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Characterizing Super-Earth and Mini-Neptune Light Scattering via Experimental Phase Curves

Presentation #305.03 in the session “Exoplanets and Systems: Terrestrial Planets”.

Published onOct 03, 2021
Characterizing Super-Earth and Mini-Neptune Light Scattering via Experimental Phase Curves

Planetary phase curves provide unique insight into the atmospheres and aerosol distributions of other worlds by measuring planetary brightness as a function of scattering angle from a planet’s host star. Since transmission spectra has shown that aerosols are ubiquitous across the array of exoplanet sizes and temperatures, optical phase curves of exoplanet atmospheres will be primarily dominated by the scattering of aerosol layers near the top of the atmosphere. In this work I will present experimental phase curves of pure zinc sulfide (ZnS) and potassium chloride (KCl) cloud species thought to form under thermochemical equilibrium in temperate (Teq < 1000 K) super-Earth (1 –2 RE) and mini-Neptune (2-4 RE) atmospheres. Past modeling studies (such as Gao & Benneke 2018 and Ohno & Okuzumi 2018 among others) have indicated that these compounds heterogeneously condense from the atmosphere around 100 – 10-2 bar. The ZnS and KCl particles studied in the laboratory have mean particle radii of ~1.0 µm and ~2.5 µm, respectively, as these size ranges are thought to form via condensation and coalescence in temperate exoplanet atmospheres. The measurement and collection of optical phase curves is completed using a photomultiplier tube that sweeps around a flow of particles, on the plane of illumination, from ~0° (forward scattering) to ~180° (back scattering); the particles are illuminated by a green (532 nm) laser and flown into the system using pure nitrogen (N2) carrier gas at 0.50 liters per minute. The particles are close enough to one another to undergo multiple scattering, which can be used to simulate how exoplanet cloud decks reflect light from their host star. In this talk, I will introduce our laboratory set-up, present collected phase curves, and discuss how this data can help place constraints on the observation and modeling of super-Earth and mini-Neptune atmospheres.

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