Brighest area on Ceres may be due to hydrothermal activity
According to a new study by scientists with NASA’s Dawn mission, the brightest area on Ceres, located inside Occator Crater, has the highest concentration of carbonate minerals ever observed anywhere other than on Earth. The study, published online in the journal Nature, is one of two recent papers about the chemical composition of Ceres.“This is the first time we see this kind of material elsewhere in the Solar System in such a large amount,” said Maria Cristina De Sanctis, lead author and principal investigator of Dawn‘s visible and infrared mapping spectrometer. De Sanctis is based at the National Institute of Astrophysics, Rome.
At nearly 80 million years old, Occator is still considered a young crater. It is 57 miles (92 kilometers) wide and has a central pit that is about 6 miles (10 kilometers) wide. In the center of the crater is a dome structure that is covered in highly reflective material and has radial and concentric fractures on and around it.
De Sanctis’ team found that the most abundant mineral of the bright area of Occator is sodium carbonate, a type of salt found in hydrothermal environments on Earth. According to the journal, this material seems to have come from within Ceres, because it could not have been delivered by an impacting asteroid.
The upwelling of this material suggests that temperatures inside Ceres may be warmer than previously thought. The results also indicate that liquid water may have been present beneath the surface of Ceres in recent geological time. The salts may have been remnants of an ocean or localized bodies of water that reached the surface and then froze millions of years ago.
“The minerals we have found at the Occator central bright area require alteration by water,” De Sanctis said. “Carbonates support the idea that Ceres had interior hydrothermal activity, which pushed these materials to the surface within Occator.”
In a paper published in Nature last year, De Sanctis’s team reported that the surface of Ceres contains ammonia-rich clays. Because ammonium is abundant in the outer Solar System, researchers have hypothesized that Ceres may have formed near the orbit of Neptune and migrated inward.
The new study also found ammonia-bearing salts, ammonium chloride / ammonium bicarbonate in Occator Crater. The carbonate finding reinforces Ceres’ connection with icy worlds in the outer Solar System.
Ammonia, in addition to sodium carbonate found at Occator, has been detected in the plumes of Enceladus, an icy moon of Saturn known for its geysers erupting from fissures in its surface. Such materials make Ceres interesting for the study of astrobiology.*
“We will need to research whether Ceres’ many other bright areas also contain these carbonates,” De Sanctis said.
The Dawn spacecraft was launched on Sept. 27, 2007, from Cape Canaveral Air Station’s Space Launch Complex 17-B atop a United Launch Alliance Delta II-Heavy rocket.
The ion-engine propelled spacecraft arrived at the asteroid Vesta on July 16, 2011. Dawn spent 14 months exploring Vesta, capturing detailed images and data about the asteroid before departing on Sept. 5, 2012, for Ceres, its second target.
Dawn was captured by Ceres’ gravity on March 6, 2015, making it the first spacecraft to orbit a dwarf planet and the first spacecraft to orbit two targets.
On June 30, 2016, NASA announced the Dawn spacecraft had completed its primary mission. Dawn transmitted a large volume of scientific data to Earth on June 27–28, and it is continuing to observe Ceres even as the prime mission concludes. On July 1–2, it will transmit more pictures and spectra from its final mapping orbit at an altitude of 240 miles (385 kilometers).
*Updated on May 22, 2017, at 04:00 EDT to remove reference to “sodium bicarbonate”, in accordance with the NASA article.
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.