Not all of the water on Mars escaped into space billions of years ago as previously thought, but instead substantial amounts may still exist deep within the planet’s mid-crust.
This water is believed to be trapped within tiny cracks and pores in rocks 11.5km to 20km below the Martian surface, a study has revealed.
While the depth of this reservoir makes it difficult for future human colonies to access, the discovery offers significant clues about whether Mars once hosted life or if it still might today.
The findings, published in the Proceedings of the National Academy of Sciences journal on Monday, are based on seismic data from Nasa's Insight lander, which allowed researchers to estimate this groundwater could potentially cover the entire planet if spread out across its surface.
Historically, research has shown that water once flowed on Mars in the form of rivers billions of years ago but much of it was thought to have either escaped into space when the planet lost its atmosphere, or became trapped as ice beneath the surface, particularly in the polar regions.
Dr Gordon Osinski, a planetary geologist and professor at Western University in Ontario, Canada, who was not involved in the study, said the research was important in advancing our understanding of the geology of Mars.
“While many planetary scientists have suspected that the subsurface of Mars – just like Earth – would contain lots of groundwater, this is one of the best studies so far to support this idea,” he said.
"Some of Mars’ water still undoubtedly escaped into space but between the evidence for water ice in the polar caps and ground ice in the middle latitudes of Mars, this evidence for water at depth in the crust does suggest less water escaped."
Although this underground reservoir may not be immediately useful for future colonists due to its extreme depth, the study still provides valuable insights into Mars' geological history and the potential for life on the planet.
“The reservoir won’t be of much use to anyone trying to tap into it to supply a future Mars colony,” said UC Berkley in California, whose academics led the research.
"Even on Earth, drilling that deep would be a challenge."
Dr Dimitra Atri, a planetary scientist at New York University Abu Dhabi, expressed optimism over the implications of the study, suggesting that life on Mars could be a reality.
“I believe that not only did life exist in subsurface Mars a few billion years ago, there is a possibility that it still exists today in some form," he said.
"We need to send missions to these regions to look for subsurface samples. ESA’s [European Space Agency] ExoMars mission is such an effort, which is scheduled to launch in 2028."
The European project will aim to search for signs of past or present life on Mars by drilling beneath the planet's surface to collect and analyse soil samples.
It will focus on regions where liquid water might have been or is still present, offering the best chances of finding evidence of life.
It was delayed from its original launch date of 2020 due to Covid-19 and was pushed back again because of Russia's invasion of Ukraine – Russia had been the main partner in the mission.
After the ESA's fallout with Russia, it managed to save the mission through an agreement with Nasa, which states the agency will help find a launch vehicle for the rover for lift-off in 2028.
