In a press release
, NASA writes about the MESSENGER craft finding "reflectance of Mercury's polar deposits at near-infrared wavelengths with the Mercury Laser Altimeter (MLA), and the first detailed models of the surface and near-surface temperatures of Mercury's north polar region."
The latest data
from MESSENGER indicate that water ice is the major ingredient 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."
It's a remarkable finding because Mercury is so close to the sun and ice is rarely found on planets with such proximity to the heat source. Area of the planet's poles never see sunlight.
NASA states water-ice concentrations are taken from the hydrogen measurements. "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 superficial layer 10 to 20 centimeters thick that is less rich in hydrogen," writes
David Lawrence, a MESSENGER Participating Scientist based at The Johns Hopkins University Applied Physics Laboratory and the lead author of one of the papers. "The buried layer has a hydrogen content consistent with nearly pure water ice."
Paul Lucey, a professor of geophysics and planetology at the University of Hawaii, points out
that MESSENGER has also revealed a number of areas where surfaces were much darker than in previous radar measurements. Lucey interprets these results as possible evidence of receding ice on Mercury’s surface.
Questions about water ice on Mercury dates back more than 20 years, this report writes
In 1991, astronomers fired radar signals to Mercury and received results showing there could be ice at both poles. "This was reinforced by 1999 measurements using the more powerful Arecibo Observatorymicrowave beam in Puerto Rico. Radar pictures beamed back to New Mexico's Very Large Array showed white areas that researchers suspected was water ice."