The Degas crater on Mercury: an interesting target for the BepiColombo mission?
- 1INAF – Osservatorio Astronomico di Roma, Monte Porzio Catone, Italy (nicolas.bott@inaf.it)
- 2LESIA, Observatoire de Paris, Université PSL, CNRS, Université de Paris, Sorbonne Université, Meudon, France
- 3INAF – Istituto di Astrofisica e Planetologia Spaziali, Rome, Italy
1. Introduction
Launched on October 19th, 2018 (local time) towards Mercury, the BepiColombo spacecraft carries 16 instruments onboard the MPO and MMO orbiters. The SIMBIO-SYS (Spectrometer and Imagers for MPO BepiColombo Integrated Observatory SYStem) instrument [1] will image the surface of the innermost planet of the Solar system at unprecedented high spatial and spectral resolutions. SIMBIO-SYS is composed of 3 channels: STC (STereo Channel), a stereo camera; HRIC (High spatial Resolution Imaging Channel), a multispectral camera with a very high spatial resolution; and VIHI (Visible Infrared Hyperspectral Imager channel), a hyperspectral imager characterized by high spectral resolution and signal-to-noise ratio. The establishment of the target list for SIMBIO-SYS is underway. Therefore, studying potential targets of interest can be very useful to support their selection.
2. Data and methods
Here, we analyse the Degas crater, localized in the Shakespeare quadrangle (H-03) [2,3], hence at mid-latitudes of the northern hemisphere of Mercury (37.08°N, 232.66°E). Degas has been classified as a Kuiperian (-1 Gyr – today) crater [4] notably because of its well-preserved ray system of ejecta. We used MESSENGER data to investigate this crater with a three-fold approch: a multispectral analysis based on MDIS-WAC (Mercury Dual Imaging System-Wide Angle Camera) images have been combined with a spectroscopic analysis of MASCS (Mercury Atmospheric and Surface Composition Spectrometer) spectra and a geological analysis based on MDIS-NAC (Mercury Dual Imaging System-Narrow Angle Camera) images.
3. Preliminary results
3.1. Multispectral analysis
Using the MDIS-WAC images at the best spatial resolution available (95-250 m/pixel) and the Integrated Software for Imagers and Spectrometers (ISIS), we produced three color mosaics: an 11-bands mosaic to use all the multispectral information available with MDIS, an 8-bands mosaic to cover a wider area around the crater and study its surroundings (Figure 1), and a 3-bands mosaic with the best spatial resolution achievable (95 m/pixel).
We also produced two high-resolution monochrome mosaics using MDIS-NAC images on which geological analysis was performed (see Section 3.3).
A Principal Component Analysis (PCA) was applied to the 11-bands mosaic. The enhanced color image obtained using PC1 and PC2 reveals an asymmetric distribution of LRM (Low Reflectance Material) [5] around the crater, which suggests an oblique impact. Finally, a K-mean clustering highlights 4 spectral units: the blue deposit on the crater floor, the floor not covered by this deposit, the LRM surrounding Degas and the ejecta blankets. Close spectral properties between hollows and the blue deposit on the floor of Degas are also evidenced.
3.2. Spectroscopic analysis
MASCS spectra have been extracted from the four multispectral units (Figure 2).