You may have heard of LCROSS, the NASA probe intentionally crashed into the lunar surface to find evidence of water. But have you heard of Chandrayaan-1? The Indian Space Research Organization (ISRO) launched the lunar probe in October of 2008 that spent 8 months collecting a wealth data and images before technical problems forced a premature shutdown. One of the instrument packages on the lunar satellite was a Miniature Synthetic Aperture Radar (Mini-SAR) supplied by the Applied Physics Laboratory at John Hopkins University. A team of lunar geophysicists led by Dr. Paul Spudis have detected some 40 craters at the north lunar pole which may contain an amount of water equivalent to 600 million metric tons! Wow!
The findings have been presented by Paul Spudis at the recent lunar conference held in Texas. He also published an this article on his online Smithsonian Air & Space blog.
The Mini-SAR sends out radar pulses with a particular symmetry, left circular polar, when the pulses echoes off of surfaces the instrument detects the echoes and compares the original signal against the opposite sense, right circular polar waves. The comparison results in a ratio known as the circular polar ratio (CPR). Some surfaces such as new rough terrain or ice water can bounce back mulitiple echoes resulting in a high CPR values.
Paul Spudis and his team have found approximately 40 craters in the north lunar pole that exibit low CPR values around their rims but very high CPR values within the shadowed interior. The corresponding strength of the CPR provides the basis for deriving the mass of the substance which, if it is really ice water, weighs collectively approximately 600 million tons. The research is soon to be published in the technical journal Geophysical Research Letters. Below is an image and diagram of the mini-SAR instrument on Chandrayaan-1.
Here are some additional articles covering the news:
NASA Radar Finds Ice Deposits at Moon's North Pole; Additional Evidence of Water Activity on Moon Science Daily
Chandrayaan experiment finds water on moon Business Standard
Scientists See Fresh Evidence of More Water on the Moon New York Times