Ceres

Ceres is the largest body in the asteroid belt, the only dwarf planet in the inner Solar System, and the first asteroid ever discovered — found by Giuseppe Piazzi on the first night of the 19th century, 1 January 1801. It was originally classified as a planet, then reclassified as an asteroid in the 1850s, and finally as a dwarf planet in 2006 alongside Pluto, Haumea, Makemake and Eris.

NASA’s Dawn spacecraft (2015-2018) orbited Ceres and revealed a remarkable world. Bright salt deposits — sodium carbonate and ammonium chloride — inside Occator Crater originate from cryovolcanic brine that reached the surface as recently as 2 million years ago. Gravity data indicate a 40 km thick upper crust, a muddy subsurface reservoir, and a still-extant deep brine layer between the rocky mantle and crust. Ceres is therefore both an asteroid and an ocean world.