Bolometric Bond Albedo and Thermal Inertia Maps of Mimas

Abstract

We use data from Cassini's Composite Infrared Spectrometer CIRS to map Mimas' surface temperatures and its thermophysical properties. This provides a dramatic improvement on the work in Howett et al. (2011), where the values were determined at only two regions on Mimas (one inside, and another outside of the anomalous region). We use all spatially-resolved scans made by CIRS' focal plane 3 (FP3, 600 to 1100 cm-1) of Mimas' surface, which are largely daytime observations but do include one nighttime one. The resulting temperature maps confirm the presence and location of Mimas' previously discovered thermally anomalous region. No other thermally anomalous regions were discovered, although we note that the surface coverage is incomplete on Mimas' leading and anti-Saturn hemisphere. The thermal inertia map confirms that the anomalous region has a notably higher thermal inertia than its surroundings: 98 +/- 42 J m-2 K-1 s-1/2 inside of the anomaly, compared to 34 +/- 32 J m-2 K-1 s-1/2 outside. The albedo inside and outside of the anomalous region agrees within their uncertainty: 0.45+/-0.08 inside compared to 0.41 +/- 0.07 outside the anomaly. Interestingly the albedo appears brighter inside the anomaly region, which may not be surprising given this region does appear brighter at some UV wavelengths (0.338 microns, see Schenk et al., 2011). However, this result should be treated with caution because, as previously stated, statistically the albedo of these two regions is the same when their uncertainties are considered. These thermal inertia and albedo values determined here are consistent with those found by Howett et al. (2011), who determined the thermal inertia inside the anomaly to be 66 +/- 23 J m-2 K-1 s-1/2 and less than 16 J m-2 K-1 s-1/2 outside, with albedos that varied from 0.49 to 0.70.