Moon Rock Mineral Hints at Watery Lunar Past

Live From the Moon: NASA Probe Beams Home New Lunar Views
NASA's LCROSS probe beamed this view of the moon's Mendeleev region, an ancient impact basin with relatively uniform floor deposits on the far side, during afirst flyby on June, 23, 2009. The probe's position at the time of the image is also shown. The probe will ultimately crash into the lunar surface to hunt for water ice on Oct. 9, 2009.
(Image: © NASA)

Amineral discovered in a volcanic rock from the moon has been found to containelements that may point to the moon's watery past, a new study suggests.

Scientistsfound the mineral apatitein a type of lunar volcanic rock called basalt, which contained the same so-calledvolatile elements as those found in common igneous rocks on Earth. The moonrock was collected by Apollo 14 astronauts in 1971.

Volatileelements, which include hydrogen, chlorine and sulfur, are those that mosteasily escape from a rock when it is heated. The presence of these volatileelements in rocks can provide insight into the crust and atmosphere of a planetor moon.

"Apatiteis a mineral that can incorporate water into its structure, but it can alsogrow in a water-free environment," Jeremy Boyce, the study's leadresearcher at the California Institute of Technology in Pasadena, Calif., in an e-mail interview. "The amount of water in the apatite is ?at least in part ? a function of the water content in the surrounding magmafrom which the apatite grew."

Inother words, apatite that grew in the presence of water will contain water,whereas apatite that grew in a water-free environment will not. So, by comparingthe volatile elements in the moon's apatite to those on Earth ? which formed inwater for sure ? scientists can determine if the lunar mineral also formed inwater, which could shine a light on the present and past compositionof the moon.?

Whatthis means for the moon

"Measuring water content in lunar minerals is one way of estimating the volatile content of themoon," Boyce said. "Water (made of volatile elements hydrogen andoxygen) is the most common volatile species on Earth, and is also essential forlife as we know it, so it is often what people refer to when speaking of volatiles."

Theresearch is detailed in the July 22 issue of the journal Nature and suggeststhat at least some lunar minerals are as rich in volatile elements as theirterrestrial counterparts.

The existence of water on the moon had long been speculated until last year, when scientists confirmed the presence of water molecules on the moon's surface and water ice in shadowed lunar craters.

Basedon the prevailing theory of its formation, the moon is commonly thought tocontain fewer volatile elements than the Earth.

"Themost popular theory on the formation of the moon is that the Earth was hit by a "Mars-sized"object, and that the Earth and moon are made of the materials that survived theimpact," Boyce said. "This impact caused these materials to beheated, and some of the volatile elements were lost to space."

Yet,this view has recently been challenged by a report of the presence of smallquantities of volatile elements, and fluorine, in tiny mineral droplets of lunar volcanic glass called spherules.

Thiswas interpreted as evidence of significant water content in the moon'spre-eruptive magma ? a conclusion that relied on modeling the diffusion ofvolatiles out of the glasses during the eruption.

Avolatile-rich environment?

Thenew study conducted by Boyce and his colleagues provides additional evidence,from a separate source, for a more volatile-rich moon.

Theresearchers measured concentrations of water, chlorine and sulfur in a lunarapatite and compared it to the hundreds of similar analyses that have been madeof apatites from Earth. The study produced some surprising results.?

"Wefound that the volatile content of lunar apatite was indistinguishable fromthat of the population of terrestrial apatites," Boyce said. "Thiswas unexpected because the Earth is 'wet' and the moon is 'dry.'"

Thefindings appear to suggest similarities in the Earth and moon's geo-chemicalhistory.

"Thesemeasurements tell us that conditions existed in lunar rocks that could createapatite crystals that are very similar to those apatite crystals that grew from'wet' magmas on Earth," Boyce said. "So we know the moon has at leasta little bit of water and these other volatile elements. But how much exactlyis a matter of some debate."

But,since the apatite could have been altered by eruption, the researchers cannotdefinitely infer the concentrations of these elements in the parent magma.Still, this study will give scientists a better understanding of the volatilebudget of lunar apatites, said Boyce.

Furtherresearch could also enable researchers to make measurements within a larger context.

"Weneed to work on relating the volatile content of the apatite to the moon as awhole," Boyce said. "There are several steps required in order tomake that connection, and we don't know enough to make a robust estimate of thewater content of the whole moon." ?
