I took off for Lake Superior yesterday evening and walked out as far as I dared on its frozen surface. The ice was thick, maybe a foot or more, but the rumbling and booming coming from deep below gave me pause. The surface felt as firm and substantial as an airport tarmac, but it subtly flexed and heaved as if somehow alive.
Above it all rose the moon shining pale orange against the dusky band of Earth’s shadow. This part of the planet would soon be plunged into night but not without a bright beacon to help us find our way in the dark.
Glowing pale orange, the moon looked anything but icy, but we know that ice is hidden like buried treasure deep within craters in both its polar regions.
NASA’s orbiting Lunar Prospector, which could detect water up to 1.5 feet below the surface, found water signatures in permanently shadowed craters at both poles.
The moon’s orbit is tilted 5.14 degrees to Earth’s and its axis just 1.54 degrees for a total possible inclination of about 6.7 degrees, a tilt small enough that sunlight only skirts the uppermost rims of craters in the north and south polar regions.
The interiors of some craters, particularly in the south polar region, are sunk so deeply in the lunar crust (up to 7.5 miles or 12 km), that no sunbeam has ever broken the darkness.
Water from ice-rich meteoroids and comets that have smacked the poles over the aeons has hidden out here for billions of years trapped in rocks or existing as solid ice in some cases. Water released by impacts elsewhere on the moon would quickly vaporize away in the sunlight except for here and there molecules that migrated to the polar regions. Bombardment of oxygen-rich rocks by protons (hydrogen plus oxygen = H2O) in the solar winds creates small amounts of water as well.
While not wet by any stretch, our satellite’s no stranger to the substance our lives depend upon. As twilight deepened and the lake shuddered I sensed that ancient icy connection across a space of 240,000 miles.