New observations by the MESSENGER spacecraft provide compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters.
Given its proximity to the Sun, Mercury would seem to be an unlikely place to find ice. But 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 and other frozen volatiles trapped at Mercury’s poles.
Images from the spacecraft’s Mercury Dual Imaging System taken in 2011 and earlier this year confirmed that radar-bright features at Mercury’s north and south poles are within shadowed regions on Mercury’s surface, findings that are consistent with the water-ice hypothesis.
Now the newest data from MESSENGER strongly indicate that water ice is the major constituent of Mercury’s north polar deposits, that ice is exposed at the surface in the coldest of those deposits, but that the ice is buried beneath an unusually dark material across most of the deposits, areas where temperatures are a bit too warm for ice to be stable at the surface itself. Read more
It has been estimated that there may be up to 1 trillion metric tons of water ice on Mercury. Scientist David Lawerence explains, how NASA’s MESENGER mission’s neutron spectroscopy data contributed to the find.