Unexplained Chemical Signature on Two Icy Worlds
The James Webb Space Telescope (JWST) has detected a chemical signature on the surfaces of Pluto and Titan—Saturn’s largest moon—that does not match any known compound in spectroscopic databases. Researchers have ruled out instrument error and believe the signal originates from an unidentified compound, possibly a mixture never studied in the laboratory or an entirely new class of material.
How the Discovery Was Made
The finding, described in a paper awaiting publication in the journal Astronomy & Astrophysics, reveals an absorption band centered at 5.113 micrometers on both worlds. The signal was observed using two different JWST instruments, leading scientists to dismiss calibration issues or technical glitches. Spectroscopy, the technique used, analyzes how molecules absorb specific wavelengths of light, producing unique spectral fingerprints. In this case, none of the known signatures in existing catalogs matched the observed pattern.
Candidate Compounds Ruled Out
Researchers examined laboratory spectra of ices and organic compounds that could plausibly exist on Pluto and Titan—including acetylene, benzene, ketene, and a family of molecules called alenes. None of them exactly match the observed signature. The most likely explanation is that the signal comes from a known compound in an unfamiliar physical state or mixture, though the team does not rule out a material whose chemistry has never been characterized.
Why the Same Signal on Two Very Different Worlds?
Physical Conditions Contrast Sharply
Titan has a thick atmosphere rich in nitrogen and methane, with a surface pressure of approximately 1.5 bar (higher than Earth’s), rivers and lakes of liquid methane, and a temperature near –180°C (–292°F). Pluto, in contrast, retains only a tenuous atmosphere of about 10 microbars—some 150,000 times less dense. Its surface is covered in ices of nitrogen, methane, and carbon monoxide, and temperatures plunge to around –235°C (–391°F). Despite these dramatic differences, both worlds share a common feature: complex organic chemistry driven by solar radiation and cosmic rays, which can create new compounds that settle on their surfaces. Scientists believe this shared chemical processing may explain the mysterious signature.
Next Steps: JWST Observations and the Dragonfly Mission
Solving the puzzle will require new JWST observations and laboratory experiments that recreate the chemistry of these icy worlds. Scientists are particularly hopeful for NASA’s Dragonfly mission, scheduled to explore Titan’s surface. Although Dragonfly cannot directly observe the infrared signature, its onboard chemistry lab could identify candidate compounds and help unravel one of the most intriguing mysteries raised by JWST about the outer solar system.
This story originally appeared on WIRED en Español and has been translated from Spanish.