posted 08-21-2018 07:10 AM               

Ice Confirmed at the Moon's Poles

In the darkest and coldest parts of its polar regions, a team of scientists has directly observed definitive evidence of water ice on the Moon's surface. These ice deposits are patchily distributed and could possibly be ancient. At the southern pole, most of the ice is concentrated at lunar craters, while the northern pole's ice is more widely, but sparsely spread.

Above: The image shows the distribution of surface ice at the Moon's south pole (left) and north pole (right), detected by NASA's Moon Mineralogy Mapper instrument. Blue represents the ice locations, plotted over an image of the lunar surface, where the gray scale corresponds to surface temperature (darker representing colder areas and lighter shades indicating warmer zones).

A team of scientists, led by Shuai Li of the University of Hawaii and Brown University and including Richard Elphic from NASA's Ames Research Center in California's Silicon Valley, used data from NASA's Moon Mineralogy Mapper (M3) instrument to identify three specific signatures that definitively prove there is water ice at the surface of the Moon.

M3, aboard the Chandrayaan-1 spacecraft, launched in 2008 by the Indian Space Research Organization, was uniquely equipped to confirm the presence of solid ice on the Moon. It collected data that not only picked up the reflective properties we'd expect from ice, but was able to directly measure the distinctive way its molecules absorb infrared light, so it can differentiate between liquid water or vapor and solid ice.

Most of the newfound water ice lies in the shadows of craters near the poles, where the warmest temperatures never reach above minus 250 degrees Fahrenheit. Because of the very small tilt of the Moon's rotation axis, sunlight never reaches these regions.

Previous observations indirectly found possible signs of surface ice at the lunar south pole, but these could have been explained by other phenomena, such as unusually reflective lunar soil.

With enough ice sitting at the surface — within the top few millimeters — water would possibly be accessible as a resource for future expeditions to explore and even stay on the Moon, and potentially easier to access than the water detected beneath the Moon's surface.

Learning more about this ice, how it got there, and how it interacts with the larger lunar environment will be a key mission focus for NASA and commercial partners, as we endeavor to return to and explore our closest neighbor, the Moon.

The findings were published in the Proceedings of the National Academy of Sciences on August 20, 2018.

NASA's Jet Propulsion Laboratory, Pasadena, California, designed and built the moon mineralogy mapper instrument and was home to its project manager.

posted 08-23-2018 11:14 AM            

1. These results (from observations made by a NASA instrument on board the Indian spacecraft Chandrayaan 1 about 10 years ago) show the presence of water ice close to the surface not just at the lunar poles, but in sheltered areas within 20 degrees latitude of both poles.

2. Delivery of ice by way of comet impacts has always been a troublesome concept. (How would the ice survive the heat of the impact? Many astronomers and space scientists are very dubious about comet delivery.)

3. Modern analyses of the Apollo volcanic glass samples show interior water content comparable with magma on Earth, suggesting that the interior of the Moon contains substantial quantities of water.

4. Migration of water towards the lunar surface, possibly by convection caused by the heat flow detected by the Apollo 15 and 17 Heat Flow Experiments, could explain the gradual accumulation of water close to the surface in places.

5. Where this water reaches the surface in polar regions, it can accumulate. Where it reaches the surface at lower latitudes, it will melt and evaporate, or just sublimate. (The results of the Heat Flow Experiments are not easy for the layman to digest, but it appears that the temperature of the lunar subsurface around 6-10 feet below the surface, is several tens of degrees below freezing, even during the lunar day, but somewhere between 10 feet and zero feet the daytime temperatures at Hadley or Taurus-Littrow would melt/sublimate any internal ice. That would not be the case inside Cabeus Crater or in other permanently-shaded areas.)