Activity detected on dwarf planet Makemake, once thought to be a frozen wasteland

Makemake, one of the brightest icy bodies beyond Neptune, just joined an exclusive club. Using NASA’s James Webb Space Telescope, experts have detected gas above its surface.

This is the second confirmed case of a trans-Neptunian object with gaseous material after Pluto. The culprit is methane, the same molecule that dominates Makemake’s frozen surface.

Study lead author Sylvia Protopapa is a principal scientist at the Southwest Research Institute (SwRI).

“Makemake is one of the largest and brightest icy worlds beyond Neptune, and its surface is dominated by frozen methane,” said Protopapa. “Methane is also present in the gas phase above the surface.”

The findings show that Makemake is not an inactive remnant of the outer solar system, but a dynamic body where methane ice is still evolving.

Methane seen in new light

At roughly 890 miles across – about two-thirds the size of Pluto – Makemake was long thought to lack a substantial global atmosphere.

Stellar occultations (brief events when the dwarf planet passes in front of a star) pointed to no more than a wisp of air.

Webb’s infrared spectra now add an important twist: the team sees methane in emission, excited by sunlight and re-emitted as a faint glow known as fluorescence.

That signal is key. Rather than seeing methane by the light it blocks – as in traditional transmission measurements – Webb picked up methane molecules that absorbed sunlight.

The molecules then re-radiated it at characteristic wavelengths. In the frigid outer solar system, that kind of fluorescent “whisper” is subtle – and squarely in Webb’s wheelhouse.

A thin, Pluto-like atmosphere

What’s producing the methane glow? The data allow for two very different, but physically reasonable, scenarios.

One possibility is a wisp-thin, Pluto-like atmosphere in equilibrium with surface ices. As seasonal sunlight warms bright methane frost, a trickle of gas sublimates into the sky, drifting until cold patches on the surface refreeze it.

“This discovery raises the possibility that Makemake has a very tenuous atmosphere sustained by methane sublimation,” said Emmanuel Lellouch of the Paris Observatory.

Models point to gas temperatures around 40 Kelvin (–233 °C/–387 °F) and surface pressures of about 10 picobars – roughly 100 billion times lower than Earth’s sea-level pressure, and a million times more tenuous than Pluto’s.

Explosive plumes from below

The other option is more dramatic: localized outgassing. “Another possibility is that the methane is being released in plume-like outbursts,” Protopapa noted.

In this picture, methane vents from hot spots or fractures at a rate of a few hundred kilograms per second – comparable to the water-rich plumes at Saturn’s moon Enceladus and far more vigorous than the faint vapor seen at Ceres.

Such activity would dovetail with earlier hints from thermal observations that some patches on Makemake’s surface are warmer or texturally unusual, potentially due to fresh deposits, rough terrain, or buried heat sources.

“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 Ian Wong from the Space Telescope Science Institute.

“Future Webb observations at higher spectral resolution will help determine whether the methane arises from a thin bound atmosphere or from plume-like outgassing.”

Methane cycles reshape Makemake

Whichever source proves correct, methane gas on Makemake is very significant.

It suggests that surface-atmosphere exchanges – processes that cycle ices into vapor and back again – are still active today far beyond Neptune. Pluto has been the standout example, but Makemake now looks poised to join it.

The research also tightens the link between chemistry and climate on distant dwarf planets.

Methane ice can brighten or darken surfaces depending on grain size and mixing. It can also alter thermal behavior. And when it vaporizes, it transports heat and material from one region to another.

Even a vanishingly thin atmosphere can smear frost from sunlit areas to shadowed ones, slowly repainting a world over seasonal timescales.

If plumes are involved, they could dust the surface with fresh, fine-grained frost, refresh colors, and even build subtle landforms.

A complex dwarf planet revealed

Makemake’s story has always hinted at complexity. Discovered in 2005 and notable for its high albedo and reddish tint (likely due to radiation-processed organics called tholins), it later surprised astronomers with the discovery of a small, dark moon.

Occultations suggested no thick blanket of air, yet infrared data – including Webb’s – have pointed to puzzling thermal anomalies and unusual characteristics of its methane ice.

The new methane fluorescence doesn’t settle every debate, but it provides a missing piece: gas is present, at least sometimes.

Next steps for Makemake research

Webb detected the methane using its ultra-sensitive infrared spectrograph. It was able to tease out faint signatures of the gas against the dim, icy backdrop nearly 40–50 astronomical units from the Sun.

The team’s ability to detect fluorescence highlights both the telescope’s power and the lofting of methane molecules above the surface.

To pin down the source, higher-resolution spectra will be crucial. If Makemake hosts a bound atmosphere, Webb can look for telltale line shapes and ratios that betray gas temperature and pressure, and perhaps the presence (or absence) of other volatiles like nitrogen or carbon monoxide.

If plumes are the source, repeated observations might catch variability – brief brightenings as vents turn on, or regional differences tied to specific terrains.

“Future Webb observations at higher spectral resolution will help determine whether the methane arises from a thin bound atmosphere or from plume-like outgassing,” Wong said.

Makemake isn’t frozen after all

Either outcome will sharpen our picture of Makemake’s volatile cycle and, by extension, the behavior of other methane-rich worlds that orbit in the deep freeze beyond Neptune.

For a dwarf planet once pegged as a quiet, frozen leftover, Makemake is suddenly looking lively  – and that’s good news.

It means the outer solar system is not just a museum of icy planets, but a place where sunlight, chemistry, and geology still conspire to keep tiny worlds active.

The study is published in The Astrophysical Journal Letters.

Image credit: NASA Visualization Technology Applications and Development

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