Mars, a planet known for its cold, dry, barren landscape, presents a stark contrast to Earth’s vibrant, water-rich environment. This prompts a thought experiment: what would Mars be like if it possessed abundant liquid water on its surface today? Exploring this hypothetical scenario offers insights into the planet’s past, present state, and the conditions that shape planetary habitability.
Mars’s Ancient Oceans
Scientific evidence indicates Mars was once a different world, hosting vast amounts of surface liquid water billions of years ago. Geological features across the Martian landscape suggest the widespread presence of oceans, rivers, and lakes. Networks of ancient river valleys and delta formations provide testimony to persistent water flow and sediment deposition.
Mineralogical findings support this watery past. The detection of hydrated minerals, such as phyllosilicates and sulfates, confirms that rocks interacted with liquid water for extended periods. Research indicates a large northern ocean likely covered nearly a third of the planet’s surface, reaching depths of up to a mile around 3.5 to 4.1 billion years ago. This period of abundant water suggests a warmer, denser atmosphere, allowing liquid water to remain stable on the surface for millions of years.
The Mystery of Mars’s Disappearing Water
The transition from a water-rich world to the arid planet seen today involved atmospheric and geological changes. A primary factor in Mars’s water loss was the weakening and diminishing of its magnetic field. Without a protective global magnetic field, the solar wind, a stream of charged particles from the Sun, was able to directly interact with and strip away Mars’s atmosphere.
This atmospheric stripping led to the escape of atmospheric gases, including water molecules, into space. As the atmosphere thinned, the planet’s surface pressure dropped, preventing liquid water from remaining stable on the surface. Any remaining water either evaporated into the tenuous atmosphere or froze into subsurface ice deposits. The planet’s smaller size and lower gravity also contributed to its inability to retain a thick atmosphere over geological timescales.
Water on Mars Today
Despite its current aridity, Mars still harbors water, primarily in frozen forms. The planet’s polar ice caps contain quantities of water ice, mixed with layers of frozen carbon dioxide, or dry ice. The northern polar cap alone holds approximately 1.6 million cubic kilometers of ice, enough to cover the entire planet to a depth of about 2 kilometers if spread evenly.
Beyond the poles, subsurface ice deposits exist, particularly at higher latitudes, forming a permafrost layer. Over 5 million cubic kilometers of ice have been identified at or near the surface. Trace amounts of water vapor are also present in the thin Martian atmosphere, varying with season and latitude. While temporary flows of briny water have been observed on slopes during warmer seasons, stable liquid water cannot persist on the surface due to the low atmospheric pressure and frigid temperatures.
Imagining a Water-Rich Mars
A hypothetical Mars with abundant liquid surface water today would be a transformed world. The presence of oceans and interconnected waterways would necessitate a denser atmosphere, likely rich in greenhouse gases, to sustain temperatures above water’s freezing point. This thicker atmosphere would create a warmer, more humid climate, enabling a hydrological cycle. Evaporation from oceans would lead to cloud cover and precipitation, replenishing rivers and lakes.
Active hydrological processes would reshape the Martian landscape, leading to erosion and the formation of new geological features. River systems would carve networks, deltas would expand, and sedimentary basins would accumulate layers of material, much like on early Earth. Weather patterns would become complex, with potential for storms, winds, and even a global ocean circulation system, influencing thermal distribution across the planet. The presence of liquid water would also moderate daily and seasonal temperature swings, creating a more stable environment.
Such a water-rich Mars would increase the potential for life to emerge or thrive. On Earth, life originated in oceans, and the sustained presence of liquid water is considered a requirement for known life forms. A “blue Mars” with a stable, warm, and wet environment would provide diverse habitats, from shallow coastal regions to deep ocean floors, fostering microbial ecosystems. If life had evolved during Mars’s ancient wet period, a return to water-rich conditions could allow any surviving subsurface life to flourish and diversify, leading to macroscopic forms over long evolutionary timescales. This imagined world underscores the role of water in shaping planetary environments and influencing the prospects for life beyond Earth.