Abstract
Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto’s haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulations of Titan’s haze, this result suggests that haze particles in reducing atmospheres undergo rapid shape change near pressure levels ~0.5 Pa and favors a photochemical rather than a dynamical origin for the formation of Titan’s detached haze. It also demonstrates that both oxidizing and reducing atmospheres can produce multi-modal hazes, and encourages reanalysis of observations of hazes on Titan and Triton.
Highlights
Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation
We report observations of a bimodal distribution of haze particles in Pluto’s chemically reducing atmosphere, which supports the scenario in which single-source organic photochemistry and microphysics can result in multimodal haze particles in chemically reducing atmospheres without contributions from dynamics
The haze has strong forward scattering, which is an indication of large particles15
Summary
Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. 1234567890():,; Hazes are common in the atmospheres of solar system bodies and exoplanets1–4 They play important roles in atmospheric composition, dynamics, and radiative transfer, most of which are highly dependent on particle sizes. The modality of haze particle distributions in reducing atmospheres is currently unknown Observations of such hazes are usually interpreted using unimodal haze models for simplicity, which encourages simplified physical haze models generating unimodal hazes as well. We report observations of a bimodal distribution of haze particles in Pluto’s chemically reducing atmosphere, which supports the scenario in which single-source organic photochemistry and microphysics can result in multimodal haze particles in chemically reducing atmospheres without contributions from dynamics
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