A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Does asteroid mining threaten the earth?

September 7, 2012

Dear Cecil:

Space companies looking to mine asteroids are thinking of bringing them into orbit for easier access. Wouldn’t several of these asteroids eventually pull on the planet so much they would change the orbit of the earth or the moon? Is there a certain weight we need to reach before it’s a problem?

Cecil replies:

What? Oh, sorry, Quinn, I was daydreaming. I was in the court of Ferdinand and Isabella in the late 1400s. In walks this plucky adventurer with a crazy but cool scheme to reach India by sailing off the edge of the world. Isabella listens, then interrupts. “Chris,” she says, “I like your plan. Who knows, it might even work. But it’ll never pass environmental review.”

Let’s talk about asteroid mining. You’re asking because of the April announcement that a group of wealthy entrepreneurs has founded a firm called Planetary Resources, Inc., which wants to send space robots to nearby asteroids and strip-mine them for precious metals. Backers include Google CEO Larry Page, X Prize founder Peter Diamandis, and many other wheels in business and high tech — the monarchs of our age. Is the idea crazy? Absolutely. Cool? That too. Nonetheless, Quinn, I agree with you. We must consider the ramifications if this deranged plan actually works.

The prize here consists of the so-called platinum-group metals, which besides platinum include osmium, iridium, palladium, ruthenium, and rhodium and are relatively abundant in some asteroids. A choice specimen might have 8,750 times the platinum concentration found in the earth’s crust, 48,000 times the rhodium, and 660,000 times the iridium. With all three metals currently selling for more than $1,000 an ounce, a near-earth asteroid, or NEA, one kilometer in diameter could yield more than $5 trillion in precious metals. Recalling how New World gold distorted the Spanish economy, I suspect a flood like that would crash the precious metals markets, wreaking who knows what financial havoc. But one problem at a time.

The first thing the Planetary Resources moguls plan to do is launch a dozen or so space telescopes to hunt out promising NEAs, particularly those whose orbits are within about 1.6 million miles of the earth. (So we’re clear, these aren’t rocks in the asteroid belt between Mars and Jupiter, which are much farther away.) Currently we know of more than 9,000 NEAs, 848 of which are one kilometer across or larger.

Once enough likely asteroids are found, probes will be sent out to assay them for mineral potential, followed by robot miners to work the claims.

From here on out things start to get challenging. Mining an asteroid is going to involve cutting, drilling, boring, or melting frozen rock. (Given an NEA’s minute size and low gravity, blasting is out.) Then you have to refine the ore, which generally means pulverizing it and extracting the desired metal with chemicals. These are resource-intensive, high-maintenance industrial processes that would have to be conducted by remote control at a distance of 1.6 million miles. Even if you’re a high-tech genius, good luck.

Mindful of the difficulties, some enthusiasts propose capturing asteroids and dragging them nearer earth, possibly allowing humans to go up and assist with mining. One idea is using a solar-electric space tug to approach a small asteroid, deploy a fiber bag to capture it, and tow it home.

Not easy, but we’ll let the billionaires sweat the details. I'm also not going to worry about messing up the orbits of the earth or moon. Under the most optimistic scenario the asteroids we’d be shipping might be a few hundred meters in diameter. A rock big enough to cause the earth to wobble would need to be a thousand times as large.

Other concerns are more troubling. The first is crashing the asteroid into the earth and taking out Tulsa. The 1908 Tunguska meteorite explosion over Siberia, thought to have involved a rock 100 meters in diameter, flattened 80 million trees over 830 square miles. Best bet: parking the asteroid in fixed orbit on the far side of the moon.

Then there’s waste disposal. While precious metals are more plentiful on asteroids than on earth, we’re still talking parts per million, meaning you’ll wind up with a monstrous quantity of tailings. You can’t let the stuff just float there, so you’ll want to bag it up and send it spiraling down to the lunar surface.

Sierra Club types will object that this will mar the scenic beauty of the Mare Tranquillitatis. What’s worse is the potential for screw-ups or terrorism. If accidentally or otherwise a bag of tailings wound up in earth orbit and ruptured, the resultant spill could lead to a chain reaction of colliding debris — a scenario known as the Kessler syndrome — leaving earth surrounded by an impassable shell of space junk. One shudders to imagine the Superfund required to clean up that.

Not saying all these concerns couldn’t be addressed. But the Planetary Resources people better reserve a good chunk of their budget for lawyers, insurance, crisis management, and PR.

Related Posts with Thumbnails


Binzel, Richard P. et al. “Physical Properties of Near-Earth Objects” Asteroids III (2002): 255-271

Bolonklin, A. “Capture and Delivery of Asteroid to the Earth” Article Asteroid (2011).

Friedman, Louis and Tantardini, Marco. “Asteroid Retrieval Feasibility” ESA ESTEC: March 14, 2012.

Gerlach, Charles L. “Profitably Exploiting Near-Earth Object Resources” 2005 International Space Development Conference National Space Society, Washington, DC, May 19–22, 2005.

Kargel, Jeffrey S. “Metalliferous asteroids as potential sources of precious metals” Journal of Geophysical Research 99.10 (1994).

Mann, Adam. “Tech Billionaires Plan Audacious Mission to Mine Asteroids” Wired (Online Edition) 23 April, 2012. Accessed 02 August, 2012. http://www.wired.com/wiredscience/2012/04/planetary-resources-asteroid-mining/

McDonald, I. et al. “Platinum-group elements in the Morokweng impact structure, South Africa: Evidence for the impact of a large ordinary chondrite projectile at the Jurassic-Cretaceous boundary” Geochimica et Cosmochimica Acta. 65.2 (2001): 299–309.

Ross, Shane D. “Near-Earth Asteroid Mining” Space Industry Report December 14, 2001.

The Straight Dope: Could we move Mars or Venus into Earth's orbit and live there? http://www.straightdope.com/columns/read/2869/could-we-move-mars-or-venus-into-earths-orbit-and-live-there

United States Geological Survey. “Platinum-Group Metals - Statistics and Information (Platinum, Palladium, Rhodium, Ruthenium, Osmium, and Iridium)” Mineral Commodity Summary, 2012.

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