The bright spots on the dwarf planet, Ceres, baffled astronomers in 2015. Hubble had managed to capture a blurry image of a bright area on Ceres back in 2008, but it was in 2015, as the Dawn spacecraft approached the dwarf planet, that the bright areas shone out with unprecedented clarity, up to four times brighter than the rest of the planet's surface. But what could they be? Lakes? Metal ores? Even artificial structures? Nobody could figure it out. Then, on the 9th December, scientists reported that they might actually be salt deposits, left as a result of brine eruptions from under Ceres' surface. The salty water shoots from the ground and instantly sublimates as it hits the extremely thin atmosphere. So, not shiny little alien Habs, but you have to be impressed with the turnaround of this one, from discovery to definition within the year.
