Short answers, pulled from the story.
Ceres was discovered by Giuseppe Piazzi, a Catholic priest and astronomer, on the 1st of January 1801 at the Palermo Astronomical Observatory in Sicily. Piazzi initially reported it as a comet before recognizing it might be something more significant.
On the 24th of August 2006, the International Astronomical Union adopted a definition of planet that required a body to have cleared the neighbourhood around its orbit. Ceres fails this criterion because it shares its orbit with thousands of other asteroids and accounts for only about forty percent of the asteroid belt's total mass. Bodies meeting the first but not the second criterion were placed in the new dwarf planet category.
The bright spots in Occator Crater are deposits of salts left by brines that percolated to the surface. On the 9th of December 2015, NASA scientists identified them as likely involving magnesium sulfate hexahydrate. Near-infrared spectra later confirmed a large amount of sodium carbonate, and in August 2020 NASA confirmed that a deep reservoir of brine had reached the surface at hundreds of locations across Ceres.
Dawn, which achieved gravitational capture on the 6th of March 2015, found a surface mixture of water ice, carbonates, and clay minerals. It confirmed cryovolcanic activity centered on Ahuna Mons, detected water ice at Oxo crater in March 2016, and identified organic compounds in the Ernutet crater. The mission ended on the 1st of November 2018 when the spacecraft exhausted its fuel.
Yes. Ceres is the closest known cryovolcanically active body to the Sun. Models indicate that roughly one cryovolcano has formed on average every fifty million years over the past billion years. Ahuna Mons, with a maximum estimated age of 240 million years, is the clearest current example, and a 2018 computer simulation identified twenty-two additional surface features as candidates for relaxed, older cryovolcanoes.
Ceres has the most water of any body in the inner Solar System after Earth, and brine pockets beneath its surface could provide habitats. Its near-surface carbon content runs to approximately twenty percent by mass, and organic compounds have been detected in the Ernutet crater. Phosphorus has not yet been detected, and unlike Europa or Enceladus, Ceres does not experience tidal heating, though long-lived radioactive isotopes can sustain liquid water in its subsurface.