New images taken from Dawn’s current orbit of just 915 miles (1,470 kilometers) above the dwarf planet Ceres show the ever-mysterious white spots in much greater detail than ever before. The image above has about three times better resolution than the images the spacecraft delivered from its previous orbit in June, and nearly 10 times better than in the spacecraft’s first orbit at Ceres in last spring.
Circle Occator Crater from above to get a feel for its topography
Finally, we can see sensible details including complex textures in the white spots spattered about the 60-mile-wide (90 km) Occator Crater. The crater itself is remarkable with a depth of 4 miles (6.4 km) and walls that are in places nearly vertical. The floor looks filled with what appears to be impact melted rock from the terrific blow that created the crater. Narrow cracks surround the central, white-topped peak.
Just what the highly reflective material is that makes the spots so white is under analysis right now after Dawn mission scientists took readings of the spots using the spacecraft’s visual and infrared mapping spectrometer or VIR. However, a recent interview with the Dawn mission’s Principal Investigator Christopher Russell by Linda Moulton Howe of Earthfiles.com, sheds a shaft of light on the mystery. Russell believes the white material is a thick dusting of some sort of powder and that whatever lies beneath the surface has been puffing out the material for some time, since the same bright spotted region appears in Hubble images taken back in 2004.
If the spots were made of ice, they would have vaporized in the near-zero atmospheric pressure on Ceres. Russell compared it to a dry lake bed salt deposit seen in many deserts across the world. Since he’s heard no report of ice detection from the team working on the VIR data, he’s assuming it’s salt. Keep in mind, this is his best guess based on limited data.
Could a meteorite strike have punched through Ceres’ crust into an icy layer beneath? Heated by impact, the ice would briefly liquify and possibly spray to the surface before freezing and then vaporizing into space. Left behind would be a mineral residue, likely salt, which easily dissolves in water. Salts are good reflectors of light and would stand out as bright patches against the dwarf planet’s darker surface.
We should know soon.