Washington, D.C. — Oceanic crust covers two-thirds of the Earth’s solid surface, but scientists still don’t entirely understand the process by which it is made. Analysis of more than 600 samples of oceanic crust by a team including Carnegie’s Frances Jenner reveals a systemic pattern that alters long-held beliefs about how this process works, explaining a crucial step in understanding Earth’s geological deep processes. Their work is published inNature on November 29.

Data collected by the MESSENGER spacecraft confirms that water ice is present at Mercury’s poles.

Although much of Mercury’s surface reaches very high daytime temperatures due to the planet’s close distance to the Sun, there are portions of impact craters in the polar regions of Mercury that are never exposed to direct sunlight and thus remain cold over geological timescales. Ground-based radar observations in 1991 suggested that these permanently shadowed craters contain deposits of material with radar-scattering properties consistent with water ice.

Three pieces of evidence from the MESSENGER spacecraft, in orbit around Mercury since March 2011, confirm the presence of water ice in permanently shadowed polar craters on Mercury. The first is the high levels of hydrogen at the poles, evident from data acquired by MESSENGER’s Neutron Spectrometer (NS). The second is data from the Mercury Laser Altimeter (MLA) instrument that reveal irregular dark and bright deposits at near-infrared wavelength corresponding to the deposits observed before by radar. Third, the first detailed models of the surface and near-surface temperatures of Mercury’s north polar regions, based on MESSENGER-derived topography, show that the deposits correspond to regions where water ice is thermally stable. All three pieces of data lead to the conclusion that water ice is abundant on the planet closest to the Sun. The dark materials indicated by MLA data most likely represent organic-rich material overlaying the water ice in some places. Both the water and the organics were likely delivered to the surface of Mercury through the impact of volatile rich comets or asteroids. Only with the continued exploration of Mercury can we hope to make progress on these new questions.”