Beneath a comparatively thin ice shell, Europa harbors a global, salty, liquid-water ocean in contact with a rocky seafloor, making it an exciting target for exploring habitability in the Solar System. The potential habitability of Europa’s ocean depends on its composition, which may be reflected in that of Europa’s geologically young, fractured surface. However, two intertwined uncertainties are the degree to which the ocean and the surface are in contact, and the degree to which surface materials truly represent oceanic signatures. The latter is complicated by the fact that Europa’s surface is continuously altered by sulfur plasma and particle irradiation due to its location within Jupiter’s magnetosphere. In this thesis, I utilize a variety of multi-spectral, Earth-based observations of Europa to explore the balance and interplay of internal and external processes in shaping its surface.
Chapters II and III focus on using visible-wavelength spectroscopy from the Hubble Space Telescope (HST) to understand the chemistry of Europa’s surface salts. In Chapter II, I present the detection of irradiated sodium chloride (NaCl) and show that its distribution correlates with geologically disrupted chaos terrain, suggesting an ocean source. In Chapter III, I investigate multiple spectral features across Europa’s sulfur-bombarded trailing hemisphere. In comparing their geographies with the distributions of large-scale geology, magnetospheric particle bombardment, and surface color, I identify some features as reflective of purely exogenous sulfur radiolysis products and others as indicative of radiolysis products formed from a mixture of endogenous material and magnetospheric sulfur.
Chapters IV and V further consider the effects of radiolytic processing through the analysis of infrared spectra obtained with Keck NIRSPEC. In Chapter IV, I report a previously unseen spectral feature at 3.78 µm in disk-integrated spectra of the trailing hemisphere. Using Hapke spectral modeling, I demonstrate that it represents an unidentified radiolytic product of potential relevance to understanding the alteration of endogenic material. Chapter V considers a radiolytic species thought to be independent of endogenic material – hydrogen peroxide (H₂O₂), a species relevant to the oxidation state and habitability of the ocean in the case of mutual exchange through the ice shell. Contrary to laboratory expectations, I observe the largest H₂O₂ absorptions within salty, low-latitude chaos terrain. I hypothesize that this distribution may reflect decreased hydrogen peroxide destruction due to electron scavenging by CO₂ within these same regions, which would suggest an internal carbon source.
Finally, Chapters VI and VII present preliminary studies of Europa’s thermal emission using four images obtained with the Atacama Large Millimeter Array (ALMA) and a global thermophysical model developed to simulate Europa’s expected thermal emission. In Chapter VI, I combine a single ALMA image with an observation from the Galileo Photopolarimeter Radiometer (PPR) to show that a thermal anomaly seen by the PPR and associated with two potential plume detections is better explained by a locally high thermal inertia than by geologic heating. Chapter VII considers all four ALMA images. While much of the large-scale thermal structure can be readily attributed to albedo variation, modeling of the images reveals a number of localized anomalies, which may indicate variations in geothermal heat flow, thermal inertia, or millimeter emissivity. In the absence of the additional observations needed to distinguish between such possibilities, I construct hypothetical maps presenting the ranges of possible thermal inertia and emissivity values.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/Z9B856BX, author = {Wong, Ian Yu}, title = {Probing the Trojan-Hilda-KBO Connection: An Empirical Test of Dynamical Instability Models of Solar System Evolution}, school = {California Institute of Technology}, year = {2018}, doi = {10.7907/Z9B856BX}, url = {https://resolver.caltech.edu/CaltechTHESIS:03012018-170927159}, abstract = {In recent decades, the paradigm of solar system formation has undergone radical change. Many current models posit that a significant reorganization of the outer Solar System occurred after the end of planet formation. Specifically, it is hypothesized that Jupiter and Saturn crossed a mutual mean motion resonance, leading to a chaotic expansion of the ice giants’ orbits that disrupted the large population of planetesimals situated further out. While the majority of these bodies were ejected from the Solar System, a fraction of them were retained as the present-day Kuiper Belt, while others were scattered inward and captured into resonances with Jupiter to become the Trojans and Hildas. These dynamical instability models invariably predict that the Trojans, Hildas, and Kuiper Belt objects (KBOs) were sourced from the same primordial body of outer solar system planetesimals. Therefore, a comparative exploration of these minor body populations serves as one of the definitive observational tests of our present understanding of solar system evolution. Over the past four-and-a-half years, I have carried out a diverse series of systematic studies aimed at synthesizing a detailed picture of Trojan, Hildas, and KBOs. By combining novel analyses of archival data with new photometric surveys, I have derived the first debiased color distributions of Trojans and KBOs and expanded our knowledge of their respective size distributions. In addition, I have explored the peculiar color bimodality attested in the all three asteroid populations, which indicates the presence of two sub-populations. Utilizing the full body of observations, I have formulated the first self-consistent hypothesis outlining the formation, composition, and dynamical/chemical evolution of the primordial outer solar system planetesimals, with special attention given to explaining the color bimodality, size distribution shapes, and collisional families. My results lay the groundwork for future studies with next-generation instruments and ultimately, the Trojan flyby mission Lucy.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/KQVW-GF86, author = {Batygin, Konstantin}, title = {Orbits and Interiors of Planets}, school = {California Institute of Technology}, year = {2012}, doi = {10.7907/KQVW-GF86}, url = {https://resolver.caltech.edu/CaltechTHESIS:05202012-233257444}, abstract = {The focus of this thesis is a collection of problems of timely interest in orbital dynamics and interior structure of planetary bodies.
The first three chapters are dedicated to understanding the interior structure of close-in, gaseous extrasolar planets (hot Jupiters). In order to resolve a long-standing problem of anomalously large hot Jupiter radii, we proposed a novel magnetohydrodynamic mechanism responsible for inflation. The mechanism relies on the electro-magnetic interactions between fast atmospheric flows and the planetary magnetic field in a thermally ionized atmosphere, to induce electrical currents that flow throughout the planet. The resulting Ohmic dissipation acts to maintain the interior entropies, and by extension the radii of hot Jupiters at an enhanced level. Using self-consistent calculations of thermal evolution of hot Jupiters under Ohmic dissipation, we demonstrated a clear tendency towards inflated radii for effective temperatures that give rise to significant ionization of K and Na in the atmosphere, a trend fully consistent with the observational data. Furthermore, we found that in absence of massive cores, low-mass hot Jupiters can over-flow their Roche-lobes and evaporate on Gyr time-scales, possibly leaving behind small rocky cores. In systems where a transiting hot Jupiter is perturbed by a long-period companion, apsidal precession of the hot Jupiter that results from its tidal bulge plays an important, and often dominant role in determining the nature of the dynamical state onto which the system settles. This precession is in turn a strong function of the planet’s degree of central concentration and is characterized by the planetary Love number. Utilizing this connection, we have shown that in tidally relaxed systems, measurement of the hot Jupiter’s eccentricity directly yields the planetary Love number, which can then be used to place meaningful constraints on the physical structure of the planet with the aid of thermal evolution calculations.
