UC Santa Cruz

An understanding of planetary histories and characteristics requires an empirical connection between planet formation and evolved planets---a long-sought goal of astrophysics and planetary science. This connection is now increasingly possible due to simultaneous revolutions in the observations of protoplanetary disks and exoplanet atmospheres. A crucial step towards relating these observations of different evolutionary stages is to characterize the fundamental properties of both disks and atmospheres.

The work presented in this dissertation uses microphysics---i.e., the physics that governs the evolution of small particles--- to constrain the fundamental properties of both disks and atmospheres. This dissertation provides evidence that protoplanetary disks are more than an order of magnitude more massive than previously appreciated, that the detailed properties of clouds shape observations of exoplanet atmospheres, and that the physics of modeling clouds gives a new understanding of the solid content and composition in protoplanetary disks.

Clouds on extrasolar worlds are abundant and interfere with observations; however, little is known about their properties. Herein, cloud properties are predicted from first principles and are used to investigate and explain the novel observational properties of hot Jupiters---massive planets close to their host stars. This work describes the use of clouds in tracing fundamental planetary properties and develops a method for probing non-uniform cloud properties using near-future observations.

The total mass available in protoplanetary disks is a critical initial condition for understanding planet formation, however, the surface densities of protoplanetary disks are largely unconstrained due to uncertainties in the dust-to-gas ratio and carbon monoxide (CO) abundance. In this dissertation, a new set of models (dust-line models) are developed that reconcile theory with observations of protoplanetary disks and create a new set of initial conditions for planet formation models. These models use recent, resolved, multiwavelength observations of disks in the millimeter to constrain the aerodynamic properties of dust grains and infer the total disk mass without an assumed dust surface density or tracer-to-total mass ratio. This work provides a picture of protoplanetary disks where they are significantly more massive than was previously appreciated. These qualitative changes to models of protoplanetary disks thus have significant implications for theories of planet formation; particularly for the important processes where the amount of gas determines the evolution of the solids.

The techniques used in modeling clouds in exoplanet atmospheres are then combined with the dust-line models of protoplanetary disks to show that the observed depletion of CO gas in well-studied disks is consistent with freeze-out processes in a moderately diffusive environment. This new model of ice formation and evolution in disks is able to use existing observations to constrain three crucial parameters that control planetary formation, namely: the solid and gaseous CO inventory at the disk midplane where planets form, the bulk disk diffusivities and mixing characteristics, and the disk mass--through resolving inconsistencies in estimates of total mass using different tracers.