Ceres is a dwarf planet that is part of the asteroid belt between Mars and Jupiter. Multiple studies revealed that the planet was once an ocean world. The planet is about 2.5 times smaller than Pluto and shares similar properties of being a frozen, lifeless 'fossil.'
In 2007, NASA sent the Dawn spacecraft to study Ceres, where it found traces of liquid within the geological composition of the crater Occator. Two contrasting theories suggest the possible reasons for salt residue.
The first theory states that the impact which created the crater left a trace of salt residue. On the other hand, a second theory states that fluid used to exist below Ceres' surface before it eventually dried up.
One of the studies co-authored by Julie Castillo-Rogez of NASA's Jet Propulsion Laboratory (JPL) found an infrared signal of hydrohalite. Hydrohalite is sea salt (sodium chloride) within water molecules. The signal was picked up by Dawn's infrared mapping device.
Castillo-Rogez's team from Italy and the United States determined that the hydrohalite had been exposed less than 100 years ago. The liquid water may still be present in Ceres, determined the team, meaning that it could have been habitable.
Bright Spots
It remains uncertain if the dwarf planet had pockets of water or if Ceres is an ocean planet. Alongside Occator's gravitational data, the Dawn team mapped out the underground liquid reservoir. The crater has a bright spot called Cerealia Facula, where salt residue shows evidence of water.
Geometrical figures determined that Cerealia Facula is younger than the crater. Most likely, an impactor formed Occator around 22 million years ago and left a 'melt chamber' after. The chamber then formed liquid containing hydrohalite and may have moved to the crater's surface to form Cerealia 20 million years later.
'We concluded that some low activity at Occator is probably still ongoing,' said Andreas Nathues of the Max Planck Institute for Solar System Research. 'It was a surprise that the old ocean is not completely frozen.'
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Ocean Worlds
Understanding Cerealia helped scientists understand the planet's other bright spots which also contained salts. Nearby, the Vinalia Faculae contains bright spots with salt residues from a deeper source of liquid.
Ceres lacks an atmosphere, meaning that tidal heating, or internal heat generated through gravitational interactions, has not been present. Since water freezes as it reaches the surface due to the lack of heat, the dwarf planet can keep liquid water through compounds that make salty liquids.
Ocean worlds have been a growing interest for scientists, especially with the ongoing Mars missions to search for signs of life. According to NASA, 'the story of our oceans envelops our home in a far larger context that reaches deep into the universe and places us in a rich family of ocean worlds that span our solar system and beyond.' Oceans have set apart Earth from other celestial bodies, but it might not have been so millions or billions of years ago.
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