Chapters four through six focus on the improvement and implications of a model for orbital evolution of the solar system, driven by dynamical instability (termed the Nice" model). Hydrodynamical studies of the orbital evolution of planets embedded in protoplanetary disks suggest that giant planets have a tendency to assemble into multi-resonant configurations. Following this argument, we used analytical methods as well as self-consistent numerical N-body simulations to identify fully-resonant primordial states of the outer solar system, whose dynamical evolutions give rise to orbital architectures that resemble the current solar system. We found a total of only eight such initial conditions, providing independent constraints for the solar system's birth environment. Next, we addressed a significant drawback of the original Nice model, namely its inability to create the physically unique, cold classical population of the Kuiper Belt. Specifically, we showed that a locally-formed cold belt can survive the transient instability, and its relatively calm dynamical structure can be reproduced. We developed a simple analytical model for dynamical excitation in the cold classical region and showed that comparatively fast apsidal precession and nodal recession of Neptune, during its eccentric phase, are essential for preservation of an unexcited state. Subsequently, we confirmed our findings with self-consistent N-body simulations, suggesting that the cold classical Kuiper belt's unique physical characteristics are a result of its remote formation site. Finally, we showed that the solar system may have initially hosted an additional ice-giant planet, that was ejected from the system during the transient phase of instability. Namely, we demonstrated that a large array of 5-planet (2 gas giants + 3 ice giants) multi-resonant initial states can lead to an adequate formation of the outer solar system, deeming the construction of a unique model of solar system's early dynamical evolution impossible.</p>
<p>The last four chapters of this thesis address various aspects and consequences of dynamical relaxation of planetary orbits through dissipative effects as well as the formation of planets in binary stellar systems. Using octopole-order secular perturbation theory, we demonstrated that in multi-planet systems, tidal dissipation often drives orbits onto dynamicalfixed points," characterized by apsidal alignment and lack of periodic variations in eccentricities. We applied this formalism towards investigating the possibility that the large orbital eccentricity of the transiting Neptune-mass planet Gliese 436b is maintained in the face of tidal dissipation by a second planet in the system and computed a locus of possible orbits for the putative perturber. Following up along similar lines, we used various permutations of secular theory to show that when applied specifically to close-in low-mass planetary systems, various terms in the perturbation equations become separable, and the true masses of the planets can be solved for algebraically. In practice, this means that precise knowledge of the system’s orbital state can resolve the sin(i) degeneracy inherent to non-transiting planets. Subsequently, we investigated the onset of chaotic motion in dissipative planetary systems. We worked in the context of classical secular perturbation theory, and showed that planetary systems approach chaos via the so-called period-doubling route. Furthermore, we demonstrated that chaotic strange attractors can exist in mildly damped systems, such as photo-evaporating nebulae that host multiple planets. Finally, we considered planetary formation in highly inclined binary systems, where orbital excitation due to the Kozai resonance apparently implies destructive collisions among planetesimals. Through a proper account of gravitational interactions within the protoplanetary disk, we showed that fast apsidal recession induced by disk self-gravity tends to erase the Kozai effect, and ensure that the disk’s unwarped, rigid structure is maintained, resolving the difficulty in planet-formation. We also showed that the Kozai effect can continue to be wiped out as a result of apsidal precession, arising from planet-planet interactions in a mature planetary system. However, if such a system undergoes a dynamical instability, its architecture may change in such a way that the Kozai effect becomes operative, giving rise to the near-unity eccentricities, observed in some extrasolar planetary systems.
This thesis presents studies in observational planetary astronomy probing the structure of the Kuiper belt and beyond. The discovery of Sedna on a highly eccentric orbit beyond Neptune challenges our understanding of the solar system and suggests the presence of a population of icy bodies residing past the Kuiper belt. With a perihelion of 76 AU, Sedna is well beyond the reach of the gas-giants and could not be scattered onto its highly eccentric orbit from interactions with Neptune alone. Sedna’s aphelion at ∼1000 AU is too far from the edge of the solar system to feel the perturbing effects of passing stars or galactic tides in the present-day solar neighborhood. Sedna must have been emplaced in its orbit at an earlier time when massive unknown bodies were present in or near the solar system. The orbits of distant Sedna-like bodies are dynamically frozen and serve as the relics of their formation process.
We have performed two surveys to search for additional members of the Sedna population. In order to find the largest and brightest Sedna-like bodies we have searched ∼12,000 square degrees within +/- 30 degrees of the ecliptic to a limiting R magnitude of 21.3 using the QUEST camera on the 1.2m Samuel Oschin Telescope. To search for the fainter, more common members of this distant class of solar system bodies, we have performed an deep survey using the Subaru Prime Focus Camera on the 8.2m Subaru telescope covering 43 square degrees to a limiting R magnitude of 25.3. Searching over a two-night baseline, we were sensitive to motions out to distances of approximately 1000 AU.
