Ceres captured the world’s attention when the first images of its famous bright spots were released. Were they ice? An alien city? In recent months, scientists have told us they believe it is a type of salt. This week, a new study shows the bright spots are consistent with a type of magnesium sulfate known as hexahydrite. Most of us are familiar with another type of magnesium sulfate – Epsom salt.
Ok, but where does the salt come from? Ceres has more than 130 bright areas. And nearly all of them correspond with impact craters. Researchers believe the salty areas are what’s left after water-ice sublimated (turning directly from a solid to a gas) in the past. When asteroids hit this area, it exposed a mixture of ice and salt. The water-ice turned into a gas while the layer of salt is left exposed.
What about the rest of Ceres’ sub-surface? Andreas Nathues, lead author of the study, explains, “the global nature of Ceres’ bright spots suggests that this world has a subsurface layer that contains briny water-ice,” says Nathues.
Occator, home of Ceres’ bright spots
Researchers are also giving us a better look at Ceres’ and one of its most prominent craters – Occator. The dwarf planet is dark. How dark? Imagine fresh asphalt and you’re on the right track.
The Occator crater is about 60 miles and has a sharp rim and walls. Combine these features with landslide deposits and we are looking at one of the youngest features on the dwarf planet. Dawn mission scientists estimate Occator is about 78 million years old.
Occator has another potential feature that’s pretty damn cool. As sunlight hits the crater, what appears to be a thin haze of dust and evaporating water forms. It seems to show up around noon Ceres time and goes away at dawn and dusk. The haze may explain the water vapor seen by the Herschel space observatory in 2014. More data and analysis should help scientists figure out if it is a haze they are seeing.
“The Dawn science team is still discussing these results and analyzing data to better understand what is happening at Occator,” said Chris Russell, principal investigator of the Dawn mission.
Where did Ceres come from?
Today, Ceres sits in the asteroid belt that separates Mars and Jupiter. Stands to reason it formed there, right? Maybe not. A second study reported evidence of ammonia-rich clays.
Maria Cristina De Sanctis, lead author of this study, explains what ammonia means for Ceres. “The presence of ammonia-bearing species suggests that Ceres is composed of material accreted in an environment where ammonia and nitrogen were abundant. Consequently, we think that this material originated in the outer cold solar system.”
There are two theories for what’s going on. One, Ceres formed in the outer solar system and drifted to its current location. Two, Ceres formed where it’s at but incorporated materials that drifted in from the outer solar system.
This second study also looked at the daytime surface temperatures on Ceres. They range from a frigid minus 136 degrees Fahrenheit to a still cold minus 28 degrees Fahrenheit.
As of this week, Dawn reached its final orbital altitude. Dawn will circle the dwarf planet at 240 miles above its surface. That’s closer than the International Space Station is to Earth. The next slate of images from Dawn will be four times sharper than the best ones we’ve seen. Besides breathtaking new looks at Ceres, Dawn will be busy gathering infrared, gamma ray and neutron spectra, and high-resolution gravity data.