SAN ANTONIO — September 9, 2025 — A Southwest Research Institute-led team has reported the first detection of gas on the distant dwarf planet Makemake, using NASA's James Webb Space Telescope (JWST). This discovery makes Makemake only the second trans-Neptunian object, after Pluto, where the presence of gas has been confirmed. The gas was identified as methane.
"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 a new paper soon to be published in The Astrophysical Journal Letters. "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 observed methane spectral emission is interpreted as solar-excited fluorescence, which is the re-emission of sunlight absorbed by methane molecules. According to Protopapa and her co-authors, this could indicate either a tenuous atmosphere in equilibrium with surface ices — similar to Pluto — or more transient activity, such as cometary-like sublimation or cryovolcanic plumes. Both scenarios are physically plausible and consistent with the current data, given the level of noise and limited spectral resolution of the measurements.
At about 890 miles (1,430 km) in diameter and two-thirds the size of Pluto, Makemake has long been a source of scientific intrigue. Stellar occultations suggested that it lacked a substantial global atmosphere, though a thin one could not be ruled out. Meanwhile, infrared data of Makemake — including JWST measurements — hinted at puzzling thermal anomalies and unusual characteristics of its methane ice, which raised the possibility of localized hot spots across its surface and potential 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, staff scientist at the Space Telescope Science Institute and 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 of the study. "Our best models point to a gas temperature around 40 Kelvin (-233 degrees Celsius) and a surface pressure of only about 10 picobars — that is, 100 billion times below Earth's atmospheric pressure, and a million times more tenuous than Pluto's. If this scenario is confirmed, Makemake would join the small handful of outer solar system bodies where surface–atmosphere exchanges are still active today."
"Another possibility is that the methane is being released in plume-like outbursts," added Protopapa. "In this scenario, our models suggest that 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 greater than the faint vapor seen at Ceres."
The team's research showcases the link between Webb observations and detailed spectral modeling, offering new insights into the behavior of volatile-rich surfaces across the trans-Neptunian region.
The paper titled "JWST Detection of Hydrocarbon Ices and Methane Gas on Makemake," is available on arXiv and will soon be published in The Astrophysical Journal Letters.
The data used in this work were acquired with JWST's Near-Infrared Spectrograph through Program 1254 (PI: A. H. Parker).
