A new study now reveals the extent of underground water on ancient Mars that was previously only predicted by models.
© European Space Agency
“Early Mars was a watery world, but as the planet’s climate changed this water retreated below the surface to form pools and ‘groundwater’,” says lead author Francesco Salese of Utrecht University, the Netherlands.
“We traced this water in our study, as its scale and role is a matter of debate, and we found the first geological evidence of a planet-wide groundwater system on Mars.”
Salese and colleagues explored 24 deep, enclosed craters in the northern hemisphere of Mars, with floors lying roughly 4000 m below martian ‘sea level’ (a level that, given the planet’s lack of seas, is arbitrarily defined on Mars based on elevation and atmospheric pressure).
They found features on the floors of these craters that could only have formed in the presence of water. Many craters contain multiple features, all at depths of 4000 to 4500 m – indicating that these craters once contained pools and flows of water that changed and receded over time.
Features include channels etched into crater walls, valleys carved out by sapping groundwater, dark, curved deltas thought to have formed as water levels rose and fell, ridged terraces within crater walls formed by standing water, and fan-shaped deposits of sediment associated with flowing water.
“We think that this ocean may have connected to a system of underground lakes that spread across the entire planet,” adds co-author Gian Gabriele Ori, director of the Università D’Annunzio’s International Research School of Planetary Sciences, Italy.
© European Space Agency
“These lakes would have existed around 3.5 billion years ago, so may have been contemporaries of a martian ocean.”
The history of water on Mars is a complex one, and is intricately linked to understanding whether or not life ever arose there – and, if so, where, when, and how it did so.
The team also spotted signs of minerals within five of the craters that are linked to the emergence of life on Earth: various clays, carbonates, and silicates. The finding adds weight to the idea that these basins on Mars may once have had the ingredients to host life. Moreover, they were the only basins deep enough to intersect with the water-saturated part of Mars’ crust for long periods of time, with evidence perhaps still buried in the sediments today.
“Findings like this are hugely important; they help us to identify the regions of Mars that are the most promising for finding signs of past life,” says Dmitri Titov, ESA’s Mars Express project scientist.
“It is especially exciting that a mission that has been so fruitful at the Red Planet, Mars Express, is now instrumental in helping future missions such as ExoMars explore the planet in a different way. It’s a great example of missions working together with great success.”