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Underground Salt Water on Ceres

Thanks to data from NASA‘s Dawn spacecraft, scientists have found evidence for underground salt water on Ceres. The spacecraft was able to provide detailed views of the mysterious bright areas on the surface of the dwarf planet. Scientists realised that these bright areas were sodium carbonate deposits, which must have been formed from a salty liquid percolating up to the surface and evaporating, leaving a salt crust behind. By studying Ceres’ gravity, they were finally able to determine where the liquid came from: a deep reservoir of salty brine beneath the surface!

A Mission to the Asteroid Belt

NASA’s Dawn spacecraft was launched in 2007, and is the only spacecraft to orbit 2 different bodies beyond Earth. In 2011, it reached the asteroid Vesta, where it remained in orbit until 2015, when it travelled to Ceres instead. It was able to journey such a distance thanks to its ion propulsion system. The mission ended in 2018.

Dawn’s focus was to investigate how planet-like bodies formed in the early solar system. By comparing Vesta and Ceres, it was able to prove that location had a big influence on how a body formed. Although these bodies are both in the Asteroid Belt now, their compositions are very different. This led scientists to believe that Vesta formed in the inner solar system and stayed there, as it appears similar to the rocky planets of this region. However, Ceres appears to have formed further out and drifted inwards. Alternatively, material may have drifted inwards and attached to Ceres as it was forming.

The new discovery comes from the analysis of the last data from Dawn, but prior to this it also showed a lot of organic material on Ceres in the Ernutet Crater. Although not necessarily an indicator for organic life, coupled with the existence of a subterranean ocean, this makes Ceres an interesting place to keep an eye on!

False colour image of salty deposits on Ceres, shown in red.
False colour image of salty deposits on Ceres, shown in red. Credit: NASA

A Salty Clue

The bright patches on the surface of Ceres have been known about for a long time. Earlier studies using Dawn data had determined that they were made of sodium carbonate, and likely formed from liquid rising to the surface and evaporating. This would leave behind a salty deposit on the surface! However, no one knew where the liquid came from.

As scientists worked through the data, they finally came across something promising from near the end of the mission. They worked out that this liquid came from a reservoir of brine (salt-enriched water), deep below the surface. They even managed to work out that it is about 25 miles deep and hundreds of miles wide.

This discovery builds on previous ones to give a clearer picture of Ceres’ geological activity. The brightness of these areas indicates that they are young, as over time the impact of micrometeorites would darken them. They also still contain some water, which should have evaporated. So the liquid is probably still moving up to the surface, showing that geological processes may still be active.

Although Dawn’s work is done, it’s still facilitating discoveries today! Ceres is a very exciting place, and learning more about it could give us a better idea of how icy bodies function in our solar system.

Sources: NASA, NASA Solar System