Analysis of multi-angular MESSENGER color observations of Hollows on Mercury
Abstract
One of the major open science questions about Mercury surface processes and landforms is the nature of hollows, puzzling features identified on MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging, Solomon et al., 2007) images (Blewett et al., 2011). Hollows are 10 m to several km-sized shallow, irregular, flat floored depressions characterized by bright interiors and haloes and found on crater walls, rims, floors, and central peaks (Blewett et al., 2013; Blewett et a., 2011). Proposed explanations for the origin and formation of hollows envision the release of volatiles from Mercury's surface (Blewett et al., 2011) through processes like sublimation, desorption, sputtering, micrometeorite impacts and pyroclastic volcanism. Multi-band photometry of hollows at Dominici crater (1.2 °N, 232.5 °E) revealed absorption features attributed to Mg and Ca sulfides (Vilas et al., 2016). However, further compositional analyses at multiple locations on Mercury showed that a more complex mineralogy is required to explain the observed hollows spectra, which may be a mixture of sulfides and Cr, Ti, and Ni pyroxenes (Lucchetti et al., 2018). In this abstract, we focus on the analysis of multi-angular Mercury Dual Imaging System (MDIS, Hawkins et al., 2007) wide angle camera (WAC) color images of hollows at Canova crater, Mercury (25.62°N, 3.75°W). The site was selected because its detailed geomorphological and compositional analysis is available in Lucchetti et al. (2018), allowing a direct comparison with our results. In addition, a relatively high (i.e >5) number of MDIS/WAC observations with 8 filters are available at this site, hence allowing to investigate the photometry of hollows. As a first step, we used high-resolution (i.e. 50 to 70 m/px) MDIS narrow angle camera (NAC) images of Canova crater with suitable observation geometry and the NASA Ames Stereo Pipeline (ASP, Shean et al., 2016) to produce a digital terrain model (DTM) of the site. The DTM and USGS Integrated Software for Imagers and Spectrometers (ISIS, https://isis.astrogeology.usgs.gov/) routines were used to orthorectify and radiometrically calibrate all the WAC observations. At each pixel within Canova crater and for each WAC filter, we extracted the flux, illumination and observation angles from all the available observations. This dataset was fitted with a Hapke photometric model allowing us to compute Hapke parameters maps for Canova crater. These maps will be used to apply more accurate photometric corrections to hollows spectra allowing the investigation of their mineralogy with high accuracy. In addition, such maps will allow to constrain the Hapke parameters for the material forming hollows, hence allowing a comparison with laboratory estimates. Finally, the photometric correction here derived will be pivotal in analyzing future observations of hollows with the SIMBIO-SYS (Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System, Cremonese et al., 2020) instrument on board the ESA's BepiColombo mission. Acknowledgements: This study is supported by the BepiColombo ASI-INAF contract n° 2017-47-H.0. References: Blewett, D.T. et al, 2011. Science,80; Blewett, D.T. et al., 2013 JGR:Planets,121,9,1798-1813; Cremonese G. et al., 2020. Space Sci Rev 216, 75; Hawkins, S.E. et al., 2007. Space Sci Rev 131, 247-338;Lucchetti, A. et al., 2018. JGR:Planets, 123-9,2365-2379;Shean, D.E., et al.2016, ISPRS J. Photogramm. Remote Sens ;Solomon, S.C., et al., 2007, Space Sci. Rev. Space Sci Rev 131, 3-39;Vilas, F., et al. 2016, GRL ,43,4, 1450-1456
- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E.454M