The Exploration of Mars
From the first grainy photographs of a rust-coloured disc to today’s high-resolution panoramas of canyon walls and crater floors, humanity’s picture of Mars has been redrawn repeatedly. Early flyby missions such as NASA’s Mariner 4 in the 1960s delivered a shock: the planet appeared cratered and inhospitable, lacking the obvious canals some astronomers once claimed to see through Earth-based telescopes. Yet even those stark images seeded a more disciplined curiosity. If Mars had been geologically active in the past, and if water had once flowed, perhaps traces of that activity still lingered in its rocks and soils.
Orbital spacecraft deepened that curiosity by mapping the planet in exquisite detail. Spectrometers and cameras aboard later missions traced the outlines of dried river valleys, alluvial fans and deltas, forms that on Earth arise where liquid water moves sediment over long periods. In addition, minerals such as clays and sulfates were detected from orbit, the sort that typically emerge when rocks interact with water. These findings did not demonstrate that surface water exists today, but they transformed Mars from a static museum piece into a world with a dynamic, watery past.
The first successful soft landings brought experiments directly to the ground. The Viking landers of the 1970s, with their chemistry packages and robotic scoops, tested soil for metabolic signs. Their results have been debated for decades: some reactions looked tantalising, while others suggested mundane inorganic processes. Regardless, those missions set a template for careful, incremental investigation. Later, the tiny Pathfinder lander and its Sojourner rover in the 1990s demonstrated mobility, showing that rolling laboratories could survey rocks across short distances instead of relying on a single dig site.
Mobility became central in the early twenty-first century. NASA’s twin rovers, Spirit and Opportunity, each the size of a small golf cart, found layered rocks and tiny spheres rich in iron, consistent with histories of water alteration. Opportunity, operating far longer than designed, trundled for years across plains and into craters, reading the geological record like pages in an exposed book. These rovers did not detect present-day surface liquid water; rather, they reconstructed ancient environments that could once have supported microbial life, given energy sources and enough time.
With the arrival of larger laboratories on wheels, scientists shifted from simply asking whether water had ever existed to examining habitability in detail. The Curiosity rover, for example, drilled into mudstones in Gale Crater and analysed powdered samples to identify organic molecules and evidence of past lakes. Later, Perseverance began its campaign in Jezero Crater, a location chosen because orbital imagery suggested an old river delta. Perseverance’s instruments search for textures and chemical signals that, on Earth, sometimes point to ancient microbial activity, while the rover also stores selected cores for eventual return to Earth by future missions.
Helicopter technology added an unexpected chapter. A small rotorcraft demonstrated controlled powered flight in the thin Martian atmosphere, providing aerial scouting that helped planners select safe paths and intriguing targets. Although the airborne demonstrator had modest range, it proved that new modes of exploration are feasible on another world. In parallel, orbiters continued to deliver global context, tracking dust storms, measuring seasonal carbon dioxide frost and monitoring the behaviour of water vapour escaping to space. These multiple vantage points—surface, sky and orbit—now combine to produce an integrated portrait of a changing planet.
Yet despite this progress, key questions remain. The consensus view is that stable, long-lived bodies of liquid water are not present at the Martian surface today because the air is too thin and cold; any exposed liquid quickly freezes or evaporates. Some researchers model the possibility of brines or transient films under specific conditions, but direct proof is elusive. Claims of present-day subsurface reservoirs or repeating slope features driven by water have been carefully reassessed as alternative mechanisms—such as dry granular flows—can mimic watery signatures. As a result, modern exploration emphasises past habitability and the careful search for preserved biosignatures rather than the assumption of ongoing surface hydrology.
Finally, the scientific logic of sample return has become compelling. Instruments on rovers are powerful but necessarily limited compared with the analytical suites available in terrestrial laboratories. Returning selected cores, contextualised by detailed field notes and imagery, would allow isotope measurements, nanoscale imaging and cross-checking by multiple teams over many years. Such an endeavour is demanding, expensive and technically intricate, but it mirrors the stepwise approach that has characterised Mars exploration from the beginning: refine questions, test with better tools and reconsider conclusions as new data illuminate old landscapes.
