So now that NASA’s Dawn spacecraft has been in orbit around Ceres for seven months, has the nature of its strange bright spots finally been determined? Are they brilliantly reflective deposits of water ice, as many initially suspected? Or just some curiously-bright rock faces? (Or the metallic remains of an ancient alien space base, like more than a few folks have imagined?) As it turns out, Ceres’ bright spots may be none of these (and especially not that last one… puh-leeze) — they may be enormous deposits of salt.
During the 2015 meeting of the European Planetary Science Congress on Sept. 28, principal investigator for the Dawn mission Dr. Chris Russell stated that “we believe that this is a huge salt deposit, and to me that tells me that this is an active surface.”
That is, some geologic process is at work to generate those bright salt deposits… they are all from Ceres.
“Some comet or asteroid didn’t come in bearing salts to this object,” Russell said, “it derived from the interior somehow.”
(Salt volcanoes — er, halovolcanoes — on Ceres?)
The determination was made based on measurements of the bright spots’ reflectivity, or albedo. If they were composed of water ice, they would be considerably more reflective — even though initially they overloaded Dawn’s sensitive imaging instruments. After obtaining accurate albedo data ice could be effectively ruled out.
But you wouldn’t want to put Ceres salt on your french fries — at least not yet. The type(s) of salt comprising Ceres’ spots still isn’t known.
“We can’t tell easily what that salt is, because the different salts don’t have very diagnostic lines in their spectrum… we’re using geochemistry in part to give us some diagnostic determination of one salt from another.”
Watch Dr. Russell’s presentation on the bright spots and other Dawn findings below (Occator crater segment is at 14:43):
While there hasn’t been any published research yet on these findings, this is obviously the direction that the mission scientists are heading in.
The bright spot on the 590-mile-wide dwarf planet Ceres was first observed with Hubble in December 2003, when it was imaged 267 times over the course of one 9-hour rotation. As Dawn made its final approach to Ceres in the beginning of 2015 the spot was discovered to actually be a cluster of bright regions within a 60-mile-wide crater, now officially named Occator.
Dawn is the first spacecraft to successfully enter orbit around two worlds* and the first to orbit a dwarf planet. Its first target was the asteroid Vesta, which it orbited from July 2011 to September 2012. Now at Ceres two and a half years later, it will remain in orbit both during its primary science phase and beyond… Ceres will be Dawn’s permanent home.
Take a tour of Ceres below (including some cool 3D anaglyph segments) narrated by mission director Marc Rayman:
Source: NASA/JPL-Caltech. HT to ScienceAlert
*The two worlds, Vesta and Ceres, are separate targeted worlds of a science mission. This does not include time spent orbiting Earth, for this mission or others, prior to departure burn.
UPDATE Dec. 9, 2015: A paper regarding these findings has been published in Nature. Read the article by Alexandra Witze here and watch the latest video from JPL of Ceres in rotation below: