Humanity has long been captivated by Mars, driving decades of robotic exploration. A primary objective of these missions is to determine if water, a molecule fundamental to life, is present on the Red Planet. This quest has shaped mission designs and scientific investigations, continually revealing new insights into Mars’ past and present.
Evidence of Ancient Water
Geological features on Mars strongly indicate a past with abundant liquid water. Images from orbiters reveal extensive networks of dried riverbeds, deltas, and ancient lakebeds, suggesting significant water flow. Jezero Crater, the Perseverance rover’s landing site, is believed to be an ancient lakebed that once hosted a river delta, indicating water flowed into a basin.
Further evidence comes from specific minerals that only form in the presence of water. Hematite spherules, often dubbed “blueberries,” found by the Opportunity rover, are concretions that form in watery environments. Phyllosilicates, or clay minerals, and sulfates detected across the Martian surface, require liquid water for their formation, pointing to a warmer, wetter early Mars. Some Martian meteorites also show evidence of past water exposure.
Where Water Exists Today
While ancient Mars hosted flowing surface water, the Red Planet today is largely a frozen desert with no large bodies of open liquid water. However, significant amounts of water are present in various forms. The most prominent reservoirs are the vast polar ice caps, containing both water ice and frozen carbon dioxide (dry ice).
Beyond the poles, substantial subsurface ice, or permafrost, is widespread across mid-latitudes, often buried just beneath the surface. More than 5 million cubic kilometers of ice have been detected at or near the surface, enough to cover the planet to a depth of approximately 35 meters (115 feet). Transient liquid brine flows, known as recurring slope lineae (RSLs), have been observed on steep slopes during warmer seasons, although their exact formation mechanism remains under study. Small amounts of water vapor are also present in the thin Martian atmosphere.
The Search for Martian Water
Scientists employ various instruments on orbiting spacecraft and surface rovers to search for water on Mars. Orbital instruments play an important role in mapping the planet’s surface and subsurface. For instance, the High Resolution Imaging Science Experiment (HiRISE) camera on the Mars Reconnaissance Orbiter (MRO) captures detailed images of geological features, including those potentially formed by water.
The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on MRO identifies water-formed minerals by analyzing their spectral signatures. Radar instruments like MARSIS on Mars Express and SHARAD on MRO penetrate the surface to detect subsurface ice and potentially liquid water layers, with radar findings in 2018 suggesting subglacial lakes. On the surface, the Phoenix lander directly dug into and confirmed the presence of water ice in 2008. Rovers like Curiosity and Perseverance analyze soil and rock samples, detecting water-bearing minerals and identifying water molecules in excavated material.
Why Martian Water Matters
The presence of water on Mars has significant implications for two primary areas: the potential for life and future human exploration. For astrobiology, water is a fundamental requirement for life as we know it, making regions with past or present water prime targets in the search for extraterrestrial microbial life. The discovery of ancient lakebeds and water-formed minerals suggests early Mars might have been a habitable environment.
Looking to the future, Martian water is a valuable resource for human missions. Water can be used directly for drinking and supporting human habitats. It can also be broken down into hydrogen and oxygen, which are essential components for producing breathable air and rocket fuel for return journeys to Earth, reducing the amount of supplies needed from Earth. Understanding the distribution and accessibility of water on Mars is a significant step toward enabling long-duration human presence.