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"We know that there's hundreds of billions of tons of water ice on the surface of the moon," Bridenstine said in a Reuters TV interview in Washington on Tuesday, a day after NASA unveiled its analysis of data collected from lunar orbit by a spacecraft from India.

The findings, published on Monday, mark the first time scientists have confirmed by direct observation the presence of water on the moon's surface - in hundreds of patches of ice deposited in the darkest and coldest reaches of its polar regions.

The discovery holds tantalizing implications for efforts to return humans to the moon for the first time in half a century. The presence of water offers a potentially valuable resource not only for drinking but for producing more rocket fuel and oxygen to breathe.

Bridenstine, a former US Navy fighter pilot and Oklahoma congressman tapped by President Donald Trump in April as NASA chief, spoke about "hundreds of billions of tons" of water ice that he said were now known to be available on the lunar surface.