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Water on the Moon - How it Forms (rerail)
This started off as a comment on dickday's blog, but I realized it should probably be an entry by itself. He included this quote:
Scientists suspect that water is created in the soil via a chemical reaction involving solar wind and oxygen atoms already in the soil.
I was interested when I read this:
Water is way more common in the universe than many people expect. Wherever you find oxygen, you're probably going to find water, at least in trace amounts like we have on the moon.
The elements with atomic number < 10 are the most common in the universe (descending order). Oxygen is # 8, and hydrogen-1 makes up ~99% of the universe's matter. Water is very stable, and its formation is chemically favorable. Think of water at a valley bottom, while octane is on a hill. All of these factors contribute to making water both easy to form and stable (long-lived) after it forms.
Oxygen is a major part of many minerals, including those on the moon. The moon is constantly bathed in solar radiation, a flux of high energy rays and various radioactive nuclear particles moving at relativistic speeds.
It's a lot of energy, with bits of elementary matter mixed in; helium nuclei, electrons, neutrons, positrons. Free neutrons will decay to form a proton and electron. The free proton can eventually pick up an electron to form hydrogen.
That's right, there should be hydrogen atoms and molecules in solar radiation.
The moon has no magnetic field or atmosphere to protect it from solar radiation, so free hydrogen gets right down to oxygen-bearing rock, where, on occasion, an oxygen atom can be knocked free and form water.
Obviously, there will be hydrogen in all solar radiation, not just the radiation from our sun. That means that anywhere you have solar radiation hitting oxygen-bearing rock, you could see this reaction occurring.
It's not enough to make oceans, but it is enough to coat a few layers of molecules of water on the rocks.
The quantity of water increases nearer the poles, where the Apollo missions never reached.
The same solar radiation can also vaporize water molecules that form, giving them enough kinetic energy to leave the soil substrate and be lost. Near the poles and in areas of shadow, there is more hope that water will accumulate.
Scientists suspect that water is created in the soil via a chemical reaction involving solar wind and oxygen atoms already in the soil.
I was interested when I read this:
Water on Mars and water on the moon!!! If this little nook in the corner of an almost infinite universe has all this life giving liquid, imagine the amount of life out there.It's definitely cool to find water on the moon, but I think there's a bit of a misconception that water may be rare or hard to find.
Water is way more common in the universe than many people expect. Wherever you find oxygen, you're probably going to find water, at least in trace amounts like we have on the moon.
The elements with atomic number < 10 are the most common in the universe (descending order). Oxygen is # 8, and hydrogen-1 makes up ~99% of the universe's matter. Water is very stable, and its formation is chemically favorable. Think of water at a valley bottom, while octane is on a hill. All of these factors contribute to making water both easy to form and stable (long-lived) after it forms.
Oxygen is a major part of many minerals, including those on the moon. The moon is constantly bathed in solar radiation, a flux of high energy rays and various radioactive nuclear particles moving at relativistic speeds.
It's a lot of energy, with bits of elementary matter mixed in; helium nuclei, electrons, neutrons, positrons. Free neutrons will decay to form a proton and electron. The free proton can eventually pick up an electron to form hydrogen.
That's right, there should be hydrogen atoms and molecules in solar radiation.
The moon has no magnetic field or atmosphere to protect it from solar radiation, so free hydrogen gets right down to oxygen-bearing rock, where, on occasion, an oxygen atom can be knocked free and form water.
Obviously, there will be hydrogen in all solar radiation, not just the radiation from our sun. That means that anywhere you have solar radiation hitting oxygen-bearing rock, you could see this reaction occurring.
It's not enough to make oceans, but it is enough to coat a few layers of molecules of water on the rocks.
The quantity of water increases nearer the poles, where the Apollo missions never reached.
The same solar radiation can also vaporize water molecules that form, giving them enough kinetic energy to leave the soil substrate and be lost. Near the poles and in areas of shadow, there is more hope that water will accumulate.
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I cannot say that i understood it all, but thank you for the good explanation. Have you seen the new photos on the NASA website? The saturn ones at its equinox are really cool; the rings are seen almost on edge, one with that little moonlet seeming to be embedded in the rings.
