Makemake’s Hidden Activity: JWST Finds Methane Gas and Hydrocarbon Ices
Makemake is one of the largest known dwarf planets in the Kuiper Belt, orbiting far beyond Neptune. For years, astronomers thought of it as a cold and inactive world, covered mainly in frozen methane. In this new study, Silvia Protopapa and colleagues use the James Webb Space Telescope (JWST) to take a closer look, and the results suggest that Makemake may be more active than previously believed.
A World of Methane and More
Earlier work had already shown that Makemake’s surface is dominated by methane (CH₄) ice, but the JWST data reveal much more. Protopapa’s team found not only methane but also its slightly heavier version, CH₃D, which allowed them to measure the ratio of deuterium to hydrogen (D/H). This ratio, often used to trace the history of planetary materials, falls between what is seen in water and methane from comets, hinting at a complex past. Along with methane, the team detected ethane (C₂H₆), acetylene (C₂H₂), and possibly methanol (CH₃OH). These molecules likely form when sunlight or cosmic rays break apart methane, creating new hydrocarbons over time.
Surface Chemistry in Layers
The researchers tested different models to explain how these ices are arranged on Makemake’s surface. Some models mixed the ices evenly, while others stacked them in layers. They found that a layered model fits best, where processed hydrocarbons like C₂H₂ and C₂H₆ coat the surface above thicker methane-rich layers. This structure supports the idea that radiation has been steadily transforming methane into more complex molecules on the surface.
Methane in the Air
One of the most surprising discoveries was evidence of methane gas above Makemake’s surface. The JWST data revealed a faint glow known as methane fluorescence, light emitted by methane molecules after absorbing sunlight. This marks the first detection of methane gas escaping from Makemake, making it only the second trans-Neptunian object (after Pluto) with confirmed volatile release. The researchers explored two possible explanations: either the gas is escaping in a comet-like plume, or Makemake has a thin, gravitationally bound atmosphere. Both options are consistent with the data, but neither fully explains the details, leaving the question open.
Comparing Atmosphere and Coma
If the gas comes from a temporary plume, the production rate is like what is seen on active moons like Enceladus or Ceres. If instead Makemake holds onto a thin methane atmosphere, the surface pressure would be extremely low, around 10 picobars, yet still consistent with earlier telescope limits. Either way, the finding challenges the older view that Makemake is completely frozen and inactive.
A Dynamic Dwarf Planet
Together, these discoveries suggest that Makemake is not a static relic of the outer Solar System but a world with ongoing chemical and physical processes. Methane gas release, complex hydrocarbon ices, and its measured D/H ratio all point to recent or even current activity. This paints a picture of Makemake as a more dynamic and evolving body, reminding us that even the coldest, most distant worlds can surprise us when observed with powerful new tools like JWST.
Source: Protopapa
