A new and thorough analysis of high-resolution images and data from NASA’s Dawn mission now provides new insights into the dwarf planet Ceres, with compelling evidence that Ceres has an ocean. salinity is below the global surface and has been geologically active in the recent past.
Dr Hannah Sizemore told Universe Today: “Evidence that Ceres has longstanding deep saltwater reservoirs is an interesting result. Sizemore is a co-author of five of the seven papers published this week in different journals in Nature, detailing Dawn’s discoveries about Ceres. “The fact that a celestial body the size of Ceres can retain both heat and internal liquid with the age of the solar system implies that small objects are more geologically active ̵1; possibly more ‘inhabited’. – than we thought. “
Dawn travels to the asteroid belt to orbit both the asteroids Vesta and Ceres. It studied Ceres for over three and a half years – from March 2015 to November 2018 – until exhausted the spacecraft’s hydrazine control fuel. At the closest approach, the spacecraft fell below 22 miles (35 km) above the surface. The spacecraft uncovered the terrains and features all over Ceres make it a unique and diverse world.
A bright area in the crater called Occator is one of the most captivating features. As suggested by the Hubble space telescope more than a decade ago, the Dawn scientists concluded the mysterious bright spots were sodium carbonate – a compound of sodium, carbon and oxygen. Compounds can come from the liquid that seeps onto the surface and evaporates, leaving a highly reflective salt crust.
But at the end of the mission, scientists have yet to determine where the liquid came from: did it come from deep inside the dwarf planet and bubble up to the surface during a volcanic process? Or the impact that caused the crater to form a shallow melting and freeze to create bright features.
New research, using images and gravitational data from Dawn, suggests both may have happened.
Sizemore, a senior scientist at the Institute of Planetary Science, said: “Gravity data tells us there could be a reservoir of salt water – salt water – about 40 kilometers below the Occator. “Some deep water may have erupted on the surface and contributed to the highlights and other features of the Occator.”
On the other hand, Sizemore continued, image-based analysis of large currents and small hills inside the crater showed that shallow layers of mud resulting from the impact melt around inside the crater.
“This creates interesting features as they evolve,” Sizemore said. “Both of these are interesting, because it means there are permanent and temporary water sources in this area, and a wide mix. Liquid water and blend have always been of interest to astrophysics.
Bright conical hills and nodes similar to those in the polar regions of the Earth are formed by groundwater under freezing pressure. These characteristics in the Occator barrel would require the movement of water and / or glacial mud to form, and this action would take place long after the crater-making impact.
But if Ceres has a subsurface ocean, how could it be warm enough to keep it liquid, since the dwarf planet does not withstand tidal forces from a large planet like some moons around Saturn or Saturn? Carpentry?
“Much of the Ceres’ subsurface ocean is frozen today,” Sizemore said in an email, “with a relatively small amount of liquid left over. Retaining any liquid is a challenge, as heating does not occur with tides. We think that the clathrate hydrates (ice with gases like methane trapped in the lattice) make the crust of Ceres very insulating. Clathrates act effectively like a blanket that allows the dwarf planet to retain its internal heat.
The Ceres has more than 130 of these bright areas, mostly inside the craters. The global nature of these bright areas hinted early on to Dawn scientists that Ceres had a layer of white water ice under the surface, and that the crater-forming effects would ‘unearth’ the ice mixture and salt.
The Ceres is about 600 miles (960 km) in diameter, giving it a size equivalent to 37% of the land area of the continental United States. The crater Occator is 57 miles (92 kilometers) above, and Sizemore says the bright spot 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 these salts lose water very quickly, the brine can still seep on the surface, suggesting that the salty liquid remains. may exist inside dwarf planets. In another paper, Andreas Nathues and colleagues found that Ceres experienced a period of cryovolcanic activity that began about nine million years ago, and existed until very recently.
Another paper, published by Britney Schmidt and colleagues in the journal Nature Geoscience, points out that mounds and hills in Occator crater may have formed when the water flow caused by the impact froze. This suggests that frozen hydrological processes extend well beyond Earth and Mars, and have been active on the Ceres in the geologically recent past.
“Dawn has achieved more than we had hoped for when embarked on her extraordinary extraterrestrial expedition,” said Marc Rayman, Mission Director of NASA’s Jet Propulsion Laboratory in Southern California. “These exciting new discoveries after the end of its long and effective mission are a great tribute to this remarkable interplanetary explorer.”
You can read the full article on Ceres published this week, found here: https://www.nature.com/collections/agdgfadcag
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Source: Institute of Planetary Science, Nature, JPL, email address to Dr. Hannah Sizemore