A mysterious wavelength of light is missing from the dwarf planet Pluto and Saturn's supersized moon Titan, new James Webb Space Telescope (JWST) observations show. The surprising discovery hints that these worlds harbor an unknown molecule that has not been seen in any other solar system world or exoplanet so far.
Every element or molecule in the universe absorbs unique wavelengths of electromagnetic radiation. Astronomers study distant worlds by examining the light that reflects off them and searching for dark 'absorption lines' — fingerprints of specific chemical compounds.
In a new study uploaded June 11 to the preprint server arXiv, researchers analyzed JWST data from Pluto and Titan, focusing on very small wavelengths that have been relatively unexplored until now. This revealed a specific absorption line at around 5.11 micrometers in both worlds' spectra. (These findings have not been published in a peer-reviewed journal yet.)
The team pored through similar studies on other planetary spectra but did not find any band referenced in these publications that corresponds to the location of the observed absorption in Titan and Pluto.
The discovery is even stranger because there are very few similarities between Pluto and Titan that could explain why they share a molecule not found anywhere else. Titan is Saturn's largest moon — larger even than Mercury — and the only solar system world besides Earth known to have liquid rivers and oceans on its surface. Pluto, on the other hand, is a completely frozen world roughly half the size of Titan and four times farther from the sun.
Both worlds do have similar atmospheres rich in methane and nitrogen. However, researchers are confident the mystery molecule is located on both worlds' surfaces, not in their atmospheres.
Pluto's absorption line is around three times thicker than Titan's, meaning the mystery molecule is likely much more abundant on the dwarf planet. On Titan, the molecule seems unevenly distributed, with a stronger signal on its trailing side.
The researchers proposed it could be benzene — a ring-shaped hydrocarbon — mixed with an unknown molecule, or some form of acetylene or ketene ice. NASA's Dragonfly spacecraft, set to launch no earlier than 2028 and fly through Titan's atmosphere in 2034, could eventually identify the mystery molecule. But in the meantime, this curious cosmic conundrum will keep astronomers guessing.
