Analysis of Charon's spectrum at 2.21- μm from New Horizons/LEISA and Earth-based observations
Abstract
We examine the 2.21- μm band from 19 disk-integrated Charon spectra measured by New Horizons/LEISA in the week leading up to its closest encounter with the Pluto system. These observations cover one Charon rotation period. Additionally, we analyze Charon's 2.21- μm band from 22 Earth-based spectra obtained over the last two decades. We measure the equivalent width of the 2.21- μm band from all observations and study it as a function of sub-observer longitude. We find no significant variation in the 2.21- μm band as Charon rotates. Compared to the same band seen on Nix and Hydra, Charon's 2.21- μm band is several times weaker. We attribute the 2.21- μm band to NH4Cl based on the appearance of a weaker band at 2.24- μm . Furthermore, we see two never-before-reported absorption features in Charon's spectrum at 1.60 and 1.63- μm , which may also be due to NH4Cl. If NH3-H2O-ice mixtures are present on Charon, they must be a small fraction of the disk-average composition to be consistent with the spectrum at 1.99- μm .
- Publication:
-
Icarus
- Pub Date:
- January 2023
- DOI:
- 10.1016/j.icarus.2022.115242
- Bibcode:
- 2023Icar..38915242C
- Keywords:
-
- Charon;
- Satellites;
- Spectroscopy;
- Infrared observations;
- Surfaces;
- Composition