Is there ice on the moon? When the spacecraft Clementine bounced a radar beam off the moon’s poles in 1994, the echoes from some of the deep, permanently shadowed craters did seem to show the signature of ice—left over, perhaps, from long-ago cometary impacts. But last June, astronomers using the giant radar telescope at the Arecibo Observatory in Puerto Rico said they could find no sign of that ice.
Donald Campbell of Cornell and his colleagues made a radar map of the moon’s poles that showed features as small as 400 feet across, a thousand times sharper than Clementine’s view. Only a few small spots showed an icelike radar signature. And when Campbell compared the map with photographs of the moon, most of those spots turned out to be in sunlight and thus would have been too warm to hold ice.
Campbell thinks the signal came from rough surfaces inside ...
