The discovery of gypsum crystals by China's Zhurong rover on Mars has sparked excitement and debate among scientists. These crystals, found in a thin layer of flat, hydrated rocks in southern Utopia Planitia, may still contain microscopic pockets of the brine they grew from, offering a glimpse into Mars' recent water history. The crystals' branching internal patterns and chemistry suggest they are selenite, a clear, well-formed variety of gypsum that forms directly from concentrated water.
This interpretation implies that Mars maintained an active water system far later than previously thought, challenging the notion of a planet-wide temperate climate. The crystals could also preserve fluid inclusions, microscopic droplets of liquid water sealed during growth, which have never been observed on Mars. This discovery raises the possibility of a chemically habitable environment without evidence of life, as no organisms or biosignatures were detected.
The study's authors propose a sequence of events involving magma intrusions, melting buried ice, and the concentration of brine through freezing. This process, known as cryoconcentration, could have led to the formation of the gypsum crystals. The timing of the crystals' growth is also significant, as it falls within the Amazonian period, a time when Mars was much colder and drier than its early history suggests.
The potential presence of fluid inclusions in the crystals is particularly intriguing. These inclusions could provide valuable information about the water's salinity, acidity, and dissolved elements. However, testing this hypothesis would be challenging, as it would require establishing that the inclusions formed with the crystal and remained sealed, and that any organic compounds were of Martian origin.
Despite the challenges, the discovery of these gypsum crystals on Mars is a remarkable achievement. It highlights the potential for future missions to explore and sample similar sites, offering a deeper understanding of Mars' geological and astrobiological history. The ongoing exploration of Mars continues to reveal fascinating insights into the planet's past and the possibility of life beyond Earth.
