Several oceans' worth of ancient water could be stored in minerals buried under Mars' surface, according to a new study published in the journal Science.
This represents a significant pivot in our understanding of the Red Planet's evolution to its current state — and hints at where we might find water (and possibly, life itself) during future missions to Mars.
Mars lost oceans' worth of water to crustal hydration, not space
The new study involved observational data and modeling, and suggests much of Mars' water — up to 99% — was lost due to an irreversible process of crustal hydration. This runs contrary to previous suspicions that the Red Planet lost most of its water to space, and helps resolve apparent contradicting accounts between the planet's predicted atmospheric loss rates, and the deuterium to hydrogen ratio (D/H) of contemporary conditions on Mars.
Additionally, this expands geological estimates regarding the scope of water coverage across ancient Mars.
The Red Planet was wet. Relic shorelines and dry riverbeds serve as signatures of a time when colossal volumes of liquid water gushed across the surface. But today, very little of these ancient oceans remain — with water deposits largely frozen in the planet's ice caps.
Earlier studies typically assumed the water was lost to space over the course of several billion years — an idea based on current observations of the D/H ratio. But measurements of present-day atmospheric water loss are far too low for the atmospheric escape hypothesis to explain the loss of so much water on Mars.
Eva Scheller and colleagues involved in the study showed how large volumes of water might have become absorbed into minerals buried deep in the planet's crust. The team used observational constraints via spacecraft in orbit of Mars — along with rovers and Martian meteorites — to build a water budget and D/H model accounting for an updated balance of atmospheric escape, volcanic degassing, and crustal hydration via chemical weathering.
The team simulated loss of water on Mars over geological time and for a wide scope of plausible conditions — and found that Mars lost between 40% to 95% of its water during the Noachian period (which was roughly 4.1 to 3.7 billion years ago).
The final results of the study show how between 30% and 99% of Mars' initial water was absorbed into minerals and buried in Mars' crust. The remaining water likely escaped to space, and accounts for the currently observed D/H ratio.
Oceans of water may not support signs of life, but it could enable human settlements
This could mean life — or at least signs of it — found a way to persist beneath Mars' surface, but the likelihood might be smaller than we expect. A study from September 2020 found that acidic fluids once flowed across the Red Planet and might have destroyed biological evidence.
The 2020 study involved simulations with clay and amino acids. "We know that acidic fluids flowed on the surface of Mars in the past, altering the clays and its capacity to protect organics," said Alberto G. Fairén — who was a corresponding author of the paper — in a Phy.org report.
However, this doesn't mean there won't be life on Mars. Several national space agencies and private aerospace companies — including NASA and SpaceX — plan to put humans on Mars in the near future. And, once there, we may find a way to extract the oceans' worth of water to support all life we see fit to deposit on it.
This was a breaking story and was regularly updated as new information became available.