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Webb reveals methane gas above Makemake
An international team led by the Southwest Research Institute (SwRI) has used the James Webb Space Telescope (JWST) to detect methane gas above the distant dwarf planet Makemake. The discovery makes Makemake the second trans-Neptunian object, after Pluto, where gas has been spectroscopically identified. The detection points to active volatile processes on this icy world at the edge of the Solar System and raises new questions about how surface ices and tenuous atmospheres interact on small, cold bodies.
An SwRI-led team used Webb telescope observations (white) to detect methane gas on the distant dwarf planet Makemake. Sharp emission peaks near 3.3 microns reveal methane in the gas phase above Makemake’s surface. A continuum model (cyan) is overlaid for comparison; the gas emission peaks are identified where the observed spectrum rises above the continuum. An artistic rendering of Makemake’s surface is shown in the background.
Observations and spectral evidence
The methane signal was extracted from JWST infrared spectra as sharp emission features near 3.3 microns, a wavelength region where methane molecules fluoresce after absorbing sunlight. The team identifies these features as solar-excited fluorescence: sunlight excites methane molecules and the molecules re-emit that energy at characteristic infrared wavelengths. To distinguish the emission peaks from the underlying reflected-light continuum, researchers compared the observed spectrum to a continuum model and located statistically significant rises above that baseline.
JWST's sensitivity in the mid-infrared and its stable spectroscopic performance enabled the detection, but current data are limited by spectral resolution and background noise. Those limitations mean the spectra alone do not yet reveal whether methane exists in a globally bound atmosphere or is released in localized, short-lived outbursts.
Scientific context: Makemake, volatiles, and the Kuiper Belt
Makemake is an icy dwarf planet roughly 1,430 kilometers across (about two-thirds the diameter of Pluto) located in the Kuiper Belt. Its bright surface is dominated by frozen methane, making spectral detections of methane gas particularly significant. Previous stellar occultation experiments placed strong limits on any thick global atmosphere, but left open the possibility of an extremely tenuous atmosphere or localized vents.
Infrared observations over the past decade have also revealed thermal anomalies and heterogeneous methane ice properties across Makemake's surface. Those results motivated the JWST follow-up: if small regions become warmer or if subsurface processes mobilize volatiles, transient gas release could occur even where a global atmosphere is absent.
Interpreting the methane: atmosphere or plumes?
Researchers consider two leading explanations that are consistent with the JWST data. One possibility is a very thin, surface-bound atmosphere in vapor pressure equilibrium with surface methane ice — a scenario analogous to Pluto’s seasonal atmosphere but far weaker. Model fits in the study point to a gas temperature near 40 Kelvin (about -233°C) and an estimated surface pressure on the order of 10 picobars: roughly 100 billion times lower than Earth’s pressure and about a million times less than Pluto’s.
The other plausible scenario is episodic, plume-like outgassing where methane is released in localized bursts. In that case, modeling suggests peak release rates could reach a few hundred kilograms per second — comparable to the mass flux of Enceladus’s vigorous water plumes and much larger than the extremely faint vapor previously measured at Ceres.
Dr. Silvia Protopapa (SwRI), lead author of the JWST analysis, emphasizes that detecting methane gas demonstrates Makemake is not a completely inert remnant. Co-author Dr. Ian Wong (Space Telescope Science Institute) notes that higher spectral resolution observations will be required to discriminate between a bound atmosphere and plume activity.
Implications and future observations
If Makemake hosts an active, even if extremely tenuous, atmosphere, it would broaden the sample of outer Solar System bodies where surface–atmosphere exchange remains ongoing. Confirming either a surface-bound atmosphere or plume activity would affect models of volatile transport, seasonal behavior in the Kuiper Belt, and how solar insolation drives sublimation at very low temperatures.
The research team highlights the importance of follow-up Webb spectroscopy at higher spectral resolution and additional observations timed to different seasonal or rotational phases. Complementary techniques — for example, targeted stellar occultations and sensitive submillimeter searches for gas — could help constrain global pressure and spatial variability.
Expert Insight
Dr. Laura Kim, planetary scientist (fictional), comments: "Detecting methane gas above Makemake with JWST is a milestone for Kuiper Belt science. Even extremely thin atmospheres can reveal much about surface composition and energy balance. The real next step is time-resolved spectroscopy to see whether the signal varies with rotation or solar heating, which would point to localized sources."
Conclusion
JWST's detection of methane emission from Makemake provides the first direct spectral evidence for gas above this distant dwarf planet. While the current data cannot yet determine whether Makemake sustains a global, surface-bound atmosphere or experiences episodic plume-like outgassing, the finding establishes Makemake as an active target for future observations. Higher-resolution JWST spectra, occultation campaigns, and continued thermal mapping will be essential to understanding volatile cycles and the mechanisms that drive gas release in the outer Solar System.
Source: scitechdaily
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