In 2007, NASA launched the Dawn spacecraft to investigate the asteroid Vesta and the dwarf planet Ceres. Dawn, the first mission to orbit two extraterrestrial bodies, entered orbit around Ceres in 2015. Imaging and spectral analysis of Ceres’ surface show that many regions have a distinctive “blue” color (negatively sloped visible spectra) and a material composition of ammoniated phyllosilicates. These regions are mainly associated with young, fresh craters. For example, Haulani crater is 34 kilometers in diameter and, at an estimated age of two million years, is one of the youngest craters on Ceres. Haulani exhibits features such as sharp rims, bright spots, and some of the strongest blue color variation on its surface and ejecta. Although blue coloration has been observed on other small bodies, such as comet 67P/Churyumov-Gerasimenko, the origins and mechanism behind it are not well understood.
Stefan Schröder from the Deutsches Zentrum für Luft- und Raumfahrt (DLR, Germany) and colleagues carried out experiments simulating a mixture of water ice and phyllosilicate minerals that might be created by an impact on Ceres and investigated how that mixture then sublimated under Ceres-like conditions. After several days, the residue structure was analyzed and found to be highly porous and “foam like” with sub-micron-sized filaments of phyllosilicates. The authors argue that these filaments are responsible for scattering light in a way that gives some areas on Ceres their blue hue, although there are potentially alternative explanations. These results provide a natural source for blue color on the craters of Ceres and opportunities to further explore this interesting, yet not well understood, phenomenon. READ MORE