These Flyover Images Reveal New Details About Ceres's Mysterious Bright Spots

The bright spots sprinkled all over the dwarf planet Ceres, the largest object in the asteroid belt, have captured the public imagination ever since the Dawn spacecraft first imaged them earlier this year. Over 130 of these eerily reflective patches have been identified by Dawn, the most luminous of which is located right smack dab in the middle of an impact formation called the Occator crater.

What could be causing such striking luminosity on an otherwise dim world? According to new research published today in Nature—including video flyovers based on Dawn's pictures—the answer is most likely deposits of salty compounds called hydrated magnesium sulfates. Our own planet's salt flats are well-known to be highly reflective, and it looks as if the same may be true of Ceres's shining spots.

Full rotation of Ceres. Video: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/NPG Press

The team, led by planetary scientist Andreas Nathues of the Max Planck Institute for Solar System Research, used Dawn's panchromatic Framing Camera (FC) to obtain up close images of the dwarf planet's bright speckles, which tend to be located inside impact craters. Not only did the FC discover that the materials behave like sulfates, it also enabled scientists to study the mysterious haze clouds that form in the Occator crater during Ceres daytime hours.

"The haze is relatively thin," Nathues told me over email. "We estimated about one particle per [cubic millimeter]."

But while this misty layer of sublimating salts is fairly faint, it would still be visible to a hypothetical Ceresian astronaut from some angles, said Nathues. The team also confirmed that one of the processes behind the haze is water-ice sublimation, or the conversion of ice to water vapour without the intermediary step of melting into liquid form. But a lot more data will need to be obtained before scientists glean a clearer understanding of its geological drivers behind the Occator crater's hazy daytime weather.

Flyover of Ceres. Video: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/NPG Press

"We need to investigate further images that show [the haze's] effect," Nathues said. "Tidal forces are not acting on Ceres. Currently, we can only confirm water ice sublimation. Whether other forces (like freezing water) could act as activity driver is currently unclear."

Fortunately, Dawn is now firmly parked in Ceres's orbit, and recently dived down to altitudes as low as 240 miles to get a better look at its plethora of odd surface features. This lonely world, speckled with sparkling salt deposits and light crater-based mists, is finally coming into focus.