Martian hydrosphere: A brief overview of water on Mars

Understanding the status of water on Mars is crucial for evaluating its capacity to support life and to serve as a resource for future possible human exploration. Investigations have been carried out in the past to find signs of water in its past or present states. It is generally agreed that Mars had significant amounts of water early in its existence, but today, only remnants exist, mostly as ice or within hydrous minerals. Current evidence of water on Mars includes geological features, Martian meteorites, sporadic wet flows on slopes, surface moisture detected by missions like Curiosity and Phoenix, and features suggesting ancient lakes and rivers. A notable recent discovery was an old streambed in Gale Crater, indicating the presence of considerable water flow in the past, which might have supported microbial life. Nowadays, Mars' arid surface is not suitable for life as we know it, leading scientists to focus on underground environments for the exploration of life and its respective biosignatures. Recent efforts have unveiled substantial underground ice reserves discovered by NASA in 2016 and a hidden subglacial lake identified by Italian researchers in 2018. The question of life on Mars still remains unresolved to date. This overview compiles the findings from diverse studies on Mars' water history and attempts to address the ongoing discussions about the potential for life on the planet.