Lunar craters may be electrified:
The researchers created computer simulations to discover what happens when the solar wind flows over the rims of polar craters. They discovered that in some ways, the solar wind behaves like wind on Earth — flowing into deep polar valleys and crater floors. Unlike wind on Earth, the dual electron-ion composition of the solar wind may create an unusual electric charge on the side of the mountain or crater wall; that is, on the inside of the rim directly below the solar wind flow.
Since electrons are over 1,000 times lighter than ions, the lighter electrons in the solar wind rush into a lunar crater or valley ahead of the heavy ions, creating a negatively charged region inside the crater. The ions eventually catch up, but rain into the crater at consistently lower concentrations than that of the electrons. This imbalance in the crater makes the inside walls and floor acquire a negative electric charge. The calculations reveal that the electron/ion separation effect is most extreme on a crater’s leeward edge — along the inside crater wall and at the crater floor nearest the solar wind flow. Along this inner edge, the heavy ions have the greatest difficulty getting to the surface. Compared to the electrons, they act like a tractor-trailer struggling to follow a motorcycle; they just can’t make as sharp a turn over the mountain top as the electrons.
“The electrons build up an electron cloud on this leeward edge of the crater wall and floor, which can create an unusually large negative charge of a few hundred Volts relative to the dense solar wind flowing over the top,” says Farrell.
One more thing to worry about. Could it be discharged with a big aluminum mesh net? Lots of aluminum on the moon…
Worry about, yes, but is there any possibility to use this phenomenon as a mechanism to harvest additional energy?
High voltage doesn’t necessarily mean high power.
Back in the day when they thought there might be ‘seas’ of dust on the moon…didn’t Clarke’s “A Fall of Moondust[title?]” anticipate an analogous problem?
Just trying to recall.
As an aside, the discharge proposal seemed similar to an approach I had for harvesting solar wind on the Moon. As I recall, the densities of normal solar wind are terrible at Earth’s distance, something like a few kg of material (mostly hydrogen and helium) can be harvested per square kilometer per year. However, you might be able to put some sort of cheap charged grid over huge tracts of lunar territory and concentrate the solar wind from hundreds or even thousands of square kilometers. Put a positive charge over most of the land with a negative charge in the center. Positive ions would concentrate at the positive charged part. Harvest your hydrogen.
For some reason all I can think of is “That would make one Hell of a big vacuum tube!” With a free electron source we just need to add a few grids and maybe a magnetic field if needed and you could have the bitchin’est guitar amp in the universe! “Eat my electrons Spinal Tap! This baby goes up to 110,000” 🙂
“Positive ions would concentrate at the negative charged part.”
Yes, I also wonder how this might be leveraged for lunar industrialization.
calculations reveal . .
correction: . . . calculations predict . . .
I’m tired of people taking unproved computer models as fact.
Once I build the largest AM radio station in the inner solar system, I start playing REAL rock and roll. I can see it now… Aliens for parsecs will stop by to request more Chuck Berry and Buddy Holly. 🙂
Sorry back to reality and work. Just make sure the lander is ESD approved, wear your ground strap and you should be OK.
K:
I agree. They don’t call it “ground” for nothing. I’ll believe it when I see it. However these computer models are good at letting us know what to look for.
Interrupting the flow of the solar wind over the crater would prevent the charge separation from being maintained. Once the charging mechanism is stopped, any charge there could decay away, if there was an ambient plasma.
A loop of conductor 100 m in diameter carrying 10 amps of current would produce a strong enough magnetic field to block the solar wind, if my BOTE calculation is correct. The current required would scale linearly with loop radius, while the area shielded would increase quadratically.
They don’t call it “ground” for nothing
You have to remember that lunar ground will be in general a lot less conductive than ground in most places on Earth (which have water and a bit of electrolytes aiding things).
After reading this I am somewhat skeptical that this will be the case. This theoretical model does not take into account the nanoscale iron or meteoric iron in the regolith that would conduct and or dissipate charge for this source.
One more reason for precursor robotic landers. Oh wait, we cancelled all these.
Just a thought. Would there be any way to view test this the theory of electrical charges from space or even Earth, perhaps not directly but by some effect they have on the soil?
I wonder if closely monitoring the suspected craters under different solar wind conditions would produce any visible changes as you would suspect if the models area actually accurate.
Re generating power, a potential of 300 volts = 1 statvolt over a scale of 100 m = 1e5 cm indicates an electric charge on the order of (1 statvolt)(1e5 cm) = 1e5 statcoulombs. Consequently, the energy available is on the order of (1e5 statcoloumbs)(1 statvolt) = 1e5 ergs = 0.01 joule. We’re definitely not going to be generating any useful power from this effect. (Sorry about the CGS units, but it’s just easier in this case).
Re harvesting the solar wind, I find less than a *microgram* per square kilometer per year, based on a solar mass-loss rate of ~2e-14 solar masses per year (Wikipedia).
Re shielding, I concur with the 10-amp current needed, based on a typical electron speed of 500 km/s (Wikipedia, again), but I find this independent of the size of the shield.
In terms of testing the existence of this phenomenon, how about measuring the motion of levitated dust at various times of the lunar day? The solar wind tends to deposit a negative charge while photoionization by solar UV will tend to create a positive charge. As night falls one might see, for example, a dust storm of positively charged particles heading toward leeward edges of craters. I believe some ALSEP data indicate “winds” near sunset or sunrise.
Just a thought. Would there be any way to view test this the theory of electrical charges from space or even Earth, perhaps not directly but by some effect they have on the soil?
I suspect you’d probably see something faint in soft X-rays or hard UV. Solar wind would hit differently, if there’s something going on here.
Re shielding, I concur with the 10-amp current needed, based on a typical electron speed of 500 km/s (Wikipedia, again), but I find this independent of the size of the shield.
I derived that figure by estimating the magnetic field needed to have a magnetic pressure equal to the stagnation pressure of the solar wind. Since the field of a loop goes as 1/R, the current cannot be independent of the radius of the loop.
@Paul Spudis: Your’re right. I committed the school-boy error of ignoring the plasma effects, treating incoming particles as isolated.