NASA announced Thursday that its Messenger probe has discovered new evidence of water ice on Mercury.

In the announcement, Sean Solomon, principal investigator for the Mercury Messenger program, said the probe had uncovered new evidence that deposits in permanently shadowed regions of Mercury's poles is water ice. The ice is found predominantly in impact craters, according to data obtained by Messenger.

According to a NASA press release, 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 average hydrogen concentrations, 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,” wrote David Lawrence, a Messenger scientist based at the Johns Hopkins University Applied Physics Laboratory. “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, some of which are viewable on NASA's website.

Messenger, an acronym of MErcury Surface, Space ENvironment, GEochemistry and Ranging, has already changed the way scientists think about the planet closest to the sun.

In 2011, data sent back by the probe provided new evidence of widespread volcanic activity on the planet's surface, including a huge expanse of volcanic plains surrounding the north polar region of Mercury. According to NASA, continuous smooth plains cover more than 6 percent of the total surface of the planet.

Other MESSENGER mission objectives include studying the nature of Mercury's magnetic fields, the structure of its core, its geologic history and the composition of its exosphere.

Prior to Messenger's mission, only the Mariner 10 probe had successfully visited the planet. The findings of the three Mariner 10 flybys in 1974 and 1975 for years constituted the bulk of what was known about Mercury.



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  • North Polar Region

    A portion of the Arecibo radar image of Mercury's north polar region. Near-surface water ice deposits are shown in bright colors.

  • Mercury's North Polar Region

    Mercury’s north polar region if it was viewed by a neutron spectrometer with perfect focus. Measurements over radar-bright regions that consist of pure water ice would show fewer neutrons per time interval than elsewhere.

  • Water Ice On Mercury

    A diagram from NASA showing what the layer of water ice might look like on Mercury and how it was found.

  • Thermal Model For Water Ice

    The grey areas are regions that are too warm at all depths for stable water ice. The colored regions are sufficiently cold for subsurface ice to be stable, and the white regions are sufficiently cold exposed surface ice to be stable.

  • Where Water Is Predicted

    Map of MLA reflectivity showing isolated areas of brighter and darker reflectance in areas of permanently shadow. Many of the brighter areas detected by MLA (as indicated by the arrows) are in unusually cold regions where surface water ice is predicted.

  • Neutron Spectrometer

    High-speed MESSENGER Neutron Spectrometer measurements of the flux of high-speed neutrons versus latitude shown in red. High-speed neutrons suggest the water ice is buried.

  • Water-Rich Asteroid Impact

    How scientists believe water got to Mercury: A comet or water-rich asteroid that also contains organic compounds impacts Mercury.

  • What Happened Next

    Scientists believe that water and organic compounds were spread over a wide geographic region, and a small fraction of both compounds migrate to the poles where they can become cold-trapped as ices.

  • Maximum Surface Temperature

    Map of the maximum surface temperature reached over a two-year period over the north polar region of Mercury. This detailed thermal map of Mercury, and others show that Mercury displays the most extreme range of surface temperatures of any body in the solar system.