Liquid water is one of the fundamental ingredients for life as we know it.
Is Mars hiding liquid water, or is it just a desert of cold, dry dust? For decades, scientists have searched for evidence of liquid water on the red planet, with promising yet inconclusive clues emerging. However, a new study challenges some of the key arguments for liquid water on Mars, pointing to significant obstacles that make its presence unlikely—at least for now.
Over a century ago, astronomer Percival Lowell famously claimed he saw canals on Mars, which he believed were built by intelligent Martians to transport water. While modern telescopes quickly disproved Lowell’s theory, the fascination with water on Mars never disappeared.
Liquid water is one of the fundamental ingredients for life as we know it. Yet, the conditions on Mars—freezing temperatures, thin atmosphere, and low water vapor pressure—make it extremely difficult for water to remain in a liquid state. Any water found would either freeze, evaporate, or boil almost instantly. Despite these challenges, researchers have remained hopeful, especially following the discovery of mysterious features known as recurring slope lineae (RSLs).
RSLs are dark streaks that appear on steep slopes, growing during warmer seasons and fading in colder ones. This behavior is reminiscent of water seeping through soil. Other evidence, such as polygonal patterns in the Martian permafrost and the presence of salts, led scientists to explore the idea of liquid brines—salty water that can stay liquid at extremely low temperatures.
However, a new paper published in the Proceedings of the National Academy of Sciences casts doubt on these possibilities.
New Evidence Points to Dry Conditions
The study, titled “The Elusive Nature of Martian Liquid Brines,” was authored by Vincent Chevrier, a planetary scientist at the University of Arkansas, and Rachel Slank, a researcher at the Lunar and Planetary Institute. Both authors have spent years analyzing Mars’ environment and potential water sources.
Their research suggests that RSLs are most likely caused by dry sand and dust flows, rather than liquid water. Despite their seasonal changes, no definitive evidence links RSLs to water. Similarly, the presence of salty brines, while promising, faces significant challenges. Brines can remain liquid at lower temperatures than pure water, thanks to salts like perchlorates—a common Martian compound. Calcium perchlorate, for instance, can stay liquid at temperatures as low as -75°C. Since Martian equatorial temperatures average around -50°C, some believed liquid brines could exist beneath the surface.
Yet Chevrier and Slank argue that the conditions for brines are too limited. There simply isn’t enough water vapor, and the required salts are not abundant enough on the surface or shallow subsurface to support stable liquid water. Even if small amounts of brines did form, they would be uninhabitable for most known organisms.
What Does This Mean for the Search for Life?
The study acknowledges that there is still a slim chance of finding life adapted to Martian brines. Some Earth organisms, known as extremophiles, can survive in highly salty, freezing environments. If similar adaptations exist on Mars, these brines could theoretically support microscopic life.
However, detecting such brines remains a major technological challenge. Current instruments lack the precision to identify small pockets of liquid water. The authors emphasize the need for advanced tools and better strategies to pinpoint the best locations for exploration. Laboratory experiments simulating Martian conditions will also play a critical role in understanding how brines might behave on the planet.
As Chevrier concludes, “Despite our best efforts to prove otherwise, Mars still remains a cold, dry and utterly uninhabitable desert.” While this new research may feel like a setback, it also sets the stage for more targeted exploration, helping scientists refine their search for one of the universe’s most elusive resources.
