Last month, NASA’s Dawn spacecraft was moved to its lowest orbit around Ceres yet, and it sent back some incredible photos of one of the dwarf planet's more remarkable features: Occator Crater. The crater is the location of the famous bright spots, which are brine deposits that were likely delivered to the surface by hydrothermal activity.
The spacecraft is now in an orbit that gets as low as 35 kilometers (22 miles) from the surface of the dwarf planet. Being so close, Dawn can make more accurate measurements. Recent data shows that the bright deposits are made of sodium carbonate, a mineral commonly found on Earth. To get this close-up view of Cerealia Facula – the central and largest of the bright spots – Dawn had to fire its ion engine, potentially for the last time.
"Acquiring these spectacular pictures has been one of the greatest challenges in Dawn's extraordinary extraterrestrial expedition, and the results are better than we had ever hoped," said Dawn's chief engineer and project manager, Marc Rayman of NASA's Jet Propulsion Laboratory, in a statement. "Dawn is like a master artist, adding rich details to the otherworldly beauty in its intimate portrait of Ceres."
Researchers hope that the close-proximity analysis can deliver answers about what lies beneath the surface of Ceres. The brine deposits are an example of cryovolcanism, but it is not clear if the source is located in a shallow sub-surface reservoir or a much deeper source. Previous studies have even hinted at a subsurface ocean.
"The first views of Ceres obtained by Dawn beckoned us with a single, blinding bright spot," said Carol Raymond of JPL, Dawn's principal investigator. "Unraveling the nature and history of this fascinating dwarf planet during the course of Dawn's extended stay at Ceres has been thrilling, and it is especially fitting that Dawn's last act will provide rich new data sets to test those theories."
The mission will continue to explore the dwarf planet until the hydrazine fuel runs out, at which point it will be placed in a stable orbit around Ceres. This is to avoid contamination. The end is expected to happen at some point during the second half of 2018. These upcoming final months will see Dawn use a gamma ray and neutron detector and a visible and infrared mapping spectrometer to map Ceres in even finer detail. Questions about its interior and the abundance of organic molecules on its surface may find more precise answers soon.