Studies show new evidence of ancient subsurface ocean on Ceres

Dwarf planet appears to have had strong crust with deformable material beneath it.
By Laurel Kornfeld | Oct 27, 2017
Two separate studies analyzing data returned by NASA's Dawn mission about the surface and sub-surface of dwarf planet Ceres suggest the small world may have once had a global underground ocean.

Some subsurface liquid water from that ocean may still be present today, adding Ceres to the growing category of solar system worlds with underground oceans that could potentially host microbial life.

Minerals containing water are ubiquitous on Ceres' surface, suggesting an ocean once existed and may still exist today.

In the first study, researchers led by Anton Ermakov of NASA's Jet Propulsion Laboratory (JPL) analyzed small changes in Dawn's orbit around Ceres using NASA's Deep Space Network. These changes enabled them to obtain data on Ceres's shape and gravity, which in turn helped them better estimate both the structure and composition of its interior.

They discovered gravity anomalies, or discrepancies between computer models of Ceres' gravity and actual observations by Dawn at four sites--the dwarf planet's sole high mountain, Ahuna Mons, and Occator, Kerwan, and Yalode craters.

The findings indicate Ceres is currently geologically active or was geologically active in its past.

"Ceres has an abundance of gravity anomalies associated with outstanding geologic features," Ermakov said. Anomalies seen at Ahuna Mons and Occator Crater suggest both are products of cryovolcanism, he added.

Also puzzling is the low density of Ceres' crust, which is more akin to that of ice than of rock. A separate study conducted by Dawn guest scientist Michael Bland of the US Geological Survey found Ceres to have a crust far too strong to be composed largely of ice.

Findings of the study by Ermakov and colleagues are published in the Journal of Geophysical Research.

The second study centered on determining the strength and composition of both Ceres' crust and its deeper interior through analysis of its surface topography.

Tracing the evolution of topography on a planet's surface enables scientists to identify its interior composition. Strong, rocky crusts likely experienced little or no change since the solar system's formation.

On the other hand, weak crusts with high levels of ices and salts likely underwent significant deformation.

Study leader Roger Fu of Harvard University and his colleagues modeled the flow of Ceres' crust based on Dawn data, and identified the crust as a mix of ice, salts, rock, and clathrate hydrate. The latter is made of water molecules that surround a gas molecule and is up to 1,000 times stronger than water ice.

Based on their findings, the researchers believe ancient Ceres had significantly more surface features that were subsequently smoothed out, meaning it had to have a strong crust on top of a weaker layer, the latter of which could have been an ocean.

Although they believe most of that ocean has since frozen, with its components left in Ceres' crust, they acknowledge some subsurface liquid could remain, as indicated by thermal evolution models of the planet.

The second study was published in the journal Earth and Planetary Science Letters.



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