Radars scans suggest shaded polar regions may hold patches of ice
By Summit Voice
SUMMIT COUNTY — Detailed radars scans of a crater near the moon’s South Pole add to the growing evidence that there may be remnants of water frozen as ice in shady cliffs and canyons.
The scans show that much as 5 to 10 percent of material, by weight, could be patchy ice, according to the team of researchers led by Bradley Thomson at Boston University’s Center for Remote Sensing.
The data came fro the Mini-RF radar on NASA’s Lunar Reconnaissance Orbiter, which did the first orbital radar measurements of Shackleton crater, a high-priority target for future exploration.
The observations indicate an enhanced radar polarization signature, which is consistent with the presence of small amounts of ice in the rough inner wall slopes of the crater. Thomson and his colleagues reported the findings in a paper recently published in the journal Geophysical Research Letters.
“These terrific results from the Mini-RF team contribute to the evolving story of water on the moon,” said project scientist John Keller of NASA’s Goddard Space Flight Center in Greenbelt, Md. “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.”
“The interior of this crater lies in permanent shadow and is a ‘cold trap’—a place cold enough to permit ice to accumulate,” ssaid Mini-RF’s principal investigator Ben Bussey, of the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “The radar results are consistent with the interior of Shackleton containing a few percent ice mixed into the dry lunar soil.”
These findings support the long-recognized possibility that areas of permanent shadow inside polar impact craters are sites of the potential accumulation of water. Numerous lines of evidence from recent spacecraft observations have revised the view that the lunar surface is a completely dry, inhospitable landscape.
Thin films of water and hydroxyl have been detected across the lunar surface using several space-borne near-infrared spectrometers. Additionally, orbital neutron measurements indicate elevated levels of near‐surface hydrogen in the polar regions; if in the form of water, this hydrogen would represent an average ice concentration of about 1.5 percent by weight in the polar regions.
The Shackleton findings are consistent with data gathered after a controlled impact in another permanently shadowed polar region near the lunar South Pole, which revealed evidence for water in the plume kicked up by its impact.
A radar instrument flown on India’s Chandrayaan-1 spacecraft in 2009 found evidence for ice deposits in craters at the lunar North Pole. Measurements of the albedo (surface reflectance) inside Shackleton crater using LRO’s laser altimeter and far‐ultraviolet detector are also consistent with the presence of a small amount of ice.
“Inside the crater, we don’t see evidence for glaciers like on Earth,” said Thomson. “Glacial ice has a whopping radar signal, and these measurements reveal a much weaker signal consistent with rugged terrain and limited ice.”