2021/02/03 by Carly J. A. Howett, Carly Howett, Emilie Royer
Engineering · Mathematics · Physics and Astronomy · #Astro and Planetary Science #Astrobiology #Astronomy #Environmental science #Geology #Geometry #Mathematics #Physics #Planetary Science and Exploration #Spacecraft Dynamics and Control #Surface (topology) #astro-ph.EP #physics.space-ph
paper · pdf · doi:10.1016/j.icarus.2021.114366
Accepted by Icarus 1st Feb 2021
arxiv created 2021/02/03 · openalex publication_date 2021/02/09 · arxiv updated 2021/03/03 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
We analyze two sets of observations of Dione's co-orbital satellite Helene taken by Cassini's Composite Infrared Spectrometer (CIRS). The first observation was a CIRS FP3 (600 to 1100cm-1, 9.1 to 16.7 μm) stare of Helene's trailing hemisphere, where two of the ten FP3 pixels were filled. The daytime surface temperatures derived from these observations were 83.3±0.9 K and 88.8±0.8 K at local times 223° to 288° and 180° to 238° respectively. When these temperatures were compared to a 1-D thermophysical model only albedos between 0.25 and 0.70 were able to fit the data, with a mean and standard deviation of 0.43±0.12. All thermal inertias tested between 1 and 2000 J m-2 K-1 s-1/2 could fit the data (i.e. thermal inertia was not constrained). The second observation analyzed was a FP3 and FP4 (1100 to 1400cm-1, 7.1 to 9.1 μm) scan of Helene's leading hemisphere. Temperatures between 77 and 89 K were observed with FP3, with a typical error between 5 and 10 K. The surface temperatures derived from FP4 were higher, between 98 and 106 K, but with much larger errors (between 10 and 30 K) and thus the FP3- and FP4-derived temperature largely agree within their uncertainty. Dione's disk-integrated bolometric Bond albedos have been found to be between 0.63±0.15 (Howett et al., 2010) and 0.44±0.13 (Howett et al., 2014). Thus Helene may be darker than Dione, which is the opposite of the trend found at shorter wavelengths (c.f. Hedman et al., 2020; Royer et al., 2020). However few conclusions can be drawn since the albedos of Dione and Helene agree within their uncertainty.