Earth's nearest dwarf planet Ceres is a 'water world' that harbours a salty ocean beneath its cratered surface, NASA observations reveal

Ceres, the nearest dwarf planet to the Earth is a water world and could have a vast reservoir of salty water hidden under its surface, according to new research.
The reservoir on the minor planet, which orbits the Sun between Mars and Jupiter, lies beneath a 20 million year old crater known as Occator - and could harbour life.
The finding is based on an analysis of images from NASA's Dawn spacecraft as it surveyed the surface of Ceres by a team from the California Institute of Technology. 
Dawn orbited Ceres, which is about 600 miles across - roughly the vertical length of the UK - between 2015 and 2018 until it ran out of fuel.
In its final few months it travelled just 20 miles above the surface and focused on the Occator crater, where it performed imaging, scanning and gravity analysis. 
The finding is based on an analysis of images from NASA's Dawn spacecraft as it surveyed the surface of Ceres including 'bright spots' within the crater
The finding is based on an analysis of images from NASA's Dawn spacecraft as it surveyed the surface of Ceres including 'bright spots' within the crater 
In its final few months it travelled just 20 miles above the surface and focused on the Occator crater where it performed imaging, scanning and gravity analysis
In its final few months it travelled just 20 miles above the surface and focused on the Occator crater where it performed imaging, scanning and gravity analysis
Dr Carol Raymond, deputy principal investigator of the mission, said: 'It suggests Ceres is an ocean world and may have been geologically active in the recent past.' 
The observations are reported in seven papers published in Nature Astronomy, Nature Geoscience and Nature Communications.
Dr Raymond's team believe the reservoir of brine found under the surface of the dwarf planet was fuelled by the impact that created the crater.
This led to the the formation of deposits of salt on the planet's surface - which appear as bright spots when viewed from a distance.
Raymond said: 'The existence of a deep-seated brine reservoir beneath Occator is supported by recent results from gravity data.'
Salt lowers the freezing point of water - increasing the likelihood of it being fluid.
Another paper described the detection of chloride salts - commonly found in sea ice - by instruments that mapped the crater using visible and infrared light.
It tops Cerealia Facula - a dome at the centre of the Occator crater and it is the first time the compound has been found beyond Earth.

Lead author Maria Cristina De Sanctis, of the National Institute of Astrophysics in Rome, said this requires liquid water in combination with hydro-thermal activity.
'The spatial distribution suggests chloride salts are the solid residue of deep brines that reached the surface in the last two million years - or are still ascending,' De Sanctis explained. 
'These salts are very efficient in maintaining Ceres' warm internal temperature and lowering the temperature of the brines - in which case ascending salty fluids may exist today.' 
At almost 600 miles wide, Ceres is the biggest object in the asteroid belt.
It lies less than three times as far as Earth from the sun - which is still close enough to feel the warmth, allowing ice to melt and reform.
Ceres was the first dwarf planet to be visited up-close. It belongs to a distinct class of objects - after the rocky inner planets like Earth and Mars and gas giants like Jupiter.
It's fascinated astronomers for decades as it's seen as being a record of the early solar system and how it developed.
Dr Julie Castillo-Rogez, a planetary scientist at Caltech who was not involved in any of the studies, said Ceres has long been believed to be a primitive body.
NASA's Dawn spacecraft orbited Ceres, which is about 600 miles across - roughly the vertical length of the UK - between 2015 and 2018 until it ran out of fuel
NASA's Dawn spacecraft orbited Ceres, which is about 600 miles across - roughly the vertical length of the UK - between 2015 and 2018 until it ran out of fuel
'Ceres is now an ocean world with deep brines at a regional and potentially global scale,' Castillo-Rogez explained.
'Further studies of Ceres' conditions and - above all - a follow-up mission are needed to study its evolution and potential habitability.'
She said the findings also have implications for finding life on icy world's - such as Jupiter's moons Europa and Ganymede.
NASA's Europa Clipper mission and the Jupiter Icy moons explorer (JUICE) are being launched in the coming decade.
Dr Castillo-Rogez said: 'The next ten years of dwarf planet exploration requires focus to be brought onto habitability through time in these evolved oceans - which are likely to be rich in organic matter.
'Exposed natural salts in Occator provide direct sourcing of the deep brine below the crater and represent an obvious target for a future mission.'
The various papers are available to read from Nature
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