Bright areas on Ceres may be geologically active

Ceres likely had more bright spots billions of years ago, when it experienced far more impacts.
By Laurel Kornfeld | Dec 15, 2017
The bright spots imaged by NASA's Dawn spacecraft on Ceres' surface may be geologically active, according to a study presented by mission deputy principal investigator Carol Raymond and her colleagues at a meeting of the American Geophysical Union (AGU) on Tuesday, December 12.

Since their discovery by Dawn in 2015, Ceres' bright, reflective spots have intrigued scientists, who eventually identified their composition as salts.

More than 300 such areas have been found on the dwarf planet's surface. According to Raymond, who is based at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, these areas constitute evidence that Ceres once had a subsurface ocean and continues to be geologically active.

"Geological processes created these bright areas and may still be changing the face of Ceres today," she emphasized.

In a new paper published in the journal Icarus, Nathan Stein of Caltech divides Ceres' bright regions into four categories.

His first category is comprised of the most reflective spots, located on crater floors. These include the two bright spots in the center of Occator Crater, made up of salt-rich materials that mixed with water in the past.

In Cerealia Facula, the brighter of Occator's spots, a six-mile- (10-km-) wide pit beneath a small dome-shaped feature is covered in bright material.

Slightly to the east is its companion, Vinalia Faculae, with less reflective and more scattered features.

According to planetary geologist Lynnae Quick of the Smithsonian Institution in Washington, DC, Occator's two bright spots may have formed through different processes.

At Vinalia Faculae, dissolved gases composed of volatile materials, such as water vapor, ammonia, methane, and carbon dioxide may have pushed salty water beneath Occator Crater to the surface through fractures that connected to the subsurface water.

Because pressure is low on Ceres' surface, this fluid would have boiled off as vapor, leaving behind particles of salt and ice.

Cerealia Facula is brighter than its counterpart and has a higher elevation. Quick hypothesizes that icy lava emerged from fractures in the crater and swelled into a dome-shape. Material ejected onto the surface boiled only intermittently, leaving behind a larger amount of salt and ice.

Dawn scientists believe fractures in Occator Crater, which is 57 miles (92 km) wide, were initially created by an impact, and water vapor later flowed through them.

"We see fractures on other solar system bodies, such as Jupiter's icy moon Europa," Quick explained. "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."

The second category of bright spots identified by Stein is found on the rims of craters from and flow down to the craters' floors. Stein proposes these were created when impacting objects exposed already existing underground bright materials.

Stein's third group of bright spots are materials that were ejected from craters during previous impacts.

His fourth group includes bright materials not formed in impacts, especially Ceres' sole mountain, Ahuna Mons, which scientists believe was created by cryovolcanism, a process in which thick, icy materials erupt onto the dwarf planet's surface.

Ceres likely had more bright spots billions of years ago, when it experienced far more impacts.

 

 

 

---

Comments
We are dedicated to maintaining a respectful community that actively engages in lively discussions about news stories and blog posts. Please keep the following in mind when writing your comments.