Scientists are attributing a mysterious bright spot on Ceres, the largest object in the main asteroid belt, to a vast reservoir of salty water beneath the dwarf planet's crust. Subsurface oceans are the kind of thing we'd expect to see in the outer solar system, particularly on the icy moons around Jupiter, Saturn, Uranus and Neptune. But according to seven (yes, seven) newly published papers in a special Nature Collection, subterranean oceans could also appear on a planet without the object's host, Ceres, a dwarf in the main asteroid belt between Mars and Jupiter. Display of planets.
As new research shows, Ceres has recently been active, and may still be active, containing vast underground reservoirs and exhibiting a type of cryovolcanism (the arrival of groundwater there) not previously seen on celestial objects. surface). Subsurface oceans on icy moons like Jupiter's Europa and Saturn's Enceladus are kept warm by tidal interactions between their host planets, but the same cannot be said for planetless objects in the asteroid belt. On Ceres, this phenomenon is more of a chemical issue, as the groundwater remains muddy due to its high salt content.
The new research is described in papers published in Nature Astronomy, Nature Geoscience and Nature Communications, including contributions from NASA, the Lunar and Planetary Institute (LPI) ), scientists at the University of Münster in Germany, the National Institute for Scientific Education and Research (NISER) in India and many other institutions. At 950 kilometers across, Ceres is the largest object in the asteroid belt. NASA's Dawn spacecraft visited Ceres from 2015 to 2018, collecting vital data during the mission's final five months as the orbiter swooped within 35 kilometers of the surface.
High-resolution images sent back to Earth reveal Occator Crater in unprecedented detail. This impact crater was formed by a huge impact and is the most striking feature of the dwarf planet. It is about 92 kilometers wide, which is quite huge even by Earth standards. Occupier Crater was revealed as a complex structure characterized by a central depression capped in a dome-like structure, various cracks and furrows, bright mineral deposits, and smaller domes scattered throughout.
It was suspected before the Dawn mission that water might be responsible for Ceres' bright surface features, but data collected by the orbiter suggests that this is the case. Some tiny impact craters on Ceres point to a relatively young surface. Occupier Crater formed about 22 million years ago, while some of Ceres' youngest surface features formed only 2 million years ago.
A unique feature of impact craters is the formation of a peak in the center. Such a feature formed inside the Occator, but it collapsed, creating depressions within it. Then, about 7.5 million years ago, water (or more saline water) rose to the surface and leaked through this collapsed mountain. The brine evaporated, leaving behind reflective deposits in the form of sodium carbonate (a mixture of sodium, carbon and oxygen). The bright white spots at Cerealia Facula in the center of Occator are the remnants of this process.
Similar deposits occur elsewhere in the crater, including a striking feature known as the Vinalia Faculae. At these locations, saltwater rises to the surface through cracks and furrows. About 2 million years ago, Cerealia Facula became active again, spewing out more brine and forming a central dome of bright material. These processes were ongoing until about a million years ago, and although cryovolcanic processes have been greatly weakened over time, they may still occur today.
Evaporation and sublimation force water to the surface in a surface-frozen form, a phenomenon not seen anywhere else in the solar system. Scientists have good reason to believe that this process may exist elsewhere on other seemingly inert objects. "Evidence of very recent geological activity on Ceres refutes the common belief that small bodies in the solar system are geologically inactive. It may have had a subsurface ocean due to the impact event that formed Occator Crater, but its continued mudiness is due to the dissolution of salts in the groundwater." .
"For the large deposits at Cerealia Facula, most of the salts were supplied from a muddy area beneath the surface that was melted by the heat of the impact that created the crater about 20 million years ago," " said first author Carol Raymond, Nature Astronomy Research and Dawn principal investigator, in a NASA press release. "The impact heat dissipated after millions of years; however, the impact also created large fractures that may reach deep, long-lived reservoirs, allowing brine to continue seeping to the surface."
Ceres has hundreds or thousands of possibly smaller depositional sites, most of which are less than 33 feet (10 meters) thick. Domes and depressions appear on the surface and are also formed by the movement of groundwater. By studying Ceres' gravity, scientists can infer its internal structure. The salty reservoir lies about 25 miles (40 kilometers) below the surface and is hundreds of miles wide. Given that Ceres itself is only 590 miles across, it's fair to call Ceres an ocean world.
Seemingly overnight, Ceres has become an attractive target for astrobiologists. Due to its complex chemistry, liquid water, and ongoing surface and subsurface dynamics, it may have been habitable at some point in its recent history. A sudden mission to send a probe to the surface seemed like a good idea.
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