Venus remains a high-priority target for unraveling the fundamental aspects of climate change and planetary evolution. A robotic lander mission to Venus has the potential of addressing the identified key outstanding scientific goals within the Venus exploration roadmap. Here, we present a new mission concept (‘KYTHERA’) for a long-duration lander system, where we present a new lander design, an entry-descent-landing sequence and corresponding landing site selection and timeline of scientific operations that can support a lander mission of up to 200 Earth days on the Venusian surface. To accommodate the long duration of the mission, the lander was designed with a vacuum-insulated core, cooled and powered by a set of radioisotope-powered Stirling generators. The identified landing site is the Lakshmi Planum region, indicated by a technical and scientific trade off. It was found that a long-duration robotic lander mission to Venus can address most outstanding key science goals outlined in the Venus exploration community. Finally, the results highlight the need for additional studies on the performance and feasibility of instrumentation and materials under Venus’ harsh surface environment.

Context. Metal-rich asteroids and iron meteorites are considered core remnants of differentiated planetesimals and/or products of oxygen-depleted accretion. Aims. Investigating the origins of iron-rich planetesimals could provide key insights into planet formation mechanisms. Methods. Using differentiation models, we evaluate the interior structure and composition of representative-sized planetesimals (~200 km diameter), while varying oxygen fugacity and initial bulk meteoritic composition. Results. Under the oxygen-poor conditions that likely existed early in the inner regions of the Solar System and other protoplanetary disks, core fractions remain relatively consistent across a range of bulk compositions (CI, H, EH, and CBa). Some of these cores could incorporate significant amounts of silicon (10–30 weight%) and explain the metal fractions of Fe-rich bodies in the absence of mantle stripping. Conversely, planetesimals forming under more oxidizing conditions, such as beyond snow lines, could exhibit smaller cores, enriched in carbon, sulfur (>1 wt%), and oxides. Sulfur-rich cores, like those formed from EH and H bulk compositions, could remain partly molten, sustain dynamos, and even drive sulfur-rich volcanism. Additionally, bodies with high carbon contents, such as CI compositions, can form graphitic outer layers. Conclusions. These variations highlight the importance of initial formation conditions in shaping planetesimal structures. Future missions, such as NASA’s Psyche mission, offer an opportunity to measure the relative abundances of key elements (Fe, Ni, Si, and S) necessary to distinguish among formation scenarios and structure models for Fe-rich and reduced planetesimals.

Phlogopite and K-richterite constitute important carrier phases for H and F in Earth's lithosphere and mantle. The relative importance depends on their stabilities at high pressure and temperature, which in turn depends on bulk composition. Most previous experimental studies focused on the thermal stability of phlogopite and K-richterite were conducted using simplified chemical compositions. Here, partial melting experiments on metasomatized and carbonated, OH ± F-bearing near-natural peridotite were performed at high pressures (2 and 5 GPa) and temperatures (1,100–1,350°C) to assess the thermal stability of F-free versus F-bearing phlogopite and K-richterite. Experimental results demonstrate that the thermal stability of F-bearing phlogopite is increased by >55°C/wt.% F, relative to F-free phlogopite, whereas K-richterite is absent in all experiments with significant degrees of melting (>2%). The thermal stability of phlogopite containing several wt.% F exceeds continental and oceanic geotherms within the upper 150 km. Fluorine-rich phlogopite would therefore be stable in virtually all of the continental lithosphere, only to be decomposed during large, regional melting events such as continental break-up, thereby acting as a major long-term sink for F and/or H. This could even be the case for the oceanic asthenosphere, depending on the oceanic geotherm of the area of interest.