We present the results of these surveys. We discuss the implications for a distant Sedna-like population beyond the Kuiper belt and discuss future prospects for detecting and studying these distant bodies, focusing in particular on the constraints we can place on the embedded stellar cluster environment the early Sun may have been born in, where the location and distribution of Sedna-like orbits sculpted by multiple stellar encounters is indicative of the birth cluster size. These surveys were specifically designed to find the select members of a distant Sedna population but were also sensitive to the dynamically excited off ecliptic populations of the Kuiper belt including the hot classicals, resonant, scattered disk, and detached Kuiper belt populations. We present our observed latitude distributions and implications for the plutino population.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/NRNC-XK21, author = {Ragozzine, Darin Alan}, title = {Orbital Dynamics of Kuiper Belt Object Satellites, a Kuiper Belt Family, and Extra-Solar Planet Interiors}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/NRNC-XK21}, url = {https://resolver.caltech.edu/CaltechETD:etd-05282009-164537}, abstract = {This thesis discusses research into four different orbital dynamics problems, where the main goal of each chapter is to characterize the strongest non-Keplerian effect. These problems are introduced and discussed in Chapter 1, to help provide context for the subsequent chapters. In Chapter 2, I discuss a new technique for probing the interior density distributions of extra-solar planets by observing apsidal precession. Using a detailed theoretical and observational model of this precession, I conclude that NASA’s Kepler mission will be able to detect the presence or absence of a massive core in very hot Jupiters with eccentricities greater than 0.003. The remaining chapters discuss the orbital dynamics of Kuiper belt objects (KBOs) orbiting the Sun beyond Neptune. The family of dwarf planet Haumea (2003 EL61) is characterized in Chapter 3, including a list of candidate family members sorted by dynamical proximity. Using a numerical integration of resonance diffusion, I also show that the Haumea family is at least 1 Gyr old and is probably primordial. In Chapter 4, I analyze and fit astrometric data for the two satellites of Haumea (Hi’iaka and Namaka) to determine their orbital properties and the masses of Haumea and Hi’iaka. The implications of the new orbital solution are discussed, including the exciting conclusion that Haumea and Namaka are currently starting a season of mutual events. A more general investigation of the orbital and tidal evolution of KBO binaries is given in Chapter 5. A new orbital evolution model is described that accounts for perturbations from the Sun, self-consistent tidal evolution, and non-hydrostatic quadrupoles of solid KBOs. Using this model, I find that the orbital parameters of KBO binaries may have been modified significantly over the age of the solar system. Applied to the Orcus-Vanth binary, this model shows that a short-period circular orbit does not necessarily imply a collisional formation. In all, the work in this thesis has sought to analyze observational data by using the theoretical tools of orbital dynamics.}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/YXFP-V230, author = {Schaller, Emily Lauren}, title = {I. Seasonal Changes in Titan’s Cloud Activity. II. Volatile Ices on Outer Solar System Objects}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/YXFP-V230}, url = {https://resolver.caltech.edu/CaltechETD:etd-05132008-173841}, abstract = {This thesis presents studies in two distinct areas of observational planetary astronomy: studies of Saturn’s moon Titan’s seasonally varying tropospheric clouds, and studies of the surface compositions of Kuiper belt objects.
I. Understanding Titan’s methane-based hydrological cycle and interpreting how and when the fluvial surface features seen by the Cassini Spacecraft were formed requires frequent long-term observations of Titan’s clouds. Using nearly 100 adaptive optics images from the Keck and Gemini Telescopes from 2002-2006, we mapped the locations, frequencies, and magnitudes of Titan’s clouds. We also developed a near-nightly cloud-monitoring program with the NASA Infrared Telescope Facility (IRTF). Nightly whole-disk infrared spectroscopy with IRTF allows us to determine Titan’s total fractional cloud coverage, magnitudes, and altitudes, complementing and providing context for the relatively infrequent Cassini flybys. Taken together, the observations presented in this thesis have shown a striking seasonal change in the behavior of Titan’s clouds as Titan has moved from southern summer solstice (October 2002) toward vernal equinox (August 2009) and indicate that seasonally varying insolation appears, to first order, to control Titan’s cloud locations (Schaller et al. 2006a & 2006b).
