by Playfuls Staff |
19th October 2006
The latest radar images of the moon deal a heavy blow to dreams of ever using the moon as an outpost or forward base for space explorations. Apparently, there's no ice on the moon. The precious substance could[more] have been used for producing drinking water, oxygen or even rocket fuel. Previous studies led to contradicting results. The radar data obtained now is the best to date, with resolution down to 20 meters and probing up to one meter into the moon's soil, even better than that obtained in the past by satellites with a more direct view from lunar orbit.
Scientific American notes that astronauts need an average of 1.6 kilograms (0.4 gallon) of water to sustain each of them every day, as well as an additional 27 kilograms (7.2 gallons) for other purposes, according to NASA, and boosting even one of these kilograms into orbit costs $25,000.
In the latest study, Donald Campbell of Cornell University in Ithaca, New York, and colleagues collected new radar images of the Moon's south pole using the Arecibo telescope in Puerto Rico. Echoes from radar signals transmitted to the moon from the giant Arecibo telescope were received at the Green Bank telescope. These images achieved a resolution of 20m (65ft), the highest resolution yet of this region. They paid special attention to Shackleton Crater, which has generated most interest. Cornell University, Smithsonian Institution and Australian scientists report the findings in the latest Nature (Oct. 19, 2006).
What they were looking for was a radar signature called the "circular polarization ratio (CPR)," which can identify with some uncertainty substances such as ice. "Ice essentially lights up under radar. It preferentially reflects the light back at the radar like a highway sign," Campbell explains. "When we looked at the poles of the moon we did not see the same sort of signature."
The authors found the previously detected CPR signature from areas of the surface that were exposed to bright sunlight, and where ice deposits could not persist. "It's the same kind of signature that's found near Shackleton Crater; it cannot possibly be related to ice," co-author Jean-Luc Margot, from Cornell University, told the BBC.
"For reasons that we're not totally sure about, the same properties can arise from the scattering of rocky ejecta on the blocky terrain of young impact craters on the moon," their paper says. The phenomenon was also found on Earth.
"These new results do not preclude ice being present as small grains in the lunar soil based on the Lunar Prospector's discovery of enhanced hydrogen concentrations at the lunar poles," said Donald Campbell, a Cornell University professor of astronomy and a principal investigator of the study. "There is always the possibility that concentrated deposits exist in a few of the shadowed locations not visible to radars on Earth, but any current planning for landers or bases at the lunar poles should not count on this."
Searching for near-surface water ice in polar cold traps on the Moon is one mission priority for NASA's Lunar Reconnaissance Orbiter probe, due to launch in 2008. "They will get a better view of the polar terrain than we can from the earth, and it will be interesting to see what they show up," Campbell says. "LCROSS is planned to impact into the moon and see if they can vaporize any water ice and then detect the vapor plume."
Since the 1960s, theories have suggested that ice may exist deep inside impact craters in permanent shadow from the sun, where temperatures on the moon's surface do not exceed minus 280 degrees Fahrenheit (or minus 173 Centigrade), at the poles. The theory was bolstered in 1992 when Earth-based radar telescopes located "ice deposits" inside impact craters at the poles of the planet Mercury.
