This dwarf planet has gas: Makemake's methane surprises scientists

Scientists have detected methane gas on the dwarf planet Makemake, indicating that the distant body is a dynamic icy world.

The discovery was made by a team led by the Southwest Research Institute (SwRI) using NASA's James Webb Space Telescope (JWST).

Makemake is one of the largest and brightest worlds beyond Neptune, and becomes only the second trans-Neptunian object, after Pluto, found to have a confirmed presence of gas.

"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," said SwRI's Silvia Protopapa, lead author of a new paper soon to be published in The Astrophysical Journal Letters, in a statement.

"It shows that Makemake is not an inactive remnant of the outer solar system, but a dynamic body where methane ice is still evolving," Protopapa added.

Makemake is about 890 miles (1,430 kilometers) in diameter, meaning it is two-thirds the size of Pluto. JWST made the methane find by picking up a telltale spectral signature of solar light re-emmitted by methane molecules.

The finding of methane in gas form could be due to either the presence of a tenuous atmosphere on Makemake, or a more transient activity such as that experienced by comets when its volatiles sublimate, or from cryovolcanic plumes, according to the study authors.

The detected atmosphere, if it is indeed a permanent feature of Makemake, is very tenuous. Its surface pressure is only about 10 picobars, or 100 billion times below Earth's atmospheric pressure, according to the authors' models.

The authors produced models for a scenario in which methane is released in plume-like outbursts. These simulations suggest that methane could be released at a rate of a few hundred kilograms per second, making the level of activity comparable to the water plumes on Saturn's ocean moon Enceladus.

"Future Webb observations at higher spectral resolution will help determine whether the methane arises from a thin bound atmosphere or from plume-like outgassing," said Ian Wong, staff scientist at the Space Telescope Science Institute and co-author of the paper.

Earlier observations of Makemake made when the icy world passed in front of a star had shown that it did not harbor a significant atmosphere, but did not rule out a much thinner one.

The paper, titled "JWST Detection of Hydrocarbon Ices and Methane Gas on Makemake," is available on the preprint repository arXiv.