The surface of Mars has been well mapped and characterized, yet the subsurface — the most likely place to find signs of extant or extinct life and a repository of useful resources for human exploration — remains unexplored. In the near future this is set to change.
Exploration of the Martian subsurface, to depths from a few metres to many kilometres, offers an unprecedented opportunity to answer one of the biggest questions contemplated by humankind: was or is there life beyond Earth? Simultaneously, Mars subsurface exploration lays the foundation for self-sufficient human settlements beyond our own planet and provides an emerging potential for synergistic collaborations with the rising commercial space sector and traditional mining companies. Our understanding of the Martian subsurface and the technologies for exploring it — with a dual focus on the search for signs of extinct and extant life, and resource characterization and acquisition — have matured enough for serious consideration as part of future robotic missions to Mars.