Bright spots on Ceres indicate geologic activity
Since NASA’s Dawn spacecraft arrived at Ceres in March 2015, both scientists and the general public have been able to see the hundreds of bright spots on the dwarf planet’s surface. Dawn mission scientists reported their most recent research about these bright areas at the American Geophysical Union meeting in New Orleans, Louisiana, on Tuesday, December 12, 2017. The team’s findings indicate that Ceres is an active, evolving world.
“The mysterious bright spots on Ceres, which have captivated both the Dawn science team and the public, reveal evidence of Ceres’ past subsurface ocean, and [they] indicate that, far from being a dead world, Ceres is surprisingly active. Geological processes created these bright areas and may still be changing the face of Ceres today,” said Carol Raymond, deputy principal investigator of the Dawn mission, via a release issued by NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California.
Researchers have discovered more than 300 bright areas on Ceres. A recent study led by Nathan Stein, a doctoral researcher at Caltech in Pasadena, California, has divided these areas into four categories.
The first category includes the most reflective material on Ceres, which occurs on crater floors. Two bright areas of this type are in Occator Crater. In the center of the crater lies Cerealia Facula, an area of bright material covering a 6-mile-wide (10-kilometer) pit inside which sits a small dome. East of the crater sits Vinalia Faculae, a collection of slightly less reflective features.
The second (and more common) type of bright feature is found on the rims of the crater, streaking down towards the floor. Impacting bodies may have exposed bright material that was below the surface or had formed in a previous impact.
The third category is that the bright material had ejected when the craters were formed.
The fourth category is that the bright material is not affiliated with an impact crater. The mountain Ahuna Mons – a likely cryovolcano with bright streaks on its flanks – is the sole example of this category.
The bright material has mixed with dark material and debris ejected during impacts over hundreds of millions of years. Billions of years ago, when Ceres experienced more impacts, the dwarf planet’s surface likely would have been peppered with thousands of bright areas.
“Previous research has shown that the bright material is made of salts, and we think subsurface fluid activity transported it to the surface to form some of the bright spots,” Stein said.
Lynnae Quick, a planetary geologist at the Smithsonian Institution in Washington, D.C., has been investigating the question of why the different bright areas of Occator Crater are so different from each other.
The leading explanation for what occurred at Occator is that there may have been a reservoir of salty water beneath the crater in the recent past. Vinalia Faculae may have formed from fluid forced to the surface by a small amount of gas, such water vapor, carbon dioxide, methane, or ammonia. Salty water could have been brought close to the surface through fractures. The lower pressure at Ceres’ surface would cause the liquid boil off as vapor. when the fractures reach the surface, the vapor could escape in an energetic fashion, depositing ice and salt particles on the surface.
Cerealia Facula, which is more elevated and brighter than Vinalia Faculae, may have formed in a different fashion. The material in Cerealia may have been more like icy lava, seeping up through the fractures and swelling to form a dome. Intermittent phases of boiling, similar to what occurred at Vinalia Faculae, may have spread ice and salt particle across the surface, forming the bright spot.
“We also see fractures on other solar system bodies, such as Jupiter’s icy moon Europa,” Quick said. “The fractures on Europa are more widespread than the fractures we see at Occator. However, processes related to liquid reservoirs that might exist beneath Europa’s cracks today could be used as a comparison for what may have happened at Occator in the past.”
Video courtesy of NASA
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.