It seems like water is everywhere lately. Mars, Mercury, our office’s storage room … and now the Moon.

Back in March S&T's Kelly Beatty described how researchers found water in tiny green-glass granules created by ancient volcanoes on the Moon — results that banished a long-coveted perception of a perfectly dry satellite. The team’s conclusions, appearing in the July 10th issue of Nature, have caused a bit of a splash in lunar science with their possible challenges to accepted Earth-Moon evolution models.

lunar glass

These glassy granules — greatly magnified from the specks they actually are — were collected in the early 1970s. Since then scientists have been worked hard to develop the technology necessary to fully examine them.


Contemporary models of lunar formation tell of a cataclysmic birth: a Mars-size object collides with Earth and throws molten material into space, where some of the fragments coalesce into the Moon. Scientists think that the high temperatures involved in this process vaporized all volatiles (lighter elements and molecules like water).

Alberto Saal (Brown University) and his colleagues offer a different lunar vision. Given how much water the glassy beads contain, the magma’s original water content may have resembled that of Earth’s upper mantle, according to team member Erik Hauri (Carnegie Institution of Washington). If this magma came from the Moon’s interior, water must have been deep inside.

The findings don’t throw out the collision model entirely. While scientists often use the lack of lunar water to support the great impact theory, there have been few attempts to link Moon-forming simulations to predictions of where the volatiles end up, explains Robin Canup (Southwest Research Institute), who specializes in planetary and lunar formation models. If a part of the Moon formed quickly after the impact — or (as simulations predict) from parts of the colliding body that didn’t hit Earth directly and therefore weren’t heated enough for the lighter elements to evaporate — it might have retained its water, she suspects.

The water could also come from meteorites or asteroids that struck the Moon. Saal’s team suggests that these collisions must have happened within 200 million years of the event that launched the molten lunar building blocks into Earth orbit.

Canup adds that the these new results may only reflect water abundance in a fraction of the Moon’s interior. Still, she agrees that the findings are important enough to kick-start attempts to pin down just how much of its light elements the Moon lost.


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July 11, 2008 at 2:55 pm

Help me with my fuzzy thinking here, people - I thought the idea that the moon was formed by coalescing in orbit around the earth at the same time as the earth was the "accepted" standard model. So these watery beads of glass would seem to give more credence to that theory as opposed to the collision theory (except as noted in the article), correct? The advantages of postulating the moon forming from the same "stuff" as the earth would be abundant prehistoric water. The problem then is explaining the disappearance of water, right? I wasn't aware that the collision theory had been the front-runner of theories so this puts me right back where I was before. I recall somewhere seeing a calculation of the lunar creation theories and the statistical probabilities of each theory listing pros and cons of each - does anyone remember that or knows where it can be found?

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Scott M.

July 11, 2008 at 9:50 pm

You never really and truly know everything.

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July 15, 2008 at 12:14 pm

Posted by Scott M. July 11, 2008 At 08:50 PM PDT
You never really and truly know everything.

...unless your name is God.


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Frank Mondana

July 15, 2008 at 11:10 pm

OK, since the question was valid, I'll make a stab at an answer.
The accretion theory was accepted until samples from the moon didn't have the volatiles that should have been there in the amounts found here on Earh.
After the chemistry of the samples didn't jive with accretion, the collision theory was born.
It was then backed up by computer models. They showed the collision worked very well. It was also very quick. The moon was formed within a year.

Finding the water sort of threw a wrench into the works. As far as I know, other volatiles are still missing.

So it seems like there has to be changes to both models with more analysis of samples and a few more sims.

That's as much as I know for now.

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