Scientists are optimistic that the recent discovery of frost on moon’s south pole could help support deep space missions in future.
The discovery was made using data collected by NASA’s Lunar Reconnaissance Orbiter (LRO). The team involved with the discover spotted bright areas that they say are the result of reflection from material deposited on the surface including frost. The area where in question near the south pole of the moon is one of the coldest places on Earth’s natural satellite and for that reason scientists didn’t expect much other than soil.
But that wasn’t the case as data indicated presence of surface frost. The icy deposits appear to be patchy and thin, and it’s possible that they are mixed in with the surface layer of soil, dust and small rocks called the regolith. Researcher say they are not seeing expanses of ice similar to a frozen pond or skating rink. Instead, they are seeing signs of surface frost.
Data indicated presence of frost in cold traps – areas that are permanently dark located either on the floor of a deep crater or along a section of crater wall that doesn’t receive direct sunlight–where temperatures remain below minus 260 degrees Fahrenheit (minus 163 degrees Celsius). Under these conditions, water ice can persist for millions or billions of years.
There have been predictions earlier that cold traps on the moon could store water ice, but confirming that hypothesis turned out to be challenging. Observations made by NASA’s Lunar Prospector orbiter in the late 1990s identified hydrogen-rich areas near the moon’s poles but could not determine whether that hydrogen was bound up in water or was present in some other form. Understanding the nature of these deposits has been one of the driving goals of LRO, which has been orbiting the moon since 2009.
Scientists found evidence of lunar frost by comparing temperature readings from LRO’s Diviner instrument with brightness measurements from the spacecraft’s Lunar Orbiter Laser Altimeter, or LOLA. In these comparisons, the coldest areas near the south pole also were very bright, indicating the presence of ice or other highly reflective materials. The researchers looked at the peak surface temperatures, because water ice won’t last if the temperature creeps above the crucial threshold.
The findings are consistent with another team’s analysis of LRO data, reported in 2015. That study compared peak temperatures with ultraviolet, or UV, data from the Lyman-Alpha Mapping Project, or LAMP. Both LOLA and LAMP are able to measure surface brightness without sunlight. LOLA does so by measuring reflected laser light, and LAMP, by measuring reflected starlight and the UV skyglow of hydrogen.
Water ice and other deposits also have been identified in cold traps near the north pole on Mercury. Though it is the closest planet to the sun, Mercury appears to have up to 400 times more ice than the moon does, by Siegler’s estimate. Scientists are still figuring out which scenario is “more normal.”