July 14, 2008 | David F. Coppedge

Watery Moon Upsets Conventional Wisdom

The moon looks pretty dry.  It may have maria (oceans) but the figurative term would not attract customers for beachfront property: its seas are made of hardened lava.  The moon’s “Ocean of storms” (Mare Procellarum) only gets rain in the form of solar wind and cosmic rays.  Still, could there be water molecules in this dry place?  New studies say yes.  What’s most interesting about this answer is the reaction of some scientists to unexpected information.
    In a paper in Nature,1 Saal et al believe they have discovered primordial water in orange and green soil samples returned by Apollo astronauts.  Since the H2O molecules are deeply embedded in crystals, they feel it rules out contamination from earth or condensation from extra-lunar sources.  The concentration of water (their best estimate being 750 parts per million) is much higher than the estimates for the earth’s upper mantle.  The researchers feel it represents magmatic water in the interior of the moon that was buried after volcanic eruptions then became exposed after meteoritic impacts.  They detected, in addition, other volatiles, including sulfur, fluorine, chlorine and carbon dioxide.
    So what?  The problem is that the favored theory for the origin of the moon would not permit these volatiles to be present.  Many astronomers feel a Mars-size object impacted the earth early in its history.  The moon condensed out of the ejecta.  This process, however, would not have left much if any water or volatile elements and molecules behind.  Commenting on this paper in the same issue of Nature,2 Mark Chaussidon (CRPG, France) explored the ramifications:

These results raise many questions.  Are the volatile contents of the melts that formed the green and orange glasses typical for the Moon?  Can the general scarcity of most volatile elements on the Moon be reconciled with the apparent abundance of sulphur, chlorine, fluorine and especially water in the lunar glasses?  What happened to all the water during the Moon’s formation?  And if the Moon is not bone dry, where did the water come from?

He tried to salvage the impact hypothesis by suggesting that maybe earth and the primordial moon exchanged volatile material for a few centuries while the moon coalesced.  Future comparisons of hydrogen-to-deuterium ratios between earth and moon may help resolve the dispute.
    EurekAlert reported the story and ended with a surprising comment about scientific discovery in general:

Lead author of the study, Alberto Saal of Brown University remarked: “Beyond the evidence for the presence of water in the interior of the Moon, which I found extremely exciting, I learned that the contributions from scientists from other disciplines has the potential to produce unexpected results.  Such a scientist is able not only to ask questions that no one has asked before, but also can challenge hypotheses that are embedded in the thinking of the scientists working in the field for many years.  Our case is a typical example.  When I suggested we measure volatiles in lunar material, everyone I talked to thought that such proposal was a futile endeavor.  We ‘knew’ the Moon was dry.”

Astrobiology Magazine also reported the story and included the above quote.  It also included artwork of the Mars-impact hypothesis.  The BBC News also reported the story.  It should be recalled from the 11/04/2002 entry that Apollo astronaut and geologist Harrison Schmidt (Apollo 17), who discovered the orange soil on the moon, denies the Mars-impact hypothesis.

1.  Saal et al, “Volatile content of lunar volcanic glasses and the presence of water in the Moon’s interior,” Nature 454, 192-195 (10 July 2008) | doi:10.1038/nature07047.
2.  Mark Chaussidon, “Planetary science: The early Moon was rich in water,” Nature 454, 170-172 (10 July 2008) | doi:10.1038/454170a.

How can science progress if scientists don’t ask the right questions?  Looking for water on the moon was futile.  They “knew” the moon was dry.  If you think science is always an unbiased collection of evidence, think about this case.  Scientists always approach a problem with a bias.  No one collects data in a strict Baconian fashion.  There is always an element of human selection, deciding what questions are interesting, and what data are most likely to yield fruitful hypotheses.  Thank goodness for a few individuals who bravely ask the questions others don’t consider worthwhile.  If the finding holds up, a lot of artwork and computer animations may get tossed out the window.  Another problem will resurface: where did our moon come from?  The Mars impact hypothesis was the leading theory for a long time, not because the data demanded it, but because the other contenders were each losers (see best-in-field fallacy).  But consider what was said in the previous entry about our privileged planet: the moon has a function.  It’s very probable that without our specific moon, its mass and distance, life could not exist.  Then there is the amazing coincidence about solar eclipses: the moon’s apparent diameter in the sky is the same as the sun’s.  Too many coincidences and the chance hypothesis sounds uncannily lucky.  Maybe the moon was created.

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Categories: Solar System

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