* Astronomy

Most Moon Water Comes From the Sun, Not Comets

The moons water came from comet and asteroid impacts, right? As it turns out, the question as to where lunar H2O came from is not so straightforward it was actually baked via reactions with the solar wind.

When Apollo astronauts returned lunar surface samples of rock and regolith (fine, pulverized rocky grains), it was assumed they would be bone dry. After all, the moon has no atmosphere any water deposited on the surface from impacts would have been long lost to space.

But in recent analysis of the regolith, scientists were surprised to find quantities of water locked in the lunar material.

There are quantities of ice deposits all over the moons surface; some large deposits exist in polar craters where sunlight never shines on the crater bottoms. And now we know that even the sun-baked surface and sub-surface has a frozen supply.

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According to new research by astrochemists Alice Stephant and François Robert, of Muséum National dHistoire Naturelle, Paris, the source of the vast majority of the surface water trapped in regolith samples is not from aeons of asteroid and comet impacts two well known sources of cosmic water ice its the sun. Rather, the water found in lunar regolith is created via chemical reactions with the solar wind.

Their findings have been published in the Proceedings of the National Academy of Sciences.

Through isotopic analysis of deuterium/hydrogen and lithium isotope ratios, the researchers were able to determine that the source of the water did not originate from ancient impacts, but from reactions in and on silicate regolith grains. High-energy protons from the solar wind impact these grains, unlocking oxygen atoms, allowing them to bond with abundant hydrogen atoms, kickstarting the formation of hydroxyl, a tracer for water. Hydroxyl is a simple molecule of one oxygen atom and a hydrogen atom, whereas water has two hydrogen atoms bonded to an oxygen atom.

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Although there is undoubtedly water deposited on the lunar surface via impacts, with this new analysis in mind, they estimate that the solar wind contribution of lunar water accounts for a whopping 85 percent. In some samples, they believe that all the water came from solar wind interactions.

Of course, this analysis only applied to the moons surface, so water sources found below the surface may have a different origin.

It appear that, once again, the moon has shrugged-off conventional wisdom and shown us a cosmic laboratory where water can be baked from dry lunar regolith and solar wind protons as the only other ingredient.

Source: PNAS via Phys.org

http://news.discovery.com/space/most-moon-surface-water-comes-from-the-sun-not-comets-141007.htm

Moon's water may have come from the Sun

Particles from the Sun may be responsible for the presence of water recently detected in lunar soil, a new study has found.
Scientists have been speculating on how minute water reached the Moon ever since its discovery over the past decade by orbiting spacecraft.
There are a number of possibilities ranging from comet or meteor impacts, through to trapped volcanic gases during the Moon's formation four and half billion years ago.
Read more

Title: Water on The Moon, I. Historical Overview
Authors: Arlin Crotts (Columbia University)

By mid-19th century, astronomers strongly suspected that the Moon was largely dry and airless, based on the absence of any observable weather. In 1892, William H. Pickering made a series of careful occultation measurements that allowed him to conclude that the lunar surface's atmospheric pressure was less than 1/4000th of Earth's. Any number of strange ideas arose to contradict this. Respectable scientists realised that significant amounts of water on the Moon's surface would rapidly sublime into the vacuum. Since 2007, however, the field has started another revolution in thought, and we describe this, including some lesser known aspects.

Read more (3142kb, PDF)

Title: Water on The Moon, III. Volatiles & Activity
Authors: Arlin Crotts (Columbia University)

For centuries some scientists have argued that there is activity on the Moon (or water, as recounted in Parts I & II), while others have thought the Moon is simply a dead, inactive world. The question comes in several forms: is there a detectable atmosphere? Does the surface of the Moon change? What causes interior seismic activity? From a more modern viewpoint, we now know that as much carbon monoxide as water was excavated during the LCROSS impact, as detailed in Part I, and a comparable amount of other volatiles were found. At one time the Moon outgassed prodigious amounts of water and hydrogen in volcanic fire fountains, but released similar amounts of volatile sulphur (or SO2), and presumably large amounts of carbon dioxide or monoxide, if theory is to be believed. So water on the Moon is associated with other gases. We review what is known (and touch on what is unknown) about outgassing of various gases from the Moon.

Read more (9348kb, PDF)