(CNN) – Data from a retired NASA mission has revealed evidence of an underground reservoir of water deep beneath the surface of Mars, according to new research.
A team of scientists estimates there could be enough water trapped in tiny cracks and pores in the rock amid the Martian crust to fill oceans on the planet's surface. The groundwater would likely cover all of Mars down to a depth of 1.6 kilometers, according to the study.
The data comes from the NASA's InSight lander which used a seismometer to study the interior of Mars between 2018 and 2022.
Future astronauts exploring Mars would face a whole host of challenges if they tried to access the water, which is located between 11.5 and 20 kilometers below the surface, according to the study published Monday in the journal Proceedings of the National Academy of Sciences.
But the find reveals new details about Mars' geological history and suggests a new place to look for life on the Red Planet if water ever becomes accessible.
“Understanding the water cycle on Mars is critical to understanding the evolution of the climate, both on the surface and in the interior,” said Vashan Wright, an associate professor and geophysicist at the Scripps Institution of Oceanography at the University of California, San Diego, in a statement. “A useful starting point is to identify where there is water and how much there is.”
Mars was likely a warmer, wetter place billions of years ago, based on evidence from ancient lakes, river channels, deltas and water-altered rocks studied by other NASA missions and observed by orbiters. But the Red Planet lost its atmosphere more than 3 billion years ago, effectively ending Mars' wet period.
Scientists are still unsure why Mars lost its atmosphere, and a multitude of missions have been developed to learn about the planet's water history, where it went, and whether the water ever created habitable conditions for human life on Mars. While the water remains trapped as ice in the planet's polar ice caps, researchers don't think that can explain all of the planet's “lost” water.
Existing theories offer a few likely scenarios for what happened to Martian water after Mars lost its atmosphere: some hypothesize that it turned to ice or was lost to space, while others suggest it was incorporated into minerals beneath the planet's surface or seeped into deep aquifers.
New findings suggest that water on Mars seeped into the planet's crust.
InSight was a stationary lander, but it collected unprecedented data on the thickness of the Red Planet's crust and the temperature of its mantle, as well as the depth and composition of its core and atmosphere. The lander's seismometer detected the first earthquakes on the planet, known as marsquakes.
While earthquakes occur when tectonic plates shift, move and rub against each other, the Martian crust is like a giant plate with faults and fractures as the planet shrinks and cools over time. As the Martian crust stretches, it cracks. InSight's seismometer was able to detect more than 1,300 Marsquakes rumbling hundreds and thousands of miles away.
Scientists studying InSight data were able to study the speed of the quakes as they traveled across the planet, which can serve as an indicator of what substances exist beneath the Martian surface.
The speed of seismic waves depends on what the rock is made of, where it has cracks and what fills those cracks, Wright said.
The team used this data and fed it into a mathematical model of rock physics, which is used on Earth to map oil fields and underground aquifers.
The results showed that InSight's data best matched a deep layer of igneous or volcanic rock filled with liquid water.
“Establishing that there is a large reservoir of liquid water provides insight into what the climate was or might be like,” said study co-author Michael Manga, a professor of earth and planetary sciences at the University of California, Berkeley, in a statement.
“Water is necessary for life as we know it. I don’t see why (the underground reservoir) wouldn’t be a habitable environment,” Manga added. “It’s certainly the case on Earth: very deep mines harbour life, the ocean floor harbours life. We haven’t found any evidence of life on Mars, but we have at least identified a place that should, in principle, be capable of supporting life.”
If Mars' crust is similar across the planet, there may be more water within the midcrustal zone than the “volumes proposed to have filled hypothesized ancient Martian oceans,” the authors wrote in the study.
Rocks help capture information about a planet's history, and understanding a planet's water cycle can help researchers uncover the evolution of Mars, Wright said.
While analysis of the data cannot reveal any information about past or present life — if it ever existed — on Mars, it is possible that the wet Martian crust is habitable in the same way that deep groundwater on Earth is hospitable to microbial life, he said.
But even drilling holes just 1 kilometer or more deep into Earth is a challenge that requires energy and infrastructure, so a huge amount of resources would need to be brought to Mars to drill to such depths, Wright said.
The team was surprised to find no evidence to suggest the existence of a layer of frozen groundwater beneath Insight, since that part of the crust is cold. Researchers are still trying to determine why there is no frozen groundwater at shallower depths above the mid-crust.
The findings add a new piece to the Martian water puzzle.
The idea that liquid water may exist deep beneath the Martian surface has been around for decades, but this is the first time that real-world data from a Mars mission can confirm such speculation, said Alberto Fairén, a visiting interdisciplinary planetary scientist and astrobiologist in Cornell University's astronomy department. Fairén was not involved in the study.
He said the water is likely “some kind of deep underground mud.”
“These new results demonstrate that liquid water does indeed exist in the Martian subsurface today, not in the form of discrete, isolated lakes, but as liquid water-saturated sediments, or aquifers,” Fairén said. “On Earth, the subsurface biosphere is truly enormous and contains most of the prokaryotic diversity and biomass on our planet. Some research even points to an origin of life on Earth precisely in the depths of the subsurface. Therefore, the astrobiological implications of finally confirming the existence of liquid water habitats kilometers below the surface of Mars are truly exciting.”
The result is “exactly the kind of thing I was hoping we would get from InSight,” said Bruce Banerdt, the principal investigator for the InSight mission.
“I was hoping that we could get good enough data to do these kinds of studies where we actually look at details of the interior of Mars that are relevant to geological questions, questions about the habitability of Mars, questions about the evolution of Mars,” he said.
Banerdt, who was not involved in the research, said that while the interpretation of the data presented in the paper is strongly supported by good arguments, he also believes it is still somewhat speculative and that there is almost always another way to explain any data set.
“I was very impressed by the fact that Wright and his team incorporated mineral physics concepts to interpret seismic data,” Banerdt said.
Banerdt and Wright expressed interest in sending more seismometers to Mars and other planets and moons in our solar system in the future. While InSight's single seismometer collected crucial data, distributing them across Mars would reveal variations in the planet's interior and provide a broader view of its diverse and complex history, Banerdt said.
“Just as on Earth, where groundwater is connected to the surface through rivers and lakes, this was likely also the case on early Mars,” Wright said. “The groundwater we see is a record of that past.”
