Good vibrations: Directly measuring Exoplanet aerosol compositions with MIRI spectroscopy
Abstract
Aerosols control the energy budget of an atmosphere and how much light is reflected, absorbed, and re-radiated. Aerosols in exoplanet atmospheres are commonly defined as either clouds (formed via condensation) or hazes (formed via photochemical reactions). The effect of aerosols as scattering in the UV-optical and muting of gas phase abundances in the near-IR has been observed in transmission spectra from giant hot Jupiters down to sub-Neptunes. However, aerosols are not all bad news for exoplanet spectra. The composition of aerosols directly measured in the IR, as condensate clouds or photochemical haze, will inform the temperature and pressure structure of the atmosphere. Without direct measurements of the aerosol composition, particle size, and abundance, we cannot fully account for the gas phase composition, the thermal structure, or the dynamical mixing in giant exoplanet atmospheres.
We will measure the first direct evidence of aerosols in the atmosphere of an exoplanet by observing the vibrational-mode absorption from sub-micron sized particles in the atmosphere of HD 209458b with MIRI LRS. With these observations, we will be able to constrain the particle size of the aerosols to less than an order of magnitude. This will enable us to constrain the magnitude of dynamical mixing in the atmosphere needed to produce such particle sizes, which in turn informs the role of mixing in the gas phase chemistry. In just a single transit, these high precision observations will not only distinguish between aerosols composed of cloud condensates and organic hazes, but also examine the role of aerosols in the radiative transfer, dynamics, and chemistry of exoplanet atmospheres- Publication:
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JWST Proposal. Cycle 1
- Pub Date:
- March 2021
- Bibcode:
- 2021jwst.prop.2667W