Celestial Mechanics seminars

Quasi-periodic eruptions are repeating X-ray transients from supermassive black holes in nearby low-mass galactic nuclei. Their regularity, timescales and energetics suggest stellar companions orbiting at about 100 gravitational radii. They may provide unusually close dynamical probes of black holes and electromagnetic counterparts to extreme mass-ratio inspirals, a target for future space-based gravitational-wave observatories such as LISA. Joheen Chakraborty reviews the thirteen known systems, including the unexpected appearance of several in accretion discs created by tidal disruption events. The talk covers observations and theoretical developments, spectroscopic constraints on emission, the use of eruption timing to investigate orbital dynamics, and what event-rate estimates imply for inspiral formation. Hybrid seminar: attend in 370 Cahill, Caltech, Pasadena, California, United States, or remotely through the public Zoom meeting.

Marta Bryan explores what gas giants reveal about the formation and evolution of planetary systems. Their brightness and mass make them useful observational targets, and their gravitational influence can reshape the orbits and environments of smaller planets. The seminar combines several approaches. High-resolution spectroscopy of directly imaged planets measures rotation and obliquity, providing evidence about angular-momentum evolution. Radial-velocity searches for Jupiter-like companions to known inner planets probe how giant planets affect system architecture and inform the search for habitable worlds. The presentation also introduces observational work on planetary interiors and magnetic fields as further ways to test formation models.

This seminar examines comet impacts during the dispersal of the outer Solar System's planetesimal disk. Instability among the giant planets sent some bodies toward the terrestrial planets. Noble gases preserved in Earth's atmosphere provide evidence for the scale of this bombardment and help relate its timing to the growth of Earth.

This lecture tests whether the Nice model can account for the detailed architecture of the Kuiper belt. It contrasts Neptune's behaviour during planetary instability with simpler gradual-migration scenarios. The distribution of distant small bodies provides constraints on the dynamical history of the giant planets.

When did the giant planets become dynamically unstable? This lecture compares evidence from lunar impact craters, binary objects in the Kuiper belt and dynamical models. It explains why these constraints matter for reconstructing Solar System evolution and why the timing remains an unresolved research question.

This seminar explores a version of the Nice model whose starting planetary configuration is produced by migration through a low-viscosity gas disk. Jupiter and Saturn enter a two-to-one resonance with larger eccentricities than in alternative scenarios. The presentation weighs the strengths and limitations of these initial conditions.

Modern versions of the Nice model connect the initial giant-planet orbits to their earlier migration through a gas disk. This lecture examines resonant chains, possible additional ice giants and the effects of planetesimal interactions. Breaking the chain can trigger instability, with simulations testing which configurations reproduce today's planetary orbits.

The Kuiper belt preserves evidence of major orbital changes among the giant planets. This lecture reviews migration-driven explanations for its resonant, dynamically excited and detached populations. It then examines why these early models required an additional instability mechanism, leading to scenarios involving resonance crossing between Jupiter and Saturn.

This lecture connects the properties of the giant planets to their diverse populations of moons and co-orbiting small bodies. It focuses on irregular satellites, whose inclined and elongated orbits suggest capture, and on Trojan objects that move around stable configurations associated with Jupiter or Neptune.

This lecture traces the origins of different comet populations and the processes that send them into the inner Solar System. It compares the scattered Kuiper-belt reservoir with the distant Oort cloud. It also examines the evidence and debate surrounding a possible additional planet beyond Neptune.

The Kuiper belt contains a complex collection of bodies beyond Neptune, including Pluto. This lecture compares dynamically cold and excited populations, resonant objects, scattered bodies and detached remnants. Their orbital structure provides a record of the Solar System's past evolution.