Ceres the Planetoid
Ceres is the largest of the asteroid objects that sit between Jupiter and Mars in our solar system. In 2015, the Dawn spacecraft visited and took these and many more images and data from the object, revealing a surprising geology and possible past at the outer edges of our solar system.
The most notable feature of Ceres was the single large crater with a bright white material within. This turned out to be salt, which may have been deposited on the surface after brine escaped from the centre.
The implication is, a salt water ocean may have existed within the planetoid, and other evidence (such as the bottom image of Ahuna Mons, a possible cryovolcano) certainly points towards water being a large component of the make up.
Additionally ammonia was found, and this is a smoking gun for the formation of this planetoid, as at it's current location, ammonia is unlikely to form, while much further out, it's found in abundance.
So it's likely that this proto-planet started off in life out beyond the orbit of Jupiter and Saturn, and during it's early life found itself flung inwards where it settled amongst the asteroids today.
Source: https://www.syfy.com/syfy-wire/ceres-may-have-formed-out-past-saturn-and-slid-in-to-the-asteroid-belt
The article was written by Phil Plait, who you can follow on Twitter under @BadAstronomer