New Evidence for Water Ice on Mercury!
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.
Three independent lines of evidence support this conclusion: the first measurements of excess hydrogen at Mercury’s north pole with MESSENGER’s Neutron Spectrometer, the first measurements of the 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 regions that utilize the actual topography of Mercury’s surface measured by MLA. These findings are presented in three papers published online in Science Express [HERE].
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 MESSENGER’s Mercury Dual Imaging System taken in 2011 and early 2012 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.
According to David Paige from the University of California, Los Angeles, a lead author of one of the three new papers, the dark material is likely a mix of complex organic compounds delivered to Mercury by the impacts of comets and volatile-rich asteroids, the same objects that likely delivered water to the innermost planet. The organic material may have been darkened further by exposure to the harsh radiation at Mercury’s surface, even in permanently shadowed areas.
This dark insulating material is a new wrinkle to the story, says Sean Solomon of the Columbia University’s Lamont-Doherty Earth Observatory, principal investigator of the MESSENGER mission. "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."
"But the new observations have also raised new questions," adds Solomon. "Do the dark materials in the polar deposits consist mostly of organic compounds? What kind of chemical reactions has that material experienced? Are there any regions on or within Mercury that might have both liquid water and organic compounds? Only with the continued exploration of Mercury can we hope to make progress on these new questions." [Learn more about this amazing discovery HERE]
Explore Mercury in Google Earth:
- New! Take a tour of some of the latest research findings on Mercury with a MESSENGER mission scientist as your guide! [Guided tours of Mercury in Google Earth]
- New! Do you have Google Earth? Would you like to explore Mercury on that platform? Try it here! Use these simple instructions.
About the MESSENGER Education and Public Outreach website
In developing this site, educators, scientists, and engineers are working together to bring the exciting science of MESSENGER to everyone. Here you will find a wealth of resources about the planet Mercury and about the MESSENGER mission. If you are a student or teacher make sure you check out the special sections containing educational materials and opportunities.
The MESSENGER Education and Public Outreach Team
The MESSENGER education and public outreach program is conducted by a dedicated team of individuals and organizations with a long track record in space science education in both formal (classroom) and informal (museum and science center) settings. Read about the partner organizations here and meet the team that makes it all happen here.