Constraining the surface properties of Helene

We analyze two sets of observations Dione's co-orbital satellite Helene taken by Cassini's Composite Infrared Spectrometer (CIRS). The first observation was a CIRS FP3 (600 to 1100 cm−1, 9.1 16.7 μm) stare Helene's trailing hemisphere, where the ten pixels were filled. daytime surface temperatures derived from these 83.3 ± 0.9 K and 88.8 0.8 at local times 223° 288° 180° 238° respectively. When compared 1-D thermophysical model only albedos between 0.25 0.70 able fit data, with mean standard deviation 0.43 0.12. All thermal inertias tested 1 2000 J m−2 K−1 s-1/2 could data (i.e. inertia not constrained). second analyzed FP4 (1100 1400 7.1 scan leading hemisphere. Temperatures 77 89 observed FP3, typical error 5 10 K. higher, 98 106 K, but much larger errors (between 30 K) thus FP3- FP4-derived temperature largely agree within their uncertainty. disk-integrated bolometric Bond have been found be 0.63 0.15 (Howett et al. 2010) 0.44 0.13 2014). Thus may darker than Dione, which is opposite trend shorter wavelengths (c.f. Hedman 2020; Royer al., 2021). However few conclusions can drawn since Dione