A narrowly missed four-body resonant chain among the Galilean moons
PARIS.
The Galilean moons of Jupiter present one of the most peculiar orbital configurations in the solar system: a 4:2:1 three-body resonance between Io, Europa, and Ganymede, known as Laplace resonance. The outer moon, Callisto, is not involved in the Laplace resonance, but it is currently very close to a 7:3 resonance with Ganymede. Considering the estimated rate of the moons' orbital migration, this 7:3 resonance was encountered approximately two million years ago. To assess the effect of this resonance crossing, we performed accurate numerical simulations of the moons' orbital evolution over the last few million years. We found that the dynamical pathway that best reproduces the current configuration of the system requires that Ganymede and Callisto were not captured into the 7:3 resonance, not even temporarily. In this scenario, the moons started with eccentricities slightly larger than today's, which decreased due to the resonance crossing, eventually matching their present-day values. Under different initial conditions, capture into the 7:3 resonance would have been almost unavoidable, and today we could admire a four-body resonant chain between the Galilean satellites. However, had the moons been captured and subsequently exited the resonance, their eccentricities would have increased far too large, making such an evolutionary path incompatible with the observed system. Nevertheless, the crossing of the 7:3 resonance explains orbital features that have remained a mystery until now, such as the libration amplitude of the Laplace resonance. Moreover, we found evidence of a three-body resonance crossing among the three outer moons that occurred just 20,000 years ago.
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Meteorites and impact processes: from planetary seismology to planetary defense
Marouchka Froment, Institut de Physique du Globe de Paris
PARIS.77 avenue Denfert-Rochereau, 75014 Paris, France.
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.
Deep learning-enabled size estimation of comets indicates a more dynamic early solar system
Shunjing Zhao, LTE
PARIS.77 avenue Denfert-Rochereau, 75014 Paris, France.
The formation and evolution of the Solar System’s two major comet reservoirs, the Oort Cloud and the Scattered Disk, remain poorly constrained. Observations of comet flux imply a population ratio between these reservoirs that exceeds predictions from models of giant planet instability by more than two orders of magnitude. A major source of uncertainty lies in determining comet sizes, as the nucleus is often obscured by the surrounding coma. Here we derive independent nucleus sizes for 28 comets by activity modeling with artificial intelligence to infer sizes directly from variations in water emission. We find that long-period comets possess significantly larger nuclei than short-period comets with comparable absolute brightness. Our results indicate that the Oort Cloud is nearly three orders of magnitude more populated than the Scattered Disk, implying that processes such as stellar flybys could have played an important role in shaping the outer Solar System.
Asteroids in Sky Surveys
Alexey Sergeyev, Observatoire de la Côte d'Azur
PARIS.
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.
Ring formation around giant planets by tidal disruption
Naoya Torii, Institute of Science Tokyo
PARIS.
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.