"Makemake is one of the largest and brightest icy worlds beyond Neptune, and its surface is dominated by frozen methane," said SwRI's Dr. Silvia Protopapa, lead author of the new study. "The Webb telescope has now revealed that methane is also present in the gas phase above the surface, a finding that makes Makemake even more fascinating. It shows that Makemake is not an inactive remnant of the outer Solar System, but a dynamic body where methane ice is still evolving."

The methane spectral emissions were interpreted as solar-excited fluorescence, sunlight re-emitted after being absorbed by methane molecules. According to the research team, this could indicate either a tenuous atmosphere in equilibrium with surface ices, similar to Pluto, or more transient activity such as sublimation-driven outgassing or cryovolcanic plumes. Current data, limited by spectral resolution and noise, remain consistent with both scenarios.

At roughly 890 miles (1,430 km) across, Makemake is about two-thirds the size of Pluto and has long intrigued planetary scientists. Earlier stellar occultation studies suggested the absence of a thick global atmosphere, though a thin one could not be excluded. Infrared data from JWST and other telescopes have also revealed thermal anomalies and unusual properties in Makemake's methane ice, raising the possibility of localized hot spots and episodic outgassing.

"While the temptation to link Makemake's various spectral and thermal anomalies is strong, establishing the mechanism driving the volatile activity remains a necessary step toward interpreting these observations within a unified framework," said Dr. Ian Wong of the Space Telescope Science Institute, co-author of the paper. "Future Webb observations at higher spectral resolution will help determine whether the methane arises from a thin bound atmosphere or from plume-like outgassing."

"This discovery raises the possibility that Makemake has a very tenuous atmosphere sustained by methane sublimation," said Dr. Emmanuel Lellouch of the Paris Observatory, another co-author. "Our best models point to a gas temperature around 40 Kelvin (-233 degrees Celsius) and a surface pressure of only about 10 picobars - about 100 billion times lower than Earth's atmosphere, and a million times thinner than Pluto's."

Alternatively, Makemake's methane may be erupting from plume-like activity. "In this scenario, our models suggest methane could be released at a rate of a few hundred kilograms per second, comparable to the vigorous water plumes on Saturn's moon Enceladus and far stronger than the faint vapor seen at Ceres," said Protopapa.

The findings highlight how Webb's observations, combined with detailed spectral models, can uncover new evidence about volatile processes on distant icy worlds and broaden understanding of trans-Neptunian activity.

Research Report:JWST Detection of Hydrocarbon Ices and Methane Gas on Makemake

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