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We present a physically motivated model for the manner in which a stellar magnetic field sculpts the inner edge of a protoplanetary disk, and examine the consequence for the migration and stopping of sub-Neptune and super-Earth planets.This model incorporates a transition zone exterior to the inner truncation of the disk, where the surface density profile is modified by the diffusion of the stellar magnetic field into the disk. This modification results in a migration trap at the outer edge of the transition zone. We first performed simulations of single planet migration, considering a range of stellar magnetic field strengths and magnetic diffusion profiles. Our simulations show a tight relationship between the final locations of planets and the total magnetic budget available for the disk from their host star. We found that a stellar magnetic field between 67 to 180G and a power-law index between 3 and 2.75 can reasonably reproduce the location at which the observed occurrence rate of close-in Super-Earth and Sub-Neptune populations changes slope. We then performed simulations of double planet migration for a dipole stellar magnetic field of 300G. Our simulations show a tight relationship between the planets' mass ratio and their next neighbor orbital period ratio. We also found that our model is capable of broadly reproducing some features seen in Kepler's multi-planet systems. Such features include the 3:2 resonance peak on the next neighbor period ratio diagram, a collection of systems in non-resonance configurations, a drop off in planet occurrence rate below {\color{red} \bf 9} days and a plateau in planet occurrence beyond 9 days.

© 2019. The American Astronomical Society. All rights reserved. We present precision 4.5 mm Spitzer transit photometry of eight planet candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01, K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four sub-Neptunes and two sub-Saturns, with radii between 2.6 and 18 R ® and equilibrium temperatures between 440 and 2000 K. In this paper we identify several targets of potential interest for future characterization studies, demonstrate the utility of transit follow-up observations for planet validation and ephemeris refinement, and present new imaging and spectroscopy data. Our simultaneous analysis of the K2 and Spitzer light curves yields improved estimates of the planet radii and multiwavelength information that helps validate their planetary nature, including the previously unvalidated candidate EPIC 205686202.01 (K2-289 b). Our Spitzer observations yield an order-of-magnitude increase in ephemeris precision, thus paving the way for efficient future study of these interesting systems by reducing the typical transit timing uncertainty in mid-2021 from several hours to a dozen or so minutes. K2-53 b, K2-289 b, K2-174 b, K2-87 b, and K2-90 b are promising radial velocity (RV) targets given the performance of spectrographs available today or in development, and the M3V star K2-124 hosts a temperate sub-Neptune that is potentially a good target for both RV and atmospheric characterization studies.

To understand the uniqueness of our solar system, we must assess the system architectures and demographic features existing in the known planet population, but such a task requires a homogeneous set of candidates. Fortunately, the Kepler spacecraft continuously collected photometry from a single patch of the sky, which in turn produced a well characterized catalog of transiting exoplanets. However, previous studies assumed multi-planet systems were subject to the same selection effects as their single-planet counterparts. I investigate this assumption, finding that a proper completeness accounting significantly increases the underlying occurrence of multi-planet systems to 5.86 planets per FGK dwarf and only requires a 1.5 degree average system mutual inclination. Using this correction I provide an updated extrapolation of the occurrence of Earth analogs and find that 5.9% of GK dwarfs have more than one planet within their habitable zone.Additionally, the K2 mission collected photometry from 18 fields along the ecliptic plane, providing a unique opportunity to understand how exoplanet formation may be affected by galactic latitude, stellar metallicity, and stellar age. For my thesis, I developed a fully automated pipeline able to detect and vet transit signals in K2 photometry, enabling assessment of sample completeness and reliability. This catalog contains 768 planets, with 235 newly identified candidates. Correspondingly, I present the first uniform analysis of small transiting exoplanet occurrence outside of the Kepler field, finding a metallicity dependence in small planet occurrence.I also discuss how the Sun’s late stage evolution and the existing solar system architecture will capture Jupiter and Saturn into a mean-motion resonance. Eventually perturbations from passing stars will trigger large-scale instability, culminating in the disassociation of all outer planets. Extrapolating this result to other systems indicates a temporal dependence on bound planet

© 2019. The American Astronomical Society. All rights reserved. We present precision 4.5 mm Spitzer transit photometry of eight planet candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01, K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four sub-Neptunes and two sub-Saturns, with radii between 2.6 and 18 R ® and equilibrium temperatures between 440 and 2000 K. In this paper we identify several targets of potential interest for future characterization studies, demonstrate the utility of transit follow-up observations for planet validation and ephemeris refinement, and present new imaging and spectroscopy data. Our simultaneous analysis of the K2 and Spitzer light curves yields improved estimates of the planet radii and multiwavelength information that helps validate their planetary nature, including the previously unvalidated candidate EPIC 205686202.01 (K2-289 b). Our Spitzer observations yield an order-of-magnitude increase in ephemeris precision, thus paving the way for efficient future study of these interesting systems by reducing the typical transit timing uncertainty in mid-2021 from several hours to a dozen or so minutes. K2-53 b, K2-289 b, K2-174 b, K2-87 b, and K2-90 b are promising radial velocity (RV) targets given the performance of spectrographs available today or in development, and the M3V star K2-124 hosts a temperate sub-Neptune that is potentially a good target for both RV and atmospheric characterization studies.