A solar wind-derived water reservoir on the Moon hosted by impact glass beads | Hacker News Reader

A solar wind-derived water reservoir on the Moon hosted by impact glass beads

nature.com

57 pointsHooke28 comments

"The amount of water held by impact glass beads in lunar soils is estimated to be 0.03–27.00 × 10^13 kg, assuming a global depth of lunar soils of 3–12m"

That's the same as a sphere of water with a radius ranging from 415 metres to 4.01 kilometres.

For comparison, all of the water on the Earth's surface could make a sphere with a radius of 693km, but just fresh water would work out to a radius of 5.34km.

Wolfram Alpha says the total fresh water on Earth would have a radius of 203 km. The Great Lakes alone would have a radius of 18 km.

https://www.wolframalpha.com/input?i=volume+of+fresh+water+o...

https://www.wolframalpha.com/input?i=volume+of+great+lakes

Thanks for the correction, I just Googled it and apparently that's wrong.

That's way closer than one would expect. So if that assumption is correct, the moon has a lot more fresh water per sqkm than Earth?

That's an apples/oranges comparison. Those numbers for earth are just surface liquid water. It is estimated that up to two orders of magnitude more water than in all the oceans is contained in earth's soil all the way down to the core, far below the surface. So earth wins easily both in terms of surface water and in terms of confined water.

Not to mention ambient water in the air.

All of earth's atmosphere weighs about as much as the first thirty/forty feet of the ocean. Of that atmosphere, only a tiny percent is water gas. The amount of water in the atmosphere is perhaps 0.01% of Earth's total water.

Is that roughly the same as the amount estimated here on the moon in the glassy beads?

Wow!

I was ready to be impressed by 0.04m radius!

If these beads are 0.1% water by weight and make up 1/20th of the lunar soil, colonists would find themselves processing dozens of kg of lunar soil per gram of water.

Given the history of past impacts and maybe even other solar system events contained in that soil perhaps it is not worth it.

It's nice that it recharges on a 15 year timescale though, which makes it something of a renewable resource.

I believe even the optimistic estimates are still at hundreds of dollars per kilogram launched. Local sourcing of water could still be more cost effective than relying upon external shipments from Earth.

Just to note something - Oxygen is fairly abundant on the moon (many rocks are oxides), hydrogen less so.

Water is H20 by composition, but since Oxygen atoms are at least 8 times heavier than Hydrogen (and usually about 16 times due to neutrons), the Hydrogen is only 11% of the water by weight.

Hence per Kg it's far more efficient to split the water into hydrogen, and re-oxidise it with native lunar Oxy; 1kg shipped water could be 1kg Hydrogen that would produce 9Kgs water once oxidised (ignoring difficulties in Hydrogen containment).

Ship an icy asteroid to the moon then.

I'm pretty sure that would require substantially more energy, unless the asteroid is already in a similar orbit to Earth's, or will coincidentally be crossing paths at just the right moment that a gravity assist can be arranged at sufficiently low cost.

You just give it a little bump at the right moment and it eventually gets there.

The post your replying to agrees with this but the conditions they made are the only ones where they believe it would be more cost effective than the above mentioned solutions.

It costs a lot of Delta v to move an ice asteroid... But on the bright side, there's a lot of ice on the ice asteroid which can be split into hydrogen and oxygen to help.

Your plan is to take water, split it into hydrogen and oxygen, and pump it through a rocket engine that turns it back into water?

I'm pretty sure that we can do better by just using the energy used to split the water to accelerate it instead.

Hydrogen and oxygen are propulsive fuels. Electrolysis and a source of water then gives you a pathway from electricity to propulsion. Where you get the electricity from is up to you; giant solar panels, nuclear reactors, etc. For moving an asteroid around, it's probably OK if it takes 10 years to get it on the right trajectory...

Here's an example of Nasa using electrolysis + water for maneuvering cubesats: https://www.nasa.gov/feature/ames/ptd-1

How do you plan to convert solar energy collected on a PV panel into thrust?

An ion thruster probably

https://en.wikipedia.org/wiki/Ion_thruster

That still needs mass in the form of a gas to push against.

Such as the aforementioned water...

This led me to Google around a bit and I came across this slashdot article from 10 years ago with a dead link https://m.slashdot.org/story/188821

I don't know why I didn't consider h2o molecules as ion engine propellant.

I'm too dumb to understand the article but anything "on the Moon" is very exciting.

The other response to your comment was overly negative. I'm quite dumb with regards to cosmology, but also research economics, and lowering resource transaction costs are a win.

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