Scientists using a high-resolution camera attached to NASA's Mars Reconnaissance Orbiter have found ice within newly formed Martian craters, about halfway between the north pole and the equator of the Red planet.

"We knew there was ice below the surface at high latitudes of Mars, but we find that it extends far closer to the equator than you would think, based on Mars' climate today," said Shane Byrne of the University of Arizona, a member of the High Resolution Imaging Science Experiment (HiRISE).

The HiRISE researchers running the orbiter's high-resolution camera said the water ice found within the new meteorite impact craters was surprisingly pure.

"The thinking before was that... there would be a 50-50 mix of dirt and ice," said Byrne. "The mixture is about one percent dirt and 99 percent ice."

Byrne and 17 co-authors report the findings in the September 25 edition of the journal Science.

Scientists used several instruments on the Mars Reconnaissance Orbiter, or MRO, in quick succession to detect and confirm that there is highly pure, bright ice exposed in new craters, ranging from about 45 centimetres to two and a half metres deep, at five different Martian sites.

When they peered into several impact craters, Byrne said, scientists saw "this bright blue material poking up from the bottom of the crater. It looked a lot like water ice.

"Sure enough, when we started monitoring this material, it faded away like you'd expect water ice to fade, because water ice is unstable on Mars' surface and turns directly into water vapor in the atmosphere."

Consequently, he said he said "all of this had to happen very quickly because 200 days after we first saw the ice, it was gone.

"If we had taken HiRISE images just a few months later, we wouldn't have noticed anything unusual. This discovery would have just passed us by."

Byrne added that the ice "is a relic of a more humid climate not very long ago, perhaps just several thousand years ago."