By rickyjames, Section News Posted on Wed Nov 12, 2003 at 07:40:41 AM PST
In a potentially serious blow to future lunar colonization efforts, new radar measurements of the poles of Earth's moon show no signs of water there in the permanent shade and shadow of deep craters. Such radar measurements by the Arecibo Radio Telescope in Puerto Rico had previously discovered polar ice deposits on distant Mercury, but similar signals from our Moon are absent.
Lunar ice had been suspected from indirect radiation measurements in the 1990s by NASA's Lunar Prospector orbiter. At a distance of tens of miles above the lunar poles, that spacecraft detected high levels of hydrogen. The most probable source of such hydrogen was believed at that time to be shaded water in the form of surface and sub-surface ice. Now, direct probing to a depth of twenty feet of that part of the lunar surface by radar beams has failed to confirm the earlier hypothesis of polar ice. The moon's orientation means only about 20 percent of its shadowed polar craters can be probed by Earth-based radar, but Bruce Campbell of the Smithsonian Institution's Center for Earth and Planetary Studies believes it is unlikely that large slabs of ice are hidden in the inaccessible areas.
"It certainly would have been nice to find some sort of lunar skating rink, or thick layers of ice, but it looks like it's just not there," he said.
Writing in the current issue of Nature, researchers wrote, "We find that areas of the crater floors at the poles that are in permanent shadow from the Sun, which are potential cold traps for water or other volatiles, do not give rise to strong radar echoes like those associated with thick ice deposits in the polar craters on Mercury".
The earlier radiation measurements indicative of hydrogen remain unexplained. Further radiation measurements by NASA's Lunar Prospector are not possible because the probe was deliberately crashed into the lunar surface at the end of its mission. However, ESA's SMART-1 spacecraft en route to the Moon carries an infrared spectrometer to make further radiation measurements that may shed additional insight into the current puzzle.
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