Constraining the formation and evolution of super-Earths via dynamics
Open Access
- Author:
- MacDonald, Mariah
- Graduate Program:
- Astronomy and Astrophysics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- January 21, 2021
- Committee Members:
- Rebekah Dawson-Rigas, Dissertation Advisor/Co-Advisor
Rebekah Dawson-Rigas, Committee Chair/Co-Chair
Eric B Ford, Committee Member
Jason Wright, Committee Member
Bradford James Foley, Outside Member
Suvrath Mahadevan, Committee Member
Randall Lee Mc Entaffer, Program Head/Chair - Keywords:
- astronomy
astrophysics
astrobiology
exoplanets
planet formation
resonant chains
planetary dynamics - Abstract:
- As more exoplanets were discovered, we as a community were surprised to find that most planets discovered orbit very near to their stars. To fully comprehend why our Solar System hosts life and potential predictors of life in other systems, we need to understand how those systems formed and their different evolutionary histories. Early discoveries of giant exoplanets orbiting near their host stars and exoplanets in or near mean motion resonances were interpreted as evidence for migration and its crucial role in the beginnings of planetary systems. In addition, long-scale migration has been invoked to explain systems of planets in mean motion resonant chains consisting of three or more planets linked by integer period ratios. However, recent studies have questioned the prevalence of planet migration since one major hallmark of migration has been orbital resonances, but most systems are not actually in resonance. We first we re-characterize the six-planet system Kepler-80 by directly forward modeling and fitting the lightcurve of the system. We find that previous studies over-estimated the two outer planet masses due to the unknown signal of the sixth planet. We also find that the four-planet resonant chain initially published by MacDonald et. al 2016 does indeed exist, but we cannot confirm a five-planet chain with new planet g. We find that the system and its dynamic behaviour are consistent with in situ formation and compare our results to two other resonant chain systems, Kepler-60 and TRAPPIST-1. We then investigate whether the observed resonant chains in Kepler-80, Kepler-223, Kepler-60, and TRAPPIST-1 can be established through long-scale migration, short-scale migration, and/or only eccentricity damping by running suites of N-body simulations. We find that each system could have formed via all three pathways, suggesting that resonant chains are as indicative of migration as they are of in situ formation. We next look to establish the diversity of exoplanets and their systems via in situ formation. We find that intrinsic variations among disks in the amount of solids available for in situ formation can account for the orbital and compositional diversity observed among Kepler’s transiting planets. Our simulations can account for the planets’ distributions orbital period ratios, spacing in mutual Hill radii, transit duration ratios, and transit multiplicity; higher eccentricities for single than multi transiting planets; smaller eccentricities for larger planets; scatter in the mass-radius relation, including lower densities for planets with masses measured with TTVs than RVs; and similarity in planets’ sizes and spacings within each system. Our findings support the in situ formation paradigm and the idea that planet properties are significantly sculpted by nature (formation) in addition to nurture (evolution). Overall, we find that resonance chains can be ued to constrain the formation and dynamical evolution of exoplanetary systems, but that they should not be used as hallmarks of wide-scale planetary migration as they are consistent with in situ formation. We also find that in situ formation alone can explain the diversity of super-Earth planetary systems we observe.