Probing planetary system histories via observations, experiments, and modelling of circumstellar gas and dust
Author(s)
Schneiderman, Tajana
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Advisor
Seager, Sara
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Circumstellar disks of gas and dust are integral parts of planetary systems from formation to maturation. Protoplanetary disks, the name for circumstellar material at the earliest stages of a stellar lifetime, provide key information about the formation processes of planets, and therefore of the initial conditions that set system evolution in motion. These disks are host to both primordial interstellar materials and reprocessed constituents that become part of nascent planets and planetesimals. Debris disks, the name for circumstellar material after the protoplanetary disk dissipates, are remnants of earlier processes and carry clues to the formation conditions and evolutionary pathways of mature systems. In this thesis, I discuss three approaches to probing planetary system histories by examining circumstellar gas and dust.
The first approach is to experimentally measure the desorption binding energies and entrapment efficiencies of neon, argon, krypton, and xenon in astrophysical ice analogs. Noble gases are valuable tracers of both nebular gas accretion and volatile delivery to planetary atmosphere; placing experimental constraints on these fundamental physical properties allows us to understand the extent to which each gas traces different sources of volatiles within the protoplanetary disk. We find that all four nobles are likely present in the nebular gas, and able to be directly accreted to nascent planets. We further find that argon, krypton, and xenon are trapped efficiently in interstellar ice analogs, with entrapment efficiencies ranging from 65-95\% in astrophysically relevant ices. This suggests that that they are valuable tracers for the solid volatile content within the disk. Lastly, we find that neon is inefficiently trapped; maximally 10\% of neon is entrapped in interstellar ices, although the actual entrapment efficiency may be lower than 1\%. Thus, neon is a tracer of only the nebular gas.
The second approach is to examine archival data from the Atacama Large Millimeter Array for the HD~172555 system. This system is unique among debris disks due to its atypical dust composition. We detect the presence of carbon monoxide gas in the circumstellar debris. By considering the morphology and composition of both CO gas and dust in the system, we are able to rule out several origins for the debris. We instead find that the only scenario that adequately describes observations of the system is that of a giant impact; the CO gas is likely the remnant of a stripped planetary atmosphere, while the dust is debris produced in the collision. These observations provide evidence for giant impacts in systems other than our own.
The third approach simulates the dust spectra of nine highly inclined debris disks for a range of compositions and particle size distributions. Multibandpass observations are required to adequately characterize dust in a system; dust spectra allow for an understanding of compositional classes of parent planetesimals, while deviations from steady-state predictions for the particle size distributions might indicate a history of giant impacts in a system. This chapter aims to develop a preliminary framework for analysis of systems in advance of data from the James Webb Space Telescope. We find that iron and troilite compositions are most easily disentangled from the suite of compositional families we consider, although silicates, water ice, and carbonaceous compounds are identifiable.
Date issued
2022-05Department
Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary SciencesPublisher
Massachusetts Institute of Technology