London, Sept 21: Lava flow could have covered features on Mars that appear to have experienced catastrophic flooding, and this could make future landing missions for search of past water on the Red Planet more troublesome, according to a new NASA study.

The results follow the detailed examination for more than three months by the agency’s Mars Reconnaissance Orbiter of the valley system called Athabasca Valles, which has long been interpreted as having been carved out by sudden, catastrophic flooding.

The new high-resolution images, however, show that the entire region is covered by a few metres of lava.

Team member Alfred McEwen of the University of Arizona in Tucson, US, said though he believed the valley system was created by flowing water; future robotic missions to Mars will probably not be able to investigate the water's effects on the surface there.

Other MRO observations also suggest it will be difficult to interpret the role of water on the Martian surface in the past.

McEwen said, the planet's extremely flat northern plains, interpreted by many as the remaining basin of an ancient ocean, did not seem to be covered by a deep layer of fine sediments as some had thought.

Instead, it is strewn by large boulders, which according to one theoretical model should have been buried under layers of sediment long ago if the ocean had been deep, long-lived and turbulent, he said.

McEwen however, said the model could be wrong and that it was still possible that an ocean once covered the region.

“There are lots of other concepts of Mars oceans and how they formed. Who knows how much evidence of oceans is buried under lava?” said McEwen.

Maria Zuber at MIT in Cambridge, US, said there was still “plenty of evidence” that water played a role in the planet's past and that large quantities of it remained in the poles and frozen in the ground.

She said the new observations had just suggested that in some places, “whatever was there has been covered up by volcanism”.

The study appears in the current issue of the journal Science, reports New Scientist. (With inputs from ANI)