James Webb Reveals Pluto’s Burning (or Rather Icy) Mist Secret

Thanks to the James Webb Space Telescope, an international team of researchers, including Panayotis Lavvas, a researcher at GSMA (UMR CNRS – 7331) at the University of Reims Champagne-Ardenne (URCA), has unveiled a new facet of Pluto’s climate. The mysterious haze surrounding Pluto contains a large amount of frozen organic condensates—tiny particles formed from the condensation of complex molecules in the atmosphere. This discovery offers a new perspective on Pluto’s climate and also shows how this haze influences the surface of Charon, its largest moon.

An icy haze at the heart of Pluto’s climate system

Pluto’s thin atmosphere is dominated by nitrogen and methane. Under the influence of sunlight, these gases undergo complex photochemical reactions, giving rise to a haze made of tiny particles. But there’s more: thanks to JWST and its MIRI instrument, scientists directly observed the infrared emission of this haze, revealing that its particles are not mere dust, but genuine organic ices.

“JWST observations confirm the theory we developed at GSMA regarding the role of organic condensates,” says Panayotis Lavvas.

These frozen condensates, including diacetylene (C4H2) and hydrogen cyanide (HCN), form in the upper atmosphere through direct condensation. Their presence profoundly affects Pluto’s energy balance. By absorbing and re-emitting heat, the haze acts as a natural thermal regulator, cooling the atmosphere and controlling seasonal variations. The formation and properties of these organic condensates were predicted and modeled by the GSMA team, and JWST has now provided experimental proof that this theory is correct.

Charon, the moon witnessing a shared climate

A second discovery concerns Charon, Pluto’s main moon. Unlike Pluto, Charon has no atmosphere. Yet its surface shows visible traces of interactions with Pluto. Dark and reddish polar regions result from methane escaping Pluto, then being trapped and chemically altered on Charon’s surface. JWST instruments directly detected Charon’s thermal emission, distinct from Pluto’s, highlighting these unique interactions. This phenomenon, where a planet’s atmosphere influences its moon’s surface, is unprecedented and enriches our understanding of material exchanges in the Solar System.

Discoveries paving the way for the study of icy worlds

These exceptional findings place the GSMA laboratory at URCA at the heart of a major advance in planetary science. Understanding how these organic haze particles form, evolve, and regulate Pluto’s atmospheric temperature will improve our knowledge of other icy and hazy worlds in the Solar System, such as Triton, Titan, and even early Earth. It also highlights the importance of subtle interactions between surface, atmosphere, and particles in shaping planetary climates. Furthermore, Pluto’s interaction with Charon offers new insights into material exchanges between celestial bodies.

With these results, Pluto ceases to be an isolated dwarf planet and becomes a unique natural laboratory for studying the climatic and chemical processes shaping icy bodies at the edge of our Solar System.

Image: Pluto with haze on the horizon (Credit: NASA/JHUAPL/SwRI)