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NASA announced that its Messenger probe has discovered new evidence of water ice on the polar regions of Mercury, the closest planet to the sun.

The ice is found predominantly in impact craters, according to data obtained by Messenger.

In the announcement, NASA said the probe had uncovered new evidence that deposits in permanently shadowed regions of Mercury’s poles is water ice.

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According to a NASA, the tilt of Mercury’s rotational axis is almost zero – less than one degree – so there are pockets at the planet’s poles that never see sunlight.

Scientists suggested decades ago that there might be water ice at Mercury’s poles, but the new findings provide”compelling support” for that claim.

Messenger used neutron spectroscopy to measure hydrogen concentrations, an indicator of water ice.

David Lawrence, a Messenger scientist at the Johns Hopkins Univ. Applied Physics Laboratory, said:

“The neutron data indicate that Mercury’s radar-bright polar deposits contain, on average, a hydrogen-rich layer tens of centimeters thick beneath a surficial layer 10-20 centimeters thick that is less rich in hydrogen.”

“The buried layer has a hydrogen content consistent with nearly pure water ice.”

Launched in August 2004, the robotic spacecraft conducted three flybys of Mercury in 2008 and 2009 before entering the planet’s orbit in March 2011.

The probe has collected more than 100,000 images of Mercury.