No lunar ice

No lunar ice

No lunar ice

Bad Astronomy
The entire universe in blog form
Oct. 18 2006 4:30 PM

No lunar ice

The south pole region of the Moon. The actual pole is just to the left of the crater marked "A", named Shackleton, and the crater marked "B" is Shoemaker, where the Lunar Prospector spacecraft crashed in 1999.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  

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Well, this is a bummer.

It sounds goofy to think there may be water (really, ice) on the Moon, but it's actually near fetched (the opposite, you see, of far fetched). Comets and other icy bodies hit the Moon. When they do, the ice in them is distributed across the surface. The lunar day is 29 Earth days long, so probably within a week or two the raw sunlight hitting the ice particles will vaporize them.

However, at the lunar poles, especially the south pole, there are very deep craters. The Sun is always low to the horizon as seen from the poles, and with a deep crater the floor of the crater may never be kissed by the Sun. In such a crater, it's always dark and cold, so any ice landing there would stay.

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So it's possible, but that doesn't mean it's actually there. But if it were there, it would be detectable using radar.

So people did that, and Lo! It looked like there was in fact ice in the lunar Antarctic. Then the US Clementine mission also searched for signs of ice, and also found them. It was looking good. People were planning on building lunar bases near the south pole, to tap into all that ice.

But now these guys at Cornell are, uh, throwing cold water on the whole thing. They used higher resolution radar, and they say they do in fact see that signal, but they see it not only in deep, dark craters, but also in places that do get hit by sunlight. They then conclude that what they are seeing cannot be from ice. It may be from rocks or some other substance, but ice it ain't. The earlier, lower resolution surveys were seeing both the dark and the lit craters at the same time, and couldn't differentiate them.

So this is too bad. Dreams of a lunar base at the south pole may have just evaporated along with the purported ice.