China’s Zhurong rover may have driven across one of the most intriguing repositories of ancient Martian water yet discovered: large gypsum crystals that could contain microscopic pockets of brine sealed inside them for hundreds of millions of years. Taken together, the crystal shapes, spectra and chemistry led the researchers to conclude “with high confidence” that Zhurong had encountered large selenite crystals. Tiny Time Capsules of Martian GroundwaterExample of selenite gypsum crystal. Large selenite crystals on Earth frequently contain fluid inclusions — tiny cavities filled with remnants of the original solution from which the crystal grew. The Zhurong crystals are therefore likely to contain ancient Martian brine.