Seminars Temps-Espace-Société
Unless otherwise stated: Monday at 2 pm – Jean-François Denisse room/Observatoire de Paris, 77 Avenue Denfert-Rochereau, F-75014 PARIS
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Seismology provides a high-precision method for constraining the internal structure of planetary bodies. Its efficiency has been demonstrated on Earth, the Moon, and Mars, with Venus, Titan and asteroids as the next mission targets. In the context of planetary seismology, meteorite impacts constitute a key source of seismic activity. Characterizing their associated signals not only refines our interpretation of seismic recordings, but also improves our understanding of the impact cratering processes themselves.
In this talk, I will describe the multiple ways in which impact science contributes to the exploration of the Solar System. I will show how impacts provided constraints on the structure of the Martian crust and lower atmosphere in the context of the InSight mission, and how they can support the search for water ice on the Moon by combining seismic measurements near the South Pole with telescopic observation of Lunar Impact Flashes (LIFs). I will also discuss the importance of theoretical and numerical modeling of impact processes for the precise interpretation of their signals.
Finally, I will present current challenges in impact science, including the complexity of modeling regolith materials in low-gravity environments such as asteroids, and the need for improved physical understanding of impact processes in the context of planetary defense.
Modern sky surveys provide an unprecedented volume of photometric and astrometric data that can be exploited to study the physical properties of asteroids on a population scale. In this work, it is demonstrated how multi-band observations from the Sloan Digital Sky Survey (SDSS) and SkyMapper are utilized to extract detections and probabilistically infer taxonomic classes for hundreds of thousands of asteroids, far surpassing the limits of traditional spectroscopic studies. These large-scale photometric datasets are complemented by statistical analyses of space-based reflectance spectra, such as those from Gaia, in which machine-learning techniques are applied to refine compositional constraints across dynamical populations. Furthermore, it is shown that survey light curves, incorporating both dense and sparse time-series data from missions like Kepler, TESS, and ZTF, enable the determination of rotational periods, shapes, and albedos. These results highlight sky surveys as a powerful and efficient tool for advancing the understanding of the physical diversity and evolutionary history of small bodies in the Solar System.
https://cnrs.zoom.us/j/98214587551?pwd=ES90wI8wRhMQ1htcq8pnxGRa44nWau.1
Planetary rings are ubiquitous structure in our Solar System, but their formation mechanisms remain under debate. One of the proposed scenarios is the tidal disruption of a nearby passing body that enters within a planet Roche limit, producing fragments that are gravitationally captured and finally form the rings. In this study, we investigate the detailed dynamical path and fate of such tidally captured fragments using direct N-body simulations including collisional fragmentation with analytical arguments. Focusing on Saturn as a representative case, we explore how the inclination (i_TD) and pericenter distance (q_TD) of the orbit of the passing body control the subsequent orbital evolution, collisional grinding, and the survival of fragments mass. Our simulations show that initially highly eccentric and inclined fragments experience differential precession driven by the planet J2 potential, followed by destructive high-velocity collisions that damp their eccentricities and inclinations. The timing and pathway of this evolution strongly depend on i_TD, modifying the dynamical picture proposed in the previous work. For low to moderate i_TD, a narrow, circular and equatorial rings finally form whose orbital radius is well predicted by an analytically derived equivalent circular radius based on the conservation of the vertical component of angular momentum. In contrast, for high i_TD, collisional damping causes a substantial fraction of the material to fall onto the planet, preventing the formation of a massive ring. We compile our results of N-body simulations with the analytical predictions on (q_TD, i_TD) parameter space and specify the parameter region where sufficient mass to form Saturn's present rings and inner satellites survives. Our results provide a unified dynamical framework linking tidal disruption events, ring formation, and the initial conditions for ring's satellite system evolution, which are also readily applied to the other giant and terrestrial planets.
https://cnrs.zoom.us/j/91889862989?pwd=KJOv4F2nl177y09GxPM5JBbWdERJci.1