Ceres may have once had a global ocean - and part of it could still remain, NASA has revealed.
The dwarf planet, best known for its strange 'alien spots', is seen as being a record of the early solar system.
Now, the Dawn mission has found minerals containing water are widespread on its surface.
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Ceres is 590 miles (950 km) across and was discovered in 1801.
It is the closest dwarf planet to the sun and is located in the asteroid belt between Mars and Jupiter, making it the only dwarf planet in the inner solar system.
Ceres is the smallest of the bodies currently classified as a 'dwarf planet'.
It lies less than three times as far as Earth from the sun - close enough to feel the warmth of the star, allowing ice to melt and reform.
Nasa's Dawn spacecraft made its way to Ceres after leaving the asteroid Vesta in 2012.
There is high interest in the mission because Ceres is seen as being a record of the early solar system.
'More and more, we are learning that Ceres is a complex, dynamic world that may have hosted a lot of liquid water in the past, and may still have some underground,' said Julie Castillo-Rogez, Dawn project scientist and co-author of the studies, based at NASA's Jet Propulsion Laboratory, Pasadena, California.
The Dawn team found that Ceres' crust is a mixture of ice, salts and hydrated materials that were subjected to past and possibly recent geologic activity, and that this crust represents most of that ancient ocean.
Landing on Ceres to investigate its interior would be technically challenging and would risk contaminating the dwarf planet.
Instead, scientists use Dawn's observations in orbit to measure Ceres' gravity, in order to estimate its composition and interior structure.
Led by Anton Ermakov, a postdoctoral researcher at JPL, the first study used shape and gravity data measurements from the Dawn mission to determine the internal structure and composition of Ceres.
The measurements came from observing the spacecraft's motions with NASA's Deep Space Network to track small changes in the spacecraft's orbit. This study is published in the Journal of Geophysical Research.
Ermakov and his colleagues' research supports the possibility that Ceres is geologically active -- if not now, then it may have been in the recent past.