Researchers from two U.S. universities have found layers of ice buried one mile (1.6 kilometers) beneath Mars' north pole are remnants of ancient polar ice sheets.

The study published on Wednesday in the journal Geophysical Research Letters showed that those layers could be one of the largest water reservoirs on the planet.

Scientists at the University of Texas at Austin and the University of Arizona used data from a radar on NASA's Mars Reconnaissance Orbiter that can penetrate up to about 2.4 kilometers beneath the surface of Mars.

They found layers of sand and ice that were as much as 90 percent water in some places and if melted, the newly discovered polar ice would be equivalent to a global layer of water around Mars at least 1.5 meters deep.

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, so the findings could reveal whether climate conditions were previously favorable for life, according to the researchers.

Another paper published on Wednesday in Geophysical Research Letters confirmed the findings. The independent study led by Johns Hopkins University scientists used gravity data to measure the water volume beneath.

The researchers suggested that 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, according to the study.

(Cover: Layers of ice buried 1.6 kilometers beneath Mars' north pole are remnants of ancient polar ice sheets, said researchers. /VCG Photo)