London, March 14 : Nasa's Mars Reconnaissance Orbiter (MRO) spacecraft has detected what might possibly be large volumes of water ice below mid-northern latitudes on the surface of the Red Planet.
Discovered by the Sharad (SHAllow RADar) radar experiment, the ice has been found in distinctive geological structures on Mars' surface that are hundreds of metres thick.
Sharad is able to probe up to 1 km beneath the Martian surface to seek out liquid or surface water.
It sends out pulses of radio waves to the Martian surface and analyses the time delay and strength of the waves that return.
Analysis of those waves that penetrate the soil and bounce back can give information on transitions between materials with different properties, such as rock and liquid water, beneath the Martian surface.
According to a report in BBC, mission scientists used Sharad to probe Martian surface features known as lobate debris aprons (LDAs). These distinctive, dome-shaped structures are concentrated around mid-latitudes in the planet's northern and southern hemispheres.
The researchers looked at LDAs in the Deuteronilus Mensae region of Mars' northern hemisphere, where the features can be found at the bases of valley walls, craters and scarps of mesas.
Scientists have long suspected that LDAs were flows consisting of mixed up rock and ice.
The radar penetrated these geological features with very little attenuation (reduction in signal strength), suggesting they were predominantly made of ice.
"We would say, robustly, more than 50% ice by volume - but it could be much more," said Jeff Plaut, the chief scientist for Sharad.
According to scientists, these features probably formed in mid- to late Amazonian times - the Amazonian being the cold, dry period of Martian history which began around 1.8 billion years ago and lasts to the present day.
"In the mid-latitudes of Mars, there were large volumes of ice that were deforming, at least, during Amazonian times. And much of this ice is preserved today," said Dr Plaut, from Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California.
If confirmed, the discovery could have important implications for the history of water and climate on Mars, because it suggests there were large reservoirs of subsurface ice when the lobate debris aprons formed.