How do planets form? What processes determine habitability of planets? These are two fundamental questions about our origin and future.
My research seeks insight into these fundamental questions by studying the birth environments of planets-- gaseous and dusty disks around young stars. I observe radiations from molecules and dust grains in young disks and use these as a powerful tool to probe fundamental physical and chemical processes that build planetary systems. I employ both numerical simulations and astronomical observations to advance our understanding of planet formation. More specific questions I am focusing on:
- How does the bulk chemical inventory evolve in planet-forming disks?
- What are the essential processes that determine the compositions of the core and atmosphere of a planet?
- How can we characterize the terrestrial planet zone?
1. How does the bulk chemical inventory evolve in planet-forming disks?
Planets are built from gas, ice, and dust in protoplanetary disks. The composition of the natal disk, such as water and organic materials, may change dramatically from the formation of disks in embedded protostars to the time of disk gas dispersal that occurs several Myr later. Thereofere, it is crucial for us to understand how chemical evolution happens at different distances from the central star, and then we can predict compositions of planets forming at different disk locations and time scales.
To map out the chemical evolution during planet formation, we can observe molecular lines from disks at different evolutionary stages, from the earliest embedded stage to the time of gas dispersal. The line emissions are complicated products of molecular abundances, temperature structures, and excitation conditions. Therefore I use numerical stimulations of chemical evolution and radiative transfer to interpret observations.
2. What processes determine compositions in planetary cores and atmospheres?
For a newborn planet, its compositions in the core and atmosphere depend not only on the local disk composition but also on how the materials are accreted. For example, the gaseous and solid materials may be accreted at different times and with varying mass ratios. Furthermore, chemical processing happens during the accretion processes. To accurately predict planetary compositions, we have to confront our best guesses of planet formation processes with observations. Excitingly, we are starting to directly probe on-going planet-forming at local disk regions. The Atacama Large Millimeter/ Submillimeter Array (ALMA) are now resolving the fine details of protoplanetary disks, including intriguing gaps that are possibly the locations of protoplanetary orbits. You can see a real image from ALMA on the left side.
With these observations, we can characterize the local birth environments of forming planets, by measuring physical conditions, chemical compositions, and dynamic interactions of the surrounding gas and solids. These characterizations are crucial for us to test different planet formation theories.
3. How can we characterize the terrestrial planet zone?
Finding another habitable world is our ultimate goal of studying exoplanetary systems. For now, we think that small and rocky planets with liquid water on their surfaces are the best candidates. To maintain liquid water on their surfaces, planets cannot be too cold, and they are most likely within several au from their suns. Therefore, the inner a few au region is of particular interest. Molecular line emissions at near/mid-IR are excellent tracers of the inner a few au regions. Observing and modeling these lines give us crucial information about the environments of terrestrial planet formation, including the physical properties, chemical abundances, and dynamical processes.
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