II. Unlike Pluto and Eris, the vast majority of Kuiper belt objects (KBOs) are too small and too hot to retain volatile ices like CH4, N2, and CO on their surfaces to the present day. As a result, their infrared spectra are either dominated by involatile water ice or dark spectrally featureless material. To understand the dichotomy between volatile-rich and volatile-free surfaces in the outer solar system, we constructed a model of atmospheric escape of volatile ices over the age of the solar system (Schaller & Brown 2007a). We predicted that Quaoar, an object about half the size of Pluto, should be just capable of retaining methane ice to the present day. We observed Quaoar with the Keck Telescope, used Hapke theory to model its spectrum, and found that it contains a small amount of methane on its surface, indicating that it is a transition object between the dominant volatile-poor small KBOs and the few volatile-rich KBOs such as Pluto and Eris (Schaller & Brown 2007b).
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/EQY1-NM23, author = {Barkume, Kristina Marie}, title = {Surface Properties of Kuiper Belt Objects and Centaurs}, school = {California Institute of Technology}, year = {2008}, doi = {10.7907/EQY1-NM23}, url = {https://resolver.caltech.edu/CaltechETD:etd-05132008-202158}, abstract = {The outer solar system is inhabited by a population of small solar system bodies called Kuiper belt Objects (KBOs) and Centaurs. I present a survey of visible and near infrared (NIR) spectra of the brightest KBOs and Centaurs. The visible spectra of 19 KBOs were obtained at Palomar Observatory. At the W.M. Keck Observatory, NIR spectra were obtained for 33 KBOs and 12 Centaurs. This data marks a significant leap in the available spectra, allowing for the population to be studied as whole.
The spectra reveal that most KBOs are covered with a material with characteristics similar to irradiate ices rich in complex organic compounds. Water ice is also observed on some KBOs and Centaurs, though its abundance is variable across the samples. A two end member mixing model is found to describe the NIR spectral properties well, but poorly fits the visible-NIR data. This suggests that the non-water ice component is heterogeneous across the KBO and Centuar populations. To characterize the non-ice component better, the visible spectra are analyzed for signatures of both organic and mineralogical features. No evidence is found for the presence of minerals, but the spectra suggest complex organics are a dominant spectral component. The abundance of water is shown to directly correlate with diameter for KBOs, but not Centaurs, suggesting it is controlled by geophysical processes on KBOs.
The analysis of these spectra has revealed an unusual population of KBOs that are now identified as mantle fragments from the large KBO 2003 EL61. The collision that spun-up 2003 EL61, formed its satellite system, and ejected the mantle fragments into the Kuiper belt is discussed. The unusual spectral properties of 2003 EL61, its brightest satellite, and the fragments are examined. Analysis suggests that the surfaces of all these objects can be composed of nearly pure water ice, suggesting that their volatile organic inventory has been lost. The discovery of crystalline water ice on these small KBOs suggests that crystallization is not an indication of recent surface activity as was previously suggested.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/7KVP-D712, author = {Bouchez, Antonin Henri}, title = {Seasonal Trends in Titan’s Atmosphere: Haze, Wind, and Clouds}, school = {California Institute of Technology}, year = {2004}, doi = {10.7907/7KVP-D712}, url = {https://resolver.caltech.edu/CaltechETD:etd-10272003-092206}, abstract = {
I present an analysis of visible and near-infrared adaptive optics images and spectra of Titan taken over 43 nights between October 1997 and January 2003 with the AEOS 3.6-m, Palomar Hale 5-m, and W.M. Keck 10-m telescopes. These observations reveal a seasonally changing stratospheric haze layer, two distinct regions of condensate clouds in the southern hemisphere, the albedo of Titan’s surface, and the zonal wind field of the stratosphere.
