Planetary surfaces hold evidence of past geological processes through the geomorphological record of landforms. Fast erosion rates, active tectonics, and a thick atmosphere contribute to partial or total loss of the terrestrial record, therefore leading to the misinterpretation and underestimation of the geological processes that formed it. Well-preserved extraterrestrial landforms, coupled with high resolution imagery, can compensate for the terrestrial missing geomorphological information. On the other hand, on Earth, we have direct access to landforms. Field observations are vital to gain insights into the mechanisms involved and into the environmental and climatic conditions in which landforms form. Therefore, the combination of terrestrial and planetary observations can be very effective in better understanding geological processes across the Solar System.

This talk will focus on long runout landslides and impact craters. I will discuss: a) the importance of comparative planetary geology in studying long runout landslides on Mars and Earth, in the attempt to understand their emplacement mechanisms and the link with climatic conditions; b) present day impact events on the Moon and the implications for Solar System chronology and impact flux rate.

Polygonal networks occur on various terrestrial and extraterrestrial surfaces holding valuable information on the pedological and climatological conditions under which they develop. However, in contrast to their periglacial counterparts, the information that polygons in the hyper-arid Atacama Desert can provide is little understood. To gain insights into their geometrical and geochemical build-up, we performed a morphometric terrain characterization in combination with geochemical and sedimentological analysis on four polygonal networks in the Yungay area of the Atacama Desert. The polygons are composed of siliciclastic sediment that is mainly cemented by sulfates in ~0–50 cm depth and by nitrates and chlorides in ~50–100 cm depth while being separated by about 1 m deep, salt-poor and V-shaped sand wedges. The high salt content (>60 wt%) and high surface temperature variations make a thermal contraction origin likely. The low clay content (~2 wt%) makes an exclusive desiccation origin less relevant but a formation based on dehydration of sulfates remains conceivable. Morphometric data indicate a link between topography and polygon geometry, as the flat-centered polygons (mean size ~4 m) are aligned either in slope direction or perpendicular to it, while being more elongated on steeper slopes. Erosion of these networks is mainly eolian-driven, but we also find signs for aqueous resurfacing of microtopography by fog and minimal rainwater infiltration. Our findings provide a basis for future polygon research in hyper-arid environments, such as Mars, while allowing for the use of polygons as environmental proxies in the Atacama Desert that indicating saline soils and hyper-arid conditions.

One of the limits of planetary habitability of Earth and other water-rich planets relates to the instability with respect to global glaciation, a fundamental property of the climate system caused by the positive ice-albedo feedback. Due to the steady increase in solar luminosity, the atmospheric concentration of carbon dioxide (CO₂) at which this Snowball bifurcation occurs evolves over time. Earlier studies on the limit of global glaciation are based on investigations with very simple climate models for Earth’s entire history or studies of individual time slices carried out with a variety of more complex models and for different boundary conditions, making comparisons difficult. Here we use a relatively fast coupled climate model of intermediate complexity to trace the Snowball bifurcation of an aquaplanet through Earth’s history in one consistent modelling framework. We find that the critical CO₂ concentration decreases more or less logarithmically with increasing solar luminosity until about 1 billion years ago, but drops faster in more recent times. Furthermore, there is a fundamental shift in the dynamics of the critical state about 1.8 billion years ago, driven by the interplay of wind-driven sea-ice dynamics and the surface energy balance. These results highlight once again the importance of climate dynamics for investigations of planetary habitability.

The Earth’s magnetic field shields our planet against highly energetic particles from the Sun and outer space. Over geological times, the time-varying geomagnetic field exhibited periods of dramatic changes, both in intensity and direction. Recent data compilations of paleomagnetic records enable us to model the long-term, global evolution of the geomagnetic field and better understand the internal dynamics and underlying phenomena. On the other hand, the spatial and temporal changes influence the shielding and cosmogenic nuclide production rates. In general, the higher the field intensity, the larger the shielding and the fewer cosmogenic nuclides are produced in the atmosphere.

We cover the evolution of the geomagnetic field over the past 100 000 years by presenting characteristics found to be robust in available global models. The period includes a few geomagnetic excursions, including the Laschamps excursion 41 000 years ago – when the intensity was globally very low, and the field had a complex, multipolar structure. Several properties of and estimates based on the models will be discussed, including the field morphology at the core-mantle boundary and Earth’s surface, global cutoff rigidity variations, impact area, global cosmic ray flux, and production rates of different cosmogenic nuclides. The latter results from the models are validated through comparison with actual measurements from ice and marine cores.