Graphic of how the solar wind flows over the Moon.  Credit: NLSI

Shocking! Lunar Craters May Be Electrified

19 Apr , 2010 by

The Moon keeps getting more interesting all the time! But now comes “shocking” news that exploring polar craters could be much harder and more dangerous than originally thought. New research shows that as the solar wind flows over natural obstructions on the moon, such as the rims of craters at the poles, the craters could be charged to hundreds of volts. “In a nutshell, what we’re finding is that the polar craters are very unusual electrical environments, and in particular there can be large surface charging at the bottom of these craters,” said William Farrell from Goddard Space Flight Center, lead author of a new research on the Moon’s environment.

The moon’s orientation to the sun keeps the bottoms of polar craters in permanent shadow, allowing temperatures there to plunge below minus 400 degrees Fahrenheit, cold enough to store volatile material like water for billions of years. And of course, any resources that may lie in those craters are of interest for any future explorers, should astronauts ever return to the Moon.
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“However, our research suggests that, in addition to the wicked cold, explorers and robots at the bottoms of polar lunar craters may have to contend with a complex electrical environment as well, which can affect surface chemistry, static discharge, and dust cling,” said Farrell, who is part of a lunar Dream Team — the Lunar Science Institute’s Dynamic Response of the Environment at the moon (DREAM) project, which is also part of NASA’s Lunar Science Institute.

Solar wind inflow into craters can erode the surface, which affects recently discovered water molecules. Static discharge could short out sensitive equipment, while the sticky and extremely abrasive lunar dust could wear out spacesuits and may be hazardous if tracked inside spacecraft and inhaled over long periods.

The solar wind is a thin gas of electrically charged components of atoms – negatively charged electrons and positively charged ions — that is constantly blowing from the surface of the sun into space. Since the moon is only slightly tilted compared to the sun, the solar wind flows almost horizontally over the lunar surface at the poles and along the region where day transitions to night, called the terminator.

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,” said Farrell.

The negative charge along this leeward edge won’t build up indefinitely. Eventually, the attraction between the negatively charged region and positive ions in the solar wind will cause some other unusual electric current to flow. The team believes one possible source for this current could be negatively charged dust that is repelled by the negatively charged surface, gets levitated and flows away from this highly charged region. “The Apollo astronauts in the orbiting Command Module saw faint rays on the lunar horizon during sunrise that might have been scattered light from electrically lofted dust,” said Farrell. “Additionally, the Apollo 17 mission landed at a site similar to a crater environment – the Taurus-Littrow valley. The Lunar Ejecta and Meteorite Experiment left by the Apollo 17 astronauts detected impacts from dust at terminator crossings where the solar wind is nearly-horizontal flowing, similar to the situation over polar craters.”

“This important work by Dr. Farrell and his team is further evidence that our view on the moon has changed dramatically in recent years,” said Gregory Schmidt, deputy director of the NASA Lunar Science Institute at NASA’s Ames Research Center, Moffett Field, Calif. “It has a dynamic and fascinating environment that we are only beginning to understand.”

Next steps for the team include more complex computer models. “We want to develop a fully three-dimensional model to examine the effects of solar wind expansion around the edges of a mountain. We now examine the vertical expansion, but we want to also know what happens horizontally,” said Farrell. As early as 2012, NASA will launch the Lunar Atmosphere and Dust Environment Explorer (LADEE) mission that will orbit the moon and could look for the dust flows predicted by the team’s research.

The research was published March 24 in the Journal of Geophysical Research.

Source: NLSI

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IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 19, 2010 1:55 PM

“I guess that we would expect [cats] to be affected in a similar manner?” wink

Aqua4U
Member
April 19, 2010 2:44 PM

I see mortars lofting a conductive doped carbon fibre netting, which expands to fill the basin of a charged crater’s floor. The netting continually collects the negatively charged electrons from the Sun which are used to generate power and a magnetic field strong enough to ward off most incoming radiation.. the field surrounds the habitat and close environs.
This might be used on the Moon AND Mars?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
April 19, 2010 11:12 AM

So the usual wisdom is that ambipolar drift acts to keep plasma neutral. But here there are surface effects around flow blockages.

Seems like a Star Treck future up ahead, add craters as good subjects for field “shields” besides radiation protection. Set them up over the area those ~ 100 s before entering, and let the dust equalize instead.

[Or perhaps a hydrogen ion spray gun would be easier – and funnier!]

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
April 19, 2010 11:14 AM

D’oh! “Star Treck” – Star Trek. (I swear I had water with dinner! But what was in it, that was some doofy spelling…)

SteveZodiac
Member
SteveZodiac
April 19, 2010 11:34 AM

so, there’s water and power …..

Olaf
Member
Olaf
April 19, 2010 1:14 PM

Is it such a big danger?
It is not like 1 meter difference will zap you with 100 volt.

