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More evidence piles up that the moon harbors lots of ice


Ice at the moon's north poleChandrayaan 1, the first moon mission launched by the Indian Space Research Organization, did not last long—in August 2009, controllers lost contact with the probe 10 months into its two-year mission. But the data Chandrayaan gathered while orbiting the moon continues to inform lunar science, especially in the realm of identifying potential stores of water on the moon.

Research to be presented (pdf) Thursday at the Lunar and Planetary Science Conference being held this week in the Woodlands, Tex., shows that a NASA radar on the Indian probe added to a growing dossier of evidence that the moon harbors large quantities of water. Paul Spudis of the Lunar and Planetary Institute and his colleagues say that Chandrayaan's Mini-SAR radar spotted what appears to be ice in dozens of north polar craters.

The research by Spudis and his colleagues follows the November announcement that NASA's Lunar Crater Observation and Sensing Satellite (LCROSS) had churned up about 100 kilograms of water during its impact into a crater near the lunar south pole. (Some of the moon's polar craters are permanently shadowed, a feature that has long made them appealing targets for finding trapped ice.) Less than two months before that, a consortium of researchers used data from Chandrayaan and two other spacecraft to show that molecular water is dispersed across the lunar surface in low concentrations.

According to a NASA press release, the Mini-SAR readings picked up waterlike signals from 40 craters [circled in green in map above], together harboring what could be 600 million metric tons of ice—a massive supply that could facilitate extended human visits to the moon. The radar bounces circularly polarized radio waves off the moon's surface to probe its composition; dry soil tends to reverse the polarization, from left-handed to right-handed, whereas ice tends to bounce back the waves with their polarization preserved.

Also at this week's Lunar and Planetary Science Conference, a pair of planetary scientists threw a bit of cold water, so to speak, on the recent ice research. Everett Gibson of NASA and Colin Pillinger of the Open University in England presented an assessment (pdf) of the available evidence for lunar water Tuesday, concluding that caution must be taken in interpreting the LCROSS data. The spacecraft's polar impact had no control experiment, Gibson and Pillinger note—what if the signals attributed to ice were also seen in presumably dry equatorial soils? Although plenty of circumstantial evidence for lunar water deposits exists, the researchers maintain that conclusive proof awaits a specially equipped lander—for instance, the Beagle moon lander Gibson and Pillinger have proposed in the past.

Image credit: NASA

The views expressed are those of the author and are not necessarily those of Scientific American.

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