Ceres’ crust, with its mixture of ice, salts and hydrated materials, represents most of the dwarf planet’s ancient ocean, according to two new studies from NASA’s Dawn mission.
This false-color image shows the dwarf planet Ceres. Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA.
The first of the two studies, published in the Journal of Geophysical Research: Planets, used shape and gravity data measurements from Dawn to determine the internal structure and composition of Ceres, the largest body in the main asteroid belt.
The measurements came from observing Dawn’s motions with NASA’s Deep Space Network to track small changes in the spacecraft’s orbit.
The research supports the possibility that Ceres is geologically active — if not now, then it may have been in the recent past.
Three craters — Occator, Kerwan and Yalode — and Ceres’ solitary tall mountain, Ahuna Mons, are all associated with ‘gravity anomalies.’
This means discrepancies between the models of Ceres’ gravity and what Dawn observed in these four locations can be associated with subsurface structures.
“Ceres has an abundance of gravity anomalies associated with outstanding geologic features,” said lead author Dr. Anton Ermakov, a postdoctoral researcher at NASA’s Jet Propulsion Laboratory.
“In the cases of Ahuna Mons and Occator, the anomalies can be used to better understand the origin of these features, which are believed to be different expressions of cryovolcanism.”
The second study, published in the journal Earth and Planetary Science Letters, investigated the strength and composition of Ceres’ crust and deeper interior by studying the topography of the dwarf planet.
By studying how topography evolves on a planetary body, planetary researchers can understand the composition of its interior. A strong, rock-dominated crust can remain unchanged over the 4.5-billion-year-old age of the Solar System, while a weak crust rich in ices and salts would deform over that time.
By modeling how Ceres’ crust flows, Harvard University researcher Roger Fu and co-authors found it is likely a mixture of ice, salts, rock and an additional component believed to be clathrate hydrate.
A clathrate hydrate is 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 scientists believe Ceres once had more pronounced surface features, but they have smoothed out over time. This type of flattening of mountains and valleys requires a high-strength crust resting on a more deformable layer, which the authors interpret to contain a little bit of liquid.
“Most of Ceres’ ancient ocean is now frozen and bound up in the crust, remaining in the form of ice, clathrate hydrates and salts,” the researchers said.
“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.”
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A.I. Ermakov et al. Constraints on Ceres’ internal structure and evolution from its shape and gravity measured by the Dawn spacecraft. Journal of Geophysical Research: Planets, published online October 18, 2017; doi: 10.1002/2017JE005302
Roger R. Fu et al. 2017. The interior structure of Ceres as revealed by surface topography. Earth and Planetary Science Letters 476: 153-164; doi: 10.1016/j.epsl.2017.07.053
