Exploration of the Permanently Shadowed Regions of the Southern Polar Terrains of Ceres using NASA/Dawn data
Abstract
Like the Moon and Mercury, Ceres's rotation axis is inclined by just a few degrees. The obliquity of 4 degrees between the normal to the orbital plane and the rotational axis of Ceres implies that Ceres' poles terrains are always slightly angled toward the sun. The combination of low angle illumination over a cratered surface creates areas never reached by the sun. In the presence of ice, these permanently shadowed regions (PSRs) create "cold traps" protecting ice from sublimation.
In 2016 Platz et al. [1] explored the topography and imagery [2,3] of the northern polar regions of Ceres, looking into 634 craters in permanent shadows, finding bright deposits in 10 of them. Out of this, 1 crater has part of the deposits exposed, so that it has been possible to detect the signature of water thanks to the data returned by Dawn's mapping spectrometer VIR [4]. The last phase of the Dawn mission, which ended in 2017 collected enough imagery to reconstruct the topography of the southern pole of Ceres by stereophotogrammetry [Preusker]. Since then, no evidence of icy terrain from the south polar terrain of Ceres has been reported. Our study will explore the PSRs in this region for a better understanding of the ice distribution on the dwarf planet. The first step of our study is to locate and characterize the southern PSRs. From the topography, we computed the PSRs using the Integrated Software for Imagers and Spectrometers (ISIS3) version 4.8.3, a suite of applications for the rigorous spatial treatment of planetary data acquired by various missions/instrument, including NASA Dawn at Vesta and Ceres [5]. The Figure below shows the map of PSRs of the southern terrain of Ceres in stereographic projection over a spheroid with a radius of 470km, prime meridian is at top and latitude grid are spaced by 10 degrees, latitude grids are spaced by 10 degrees, central is at the top. The basemap is the shaded relief extracted from the topography data. The blue patches are the area permanently in shadow and color indicates the area in square kilometers. The PSRs are reported in blue shades corresponding to their area (see legend), over the shaded relief extracted from the topography. The hatched area at the south pole locates the place where stereo reconstruction of topography was not possible, thus was excluded from PSRs computation. We have located about 950 PSRs with areas ranging from 1 to over 500 square kilometers. The largest PSRs locates in an unnamed 75 km wide crater at 223.6°E 74.9°S. Most of PSRs are in areas smaller than 10 square km. The map of PSRs represents the base for observations into the dark areas with Framing Camera and possibly the VIR spectrometer, looking for sings on icy deposits in the south polar regions of Ceres. References- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMP032.0010F
- Keywords:
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- 6040 Origin and evolution;
- PLANETARY SCIENCES: COMETS AND SMALL BODIES;
- 6205 Asteroids;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6224 Kuiper belt objects;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS