For most of us amateur science followers, Mercury is probably the very last place we would think to look for water or ice. The closest planet to our sun orbits at distances between 28.5 million miles and 43.5 million miles, and the side of the planet facing the sun at any time can get up to 430 °C, hot enough to melt lead. However, the dark side of the planet can drop to -163 °C, and because the planet rotates in a manner perpendicular to its orbit around the Sun, parts of its poles are forever in shadow, allowing for persistent, extreme cold. It’s in those polar cold regions, specifically inside some of the region’s craters, that NASA’s MESSENGER probe (MErcury Surface, Space ENvironment, GEochemistry and Ranging) has found evidence of water ice…and lots of it.
According to Nature, scientists are estimating that there could be a trillion tons of water ice inside the craters. Aside from the counter-intuitive thought of finding ice on the planet closest to the Sun, scientists believe these polar icy patches could be excellent places to search for materials left over from asteroid or comet impacts with the planet. These materials wouldn’t have to impact in one of the cold spots; over time, the components of a wayward comet could have vaporized and then rained back down as a liquid, over and over, until they eventually landed in one of the cold craters and remained trapped there in the form of ice.
Scientists have theorized for a while now that Mercury’s poles could contain water ice, and this new evidence confirms that line of thinking. First, MESSENGER’s Mercury Laser Altimeter spotted “bright regions” in the craters near the planet’s north pole, and these bright areas are all located in spots that should never warm above -170 °C. Another research team, using MESSENGER’s Neutron Spectrometer, has found evidence of hydrogen, believed to be frozen in the form of water ice. David Lawrence, a planetary scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, says, “Not only is water the best explanation, we do not see any other explanation that can tie all the data together.”
There you have it, folks. Next time somebody tells you, “not until Hell freezes over,” just drop Hell into a crater on Mercury.