An announcement by NASA in 2015 that liquid water had been found on Mars was premature, according to new research.

At a news conference that year, NASA's director of planetary science declared: "Liquid water has been found on Mars."

Scientists reasoned that water must be present on the red planet to explain mysterious darkish streaks that appeared to ebb and flow with the seasons.

However, while there is water on Mars - existing on the polar caps, ground ice, as well as in frosts and hydrated minerals - the evidence suggesting larger volumes of liquid water is ambiguous, according to researchers from the US Geological Survey.

In a new paper published in Nature Geoscience, they claim that Recurring Slope Lineae (RSL) in Eos Chasma, a deep depression on the planet, are "inconsistent with models for water sources".


Image: This HiRISE image cutout shows RSL on Mars in enhanced colour. Pic: NASA/JPL/University of Arizona/USGS

The researchers - working in cooperation with the NASA Mars Reconnaissance Orbiter Project - found that the RSL were instead "identical to the slopes of sand dunes where movement is caused by dry granular flows".

"Water almost certainly is not responsible for this behaviour, which would require the volume of liquid to correspond to the length of slope available, producing more liquid on longer slopes.

"Instead, the 151 RSL examined by the study authors all end on similar slopes despite very different lengths."