(Sen) - NASA’s Lunar Reconnaissance Orbiter (LRO) has discovered that the Shackleton crater near the Moon's south pole may contain up to ten per cent ice.
The Mini-RF radar aboard LRO was used to estimate the maximum amount of ice that could exist inside the crater. The crater is permanently shadowed, which means that water can exist in a frozen state as sunlight never touches it. These orbital radar measurements are the first made of Shackleton crater, and the observations show signatures of ice in the rough crater walls. Using radar allows scientists to peer into these otherwise dark regions to look for ice, as the radar signature of ice is different compared to surrounding material. Radar also has the advantage of penetrating the lunar surface by up to two metres, meaning it can hunt for subsurface ice.
"The radar results are consistent with the interior of Shackleton containing a few per cent ice mixed into the dry lunar soil" said Mini-RF's principal investigator, Ben Bussey. The laser altimeter and far-ultraviolet detector on LRO were also used to ascertain the existence of ice by measuring how light is reflected from the surface.
"Inside the crater, we don't see evidence for glaciers like on Earth," said Bradley Thomson at Boston University's Center for Remote Sensing. "Glacial ice has a whopping radar signal, and these measurements reveal a much weaker signal consistent with rugged terrain and limited ice."
The findings of LRO agree with recent measurements by the LCROSS spacecraft, which revealed evidence of water in a plume of material ejected during the controlled collision with the Moon. India’s Chandrayaan-1 also saw signs of ice in 2009 in craters at the north pole.
Sparse amounts of water and hydroxyl were also detected close to the lunar surface using infrared spectrometers, and neutron measurements from spacecraft have shown elevated levels of hydrogen near the surface in the polar regions. Hydrogen is a component of water, and if this hydrogen signifies that ice exists then the ice would comprise 1.5 per cent of the weight in the polar regions.
CPR indicates the actual radar measurements, while the other maps are models that the observations are compared to in order to estimate the maximum amount of ice present. Credit: NASA
"These terrific results from the Mini-RF team contribute to the evolving story of water on the Moon," said LRO's deputy project scientist, John Keller. "Several of the instruments on LRO have made unique contributions to this story, but only the radar penetrates beneath the surface to look for signatures of blocky ice deposits."
"We are following up these tantalizing results with additional observations," said Bussey. "Mini-RF is currently acquiring new bistatic radar images of the moon using a signal transmitted by the Arecibo radio telescope in Puerto Rico. These bistatic images will help us distinguish between surface roughness and ice, providing further unique insights into the locations of volatile deposits."