A new and complete analysis of high-resolution images and data from NASA’s Dawn mission has now provided a fresh insight into the dwarf planet Ceres, with intriguing evidence that Ceres has a global sub-surface salt ocean , and has been geologically active in the recent past.
“The evidence that Ceres has deep long water reservoirs is an exciting result,” said Dr. Hannah Sizemore for Universe Today. Sizemore co-authored five of the seven papers published this week in various journals in Nature, detailing Ceres Dawn explorations. “For a Ceres-sized body” to be able to retain heat and internal fluids during the age of the solar system means that smaller bodies are more geologically active ̵1; they may be more “habitable” – than we thought. “
Dawn traveled the asteroid belt to orbit both asteroids Vesta and Ceres. He studied Ceres for more than three and a half years – from March 2015 to November 2018 – until the spacecraft’s hydrazine maneuvering fuel was depleted. By the closest approach, the orbiter had sunk to less than 22 miles (35 kilometers) above the surface. The spacecraft noticed terrestrial shapes and intriguing features throughout Ceres that showed it was a unique and diverse world.
A bright area in a crater called the Octator was among the most attractive features. Warned more than a decade ago by the Hubble Space Telescope, Dawn scientists concluded that the mysterious bright spots were sodium carbonate – a compound of sodium, carbon and oxygen. The compounds were likely to come from the liquid that penetrated to the surface and evaporated, leaving behind a crust of salt that was highly reflective.
But by the end of the mission, scientists had not yet determined where the fluids came from: did it come from deep inside the dwarf planet and bubble to the surface in a volcanic process? Or the impact that created the crater formed a shallow fusion that breaks down to create bright features.
New research, using images and data on gravity from Dawn, suggests both may have occurred.
“Gravity data tells us that there is likely a deep reservoir of salt water – salt water – about 40 kilometers below,” said Sizemore, who is a Senior Scientist at the Institute of Planetary Sciences. “Some of that deep water is likely to erupt to the surface and contribute to bright spots and other features in Oqtor.
On the other hand, Sizemore continued, analysis based on images of large streams and small hills within the crater suggests that shallow mud-impact melting sheets flowed around the inside of the crater.
“It created interesting features as they regenerated,” Sizemore said. “Both of these are exciting because it means there were transient and long life resources in the area, and extensive mixing. Liquid water and mixing are always attractive to astrobiology.”
Bright conical hills and ridges are similar to small ice hills in the polar regions of the Earth formed by pressurized groundwater. These features in the Octator coffin will require the formation of water movement and / or ice slag, and this activity must have continued for a long time after the impact created by the crater.
But if Ceres has an ocean beneath the surface, how can it remain warm enough to keep it liquid, since the dwarf planet does not experience tidal forces from a large planet like some of the moons around Saturn or Jupiter?
“Most of Ceres’ underground ocean is frozen today,” Sizemore said in an email, “with relatively small amounts of liquid remaining. Holding any liquid is challenging, given that tidal warming does not occur. “Clathrates hydrates (gaseous water ice such as methane trapped in the crystal lattice) make Ceres crust very insulating. Clathrates act effectively as a blanket that allows the dwarf planet to depend on its internal heat.”
Ceres has over 130 of these bright areas, most within impact craters. The global nature of these bright regions early suggested to Dawn scientists that Ceres had a layer beneath the surface of ice with bright water, and the impacts formed by the craters would have ‘discovered’ the mixing of ice and salt.
Ceres has a diameter of about 600 miles (960 km), giving it a size equal to 37% of the land area of the continental United States. The occupying crater is 57 miles (92 kilometers) beyond, and Sizemore said the bright spots inside the crater formed much later, 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 these salts dehydrate very quickly, brine may still be penetrating the surface, indicating that saline liquids may still exist inside the planet. dwarf. In another paper, Andreas Nathues and colleagues found that Ceres underwent a period of cryovolcanic activity beginning about nine million years ago, and continued until very late.
Another paper, published by Britney Schmidt and his colleagues in Nature Geoscience, shows that hills and hills in the Oktator Crater may have formed when impact-induced water leaks freeze. This suggests that cryo-hydrological processes extend beyond Earth and Mars, and were active in Ceres in the recent geological past.
“Dawn achieved far more than we expected when it began its extraordinary extraterrestrial expedition,” said Mission Director Marc Rayman of NASA’s Jet Propulsion Laboratory in Southern California. “These interesting new discoveries from the end of his long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”
You can read the full list of Ceres papers published this week, available 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, 1100 et al. Nature 536, 54-57 (2016).
- Nathues, A. et al. Nat. Astron. https://doi.org/10.1038/s41550-
- De Sanctis, 1100 et al. Nat. Astron. https://doi.org/10.1038/
- Scully, JEC et al. Nat. Usual. https://doi.org/10.1038/
- Raymond, CA et al. Nat. Astron. https://doi.org/10.1038/s41550-
- Fu, RR et al. Planet Earth. Sci. Lett. 476, 153–164 (2017).
- Hendrix, AR et al. Astrobiology 19, 1–27 (2019).
Sources: Institute of Planetary Sciences, Nature, JPL, email correspondence with Dr. Hannah Sizemore