Revealing the Early Solar System through Small Body Spectroscopy and Dynamics

Author: Belyakov, Matthew

Year: 2027

Degree: Dissertation (Ph.D.)

Advisor: Brown, Michael E.

Committee Members: Batygin, Konstantin; Blake, Geoffrey A.; de Kleer, Katherine R.; Brown, Michael E.

Option: Planetary Sciences

DOI: 10.7907/gf2y-n237

Abstract

One key event is thought to have defined the early outer Solar System, a so-called "dynamical instability", which simultaneously excited the orbits of the giant planets, scattered planetesimals throughout the solar system, and shaped the dynamics of the nascent Kuiper belt. The goal of my thesis has been to constrain the nature of the early dynamical instability and the outer solar system's original architecture. My tools of choice are its many small bodies. These are remnant planetesimals whose compositions and dynamical histories encode the conditions of the early solar system, and include Kuiper belt objects, Jupiter and Neptune Trojans, irregular satellites and small inner moons of the giant planets. Through spectroscopic observations with James Webb, ground-based photometry, and dynamical modelling, I have contributed towards a more refined picture of the early Solar System. These contributions constitute the six research chapters of my thesis.

The second chapter of my thesis presents observational evidence for a key prediction of dynamical instability models: that Jupiter's Trojan asteroids and the Kuiper belt share a common source population in the outer planetesimal disk. By analyzing photometry obtained from our own survey on Keck and Palomar telescopes combined with archival surveys, I find that the low-perihelion Kuiper belt has a bimodal color distribution resembling that of the Jupiter Trojans. By simulating the dynamical evolution of a model Kuiper belt, I demonstrate that the observed colors of low-perihelion objects do not arise from thermal processing, but are instead inherited from the scattered disk, connecting the Kuiper belt and Jupiter Trojans.

The third chapter of my thesis develops analytic methods for characterizing the onset of chaos in the scattered disk, a population of Kuiper belt objects with both high-eccentricity and relatively planar orbits. I develop a perturbative treatment of the circular three-body problem to qualitatively understand the machinery underlying chaotic diffusion in the scattered disk. At distances where most known scattered disk objects reside, a complex network of resonances drives diffusion in two distinct regimes. One is a fully chaotic layer in which transport is rapid. The second is a zone of slower diffusion in which 1:n resonances with Neptune emerge as increasingly strong barriers to diffusion at low eccentricity. My analytic framework provides a predictive tool for future population studies.

Chapters four, five, and six use James Webb Space Telescope Near-Infrared Spectrograph (JWST NIRSpec) observations of the small and irregular moons of the giant planets to constrain the history of the satellite systems of these planets. Chapter four presents NIRCam spectrophotometry of the small inner satellites of Uranus and Neptune. I detect a prominent 3 micron absorption feature on all observed satellites in both systems, consistent with water ice or hydrated minerals and comparable to the water-type class of Kuiper belt objects. Chapter five presents JWST NIRSpec observations of the three largest Saturnian irregular satellites: Phoebe, Siarnaq, and Albiorix. Phoebe had already been observed by the Cassini spacecraft, but my study pinpoints Phoebe as related to water-rich Kuiper belt objects, linking irregular satellites to the Kuiper belt as predicted by dynamical instability models. Chapter six resolves a 77-year-old Neptunian mystery regarding Nereid, the planet's third largest moon and one of the most eccentric in the solar system. Leveraging JWST NIRSpec spectroscopy of Nereid, combined with dynamical simulations of the Neptunian system's early history, I propose that Nereid did not originate in the outer planetesimal disk, but is instead the sole surviving intact regular satellite of Neptune.

The final chapter of my thesis addresses a new class of small body, interstellar objects. I present the first ever mid-infrared spectroscopic observations of an interstellar comet. Using the James Webb Space Telescope's Mid-Infrared Instrument (MIRI), I measure production rates and map the outflows of water, carbon dioxide, methane, and atomic nickel on 3I/ATLAS across two observing epochs. Methane is detected for the first time in an interstellar object, and 3I's sudden jump in methane production post-perihelion evinces the activation of a pristine subsurface reservoir. This work closes the thesis with a perspective connecting the solar system to our galactic neighborhood.

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