Characterisation of hot Jupiter atmospheres with phase-resolved emission spectra

Thesis

Hot Jupiters are gaseous giant planets with orbital periods of less than ten days. They are currently the only class of exoplanets that can be characterised with high-quality spectroscopic observations over multiple orbital phases owing to their large radii and high atmospheric temperatures. Constraints on their atmospheric properties, such as molecular abundance and thermal structure, give us insight into how planetary atmospheres behave under extreme conditions and help us understand their formation and evolution pathways.

This thesis uses infrared emission spectra observed at multiple orbital phases with space telescopes to characterise the atmosphere of the hot Jupiter WASP-43b, which is a planet roughly twice the mass of Jupiter orbiting a solar metallicity K star with an orbital period of just 19.5 hours. I analyse data taken with four instruments, spanning roughly 1- 10 μm in wavelength: (1) HST /WFC3; (2) Spitzer /IRAC; (3) JWST MIRI/LRS; and (4) JWST NIRSpec/G395H. To extract information from the data, I develop a method to fit emission spectra at multiple orbital phases simultaneously and an open-source spectral retrieval code.

I report the detection of key molecules in the atmosphere of WASP-43b: H₂O, CO₂, CO, NH₃, HCN, and H₂S, and place a strict upper bound on the abundance of CH₄. The retrieved molecular abundance suggests that the atmosphere of WASP-43b has a super-solar metallicity and a super-solar C/O ratio. The results of this thesis are critical inputs for atmospheric models of WASP-43b and offer insights into the planet’s formation history. The high atmospheric metallicity and C/O ratio rule out gas-accretion-dominated formation at large orbital radius followed by disc-free migration. Instead, these constraints suggest that processes such as pebble drift and accretion and in situ heavy element enrichment likely played important roles in the formation history of WASP-43b.

Authors: Yang, J

• DOI: 10.5287/ora-9rmykm9v5
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: atmospheric retrievals; exoplanet atmospheres; hot Jupiters; WASP-43b; radiative transfer
• Subjects: Extrasolar planets--Atmospheres; Radiative transfer