The Closest Ice to the Sun

MercuryNorthPoleOK, Mercury isn’t a likely spot for the Winter Olympics. But new data from the Mercury orbiting MESSENGER spacecraft indicate that it has a substantial amount of water ice in permanently shadowed regions found in craters near its north pole. The idea that ice might be found on Mercury has been around for years. For many years, it was thought that one side of the planet was always pointed away from the sun and, thus, very cold. More recently, it was found that the planet slowly rotated, ending that speculation. Then, radar observations of Mercury showed bright, hence highly reflective, regions near the north pole. Those areas are marked in yellow in this map derived from MESSENGER images. The radar bright regions correspond with floors and walls of north polar impact craters. Farther from the pole the regions are mostly on the north facing crater walls. MESSENGER‘s neutron spectroscopy and thermal models for the craters indicate material in these regions has a hydrogen content consistent with nearly pure water ice and is trapped in an area with temperatures that remain below 100 K (-280 °F, -173 °C). Comet impacts are thought to be the source of the ice on Mercury.

Image Credit: NASA