteorites that document the early Solar System evolution and witness the geological processes taking place on other planetary bodies. The proposed research also relies on spectroscopic and isotopic laboratory measurements, geochemical analytical developments, and theoretical calculations to determine reference parameters and to unravel reaction mechanisms, allowing the optimal retrieval of information from observation data, and providing a deeper insight into the chemistry, physics, and dynamics of atmospheres and rocky materials.

The research to be carried out by the IAP is organized as follows:

to better understand the concept of habitability, i.e. the environmental conditions capable of sustaining life.


- To improve our understanding of the thermal and compositional evolution of the different reservoirs (core, mantle, crust, atmosphere, hydrosphere, cryosphere, (and space)) considering interactions and feedback mechanisms;
- To investigate the chronology of differentiation processes, the onset conditions of plate tectonics and recycling of the crust and their implications for the early thermal and compositional evolution of a planet;
- To examine the role of impacts of meteorites and comets in the atmospheric evolution of the planets, providing loss and replenishment of the atmosphere or possibly even changing the magnetic field;
- To determine the observational constraints related to meteorites, in order to better understand the impact process and impact fluxes as a function of time;
- To identify preserved biosignature and to understand the interactions through time between life and geochemical reservoirs; to search for traces of life, with early Earth as a case study;
- To perform a detailed comparison of the habitability of Mars, Earth, and Venus, based on the integrated analysis of the interacting reservoirs.


- Remote sensing: analyzing and interpreting data recorded by existing instruments (space-based and ground-based), using improved models, such as radiative models of planetary atmospheres or thermal and compositional models of planetary interiors; - In situ measurements: examining tracers of life in early Earth material (biosignatures) and extraterrestrial samples (meteorites), measurement of fields and particles in space from existing and future missions;
- Performing laboratory measurements and developing analytical and theoretical methods in support of such data;
- Developing and improving models and incorporating new results from laboratory data or spacecraft observations.

Of prime interest in terms of global system evolution are the early states of Mars, Venus, and Earth. Though the conditions on these planets were similar soon after their formation, their histories have diverged about 4 billion years ago. The reasons for this decoupling in evolution is addressed through comparative studies with other rocky bodies that from the start followed a different evolutionary pathway, such as Mercury, the moons or the small rocky bodies in the asteroid belt.

The IAP network involves teams combining different but highly complementary expertise. The partners belong to two Belgian federal institutions, four Belgian universities and one German Research Center. The Pole gathers existing and internationally recognized expertise in planetary sciences, geobiology, cosmo/geochemistry, and analytical and physical chemistry, with the aim of establishing a solid interdisciplinary network infrastructure in Belgium. Through this synergy, it enables the most advanced research in planetary evolution to be carried out and reinforces the international competitiveness of the Belgian teams involved. Backbone activities of the IAP include PhD student and post-doc training, working groups, PLANET TOPERS weeks meetings, and public outreach activities. All these activities will further be strengthened by soft skill exchange and communication that focus on optimizing the interactions between the participating scientists.

As the research strategy mainly focuses on unraveling and understanding the mechanisms and exchanges between the various planetary reservoirs, specific methods will be developed to boost internal collaborations, e.g. by putting the emphasis, through the definition of PhD and Postdoctoral research topics, on the interaction between the different reservoirs, in a trans-disciplinary approach between teams. In cooperation and full synergy with the foreign partner, the goal is to evolve into an excellence center in planetology, astrobiology and habitability at the international level. Determining the possibility and limitations of extraterrestrial life is of fundamental importance to mankind with profound philosophical implications. By evaluating the interactions between planetary evolution and life on such a large scale, the PLANET TOPERS project puts the evolution of our home planet (even the current anthropogenic effects) into perspective.