Astronomy Picture Of The Day: Mysterious Unknown Substance Detected on Titan and Pluto by James Webb Space Telescope

 

#Astronomy, #NASA , #Space, #διάστημα

In a striking discovery that highlights the surprises still hidden in our Solar System, the James Webb Space Telescope (JWST) has identified an unidentified absorption feature in the spectra of Saturn’s largest moon, Titan, and the dwarf planet Pluto. The finding, centered at a wavelength of 5.113 micrometers (μm), points to the presence of an unknown surface compound that scientists have yet to identify. During detailed spectral analysis of reflected light from both worlds, JWST’s NIRSpec and MIRI instruments detected a clear absorption band at 5.113 μm (equivalent to 1956 cm⁻¹). On Titan, the feature is approximately 6–7% deep, while on Pluto it appears with a depth of 4–5%. The signal is most likely originating from the surface rather than the atmosphere, particularly in the case of Titan. Key Differences Between the Two Bodies Researchers noted intriguing variations in the feature’s characteristics. On Titan, the absorption line is relatively narrow, with a width of about 0.024 μm (9.2 cm⁻¹) on the trailing hemisphere. It may be even narrower on the leading side. In contrast, the same feature on Pluto is roughly three times broader. Scientists attribute these differences to the physical or aggregate state of the mysterious compound under the distinct environmental conditions of each body. Titan possesses a thick nitrogen-methane atmosphere and complex organic chemistry, while Pluto has a much thinner atmosphere and icy surface. Despite these vast differences, the near-identical central wavelength strongly suggests a common underlying chemical or physical process at work on both distant worlds. Possible Candidates for the Unknown Substance The team, led by researchers including B. Bézard, thoroughly searched laboratory spectra of ices and organic compounds relevant to these environments but found no exact match. Several plausible candidates have been proposed: Allenes**: A class of hydrocarbons featuring cumulated double bonds between carbon atoms. Ketenes**: Reactive organic compounds containing a carbonyl group adjacent to a carbon-carbon double bond. Benzene mixtures**: Benzene combined with other species, which could shift the spectral signature. Irradiation products**: Compounds formed by cosmic ray bombardment of methanol ice. The similarity in the spectral lines implies that a shared mechanism—perhaps involving the processing of simple organics like methane or nitrogen compounds by ultraviolet light or cosmic rays—produces this substance across both bodies. Implications and Future Exploration This discovery underscores how much remains unknown about the surface chemistry of icy bodies in the outer Solar System. The unidentified absorber could represent a new class of organic material or a mixture whose spectroscopic properties have not yet been replicated in laboratory conditions. Fortunately, answers may be on the horizon. NASA’s Dragonfly mission, a rotorcraft lander scheduled to arrive at Titan in the early 2030s, will directly explore the moon’s surface. By analyzing materials in situ, it could help identify the mysterious compound and shed light on the organic chemistry that links Titan and Pluto. As JWST continues its observations and more laboratory studies are conducted, this enigmatic 5.113 μm feature may soon reveal its secrets—potentially offering new insights into the formation and evolution of complex molecules on distant, frigid worlds. The study, titled “An unidentified absorption feature at 5.11 μm on the surface of Titan and Pluto from JWST spectroscopy,” is available on arXiv and is forthcoming in Astronomy & Astrophysics. It represents another milestone in JWST’s transformative exploration of our cosmic neighborhood.