Transient convective CH4 clouds are identified near Titan’s south pole, rising to 16±5 km above the surface. These clouds have been continuously present south of 70°S since at least December 2001, currently account for 0.5-1% of Titan’s 2μm flux, and appear to be gradually brightening or thickening as the insolation of the south polar region increases. Above the polar clouds, an extensive but optically thin (τ≈0.05 at 2μm) cloud layer is noted near the tropopause south of 30°S. This cirrus-like structure has remained unchanged in extent and thickness since September 1999 despite seasonal changes in the underlying convective clouds and the overlying stratospheric haze. Aside from the convective CH4 clouds near the south pole, Titan’s troposphere is free of aerosols with an upper limit of τ<0.01 on the 2μm vertical optical depth in the 5-30 km altitude region.
The albedo of Titan’s surface at 2.0μm is derived from the radiative transfer analysis of spatially resolved spectra and images, and presented in the form of a ~600 km resolution global surface albedo map. At this resolution, the 2.0μm albedo ranges from 0.05 to 0.17, consistent with extensive exposure of clean water ice in some regions, while hydrocarbons and atmospheric sediments blanket others.
The zonal wind field of Titan’s stratosphere near southern summer solstice is derived from adaptive optics observations of the occultation of a binary star on 20 December 2001. Multiple refracted stellar images were detected on Titan’s limb during the each successive occultation, allowing the angular deflection of the starlight at two altitudes over both hemispheres to be measured with an uncertainty of ~2 milliarcseconds. The zonal wind field derived from this measurement of the shape of Titan’s limb exhibits strong but asymmetric high latitude jets, with peak wind speeds of 230±20 m s-1 at 60°N and 160±40 m s-1 at 40°S, and lower winds of 110±40 m s-1 at the equator. The direction of the wind is not constrained.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, } @phdthesis{10.7907/C9V4-8050, author = {Fenton, Lori Kay}, title = {Aeolian Processes on Mars: Atmospheric Modeling and GIS Analysis}, school = {California Institute of Technology}, year = {2003}, doi = {10.7907/C9V4-8050}, url = {https://resolver.caltech.edu/CaltechETD:etd-03052003-124751}, abstract = {Wind is currently the dominant geological agent acting on the surface of Mars. A study of Martian aeolian activity leads to an understanding of the forces that have sculpted the planet’s face over the past billion years or more and to the potential discovery of climate shifts recorded in surface wind features that reflect ancient wind patterns. This work takes advantage of newly available tools and data to reconstruct the sedimentary history reflected in aeolian features on Mars. The thesis is divided into two main projects. In the first section, a widely accepted hypothesis, that oscillations in Martian orbital parameters influence atmospheric circulation patterns, is challenged. A Mars global circulation model is run at different obliquity, eccentricity, and perihelion states and the predicted surface wind orientations are correlated with observed aeolian features on the Martian surface. The model indicates that orbital parameters have little effect on wind patterns, suggesting that aeolian features not aligned with the current wind regime must have formed under atmospheric conditions unrelated to orbital parameters. In the second project, new spacecraft data and a mesoscale model are used to determine the sedimentary history of Proctor Crater, a 150 km diameter crater in the southern highlands of Mars. Using high-resolution imagery, topography, composition, and thermal information, a GIS was constructed to study the aeolian history of the crater, which was found to have a complex interaction of deposition and erosion. Surficial features include 450 m of sediments filling the crater basin, small bright bedforms, dust devil tracks, and a dark dunefield consisting of coarse, basaltic sand and containing slipfaces indicative of a multidirectional, convergent wind regime. All wind features, both ancient and contemporary, are coaligned, indicating that formative wind directions have changed little since the first aeolian features formed in this area. Mesoscale model runs over Proctor Crater indicate that two dune slipfaces are created by winter afternoon geostrophic westerlies and summer evening katabatic easterlies, and that dust devil tracks are created by summer noontime rotational westerlies. Using all available tools, this thesis begins the work of understanding how aeolian processes have influenced the Martian surface.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Brown, Michael E.}, }