Abstract
JWST measured the infrared spectra of Saturn's rings and several of its small
moons (Epimetheus, Pandora, Telesto and Pallene) as part of Guaranteed Time
Observation program 1247. The NIRSpec instrument obtained near-infrared spectra
of the small moons between 0.6 and 5.3 microns, which are all dominated by
water-ice absorption bands. The shapes of the water-ice bands for these moons
suggests that their surfaces contain variable mixes of crystalline and
amorphous ice or variable amounts of contaminants and/or sub-micron ice grains.
The near-infrared spectrum of Saturn's A ring has exceptionally high
signal-to-noise between 2.7 and 5 microns and is dominated by features due to
highly crystalline water ice. The ring spectrum also confirms that the rings
possess a 2-3% deep absorption at 4.13 microns due to deuterated water-ice
previously seen by the Visual and Infrared Mapping Spectrometer onboard the
Cassini spacecraft. This spectrum also constrains the fundamental absorption
bands of carbon dioxide and carbon monoxide and may contain evidence for a weak
aliphatic hydrocarbon band. Meanwhile, the MIRI instrument obtained
mid-infrared spectra of the rings between 4.9 and 27.9 microns, where the
observed signal is a combination of reflected sunlight and thermal emission.
This region shows a strong reflectance peak centered around 9.3 microns that
can be attributed to crystalline water ice. Since both the near and
mid-infrared spectra are dominated by highly crystalline water ice, they should
provide a useful baseline for interpreting the spectra of other objects in the
outer solar system with more complex compositions.