A “Crazy Idea” Proven True: Pluto’s Breath Changes Its Moon’s Color

JWST) has delivered a stunning new look at Pluto, revealing dramatic activity on its distant surface. Scientists observed seasonal shifts in icy material moving across the landscape—and even more surprisingly, particles from Pluto’s atmosphere appear to be drifting through space and settling onto its largest moon, Charon. This eerie exchange of gases between worlds is something we’ve never seen anywhere else in the solar system.

These fascinating discoveries are part of a series of studies published this spring by an international team of researchers. For one scientist on the team, Xi Zhang of UC Santa Cruz, the findings are especially rewarding. The latest study, published June 2 in Nature Astronomy, confirms a bold prediction he made years ago about Pluto’s unusual atmosphere, first sparked by data from NASA’s 2015 New Horizons flyby.

At the time, Pluto had already been reclassified from a planet to a dwarf planet, but interest in its complex features only grew. That 2015 flyby offered our closest-ever view of this icy world, located at the outer edge of the solar system.

The Birth of a Wild Hypothesis

In the wake of New Horizons’ observations of Pluto, Zhang published a paper in 2017 that hypothesized that Pluto’s atmosphere was dominated by haze particles, which would’ve made it completely different from other atmospheres in the solar system. Zhang, a professor of Earth and planetary sciences, posited that these haze particles heat up and cool down, controlling the whole energy balance in Pluto’s atmosphere.

“It was a crazy idea,” said Zhang, adding that many of his peers at the time expressed skepticism. But he and his co-authors also made a clear prediction in their 2017 paper: If the haze is cooling Pluto, it should be emitting strong mid-infrared radiation, and that should be observable once a big and powerful enough telescope was available to astronomers.

That moment arrived on Christmas Day 2021, when NASA launched JWST into space to enable observations that would far surpass those made by its ground-based predecessors over the last several decades. Zhang said the current JWST study was motivated by his 2017 hypothesis. “We were really proud, because it confirmed our prediction,” he said. “In planetary science, it’s not common to have a hypothesis confirmed so quickly, within just a few years. So we feel pretty lucky and very excited.”

A Hazy, Alien World

The Pluto flyby in 2015 revealed a world with surprising landscapes, marked by complex topography—basins, mountains, and valleys—ongoing geological activity like nitrogen (N₂) and methane (CH₄) glaciers, and a chemically rich atmosphere containing volatile compounds such as N₂, CH₄, and carbon monoxide. Pluto’s hazy atmosphere formed from coupled methane and nitrogen photochemistry, similar to the haze around