Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy
Session 1.02 Spectroscopy
Monday 06-24 | 09:30 - 09:50

Sedna, Gonggong, and Quaoar are somewhat smaller than the methane-rich bodies of the Kuiper Belt (Pluto, Eris, Makemake), yet large enough to be spherical and to have possibly undergone interior processing. They also reside on very different orbits, making them ideal for untangling effects of size and orbit on surface composition. We observed Sedna, Gonggong, and Quaoar with NIRSpec on JWST. All three bodies were observed in the low-resolution prism mode at wavelengths spanning 0.7 to 5.2 μm. Quaoar was additionally observed at ~10× higher spectral resolution from 0.97 to 3.16 μm using medium-resolution gratings. Sedna's spectrum shows a large number of absorption features due to ethane (C2H6), as well as acetylene (C2H2), ethylene (C2H4), H2O, and possibly CO2. Gonggong's spectrum also shows several, but fewer and weaker, ethane features, along with stronger and cleaner H2O features and CO2 complexed with other molecules. Quaoar's prism spectrum shows even fewer and weaker ethane features, the deepest and cleanest H2O features, a feature at 3.2 μm possibly due to HCN, and CO2 ice. The higher-resolution medium grating spectrum of Quaoar reveals several overtone and combination bands of ethane and methane (CH4). Spectra of all three objects show steep red spectral slopes and strong, broad absorptions between 2.7 and 3.6 μm indicative of complex organic molecules. The suite of light hydrocarbons and complex organic molecules are interpreted as the products of irradiation of methane. We infer that the differences in apparent abundances of irradiation products among these three similarly-sized bodies are likely due to their distinctive orbits, which lead to different timescales of methane retention and to different charged particle irradiation environments. Feature identification presented here is the first analysis step, and additional insight into the relative abundances and mixing states of materials on these surfaces will come from future spectral modeling.

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