Ancient Mars was a warm and wet place, coursing with rivers and lakes. Though the lakebeds are now dusty and the water long gone, researchers have recently discovered evidence that the present-day Mars may not be as dry as we thought. The evidence suggests that a thin layer of salty liquid water may exist just under the Martian surface, condensing in the cool hours of night and evaporating in the morning.
Conditions on Mars are not favorable for liquid water — Martian temperatures and atmospheric pressures only allow water to exist as ice or vapor. However, the Curiosity rover recently detected a chemical compound in the Martian soil that could make it possible for water to exist in a liquid form.
The compound, called calcium perchlorate, lowers the freezing point of water, acting like an anti-freeze by allowing water to exist in a liquid state even under temperatures where it would normally form ice. Under particular humidity and temperature conditions, perchlorates can also absorb water vapor from the atmosphere, forming salty liquid solutions called brines that can then trickle down into the soil.
While perchlorates are abundant in many places on Mars, this is the first time they have been detected along with the right humidity and temperature for brines to form. Additionally, these conditions were detected at the equator — the driest and hottest region of Mars. If the delicate brine-forming conditions can exist even on the harshest region of the planet, it’s likely that milder regions can stably support brines as well.
The authors measured air humidity and temperature at the equator using Curiosity’s Rover Environmental Monitoring Station (REMS) over a Martian year. They describe the brines as “transient” because the proper humidity and temperatures for brine formation don’t last throughout a full Martian day. The salty solutions only have one night to condense before evaporating with the sunlight.
Liquid water is considered a crucial building block for life, but these brines are unlikely to harbor it — they are simultaneously too short-lived, too cold, and too exposed to solar radiation to support terrestrial organisms.
“Conditions near the surface of present-day Mars are hardly favorable for microbial life as we know it, but the possibility for liquid brines on Mars has wider implications for habitability and geological water-related processes,” says the lead author on the study, Javier Martin-Torres of the Spanish Research Council in Spain and Sweden’s Lulea University of Technology. He is also a member of Curiosity’s science team.
Though for now this finding seems to have few extraterrestrial implications, it is part of a collection of Curiosity’s discoveries that are transforming our perception of Mars. Last year, Curiosity measured sharp spikes and drops in atmospheric methane concentration, implying that somewhere on Mars is a source producing the organic chemical. Scientists have also observed dusty geysers of carbon dioxide erupting from the polar ice caps in the warming of spring. Mars is turning out to be a much more diverse and dynamic planet than we thought.