Abstract | Hollows are steep-walled, ~1 km-wide rimless depressions commonly associated with bright deposits on the surface of Mercury, related to volatile loss (Blewett et al., 2011, Thomas et al., 2014). These features are usually found in clusters and commonly occur within craters and their ejecta, as well as in areas of low reflectance material (LRM) (Thomas et al., 2014). Within individual craters, hollow location has been found to depend on crater type (simple, complex) and degradation state (Thomas et al., 2014). At complex craters, hollows are found on proximal ejecta blankets and on the crater walls, floors and central structures. At simple craters, hollows generally occur as bands at the tops of crater walls. At some degraded craters, hollows have been observed to occur on cross-cutting faults or superposed simple craters. Here we further investigate relationships among the locations of hollows on crater walls, floors and within central structures as a function of degradation class (Kinczyk et al., 2020). We select craters from the named crater database at the PDS Geosciences Node Mercury Orbital Data Explorer (ODE), and use the degradation classification index from Kinczyk et al. (2020). Hollows were identified using MDIS-Narrow Angle Camera and MDIS-Wide Angle Camera Regional Targeted Mosaics (RTMs) of 208 of the 415 named craters . We report findings for 57 of the 73 named craters with hollows that have a degradation index of 1 to 5, where Class 1 represents highly degraded craters, and Class 5 represents fresh, rayed craters. Hollows are preferentially found in relatively fresh craters. Of the 3253 craters indexed by Kinczyk et al. (2020), named craters with hollows comprise 34% of craters in degradation class 4 or 5, 3.5% of craters in Class 3 and ~1% of craters in Class 1 or 2. Of the 57 named craters with hollows, 21 are in Class 4 or 5, 18 in Class 3, and 18 in Class 1 or 2. We classify hollows according to their location inside the crater: wall, floor, wall-floor intersection, central structure and superposed craters. In named craters with degradation class 1 or 2, hollows occur mostly in superposed craters. Although RTM coverage of degraded craters is less extensive than that of fresher craters, degraded craters of Class 1 or 2 sometimes have hollows on their central structures or floors and only occasionally on the walls, unassociated with superposed craters. In named craters of classes 4 and 5, hollows are more likely to be found on the central structures, but are also found on the walls and floors. |
