Potentially Young Carbonates in a Small Crater in Huygens Basin, Mars

Abstract:

Prao crater is a small (~20 km diameter) crater located on the northeastern floor of Huygens Basin. Carbonate signatures have been previously identified both inside and outside the crater. The crater has been hypothesized to be one of a handful of Martian craters formed by a cometary impactor and has been dated at ~80 My. Prao has a fluidized ejecta blanket and a central pit, and it appears to have been filled since its formation.

We have made a quantitative map of mineral abundances in Prao crater using a set of 11 hyperspectral visible/near-infrared images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) that cover the crater and its ejecta blanket. We use a radiative transfer-based CRISM atmospheric correction that provides comparable surface single scattering albedo (SSA) images despite differences in time of day/year, viewing geometry, and atmospheric conditions. The conversion of CRISM I/F spectra to SSA allows us to use a linear unmixing model to produce quantitative mineral maps for each image.

Our mapping has identified two different carbonate populations in and around Prao. Ca-rich carbonates are found around the central pit and ejecta blanket, and were likely excavated by the crater, coming from a depth of ~19 km below their current elevation. Fe-rich carbonates, however, are largely found in a dark spot found inside the crater (Figure 1, yellow/orange hues), which appears visually different from most carbonates previously identified on Mars. These carbonates may have been formed in a post-impact hydrothermal system (for which we find potential evidence around the central pit) or formed even later in a ponded water or groundwater-fed environment. Given the young age of crater formation, the formation of these carbonates may prove important for growing our understanding of recent water activity on Mars.