Astronomers have found faint methane gas around Makemake, a small icy world much farther from the sun than Pluto. The gas is much thinner than Pluto’s atmosphere — and far weaker than Earth’s.
Makemake is over 2 billion kilometers farther from the sun than Pluto and takes 306 years to complete one orbit. For comparison, Pluto takes 248 years.
Scientists were surprised to find any gas at all. Earlier, when Makemake passed in front of a star, no gas was detected. That’s because the gas is extremely thin — the pressure is about one 100 billionth of Earth’s atmosphere, and one millionth of Pluto’s.
In 2023, the James Webb Space Telescope (JWST) finally detected the faint methane. JWST is very powerful because of its large size and ability to study infrared light, which helps reveal details of distant icy worlds.
“This discovery shows how powerful the Webb telescope is,” says William McKinnon, a planetary scientist who was not part of the research. “It’s opening up the mysteries of the outer solar system.”
Makemake is so cold that methane turns solid and forms an icy layer on its surface. This ice reflects about 80% of the sunlight. Some of the methane gas may come from the ice slowly turning back into vapor under the weak sunlight, creating a thin atmosphere.
But there might be a more exciting explanation, says Protopapa. Gas plumes could be erupting from Makemake’s interior, much like the geysers that shoot water from Saturn’s moon Enceladus.
Enceladus, which is only about a third the size of Makemake, gets its activity from the strong pull of Saturn’s gravity. Makemake doesn’t have a nearby planet to cause this effect, but its large size may help keep it active. At about 1,430 kilometers wide — around 60% the width of Pluto — Makemake is likely the fourth-largest object orbiting the sun beyond Neptune.
Like Pluto, Makemake looks orange. This color probably comes from sunlight and cosmic rays changing methane into more complex chemicals. But unlike Pluto, which has plenty of nitrogen ice and gas, JWST found no nitrogen on Makemake. Scientists think it may have lost its nitrogen over time, since nitrogen evaporates more easily than methane at Makemake’s freezing temperature. Its weak gravity may also have failed to keep nitrogen gas from escaping. Still, there could be nitrogen ice hidden below the methane ice.
If Makemake can have gas, could even more distant worlds also have it? Eris, which is almost as big as Pluto and nearly twice as far from the sun as Makemake, has both methane and nitrogen ice on its surface. But when Eris passed in front of a star in 2010, no gas was detected, and JWST hasn’t seen any either. For now, Makemake is the only world this far from the sun showing methane gas. Still, Protopapa says, JWST’s powerful infrared view may one day find it on Eris too.
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