Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p41a..06t&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P41A-06
Other
[5455] Planetary Sciences: Solid Surface Planets / Origin And Evolution, [5724] Planetary Sciences: Fluid Planets / Interiors, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Recent definitive discoveries that at least some lunar samples contain water indigenous to the Moon have great implications for lunar origin and subsequent differentiation and bombardment. Key observations pertinent to these issues are summarized here. (1) The water content of the lunar mantle varies considerably, from as low as undetectable (<100 ppb) to as high as tens of ppm, suggesting complex, possibly random (impact?) additions of water to the Moon. (2) Water does not seem to be correlated with REE, though many more data are needed. The Apollo 15 volcanic green glass magma has the highest estimated water content, but the lowest REE. This suggests a decoupling of REE enrichment from water enrichment. Water behaves as an incompatible element (similar to Ce), so would have concentrated in late-stage magma ocean products, along with the REE and other incompatibles. The lack of correlation with REE indicates water addition to the Moon after the magma ocean had crystallized. (3) Water ended up in the mantle source regions for pyroclastic glasses, 400-500 km deep in the Moon. This deposition of water must have happened after magma ocean crystallization because cumulates of olivine and orthopyroxene that formed at a depth of 500 km in the magma ocean with an initial water content of 100 ppm would contain only 1-2 ppm, not the tens of ppm inferred from the pyroclastic glasses. (4) Lunar water has higher D/H than does water on Earth. This likely means addition of water after the Moon formed. If water was incompletely lost as a result of the Moon-forming impact, D/H might be expected to be enriched. However, the vaporization rate would have to exceed the rate at which isotopes equilibrate with the Earth, yet not be so rapid that all the water was lost. (5) The Moon is strongly depleted in highly volatile elements (those condensing below 600 K), although the depletion is not correlated with volatility. Thus, the mechanism of volatile loss is more complicated than simple volatility. This might constrain the extent of water loss from the proto-lunar disk, if it had any. One can make a case that water and volatile elements were lost from the proto-lunar disk, but it seems more likely that the proto-Earth and the impactor were depleted in water and volatile elements and that they were added later. The lack of correlation of water with KREEP suggests that the addition came after the magma ocean had solidified. The oldest zircon ages for lunar samples suggest that the magma ocean had almost completely solidified by 4.42 My ago, about 100 My after the Moon formed. Thus, water arrived after that time. Depositing the water 500 km deep in the Moon requires impactors to scramble the upper few hundred kilometers of the Moon or to initiate cumulate overturn (from pressure release melting or decreased mantle viscosity by water addition), causing water, volatile elements, and whatever else was in the projectiles to descend with dense, relatively shallow, late-stage magma ocean cumulates. Assuming that formation of the oldest mare basalts (4.35 Gy) involved cumulate overturn and that the overturn was associated with late addition of water-bearing projectiles, this damp bombardment would have taken place between approximately 4.42 and 4.35 Ga, or between 100 to 130 after formation of the Moon.
No associations
LandOfFree
Water in the Moon: Implications for Lunar Formation, Differentiation, and Early Bombardment (Invited) does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Water in the Moon: Implications for Lunar Formation, Differentiation, and Early Bombardment (Invited), we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Water in the Moon: Implications for Lunar Formation, Differentiation, and Early Bombardment (Invited) will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1497071