Isidis Planitia is the third-largest impact basin on Mars, located on the north-south dichotomy boundary. It is marked by major geological events that have occurred both globally and regionally. The basin shows two distinct faces. The first is the presence of a high-density subsurface mass concentration, the strongest on Mars, outside of the major volcanic provinces. The second is a clustering of kilometre-scale pitted cone chains of unknown origin, hypothesised to be of volcanic, glacial, or sedimentary origin. This thesis investigates whether and to what extent the subsurface structure of Isidis Planitia controls the surface formation of the pitted cones.

To investigate the interior structure, this thesis combines topographic and gravitational data to construct subsurface models. The models are constrained against observed gravitational anomaly to fit plausible layer geometries and densities. The best-fit model is used to assess the basin’s thermal and stress conditions. The relationship between this subsurface structure and the distribution of pitted cones is then evaluated by correlating with both surface and interior features.

The best-fit structure contains a sedimentary layer that is significantly thicker than previous estimates, at approximately 1.3 km. It also contains a central melt sheet (combined with lava deposits) up to 19 km thick, extending across the plains. Most importantly, the model requires a large volume (approximately 1.7 x 10^6 km³) of mantle-like, high-density materials in the inner basin. This element reaches the near-surface and is identified as a significant plutonic intrusion. The pitted cone distribution shows a poor direct correlation with this subsurface, but aligns strongly with the surface topography, conforming to pre-existing wrinkle ridges. Two distinct sets of wrinkle ridges are observed, with the latter one linked to pluton-driven deformation and subsequent cone emplacement.

Findings support the formation of pitted cones as volcanic rootless cone analogues, resulting from the interaction of a lava deposit with near-surface volatiles. The lava deposit is likely sourced in the north-west, flowing out to the north-east and south-east. The evidence suggests the source is located on the Syrtis Major Planum complex, or derived from the basin floor linked to the plutonic intrusions. Although limited by the available topographical and gravitational data, this first complete synthesis of Isidis Planitia is capable of explaining all its key characteristics in a coherent timeline.

Related dataset 4TU.ResearchData: https://doi.org/10.4121/7f02991f-daac-44c4-8f86-1deb5236b1ec

Surface heat flux, which can be defined as the heat flowing out of the interior of a planetary body, provides important constraints on the present-day thermal state of the lunar interior. Measurements, performed in situ during the Apollo program, and from orbit by Chang’E 1, Chang’E 2, and by the Diviner radiometer instrument, indicate important lateral variations in surface heat flux on the Moon (~5-180 mW/m²). The differences between Apollo 15 and Apollo 17 measurements have been explained by the presence of an anomalous region, enriched in uranium (U), thorium (Th), and KREEP (Potassium, Rare Earth Elements, and Phosphorus) elements, located on the lunar nearside. Previous modeling efforts also identified crustal thickness and thermal conductivity variations as secondary causes for surface heat flux differences. However, detailed explanations for the remaining two estimates and their implications for the evolution of the Moon remain highly debated. Additionally, the structure and properties of this putative KREEP-rich layer have remained uncertain.

Therefore, this study proposes a new global geodynamic model of lunar thermal evolution that includes lateral variability in the distribution of radiogenics, crustal thickness, and thermal conductivity. The present setup is capable of simultaneously explaining the variability between the Apollo 15, Apollo 17, and Region 5 heat flux values, while also providing further constraints on the KREEP layer structure and lunar crustal properties. The research question addressed in this work is: What is the effect of crustal structure (radiogenics, thickness, and thermal conductivity distribution) on 3D thermal evolution models of the Moon?

Here, we model the interior dynamics and thermal evolution of the Moon after magma ocean solidification using the fluid solver GAIA. We investigate the abundance and distribution of radiogenics on the Moon, and how they shape the interior temperature distribution through time. Additionally, we account for a spatially variable crustal thickness, derived from gravity and topography data. We also include a laterally variable thermal conductivity model, derived from porosity data, which we constrain using the nearside-farside differential thermal state of lunar basins. We model and vary the extent of a putative KREEP layer underlying the PKT (Procellarum KREEP Terrane) region. We enrich the KREEP layer and crust in heat-producing elements compared to the mantle, simulating an asymmetrical distribution of radiogenics as an initial condition.

We find that measurably lower heat flux values at the lunar south pole compared to Apollo 15 and 17 require KREEP material to extend at least partly beneath Mare Serenitatis. In this case, the Apollo 15 measurement would be representative of the KREEP region average heat flux, while Apollo 17 would lie on its edge. On the other hand, a smaller KREEP region (<1200 km in diameter) would make the Apollo 17 location representative of non-KREEP terrane, and show heat flux comparable to south pole values. This is incompatible with estimates based on the Diviner Lunar Radiometer Experiment onboard Lunar Reconnaissance Orbiter, although uncertainties associated with these estimates are unclear. Heat flux measurements that will be performed by the NASA CLPS-CP12 mission at Schrödinger crater will provide key information to exclude one of these two scenarios, and thus potentially constrain the extent of the KREEP layer underneath the PKT region.

Our results also show that a laterally variable thermal conductivity helps reduce the interior temperatures, while maintaining surface heat flux distribution unchanged. We find an effective farside crustal conductivity of ~2 W/(mK) (comparable to that of compact anorthosite) to best match the differential basin relaxation constraints, implying negligible effect of a porous megaregolith layer on the thermal conductivity. In the KREEP region, we favour models with effective crustal conductivity below 2 W/(mK), suggesting that lunar volcanic basalts may have an even lower bulk conductivity than the 2.6-2.7 W/(mK) values considered here. This could be due to the porosity of lunar volcanic material, a more complex layering of basaltic eruptions, or the effect of the temperature and pressure dependence of thermal conductivity. Although our model setup is simplified, it provides novel insights on the distribution of radiogenics and crustal properties on the Moon, and shows the potential to further constrain the asymmetrical character of lunar evolution.

With new rovers landing on Mars, like the Perseverance rover in 2020, the interest in Mars has grown recent years. The atmospheric conditions on Mars result in challenging conditions due to its low density atmosphere and extremely low temperatures. With a density on Mars that is 1% of that on Earth, creating sufficient lift for vehicles to fly becomes a challenge. The low density results in low Reynolds numbers. The low temperature has an effect on the speed of sound, due to which the Mach number is significantly higher at the same flow velocity compared to Earth. Airfoil data at these conditions, low Reynolds number - high Mach number, are sparse, but crucial for design of aerial vehicles. Next to the aerodynamic conditions, dunes on Mars are formed and migrate. The parameter of interest which defines the conditions required for transportation of particles is the threshold shear velocity. This parameter has been determined by different analytical expressions. However, the outcome remains a broad range, which point out the difficulty and inaccuracy of the results. Therefore, in this document, the design of a carousel wind tunnel is investigated to determine its feasibility to perform aerodynamic and aeolian measurements. The carousel wind tunnel consists of two concentric drums, of which the inner one rotates. The carousel wind tunnel is analysed by a computational fluid dynamics analysis with the k - ω turbulence model. The results indicate that due to secondary flow effects and the wake of a test object, no accurate aerodynamic measurements can be performed. Aeolian measurements are deemed feasible, with increased accuracy at sufficiently high rotational velocities.