A new and in-depth analysis of high-resolution images and data from NASA’s Dawn mission has now provided fresh insight into the dwarf planet Ceres, with intriguing evidence that Ceres has a globally salty ocean, and has been geologically active in the recent past has got.
“Proof that Ceres has long deep brine reservoirs has an exciting result,” said Dr. Hannah Sizemore to Universe Today. Sizemore is a co-author on five of seven articles published this week in various journals in Nature, with details of Dawn’s exploration of Ceres. “That a Ceres-sized body can retain both heat and interior fluids over the age of the solar system implies that small bodies are more geologically active – perhaps more ‘habitable’ than we thought.”
Dawn traveled to the asteroid belt to spin both the asteroid Vesta and Ceres. It studied Ceres for more than three and a half years – from March 2015 to November 2018 – until the spacecraft’s hydrazine maneuver was exhausted. At the nearest approach, the orbiter had submerged less than 35 kilometers above the surface. The spaceship played intriguing landforms and features across Ceres that showed it was a unique and varied world.
A bright area in a crater called Occator was one of the most fascinating features. Commissioned more than a decade ago by the Hubble Space Telescope, Dawn scientists concluded the mysterious bright spots were sodium carbonate – a compound of sodium, carbon, and oxygen. The compounds probably came from liquid that percolated and evaporated to the surface, leaving behind a salt chorus that was highly reflective.
But by the end of the mission, scientists had not yet determined where the liquid came from: did it come from deep inside the dwarf planet and bubble it to its surface in a volcanic process? Or did the impact the crater made create a shallow melt that exaggerated again to create the light features.
The new research, using images and gravity data from Dawn, suggests that both may have happened.
“Gravity data tells us that there is probably a deep reservoir of brine – salt water – about 40 miles below Ocator,” said Sizemore, a senior scientist at the Institute of Planetary Science. “Some of that deep water probably brought out to the surface and contributed to bright spots and other features in Occator.”
On the other hand, Sizemore’s passage, based on image analysis of the large currents and small hills inside the crater, suggests that shallow leaks of muddy impact melt around the inside of the crater.
“This formed interesting features as they flashed,” Sizemore said. ‘Both are exciting because it means there were transient and long-lived water sources in this area, and extensive mix. Liquid water and mixtures are always exciting for astrobiology. ”
The light conical hills and buds are similar to small icebergs in the polar regions of the earth formed by frozen pressure groundwater. These features in Occator crater would require the movement of water and / or ice slurries to form, and this activity must have been a long time after the impact the crater made.
But if Ceres has an ocean beneath the ground, how can it stay warm enough to keep it afloat, because the dwarf planet does not experience the forces of time of a large planet like some of the moons around Saturn or Jupiter?
Top left: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA; Top right: NASA / JPL-Caltech; Bottom: NASA / JPL
“Most of the ocean of Ceres’ subsoil is frozen today,” Sizemore said in an email, “with relatively small amounts of residual fluid. Liquid retention is challenging, given that tidal warming does not occur. We think that “Clathrate hydrates (legal ice with gases such as methane in the crystal lattice) make the Ceres crust very insulating. Clathrates act effectively as a blanket which hangs the dwarf planet on its interior heat.”
Ceres has more than 130 of these bright areas, most within craters of influence. The global nature of these clear regions suggested early on to Dawn scientists that Ceres had an underground layer of ice with briny water, and the effects that the craters would have ‘discovered’ the mixture of ice and salt.
Ceres has a diameter of approximately 600 miles (960 km), making it a size equivalent to 37% of the land area of the continental United States. Occupier crater lies 92 miles (92 kilometers), and Sizemore said the bright spots in the crater formed much more recently, perhaps less than 20 million years ago.
The brightest area in the center of the crater, called Cerealia Facula, was found to have hydrated chloride salts. In a study led by Maria Cristina De Sanctis, she and her team found that since this salt dehydrates very quickly, the brine may percolate to the surface, indicating that salty liquids may still exist in the interior of the dwarf planet. In another paper, Andreas Nathues and colleagues found that Ceres was undergoing a period of cryovolcanic activity, beginning about nine million years ago, and existed until very recently.
Another paper, published by Britney Schmidt and colleagues in Nature Geoscience, shows that the mounds and hills in the Ocator Crater may have formed when impact-induced water flowed frozen. This suggests that cryo-hydrological processes run farther than Earth and Mars, and were active on Ceres in the geologically recent past.
“Dawn has achieved much more than we had hoped for when it began its extraordinary foreign expedition,” said Mission Director Marc Rayman of NASA’s Jet Propulsion Laboratory in Southern California. “These exciting new discoveries from the end of its long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”
You can read the full paper on Ceres published this week, here: https://www.nature.com/collections/agdgfadcag
- Castillo-Rogez, JC & Rayman, MD Nat. Astron. https: // doi.
org / 10.1038 / s41550-020-1031-5 (2020). - De Sanctis, MC et al. Nature 536, 54–57 (2016).
- Nathues, A. et al. Nat. Astron. https://doi.org/10.1038/s41550-
020-1146-8 (2020). - De Sanctis, MC et al. Nat. Astron. https://doi.org/10.1038/
s41550-020-1138-8 (2020). - Scully, JEC et al. Nat. Commun. https://doi.org/10.1038/
s41467-020-15973-8 (2020). - Raymond, CA et al. Nat. Astron. https://doi.org/10.1038/s41550-
020-1168-2 (2020). - Fu, RR et al. Earth Planet. Sci. Easy. 476, 153–164 (2017).
- Hendrix, AR et al. Astrobiology 19, 1–27 (2019).
Sources: Planetary Science Institute, Nature, JPL, Email Correspondence with Dr. Hannah Sizemore
