A bimodal distribution of haze in Pluto's atmosphere

TL;DR

This paper presents observational evidence that Pluto's haze particles are bimodally distributed, providing insights into haze formation processes in reducing atmospheres and implications for other celestial bodies like Titan and Triton.

Contribution

It reveals the bimodal size distribution of Pluto's haze particles and suggests a photochemical origin, advancing understanding of haze formation in icy, reducing atmospheres.

Findings

Pluto's haze particles are bimodally distributed.

Haze formation likely involves rapid shape change near 0.5 Pa pressure.

Results support a photochemical origin over dynamical processes.

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 ~0.5Pa 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.