  We observed Sedna, Gonggong, and Quaoar with the NIRSpec instrument on the
James Webb Space Telescope (JWST). All three bodies were observed in the
low-resolution prism mode at wavelengths spanning 0.7 to 5.2 $\mu$m. Quaoar was
also observed at 10x higher spectral resolution from 0.97 to 3.16 $\mu$m using
medium-resolution gratings. Sedna's spectrum shows a large number of absorption
features due to ethane (C$_2$H$_6$), as well as acetylene (C$_2$H$_2$),
ethylene (C$_2$H$_4$), H$_2$O, and possibly minor CO$_2$. Gonggong's spectrum
also shows several, but fewer and weaker, ethane features, along with stronger
and cleaner H$_2$O features and CO$_2$ complexed with other molecules. Quaoar's
prism spectrum shows even fewer and weaker ethane features, the deepest and
cleanest H$_2$O features, a feature at 3.2 $\mu$m possibly due to HCN, and
CO$_2$ ice. The higher-resolution medium grating spectrum of Quaoar reveals
several overtone and combination bands of ethane and methane (CH$_4$). Spectra
of all three objects show steep red spectral slopes and strong, broad
absorptions between 2.7 and 3.6 $\mu$m 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 are likely due to their distinctive
orbits, which lead to different timescales of methane retention and to
different charged particle irradiation environments. In all cases, however, the
continued presence of light hydrocarbons implies a resupply of methane to the
surface. We suggest that these three bodies have undergone internal melting and
geochemical evolution similar to the larger dwarf planets and distinct from all
smaller KBOs.
