Ice Water Discovered on Mercury: NASA

According to a NASA press release, the tilt of Mercury's rotational axis is almost zero, hence there are certain parts that have 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.

"For more than 20 years the jury has been deliberating on whether the planet closest to the Sun hosts abundant water ice in its permanently shadowed polar regions. MESSENGER has now supplied a unanimous affirmative verdict," said team member Sean Solomon in a NASA press release.

With the help of neutron spectroscopy, average hydrogen concentration was measured, which  is an indicator of water ice.

"The neutron data indicate that Mercury's radar-bright polar deposits contain, on average, a hydrogen-rich layer more than tens of centimeters thick beneath a surficial layer 10 to 20 centimeters thick that is less rich in hydrogen," David Lawrence, a Messenger scientist based at the Johns Hopkins University Applied Physics Laboratory was quoted in Huffington Post. "The buried layer has a hydrogen content consistent with nearly pure water ice."

The new findings reveal that both ice and organic material may have been deposited on Mercury's surface due to the impact of comets or asteroids. Over time, this volatile material could then have migrated to the planet's poles.

"We thought the most exciting finding could be that this really was water ice," said Maria Zuber, the E.A. Griswold Professor of Geophysics in MIT's Department of Earth, Atmospheric and Planetary Sciences, and a member of the research team to MIT News. "But the identification of darker, insulating material that may indicate complex organics makes the story even more thrilling."

Paul Lucey, a professor of geophysics and planetology at the University of Hawaii, points out that MESSENGER has also revealed a number of regions where surfaces were much darker than in previous radar measurements. Lucey interprets these results as possible evidence of receding ice on Mercury's surface.

"This suggests that in the past, ice was more extensive on Mercury, and retreated to its current state," says Lucey, who was not involved in the research. "Even Mercury experiences global warming."

MESSENGER will continue to orbit Mercury, and Zuber says future data may reveal information beyond the planet's surface. "There are still some really good questions to answer about the interior," Zuber says. "I'll tell you, we're not done."