Spectral evidence of hydrous minerals and water ice on southern Utopia Planitia, Mars

Previous mineralogical investigations on Utopia Planitia only show sporadic hydrous minerals in localized areas, limiting the modeling of the regional aqueous activities. Although the periglacial landforms and radar observations allude to the presence of subsurface water ice in Utopia Planitia, evidence of water ice on the surface is not detected. Using a total of 330 CRSIM images covering the southern Utopia Planitia and the bordering highland, we identify widespread phyllosilicates and carbonates on the highland, and four possible water ice spectra at a midlatitude on the lowland, three of which are mixed with monohydrated sulfate. Moreover, orbital data near the landing site of Zhurong rover in southern lowland show a thick dust cover. The restriction of phyllosilicates and carbonates to the Noachian/Hesperian highland units and sulfate to the Hesperian/Amazonian lowland units suggest that the ancient water retreated from highland to lowland when the aqueous environment changed from alkaline/neutral to acidic. Spectral evidence for water ice indicates that Utopia Planitia is still a reservoir on Mars.