Scientists have discovered one of the largest water reservoirs on Mars, in the form of ice layers buried over a kilometre beneath the surface, a finding that may reveal whether the Red Planet was habitable in the past.
The team from The University of Texas at Austin and the University of Arizona in the US estimate that if melted, the massive ice deposits discovered in this region would cover the planet in 1.5 metres of water.
Researchers made the discovery using measurements gathered by the Shallow Radar (SHARAD) on NASA's Mars Reconnaissance Orbiter (MRO). SHARAD emits radar waves that can penetrate up to a mile and a half beneath the surface of Mars.
The findings, published in the journal Geophysical Research Letters, are important because the layers of ice are a record of past climate on Mars in much the same way that tree rings are a record of past climate on Earth.
Studying the geometry and composition of these layers could tell scientists whether climate conditions were previously favourable for life, researchers said.
The team found layers of sand and ice that were as much as 90 per cent water in some places.
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"We didn't expect to find this much water ice here. That likely makes it the third largest water reservoir on Mars after the polar ice caps," said Stefano Nerozzi, a graduate research assistant at the University of Texas.
According to the researchers the layers formed when ice accumulated at the poles during past ice ages on Mars.
Each time the planet warmed, a remnant of the ice caps became covered by sand, which protected the ice from solar radiation and prevented it from dissipating into the atmosphere.
Until now, scientists thought that the ancient ice caps were lost. The research shows that in fact significant ice sheet remnants have survived under the planet's surface, trapped in alternating bands of ice and sand, like layers on a cake.
The study provides new, important insights into the exchange of water ice between the poles and the midlatitudes, where his research group previously confirmed the presence of widespread glaciers, also using the SHARAD instrument.
"Surprisingly, the total volume of water locked up in these buried polar deposits is roughly the same as all the water ice known to exist in glaciers and buried ice layers at lower latitudes on Mars, and they are approximately the same age," said Jack Holt, a professor at the Lunar & Planetary Laboratory of the University of Arizona.
Nerozzi said that studying this record of past polar glaciation could help determine whether Mars was ever habitable.
"Understanding how much water was available globally versus what's trapped in the poles is important if you're going to have liquid water on Mars," Nerozzi said.
"You can have all the right conditions for life, but if most of the water is locked up at the poles, then it becomes difficult to have sufficient amounts of liquid water near the equator," he said.