What would happen if large-scale lunar mining operations became commonplace?

February 27, 2012 3:36 PM

Could mining the moon destroy the oceans?

I was talking to a few people about the recent news about mining the moon and someone mentioned that this is a bad idea because it'll decrease the mass of the moon (and increase the mass of the Earth, as the raw ore comes home for processing), thus affecting the tides and potentially destroying some or all ocean habitats.

On a purely theoretical level, I realize that this is true. But how realistic are these concerns?

How much mass would actually need to be removed from the moon in order to significantly affect the tides, especially if the mass isn't just disappearing, but is being transferred to the Earth?

My question is actually three-fold:

1. How much would the mass of the moon need to decrease in order to have an impact on the tides, assuming that the missing mass is added to the mass of the Earth?
2. How likely is it that this would ever happen, even assuming large-scale lunar mining operations become commonplace?
3. Assuming the mass of the moon and/or Earth was changed dramatically enough to alter the tides, what impact would this have on the oceans and on life on Earth more generally?

This question is related, but doesn't quite answer the questions that I'm asking.

posted by asnider to Science & Nature (12 answers total)

2) If we brought back 1000 tons a day of material from the moon, it would take 220000000000 years to decrease the mass of the moon by 0.1%.
posted by ftm at 3:43 PM on February 27, 2012 [10 favorites]

Should have clicked - I see this aspect was addressed in the link.
posted by ftm at 3:44 PM on February 27, 2012

Response by poster: Yeah, I guess I'm really just asking about points 1 and 3, since number 2 was essentially answered in the other question that I linked to.
posted by asnider at 3:49 PM on February 27, 2012

You are not considering the mass of the fuel and other earthly resources consumed in building mining operations and getting that ore back to the earth.
posted by Ardiril at 3:53 PM on February 27, 2012 [1 favorite]

Response by poster: You are not considering the mass of the fuel and other earthly resources consumed in building mining operations and getting that ore back to the earth

You're right, but I assume that would be negligible in comparison to the mass of the material that would be coming to Earth from the moon, if we are to assume mass-mining of the moon. Maybe I'm wrong, though, and this should be accounted for in answering my questions.
posted by asnider at 4:04 PM on February 27, 2012

Best answer: How much would the mass of the moon need to decrease in order to have an impact on the tides, assuming that the missing mass is added to the mass of the Earth?

More than we could ever do -- let's say they scraped a mile off the top, all the way around. That would be the 3.79300 * 10^7 km^3 * 3.34600 g / cm^3 (the density of the moon) = 1.2691378 × 10^20 kilograms

That's (1.2691378 * 10^20 kilograms)/ (7.36 * 10^22 kilograms) or 0.17% of the mass of the moon. And that's removing 126,000,000,000,000,000,000 kgs. of mass. To put that in perspective, if you add up all the gold that has ever been mined in the world, you're going to get something south of 283,495,231 kilograms.

But anyway, in the event that we did remove that much, you can just multiply .17% the difference in sea level caused by the tides (3.67 meters), and you'd get a difference of about .62 millimeters. So not even a millimeter in difference in sea levels.

It wouldn't even counter act the effects of global warming.
posted by empath at 4:22 PM on February 27, 2012

(sorry, .367 meters)
posted by empath at 4:23 PM on February 27, 2012

(how the tides work)
posted by empath at 4:24 PM on February 27, 2012

The moon is gradually moving away from the Earth anyways so even if we could remove however many billions of tons of material would be necessary to have any material impact on the oceans we would have to do it faster than that phenomenon.
posted by XMLicious at 4:24 PM on February 27, 2012

We just need to ship an equivalent amount of waste back to the moon - win / win (just kidding)
posted by NoDef at 4:39 PM on February 27, 2012

Best answer: asnider, as you've eliminated Question 2, let's concentrate on 1 and 2. Which, by the way, are also equally implausible: anything capable of taking away a serious chunk of our moon would almost certainly also destroy the Earth in the process. But let's assume some sort of Space: 1999 scenario (which is being remade: woohoo childhood nostalgia!) and say that the Moon just disappears. In which case:

• our orbit around the sun would remain unaffected.
• we would still have tides, but these would be solar, not lunar: about ½ of the height we experience today. You can calculate the changes (removing, say, one half of the moon's mass would diminish the tidal changes by roughly 25%. To put this in perspective, mean current high tide for Honolulu is 1.35 meters, and mean low tide 0.9 meters.)
• The rotation of the Earth would not speed up: the moon's tidal dragging has slowed us from a six-hour day to our current rate, but that withdrawn energy has no way of being replaced.
• Animals that orient themselves by moonlight, such as some species of turtles, would be confused and immediately endangered.
• Environments that depend on regular tidal flooding, such as mangrove swamps, would dry up where high tide no longer reached, and be overwhelmed where salt water remained.

Perhaps in part due to the moon illusion, people usually underestimate just how huge the Moon is: it's by far the biggest natural satellite relative to its parent planet in the solar system. It has mountains higher than Everest. No mining operation that could be conceived by modern humans could cause a measurable drop in its mass.
posted by Bora Horza Gobuchul at 4:48 PM on February 27, 2012

I would assume that rather than moving a mass of ore back to the earth for processing, we would do most of the extraction on the moon itself. When an ounce of gold on earth means sorting ten tons of ore-bearing rock, it wouldn't make sense on any level to schlepp all that raw material back to process it.

This means doing it differently of course, but it would be nice to have methods of refining ore that didn't require millions of gallons of water or terawatts of fossil-fueled power. That might improve things here on the planet, as well.

Just sayin.
posted by halfbuckaroo at 4:50 PM on February 27, 2012 [1 favorite]