NASA's Dawn Mission To Dwarf Planet Ceres Finds Evidence Of Ancient Ocean

A team from NASA studying data from Ceres has found a mixture of ice, salts and hydrated material on the crust of the dwarf planet, a report released Thursday revealed. The findings, along with other shreds of evidence, point to recent geological activity on Ceres that has led the team to believe that the dwarf planet could have had an ocean in the past.

NASA launched Dawn mission, which is now exploring the dwarf planet, in September 2007. According to its official website, the Dawn, "is the only spacecraft ever to orbit two destinations beyond Earth and the only to orbit an object in the main asteroid belt between Mars and Jupiter."

The mission was supposed to end in 2016 but it received a two-year extension to get more insight about Ceres, the largest body in the asteroid belt. A NASA statement released Oct. 18 said the spacecraft would orbit the dwarf planet until 2018.

Now, two studies done on the crust data received from Dawn has revealed the presence of minerals containing water. In fact, these minerals were rather widespread suggesting Ceres may have had a vast ocean in the past.

A second team, on a different study also mentioned in the report released Thursday, found a soft layer underneath this rocky crust. This easily deformable layer signaled the team towards residual liquid left over from the ocean too.

"More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground," Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA's Jet Propulsion Laboratory, Pasadena, California, said in the report.

To counter the challenge of contamination that comes with landing on Ceres, the team is studying the dwarf planet’s interior by using Dawn's observations in orbit to measure the gravity of Ceres. This would help the team understand the interior of the planet without landing and risking contamination.

The first study led by Anton Ermakov, a postdoctoral researcher at JPL, has been published in the Journal of Geophysical Research. The team used the captured shape of the planet and the gravity data measurements from the Dawn mission to determine the internal structure and composition of Ceres.

According to the NASA report, “the measurements came from observing the spacecraft's motions with NASA's Deep Space Network to track small changes in the spacecraft's orbit.”

The findings from this analysis revealed that Ceres could be geologically active. Even if there is no geological activity now, there is plenty of evidence suggesting very recent activity on the crust.

The Dawn also found three craters here named Occator, Kerwan, and Yalode. The spacecraft captured images of Ceres' solitary tall mountain, Ahuna Mons. All these structures were deemed as “associated with gravity anomalies." These structures point to a clash between the existing model of Ceres' gravity and newly observed gravitational anomalies.

"Ceres has an abundance of gravity anomalies associated with outstanding geologic features," Ermakov said in the report. The gravitational anomalies seen on Ahuna Mons and Occator can be used to better understand the planet’s origin.

The team believes that cryovolcanism could be a likely suspect. Cryovolcanoes are theoretical volcanoes that can spew water, ammonia or methane, instead of molten rock.

Studying the gravity data from Dawn also showed a very low-density crust. The crust was found to be just as dense as ice. But the crust was also was too strong to be primarily made of ice. The uniqueness of Ceres is that its crust is as light as ice but much stronger.

The second study led by Roger Fu at Harvard University in Cambridge, Massachusetts, was published in the journal Earth and Planetary Science Letters. This study attempted to answer the question about Ceres’ mysterious crust.

The researchers studied the “strength and composition of Ceres' crust and deeper interior by studying the dwarf planet's topography,” said the report. The evolution of topography can lead to findings of its constituents. This is because a rocky crust will not change much over the course of 4.5-billion-years. But a crust made of ice and salts would deform over that time.

According to the report, “Fu and colleagues found it is likely a mixture of ice, salts, rock and an additional component believed to be clathrate hydrate, a cage of water molecules surrounding a gas molecule. This structure is 100 to 1,000 times stronger than water ice, despite having nearly the same density.”

The team says that Ceres did have an ancient ocean which is now frozen and embedded in the crust. This gave the crust the unique mixture of ice, clathrate hydrates and salts. The team also underlined, “it has mostly been that way for more than 4 billion years. But if there is residual liquid underneath, that ocean is not yet entirely frozen. This is consistent with several thermal evolution models of Ceres published prior to Dawn's arrival there, supporting the idea that Ceres' deeper interior contains liquid left over from its ancient ocean.”