Revealing Pluto’s Frosty Secrets: How Hazy Skies Are Deepening the Chill—Insights from the James Webb Space Telescope

The James Webb Space Telescope (JWST) has made an exciting discovery about Pluto. It found that the dwarf planet’s hazy sky is crucial for cooling its atmosphere. This haze is also helping to kick methane and other organic molecules out of Pluto’s atmosphere, which some of this material ends up on its large moon, Charon.

This haze was first predicted in 2017 by Xi Zhang, a planetary scientist at UC Santa Cruz. He sought to explain why Pluto’s thin atmosphere is so prone to leaking. Previous measurements from NASA’s New Horizons spacecraft show that Pluto is losing around 1.3 kilograms (2.9 pounds) of methane every second. Interestingly, Charon is catching about 2.5% of that methane, causing its poles to develop a reddish tint from organic compounds. This unique phenomenon of one body’s atmosphere leaking onto another has not been seen elsewhere in the solar system.

The role of haze in this dynamic was a big question mark until Zhang proposed that the haze absorbs some extreme ultraviolet light from the Sun. This absorption gives a little extra energy to atmospheric molecules, allowing them to break free and escape into space.

Additionally, this haze doesn’t just help material escape; it also cools Pluto’s atmosphere. It’s a fascinating two-way street: heating some molecules while simultaneously creating a cooling effect. This cooling was previously noted high in Pluto’s mesosphere, the third layer in its very thin atmosphere. The mesosphere stretches between 20 to 40 kilometers (12.4 to 24.9 miles) above the surface and gets extremely cold, plunging to temperatures below minus 200 degrees Celsius (about minus 328 degrees Fahrenheit).

Until the JWST came into play, scientists hadn’t been able to confirm the existence of this haze. Thanks to its advanced instruments, the JWST has been able to collect detailed data on thermal emissions from both Pluto and Charon. Tanguy Bertrand from the Observatoire de Paris, who led the JWST study, explained that the haze consists of tiny solid particles suspended in the atmosphere. This haze scatters light, creating a diffuse layer that softens visibility.

Pluto’s atmosphere is primarily nitrogen, with minor amounts of carbon dioxide and hydrocarbons like methane and benzene. It’s incredibly thin, with surface pressure only 13 microbars compared to Earth’s 1 bar. This means that even a tiny nudge from energy can send molecules into space. As Bertrand notes, solar extreme ultraviolet rays heat up these upper atmospheric gases, leading to atmospheric loss.

A puzzling aspect of this haze is how it can both heat and cool the atmosphere simultaneously. Bertrand pointed out that this depends on the haze’s properties—like the size, shape, and composition of the particles—which researchers are still trying to fully understand with new models.

This haze affects the energy balance in Pluto’s atmosphere, influencing temperature, air circulation, and the overall climate on this icy world. Pluto experiences extreme seasonal changes due to its unique orbit, which takes it closer to and farther from the sun than Neptune. This dramatically alters how much sunlight it receives, impacting its climate.

Interestingly, Pluto’s haze resembles the hydrocarbon-rich haze found on Titan, Saturn’s largest moon. Both are caused by the interaction of solar light with nitrogen and methane. Even early Earth likely had a denser haze of hydrocarbons before developing a richer oxygen atmosphere. Studying Pluto’s haze might give scientists insights into the early atmospheres of other planets, including Earth.

A study detailing these findings was published in *Nature Astronomy.* Understanding the atmospheric dynamics of distant worlds like Pluto can enhance our knowledge of planetary processes, not just within our solar system, but potentially across the universe.

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