Bengaluru: The dwarf planet Ceres is a “water-rich” world that holds large reservoirs of sea water beneath its surface, according to data from NASA’s Dawn spacecraft.
Ceres is one of the solar system’s five dwarf planets, and the only one in the asteroid belt between Mars and Jupiter. It is also an asteroid.
European and American scientists processed Dawn data to determine that there is an “extensive reservoir”, or ocean, of salt water (brine) underneath the dwarf planet’s surface. The scientists estimate the brine reservoir to be 40-km deep and hundreds of kilometres wide. Ceres is about 950 km wide.
The team has also concluded that Ceres is geologically active, currently enabling the seeping of liquid to the surface.
The conclusions were arrived at from data collected during the last few months of Dawn’s operation around Ceres in 2018, when it dropped to an orbit of just 35 km above the surface.
The findings were published across five new papers in the journal Nature Monday.
Dawn is currently retired and in an uncontrolled orbit around Ceres.
During the mission, Dawn lowered itself to a 35-km orbit and imaged the dwarf planet, making a series of close passes over the 92-km-wide Occator Crater. Images of the crater showed flecks of white, which were thought to be salt, snow, or minerals at various times, on the surface. These distinctive white and reflective areas were named Cerealia Facula.
Scientists had earlier understood that the bright areas were composed of sodium carbonate, which likely came from liquid that seeped upwards to the surface and evaporated. However, the source for this liquid had not been determined.
One of the new studies found that the minerals contained hydrohalite, which are salt molecules held in water molecules.
This is the first time that hydrohalite has been discovered outside earth.
Hydrohalite dehydrates in less than 100 years if left undisturbed, so the authors believe liquid water was present less than 100 years ago.
Another study from Dawn’s data theorises that the Occator Crater’s formation, thought to have been caused by a large impact, had created fractures on the outer skull of the dwarf planet. The authors state that these fractures allow salt water to reach the surface from underneath by percolation.
Another study analysed the evolution of the crater, the bright spots, and the planet’s underground architecture using data from studying Ceres’s gravity — the presence of surface features or the reduction in surface material leads to a spread of uneven gravitational pull that can be recorded and analysed for physiography.
The scientists also used thermal modelling to recreate and model the dwarf planet, analysing the short and long term effects of the impact, and the thickness of the crust along with gravitational data.
A group of researchers also studied cry-volcanism or ice volcanoes in the Occator crater caused by a crash. The activity was dated to about 22 million years ago. The crash formed a chamber of molten liquid, which then started seeping to the surface roughly 2 million years ago.
These findings show that Ceres is different from other ocean worlds like Jupiter’s moon Europa and Saturn’s moon Enceladus, both of which are thought to harbour oceans of water under a solid, icy crust. Ceres seems to comprise rocks more than ice.
The confirmation of liquid water on the astronomical body promises to invite increased astrobiological interest into the dwarf planet.