A Circumplanetary Dust Ring May Explain the Extreme Spectral Slope of the 10 Myr Young Exoplanet K2-33b

Abstract

Young exoplanets are attractive targets for atmospheric characterization to explore the early phase of planetary evolution and the surrounding environment. Recent observations of the 10 Myr young Neptune-sized exoplanet K2-33b revealed that the planet's transit depth drastically decreases from the optical to near-infrared wavelengths. Thao et al. (2022) suggested that a thick planetary haze and/or stellar spots may be the cause; however, even the best-fit model only barely explains the data. Here, we propose that the peculiar transmission spectrum may indicate that K2-33b possess a circumplanetary dust ring, an analog of Jupiter's dust ring. We demonstrate that the ring could produce a steep slope in the transmission spectrum even if its optical depth is as low as $\sim {10}^{-2}$. We then apply a novel joint atmosphere-ring retrieval to K2-33b and find that the ring scenario could well explain the observed spectrum for various possible ring compositions. Importantly, the dust ring also exhibits prominent absorption features of ring particles around $\sim$10 $\mu \mathrm{m}$, whose shape and strength depend on the composition of the ring. Thus, future observations by JWST-MIRI would be able to test not only the ring hypothesis but also, if it indeed exists, to constrain the composition of the ring -- providing a unique opportunity to explore the origins of the dust ring around its parent planet, soon after the planetary system's formation.

8 pages, 4 figures, Accepted for publication in ApJL. Please also see Thao et al. (2022) for the transmission spectrum of K2-33b

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Cited by in corpus (5)

• Stability and detectability of exomoons orbiting HIP 41378 f, a temperate Jovian planet with an anomalously low apparent density
• Hazy with a chance of star spots: constraining the atmosphere of the young planet, K2-33b
• Exploring Exoplanet Dynamics with JWST: Tides, Rotation, Rings, and Moons
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• ASTEP confirmation of a pair of long-period Jupiter-sized planets with extremely low densities transiting TOI-791