Colour lithologies of Ceres' south pole

Ceres, the largest object in the main asteroid belt (940 km in diameter), is a survivor of the earliest period of Solar System formation. It orbits the Sun at a mean distance of approximately 2.8 AU. Information about its interior provides essential insights into the formation and evolution of volatile-rich planetary embryos that originated within the protoplanetary disc. From 2015 to 2018, NASA’s Dawn spacecraft collected data in orbit around Ceres [1, 2], returning a wealth of imaging information obtained by the Framing Camera (FC) [3] and the Visible and Infrared Spectrometer (VIR) [4].    

Although the equatorial to mid-latitude regions of Ceres have been extensively mapped and analysed, the polar latitudes (> ±60°) have received comparatively little investigation, primarily due to the suboptimal quality of the returned imaging data, which is a consequence of the challenging illumination conditions. Notably, the south pole was poorly illuminated during the prime mission, a period in which most of the global high-res imaging data were collected.

However, following some improvements in the mosaicking of polar FC imagery in clear (Fig. 1) and colour filters, the analysis of certain sufficiently illuminated surface areas became possible. Contrary to our initial expectations, the south pole region has been found to show a number of distinctive colour lithologies that are also present at lower latitudes. It is noteworthy that the colour of the polar background material often deviates from the global average of Ceres, exhibiting an increased spectral redness. The spectral appearance of the polar lithologies is influenced by this redder background material due to the occurrence of mixing. Also, a dependence on the longitudes of their distribution indicates specific contexts of origin.

Fig. 1: Clear filter mosaic of Ceres' south pole from LAMO orbit (resolution about 35 m/pix.).

[1] Russell, C.T., Raymond, C.A. The Dawn Mission to Vesta and Ceres. Space Sci Rev 163, 3–23 (2011). https://doi.org/10.1007/s11214-011-9836-2

[2] Russell, C.T. et al. Dawn arrives at Ceres: Exploration of a small, volatile-rich world. Science 353, 6303, 1008–1010 (2016). https://doi.org/10.1126/science.aaf4219

[3] Sierks, H. et al. The Dawn Framing Camera in: The Dawn Mission to Minor Planets 4 Vesta and 1 Ceres. Springer, 263–327 (2011). https://link.springer.com/content/pdf/10.1007%2F978-1-4614-4903-4_2.pdf (book)

[4] De Sanctis, M. C. et al. The VIR Spectrometer. Space Sci Rev 163, 329–369 (2011). https://doi.org/10.1007/s11214-010-9668-5