Scientists discover Traces of water on moon's oldest rocks
 |
Lunar sample of unbrecciated anorthosite collected during the Apollo 15 mission was thought to be a
piece of the moon's primordial crust
Image courtesy of NASA/Johnson Space Center.
|
 |
| Image showing water absorption strength |
Researchers used Infrared spectroscopy to analyse the water content in grains of plagioclase feldspar from lunar anorthosites - highland rocks composed of more than 90 per cent plagioclase.
The bright-coloured highlands rocks are thought to have formed early in the Moon's history when plagioclase crystallised from a magma ocean and floated to the surface. The infrared spectroscopy work detected about 6 parts per million of water in the lunar anorthosites.
The infrared spectroscopy work, which was conducted at Zhang's U-M lab and co-author Anne H. Peslier's lab, detected about 6 parts per million of water in the lunar anorthosites.
"The surprise discovery of this work is that in lunar rocks, even in nominally water-free minerals such as plagioclase feldspar, the water content can be detected," said Zhang, James R. O'Neil Collegiate Professor of Geological Sciences.
"It's not 'liquid' water that was measured during these studies but hydroxyl groups distributed within the mineral grain," said Notre Dame's Hui. "We are able to detect those hydroxyl groups in the crystalline structure of the Apollo samples."
The hydroxyl groups the team detected are evidence that the lunar interior contained significant water during the Moon's early molten state, before the crust solidified, and may have played a key role in the development of lunar basalts. "The presence of water," said Hui, "could imply a more prolonged solidification of the lunar magma ocean than the once-popular anhydrous Moon scenario suggests."
The researchers analyzed grains from ferroan anorthosites 15415 and 60015, as well as troctolite 76535. Ferroan anorthosite 15415 is one the best known rocks of the Apollo collection and is popularly called the Genesis Rock because the astronauts thought they had a piece of the Moon's primordial crust. It was collected on the rim of Apur Crater during the Apollo 15 mission.
Rock 60015 is highly shocked ferroan anorthosite collected near the lunar module during the Apollo 16 mission. Troctolite 76535 is a coarse-grained plutonic rock collected during the Apollo 17 mission.