BY ALAN BOYLE
NASA’s mission to that other dwarf planet, Ceres, has delivered a fresh bird’s-eye view of one of the asteroid’s most mysterious features: a cone-shaped, 4-mile-high “pyramid” mountain whose sides are covered with bright material.
The Dawn mission’s principal investigator says those shiny sides may be connected to Ceres’ other big mystery: the bright spots that shine out from the mini-world’s dark surface.
“The bright material on the mountain and in the bright spots are probably the same material,” UCLA’s Christopher Russell told GeekWire in an email. “How the material got on the sides of the mountain and also in the bottom of the craters is unknown.”
Which begs the question: What is that stuff?
“We don’t yet have any consensus on how this mountain appeared,” Russell said. “The bright material is probably salt, and probably the same salt type everwhere. It is difficult to tell one salt from another, especially in the visible part of the spectrum.”
Russell said one possibility is a type of salt called hexahydrite, also known as hydrous magnesium sulfate or MgSO4·6H2O. On Earth, it’s a rare mineral with a bright appearance, and it’s also been detected on the surface of Europa, an ice-covered moon of Jupiter. Maybe it’s on Ceres as well.
“One of Dawn’s scientists, Vishnu Reddy, has proposed this, and it could be correct,” Russell said. “Some people expect this salt to be produced inside Ceres and then get transported to the surface.”
The hypothesis is a subject of continuing debate among the scientists on the Dawn team. An alternate view is that the bright spots contain water ice.
The latest view of the 6-kilometer-high mountain was taken on Aug. 19, from a height of 915 miles (1,470 kilometers). Over the next two months, Dawn will map the entire surface of Ceres from that altitude six times and collect spectral data that should provide a better fix on the mysterious bright material.
In late October, Dawn will start descending to its closest scheduled mapping orbit, heading for an altitude of 230 miles (375 kilometers). The car-sized spacecraft was launched in 2007, studied the asteroid Vesta in 2011-2012, and entered orbit around 590-mile-wide (950-kilometer-wide) Ceres this March after 3.1 billion miles of traveling.
Dawn’s latest revelations come as the team behind New Horizons, NASA’s mission to the dwarf planet Pluto, is getting ready to resume releasing data from the probe’s July flyby.