James Webb Space Telescope Feed Post

JWST Spectrophotometry of the Small Satellites of Uranus and Neptune

Background subtraction for an F140M image of Neptune’s moon Despina. Despina is situated adjacent to the Le Verrier ring, which has a significant contribution to the flux around the moon. The left panels show the data after stage 2 pipeline reduction which produces absolute flux-calibrated images. The middle panels show the composite background made by combining a model for the rings with a second-degree polynomial surface that characterizes the scattered light background from Neptune The background-subtracted data is on the right, showing effective subtraction of the scattered light gradient and the ring contribution. Note that while each image is 30×30 pixels, the pixel scale in the F300M image is twice that of the F140M image, which accounts for the difference in the apparent shape of the rings and the masking of Neptune in the F300M data. Abstract: We use 1.4-4.6 micron multi-band photometry of the small inner Uranian and Neptunian satellites obtained with the James Webb Space Telescope's near-infrared imager NIRCam to characterize their surface compositions. We find that the satellites of the ice giants have, to first-order, similar compositions to one another, with a 3.0 micron absorption feature possibly associated with an O-H stretch, indicative of water ice or hydrated minerals. Additionally, the spectrophotometry for the small ice giant satellites matches spectra of some Neptune Trojans and excited Kuiper belt objects, suggesting shared properties. Future spectroscopy of these small satellites is necessary to identify and better constrain their specific surface compositions.