Water Moving on the Moon

NASA’s Lunar Reconnaissance Orbiter (LRO) has observed water molecules moving around the dayside of the Moon.

The Lyman Alpha Mapping Project (LAMP) measurements of the sparse layer of molecules temporarily stuck to the surface helped characterize lunar hydration changes over the course of a day.

Geophysical Review Letters – Diurnally‐Migrating Lunar Water: Evidence from Ultraviolet Data

The amount and locations vary based on the time of day. This water is more common at higher latitudes and tends to hop around as the surface heats up.

Scientists have hypothesized that hydrogen ions in the solar wind may be the source of most of the Moon’s surface water. With that in mind, when the Moon passes behind the Earth and is shielded from the solar wind, the “water spigot” should essentially turn off. However, the water observed by LAMP does not decrease when the Moon is shielded by the Earth and the region influenced by its magnetic field, suggesting water builds up over time, rather than “raining” down directly from the solar wind.

“These results aid in understanding the lunar water cycle and will ultimately help us learn about accessibility of water that can be used by humans in future missions to the Moon,” said Amanda Hendrix, a senior scientist at the Planetary Science Institute and lead author of the paper. “Lunar water can potentially be used by humans to make fuel or to use for radiation shielding or thermal management; if these materials do not need to be launched from Earth, that makes these future missions more affordable.”

Plain Language Abstract

Data from the Lunar Reconnaissance Orbiter’s UV spectrograph are used to measure the signature of a partial monolayer of water on the top surface of the lunar regolith. The diurnally‐varying signature is interpreted as water molecules thermally desorbing close to local noon each day, when the surface temperature reaches a maximum value. These measurements represent the first time the UV absorption signature has been used to detect water on a rocky airless body, and are the only set of data currently providing diurnal coverage of lunar hydration.


10 thoughts on “Water Moving on the Moon”

  1. One final thought to consider: once the protons hit the lunar surface, they don’t just disappear.

    Since they hit the surface at some velocity, they probably penetrate a certain average depth. From there, some may diffuse back to the surface and may be able to escape the moon’s gravity (maybe grabbing an electron along the way to form a hydrogen radical), but at least some should remain.

    H+ ions are quite reactive, so the ones that remain should eventually react with whatever’s available, and that’s mostly oxides. That should produce hydroxides, like I wrote earlier, some of which are equivalent to hydrates. That doesn’t even even require the oxygen to be liberated.

  2. The excited ones are easier to break. And some molecules probably do break, even if that doesn’t cause light emission. I’d be more surprised if the solar wind energy spectrum is limited to only exciting stuff without breaking anything. Later, when such molecule fragments react, that should emit EM too, I think, though probably not in the visible spectrum.

    As for hydrogenation of lunar oxides by the solar wind, even if indeed it happens (I expect it does, though maybe I got the chemistry wrong), the next question after that is how much? AFAIK water and hydrate concentration on most of the lunar surface is in the range of trace amounts. But recent measurements suggest significant ice deposits in permanently shadowed areas near the poles.

  3. We get auroras from the exciting of the molecules, not the breaking of them. And that would be a big maybe on the moon. But if so, I am putting in a pool at my moon-house.

  4. I was hoping for a little more heat in your argument. Those electrons are old and set in their ways.

  5. My guess:
    Oxides bombarded by protons (hydrogen ions) yield hydroxides, which are chemically equivalent to hydrated minerals (at least in some cases). From there, there are too options:
    – Either proton exchange with other hydroxides, or
    – Further bombardment by protons.

    Either way, that should produce water and leave metal cations, which are later neutralized by electrons from the solar wind (the solar wind contains both protons and electrons). Something like this:

    MO + p+ –> MOH+
    MOH+ + e- –> MOH
    MOH + p+ –> M+ + H2O
    M+ + e- –> M
    2MOH <–> M2O + H2O

    etc. In most oxides, the metal to oxygen ratio isn’t 1:1, and the metal can have any of several oxidation states, so it’s actually more complicated. But it’s basically redox chemistry (edit: and acid-base).

    Also, don’t forget that the solar wind has enough energy to excite chemical bonds, maybe even break some of them. That’s how we get the auroras, and that helps move the chemistry along. UV radiation can also excite chemical bonds.

  6. Just because the surface of the moon seems dry does not mean the moon does not have water. I would drill first before making that claim.

  7. If the hydrogen has a greater affinity for the Oxygen than whatever the Oxygen is current bound to then water will happen.

  8. There’s plenty of oxides on the moon surface. This doesn’t require fusion – just chemistry.

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