Aqua4U
Member
April 19, 2010 5:50 PM

@iantresman – The Moon’s surface is exposed to +/-1,370 watts per square meter in the solar wind. There is a temperature difference of 275 degrees F between sunlight and dark. As the terminator processes across the surface the solar wind abruptly starts or stops energizing the regolith as the temperature simultaneously rises or falls. It has been recently speculated that rolling dust storms of thermal or triboelectrically levitated dust and gas particles proceed along with the terminator on the Moon as an artifact of those temperature and energy density oscillations. It is possible that this ‘terminator energy’ field is circumlunar and interacts with the cold sink electrons?

Aqua4U
Member
April 19, 2010 6:02 PM

BuzzzzZAP! A way to make and transport water vapor on the Moon?

PrometheusOnTheLoose
Member
April 19, 2010 4:18 PM

Brinf a few mirrors and set the up downwind of the solar wind, to reflect into the crater. . . . warm it up and reduce the charging at the same time.

vagueofgodalming
Member
April 20, 2010 12:55 AM

Lunar Craters May Be Electrified

I agree. Time to dispense with those polluting diesel and coal-fired craters.

IVAN3MAN_AT_LARGE
Member
IVAN3MAN_AT_LARGE
April 19, 2010 7:02 PM

Aqua:

The Moon’s surface is exposed to +/-1,370 watts per square meter in the solar wind.

Dude, I think that you’ve confused protons in the solar wind with photons — it is light energy from the Sun that is equivalent to ~1368 W/m² at a distance of 1 AU.

Lawrence B. Crowell
Member
Lawrence B. Crowell
April 19, 2010 7:08 PM

The low conductivity of the lunar regolith is what permits this charge build up to grow. The sun charges this up as a sort of natural Leyden jar. This is rather unexpected.

LC

The Eclectic Exterminator of Stupid Electricians
Member
The Eclectic Exterminator of Stupid Electricians
April 19, 2010 10:06 PM

I, for one, do believe it. I’ll wait for the evidence thank you.

What is the conductive of the regolith here, eh?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
April 20, 2010 1:31 AM

It is not like 1 meter difference will zap you with 100 volt.

Well, if the discharge time is on the order of 100 s, you will collect more of a charge difference traveling in and out of these “Leyden” craters.

Sure, I would wait for evidence before crying “charge!” But seeing the dust effects already observed, it is a compelling model.

Olaf
Member
Olaf
April 20, 2010 5:07 AM

@Torbjorn Larsson
“Well, if the discharge time is on the order of 100 s, you will collect more of a charge difference traveling in and out of these “Leyden” craters.”

Yes you collect more charge if you move to one side but you lose the charge step but step when you jump to the other side. (Assuming you have a conducting suit)

It is a big story if you would jump 100 meters. Or have a long conducting cable and then touch it.

Aodhhan
Member
Aodhhan
April 20, 2010 5:39 AM
iantresman… nice job finding and posting the research info. It is somewhat interesting information. I don’t think there is any direct danger to astronauts on the surface. Although there is the capability to build up volts… from this information anyhow… I don’t see an amperage threat. However, the damage it could do to electronics is obvious. Just like many other instruments on Earth, have to ensure they are grounded when used. All in all, I think there is probably more of a threat on Mars, where any piece of equipment in a dust storm will begin to collect a charge. If you could think of a way to collect & store this energy to a point where it… Read more »
Aqua4U
Member
April 20, 2010 9:48 AM
IVAN3MAN_AT_LARGE The solar wind is made of Hydrogen (95%) and Helium (4%) and Carbon, Nitrogen, Oxygen, Neon, Magnesium, Silicon and Iron (~1%). These atoms are all in the form of positive ions which means they have lost electrons because the temperature is so hot. So really, solar wind is positive ions and the electrons these ions have lost. We call this plasma. How does this plasma effect the lunar surface? Scott M. Auerbach, a theoretical chemist at the University of Massachusetts at Amherst offers a more detailed answer: “Light from the sun excites electrons in the atoms which constitute the brick wall. How does that electronic energy get converted to heat, you ask. The key is ‘radiationless transitions.’… Read more »
Hannes
Member
Hannes
April 20, 2010 11:35 AM

Is there any possibility that this build-up of negative charge somehow has influenced the signature traces of the imaging spectrometers from Chandrayaan-1 and others?

Aqua4U
Member
April 20, 2010 4:42 PM
“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,” said Farrell. The negative charge along this leeward edge won’t build up indefinitely. Eventually, the attraction between the negatively charged region and positive ions in the solar wind will cause some other unusual electric current to flow. The team believes one possible source for this current could be negatively charged dust that is repelled by the negatively charged surface, gets levitated and flows away from this highly charged region.” The key words here are “…can create an unusually… Read more »
Hannes
Member
Hannes
April 20, 2010 12:46 PM

I mean hydroxyl groups are negatively charged. And there is water on the moon, presumably…

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