June 17, 2014
Astronauts Visiting Moon Will Not Find Water On The Sunny Side
Brett Smith for redOrbit.com - Your Universe Online
Astronauts looking to lay the groundwork for a future settlement or station on the Moon will be looking for water to use as a resource. According to a new study, however, they may want to save some time by not looking for it on areas of the Moon that are exposed to the Sun.
Published in the Journal of Geophysical Research: Planets, the study found that ultraviolet photons released by the Sun probably result in water molecules to either swiftly "desorb" or disintegrate. These parts of water may stay on the lunar surface, but the existence of practical amounts of water on the sunlit areas is not likely, the study authors reported.
For the study, researchers from the Georgia Institute of Technology constructed an ultra-high vacuum model that mimics conditions in space, and conducted measurements of the water photodesorption using an actual lunar sample. The machine irradiated this sample with ultraviolet photons to produce excited states and record what happened to the water molecules. According to the team’s measurements, around one in every 1,000 molecules leaves the lunar surface as a result of absorption of UV light.
The study team found two “cross section values” that can now be used to find water throughout the Solar System and beyond.
“The cross section is an important number planetary scientists, astrochemists and the astrophysics community need for models regarding the fate of water on comets, moons, asteroids, other airless bodies and interstellar grains,” said study author Thomas Orlando, a professor of biophysical chemistry at Georgia Tech.
The team said because their number is relatively large it establishes that solar UV photons are probably removing water from the lunar surface. The team also concluded the cross sections raise even more with reducing water coverage. Orlando compared the situation to sitting outside on a summer day.
“If a lot of sunlight is hitting me, the probability of me getting sunburned is pretty high,” Orlando said. “It’s similar on the moon. There’s a fixed solar flux of energetic photons that hit the sunlit surface, and there’s a pretty good probability they remove water or damage the molecules.”
According to a study published in September 2013, any water that is locked up in Moon rocks probably got there from Earth.
The study looked at rocks returned to Earth during the Apollo Moon missions, and researchers were able to identify the water concentrations in the mineral apatite, a calcium phosphate mineral in the lunar crust.
“The water locked into the mineral apatite in the Moon rocks studied has an isotopic signature very similar to that of the Earth and some carbonaceous chondrite meteorites,” said study author Jessica Barnes from The Open University. “The remarkable consistency between the hydrogen composition of lunar samples and water-reservoirs of the Earth strongly suggests that there is a common origin for water in the Earth-Moon system.”
The study’s conclusion is consistent with a theory that says the Moon was formed when the Earth was impacted by a body roughly the size of Mars. Over time, material from the collision, including any water, merged to form our Moon.