More water ice could be hiding at the dark poles of Mercury and the Moon
Earth's poles are famously icy places, but they're far from alone in that regard. The poles of other planets and moons are often the best places to look for ice, and now a new analysis of NASA data has found evidence of much more water ice on the Moon and Mercury than previously thought.
The Moon may be drier than any desert on Earth, but that's not to say there's no water at all. Most of it is probably locked away in hydrated minerals deep underground, and what there is on the surface would take the form of ice.
Mercury, meanwhile, might not be on most people's short list for surface ice, with its proximity to the Sun raising daytime temperatures to a sweltering 427° C (801° F). But thanks to its lack of a serious atmosphere, that heat vanishes pretty quickly at night, with the mercury (pun intended) plummeting to -173° C (-279° F). That's plenty cold enough for ice to gather.
And now, a new analysis has shown that there is in fact ice at both poles of Mercury and the south pole of the Moon. That's because in both cases, these regions never actually see any sunlight, staying perpetually cold and dark, allowing thick glacier-like sheets of ice to form at the bottom of the craters that pock the surface.
Previous studies have found hints of this ice before. After Earth-based instruments noticed reflective patches at the poles of Mercury, the MESSENGER probe in orbit around the tiny planet confirmed the presence of water ice using data from its laser altimeter. On the Moon, smaller patches were spotted and analyzed by the Indian Space Research Organization's Chandrayaan-1 lunar orbiter.
Now, a team from the University of California Los Angeles (UCLA) has analyzed data from MESSENGER and the Lunar Reconnaissance Orbiter (LRO) and found new evidence of even more ice in craters in those locations than previously thought.
The team started by analyzing around 15,000 simple craters, which are depressions measuring between 2.5 and 15 km (1.5 and 9.3 mi) wide, made by small impacting objects. Using elevation data gathered by the two orbiters, the researchers realized that on average these craters tend to become up to 10 percent shallower near the north pole of Mercury, and the south pole of the Moon.
The most likely explanation, they say, is that thick sheets of ice are filling the bottoms of these craters, where the sun never shines. The Mercury ice appears to be almost pure, while that on the Moon seems to be more mixed with dust.
"We showed Mercury's polar deposits to be dominantly composed of water ice and extensively distributed in both Mercury's north and south polar regions," says Nancy Chabot, an instrument scientist for MESSENGER. "Mercury's ice deposits appear to be much less patchy than those on the Moon, and relatively fresh, perhaps emplaced or refreshed within the last tens of millions of years."
The team says that the Moon ice in particular could be accessible for future astronauts, who are due to return to the lunar surface within a few years.
The research was published in the journal Nature Geoscience.