Have you been tracking the space station in your sky? It is so great, and moves so fast. When the shuttle was docked, it looked even larger, of course.
September 25, 2009 12:26 PM | Reply | Permalink
feel free to post any questions you have about parts you didn't understand, i'll answer them later today.
i haven't had a chance to check out the new photos, so thanks for reminding me.
September 25, 2009 12:40 PM | Reply | Permalink
Thanks for the post.
It does make me think that there is so much energy in the universe bouncing around, and here we struggle to find a way to power our world.
September 25, 2009 12:56 PM | Reply | Permalink
the energy radiating off of stars and flying off into space might be important energy that humanity harnesses, but in a different way than you're probably imagining.
the solar or light sail promises to be the easiest, cheapest way to ply the stars.
engines? hah. who needs 'em? analog r00lz.
September 25, 2009 10:32 PM | Reply | Permalink
This is JUST GREAT. Tonite I can tell all my friends to read this.
The chemical process that you describe underlines to me, anyway, that there must be water throughout the universe. At least on rocky if not gaseous planets like ours. And we are already finding out how common it is for suns to have planets in the first place.
Thank you so much for this!
September 25, 2009 2:17 PM | Reply | Permalink
Yup, it's exciting stuff. We need to do confirm this phenomenon on Mars, Deimos and Phobos.
September 25, 2009 11:23 PM | Reply | Permalink
That brings up another point - the ability of a planet/moon etc. to have an atmosphere depends not just on its gravitational pull but its temperature.
A cooler planet (or moon, or other astronomical body) can hold on to an atmosphere with much less gravity, because the kinetic energy of the gas molecules is not high enough for them to achieve escape velocity.
This is why, for example, Pluto may have an atmosphere despite its small size - whatever gases it may have are too cold (i.e. slow-moving) to escape.
September 25, 2009 5:54 PM | Reply | Permalink
Good point. Geophysical chemistry FTW.
September 25, 2009 6:10 PM | Reply | Permalink
Forgot to mention that magnetic fields help, too.
September 25, 2009 11:40 PM | Reply | Permalink
makes sense to me. Probably also why you cannot find unbound hydrogen on earth.
C
September 25, 2009 7:55 PM | Reply | Permalink
Unbound hydrogen on earth is present in trace amounts; you're right, we don't find it on earth in the same way we don't find water on the moon.
Under earthly conditions, hydrogen is a gas, the fastest, tiniest molecule, so it ends up in the atmosphere eventually. In the atmosphere, it will quickly form water through a series of photochemical and free radical reactions. UV Light and very common free radicals (ozone, hydroxyl) covert it into water.
September 25, 2009 11:36 PM | Reply | Permalink
Even if it weren't chemically reactive, unbound hydrogen would have such a high velocity that it would escape the atmosphere before it could build up in any significant amounts - that is what happens to helium.
As I recall, all gas molecules in the atmosphere tend to have the same kinetic energy at any given temperature (technically, they cluster around a particular kinetic energy in a normal distribution). This means that the speed of a molecule is inversely proportional to the square root of its molecular weight. Hydrogen and helium molecules are light enough that their average velocity is greater than escape velocity (H2 has a molecular weight beween 2 and 6, but almost all of it is 2, as hydrogen-1 (protium) is far more abundant that hydrogen-2 (deuterium) or hydrogen-3 (tritium)). Helium molecules have a molecular weight of 4. (A helium molecule consists of a single helium atom).
Another note here: a molecule is the smallest amount possible of a particular substance - although we think of molecules as being combinations of atoms, unbound atoms count as molecules of a substance (such as a noble gas) that consists of unbound atoms).
September 26, 2009 10:18 AM | Reply | Permalink
Preaching to the choir about Graham's law.
If it's a single atom, you don't call it a molecule, so they are just helium atoms. Not molecules. At least that's how it is in every chemistry book i've ever read. You need at least two atoms to have a molecule. Please show me a cite that says otherwise, if you've got one.
September 26, 2009 6:49 PM | Reply | Permalink