MESSENGER spacecraft spots recent ice deposits on Mercury

NASA's Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) spacecraft has provided the first optical images of ice and other frozen volatile materials within permanently shadowed craters near Mercury's North Pole.

The MESSENGER's first extended mission in 2012, scientists launched an imaging campaign with the broadband clear filter of MDIS's wide-angle camera (WAC) images revealed the morphology of the frozen volatiles, and also provided insight into when the ices were trapped and how they've evolved.

After zeroing in on Prokofiev, the largest crater in Mercury's North Polar Region, scientists found the images showed extensive regions with distinctive reflectance properties. A location interpreted as hosting widespread surface water ice exhibited a cratered texture indicating that the ice was emplaced more recently than any of the underlying craters.

In other areas, water ice is covered by a thin layer of dark material inferred to consist of frozen organic-rich compounds and the dark deposits display sharp boundaries. Sharp boundaries indicate that the volatile deposits at Mercury's poles are geologically young, relative to the time scale for lateral mixing by impacts.

Although the polar deposits are in permanent shadow, through many refinements in the imaging, the WAC was able to obtain images of the surfaces of the deposits by leveraging very low levels of light scattered from illuminated crater walls.

Lead author Nancy Chabot suggested that understanding the age of these deposits has implications for understanding the delivery of water to all the terrestrial planets, including Earth.

Overall, the images indicate that Mercury's polar deposits either were delivered to the planet recently or are regularly restored at the surface through an ongoing process and also reveal a noteworthy distinction between the Moon and Mercury, one that may shed additional light on the age of the frozen deposits.

Chabot also added that if one could understand why one body looks one way and another looks different, they gain insight into the process that's behind it, which in turn is tied to the age and distribution of water ice in the solar system. This will be a very interesting line of inquiry going forward.

The study was published in journal Geology.