What a feast for the eye! Some of us have been waiting more than three years for this image. It’s the closest view yet of the brightest spot on Ceres, an asteroid and dwarf planet orbiting within the main asteroid belt. Once known as “Spot 5”, the scintillating splotch has since been named Cerealia Facula (Latin for ‘Ceres bright spot’). Early in the Dawn spacecraft’s mission to dwarf planet, it immediately caught everyone’s eye and sparked a lot of speculation about its origin.
NASA’s Dawn spacecraft took this and other photos of small, highly reflective patches inside Occator Crater from an altitude of just 21 miles (34 km) earlier this month. The wealth of detail is incredible — the entire dome is crisscrossed by fractures and pocked with depressions.
The bulbous dome and surrounding terrain span about 6 miles (10 km); their brilliant, white highlights are composed primarily of sodium carbonate and ammonium chloride, both salts. They’re what remained after briny waters percolated up from below to the surface. The water quickly vaporized on the airless dwarf planet, depositing its load of salts as a bright, white coating. Astronomers believe Cerealia Facula formed through recurring eruptions, with material sprayed across the local landscape, so we’re probably looking at layers of sodium bicarbonate, thicker in some places than others. Geologic activity involving ice and water instead of magma is known as cryovolcanism.
Based on crater counts, Occator Crater is estimated to be 34 million years old, but the bright spots inside are much younger, only about 4 million years old. That’s almost like yesterday in geologic time. Dawn also mapped Ceres’ gravity field and discovered that it has a rocky core and icy mantle. It’s likely that crater-forming asteroid impacts tapped into that mantle, creating the fractures and low spots that later led to the release of trapped liquids from beneath the surface.
Ceres may still be active to this day. Check out more recent photos taken from Dawn’s new, low orbit.