July 9, 2008 -- A new analysis of Apollo 15 moon rocks has for the first time uncovered water locked up inside.
It's just a miniscule amount of the wet stuff -- not enough to sustain even a lunar cactus or to power any hydrogen jetpacks -- but the discovery does bolster hopes that there has always been water in moon rocks and perhaps some locked away as ice in the dark crannies of polar craters.
The discovery also overturns 40 years of studies which had failed to find the water and which led to the conclusion, drawn by most planetary scientists, that moon rocks must be all dry.
"Folks said it was a waste of time," said lead researcher Alberto Saal of Brown University, regarding their proposal to look at the moon rocks one more time. "It took us three years to get it funded."
Still, using a refinement of a method called secondary mass spectrometry, Saal and his colleagues eventually were able to count molecules two orders of magnitude lower than in the past -- down to just four or five of water molecules per million. As it turned out, they found up to 46 parts per million in tiny volcanic glass balls brought back from the moon.
What really makes the case that this is truly old lunar water -- and not water made from hydrogen blasted from the sun into the moon rocks -- is the manner water is distributed inside the volcanic glass balls. Saal and his team found more water in the middle and less nearer the rims of the balls.
The only way for that to happen is if the water was in the rocks when they originally flowed out of lunar volcanoes and has been gradually diffusing away -- and perhaps some settling in cold dark craters -- over the billions of years since the rocks solidified.
"That's the nailer," said Saal of the glass spheres. He and his colleagues published their discovery in the July 10 issue of the journal Nature.
One of the ramifications of the newfound water is that it calls into question some of the details about the way the moon formed. The most popular current theory is that a Mars-sized body sideswiped Earth about 4.5 billion years ago, creating a ring of debris that eventually coalesced into the moon.
The debris-ring period, it's been argued, is the perfect time for all of the water in the moon rocks to have dissipated into space. This nicely explained the apparent dryness of moon rocks.
"It could means that part of the moon (the deepest part, perhaps) was derived by condensation and cooling of the outer edge of the disk from which the moon formed and thereby incorporated water from Earth and the projectile that hit Earth," surmised David Stevenson, a planetary scientist at Caltech. He and Kaveh Pahlevan previously proposed the ring was the cause of the dry moon rocks.
"The new paper by Saal is important because it challenges a long-held view that the moon is fundamentally different because it is bone-dry," Pahlevan told Discovery News. "Now the debate moves towards a quantitative comparison of lunar and terrestrial water budgets, and what they might tell us about events transpiring after the giant impact."
Related Links:
Larry O'Hanlon's blog: Earth Impacts
David Chandler blogs on how a student helped in the moon water discovery.
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