Dome Craters on Ganymede and Callisto May Form by Topographic Relaxation of Pit Craters Aided by Remnant Impact Heat (2403.15653v2)

Abstract: The icy Galilean satellites display impact crater morphologies that are rare in the Solar System. They deviate from the archetypal sequence of crater morphologies as a function of size found on rocky bodies and other icy satellites: they exhibit central pits in place of peaks, followed by central dome craters, anomalous dome craters, penepalimpsests, palimpsests, and multi-ring structures. Understanding the origin of these features will provide insight into the geophysical factors that operate within the icy Galilean satellites. Pit craters above a size threshold feature domes. This trend, and the similarity in morphology between the two classes, suggest a genetic link between pit and dome craters. We propose that dome craters evolve from pit craters through topographic relaxation, facilitated by remnant heat from the impact. Our finite element simulations show that, for the specific crater sizes where we see domes on Ganymede and Callisto, domes form from pit craters within 10 Myr. Topographic relaxation eliminates the stresses induced by crater topography and restores a flat surface: ice flows downwards from the rim and upwards from the crater depression driven by gravity. When the starting topography is a pit crater, the heat left over from the impact is concentrated below the pit. Since warm ice flows more rapidly, the upward flow is enhanced beneath the pit, leading to the emergence of a dome. Given the timescales and the dependence on heat flux, this model could be used to constrain the thermal history and evolution of these moons.

• The paper reveals that dome crater evolution is size-dependent, occurring mainly for pit craters larger than 60 km in diameter.
• The paper shows that remnant impact heat significantly enhances upward ice flow beneath pit craters, facilitating dome formation.
• The paper employs finite element simulations to link thermal history with surface morphological changes on icy moons.

Analysis of Dome Crater Formation Processes on Ganymede and Callisto

The paper conducted by Caussi et al. addresses the origin and formation of dome craters observed on the icy moons Ganymede and Callisto. These features challenge the typical crater evolution sequence found on other celestial bodies by exhibiting central pits and domes. This paper proposes a novel mechanism of dome crater evolution through topographic relaxation, enhanced by residual impact heat, providing insights into the geophysical dynamics of these Jovian satellites.

Key Findings

Caussi et al. utilize finite element simulations to investigate the possibility that dome craters arise from the relaxation of pit craters. The simulations emphasize several key points:

1. Crater Size Dependency: The evolution from pit to dome craters is dependent on size. Dome craters are more likely to form from pit craters with diameters exceeding approximately 60 km. Within the size range of 60–175 km, domes can appear due to topographic relaxation over timescales of about 10 million years.
2. Remnant Impact Heat Role: Remnant heat from the impact plays a crucial role in facilitating the formation of dome craters, particularly by enhancing upward ice flow beneath the central pit. Without this residual heat, the simulations suggest that dome formation is significantly inhibited.
3. Thermal Influence and Age Correlation: Higher ambient heat flux, indicative of more ancient cratering environments, correlates with the dome formation. This suggests that ancient surfaces may exhibit different impact crater morphologies compared to more recently cooled areas.

Implications

The paper shows that the mechanism of topographic relaxation aided by remnant heat provides a plausible explanation for the distinct dome morphologies seen on Ganymede and Callisto. This highlights the importance of considering thermal histories alongside physical crater attributes in understanding surface processes on icy satellites. Furthermore, this mechanism can serve as a chronometer for evaluating the thermal evolution of these moons.

Theoretical and Practical Considerations

Theoretically, the results offer a framework for understanding how impact craters may evolve differently on icy satellites in contrast to rocky bodies. These findings underscore the influence of internal heat and surface temperatures on impact-related morphology. Practically, such research informs future exploration missions by predicting geological features that spacecraft might observe, aiding navigation and data collection strategies.

Future Directions

Future research could involve more complex simulations encompassing a broader range of thermal and mechanical properties, addressing the sensitivity of domes to different initial conditions. Comparative studies with craters on other icy bodies in the solar system could further validate the universality of these phenomena. Enhanced imaging and topographic data from upcoming missions to the Jovian system would provide additional validation and refinement of the models proposed in this paper.

Conclusion

Caussi et al. contribute substantial insights into the formation and evolution of dome craters on Ganymede and Callisto, proposing topographic relaxation driven by impact heat as a key mechanism. This paper enriches our understanding of Galilean moons' geologies and raises intriguing questions about the interplay between impacts and internal planetary processes on icy bodies. As space exploration progresses, continued investigations will undoubtedly yield an even fuller understanding of these enigmatic terrains.