Lunar Soil Contain Solar Wind Particles

The constant stream of charged particles from the sun known as the solar wind is the source of the water that is locked inside the soils on the moon's surface.

This finding was made by the researchers at the University of Michigan.

The spacecraft observations and new lab measurements of Apollo lunar samples have overturned the long-held belief that the moon is bone-dry.

When NASA's Lunar crater Observation and Sensing satellite (LCROSS) crashed into the lunar crater in 2009, there was some material ejected that was surprisingly rich in water ice. Within the lunar layers, water and related compounds were detected. Whereas, the original lunar surface water has remained unclear.

So the researchers wonder whether it is the result of impacts from water-bearing comets and other chunks of space debris, or could there be other sources?

Theoretical models of lunar water stability suggest that hydrogen ions from the solar wind can combine with oxygen on the moon's surface to form water and related compounds called hydroxyls.

U-M's Youxue Zhang and colleagues from the University of Tennessee and the California Institute of Technology present findings that support solar-wind production of water ice on the moon. This study was published online October 14 in the journal Nature Geoscience.

The first author of the paper is Yang Liu of U-T. She is a U-M alumna who earned her doctorate under Zhang, who is a professor in the Department of Earth and Environmental Sciences.

In the paper, the researchers present infrared spectroscopy and mass spectrometry analyses of Apollo samples that reveal the presence of significant amounts of hydroxyl inside glasses formed in the lunar regolith by micrometeorite impacts. Most of the infrared spectroscopy work was done at Zhang's U-M lab, and the mass spectroscopy was conducted at Caltech.

"We found that the 'water' component, the hydroxyl, in the lunar regolith is mostly from solar wind implantation of protons, which locally combined with oxygen to form hydroxyls that moved into the interior of glasses by impact melting," said Zhang, the James R. O'Neil Collegiate Professor of Geological Sciences.

"Lunar regolith is everywhere on the lunar surface, and glasses make up about half of lunar regolith. So our work shows that the 'water' component, the hydroxyl, is widespread in lunar materials, although not in the form of ice or liquid water that can easily be used in a future manned lunar base."

This indicates that ice inside the polar craters on the moon, could contain hydrogen atoms that is derived from the solar wind.

Apart from this individual grains from Apollo 11 mare soil, Apollo 16 highland soil and Apollo 17 mare soil were also analyzed. The researchers noticed that the grains included agglutinates and impact glasses.