# How much space mining would begin to affect earth

1. Oct 7, 2012

### VegaMan

Just curious but:

Suppose that in the future we begin mining asteroids and other rocky objects in the asteroid belt for resources.

#1 how much material would we be able to bring back to earth before we start noticing increased gravitational effects (especially considering that recovered material would almost exclusively return to a land mass therefore making the distribution uneven)?

#2 how much additional material would be needed to affect the orbit of the moon? IIRC the moon is moving something like 1 cm a year away from us. At some point the additional mass will cause additional gravitational pull on the moon stopping or even reversing this movement. What would be this critical mass?

#3 What other problems could we potentially face due to space mining?

2. Oct 8, 2012

### Charmar

Hopefully someone can add to my answers here or provide better ones. Just my thoughts.

1. If we brought back the 18 largest known asteroids in the solar system it would add 0.03105% to our mass. (Just used wiki and a spreadsheet) I don't think we would use asteroids to provide materials to earth though. I believe the materials on asteroids will more be used to build things in space. It costs a large amount of money to get things out of our gravity well, so leaving materials in space that we can use could be of more benefit. Asteroids also often contain water so if we did bring them back they could add to our amount of water as well.

2. I don't have enough knowledge to answer this for sure, but I can't imagine it being affected greatly even if we add 100's of local asteroids to Earth's mass.

3. We could maybe lose control of a rocket guiding an asteroid home and drop a huge rock on ourselves. Perhaps there is a dormant virus on an asteroid and bringing it back to earth to breed in an environment with no immunity to combat it. I don't think these events are probable though.

3. Oct 8, 2012

### Drakkith

Staff Emeritus
The Earth's mass is 5.9736×1024 kg. A 1% increase in gravitational force would need an increase of around 1% of this mass, which is about 6x1022 kg. 60,000,000,000,000,000,000,000 kg. Sixty-thousand billion billion kilograms. That's a LOT of mass.

This would not happen like you imagine it to. The Moon moves away from us due to tidal effects which transfer rotational energy from the Earth and impart it into the orbital energy of the Moon. As you add material to the Earth you pull the Moon a little harder as the mass increases. This would slightly reduce the Moon's orbital radius and increase it's orbital velocity. It's a gradual increase with no tipping point that would suddenly cause the Moon to react, and you would need to add enough material over a year to counteract the 1 cm increase. I don't know how much mass it would take to pull the Moon into an orbit 1 cm closer. However, the transfer of energy from the Earth to the Moon does not end, it continues. So even if you add mass to the Earth the Moon will still move away, or will at minimum not move as close to the Earth as it would without the tidal effects.

Other than legal issues, I don't see any major problems from mining them.

4. Oct 8, 2012

### Staff: Mentor

The influence on the moon depends on the way the mass approaches earth (or some orbit around earth). If you use the moon to capture asteroids, it might even increase its orbital radius.

If you suddenly increase earth's mass by .002% (10^20kg), the average orbital radius would decrease by something similar, which is about 8km. Afterwards, the radius would continue to increase with ~4cm/year. Nothing serious happens, you just delayed the whole process by 200,000 years.

To put the mass number in context: One of the most-used materials in the world is steel, with an annual production of ~1 billion tons per year. 10^20kg correspond to 100 million years of our current steel production.

5. Oct 8, 2012

### girlgeeky2

If you guys would like to find out more about mining asteroids I just read a great piece on this site: http://www.mining-technology.com/features/featureplanetary-resources-age-asteroid-mining/ [Broken]

Last edited by a moderator: May 6, 2017
6. Oct 8, 2012

### Drakkith

Staff Emeritus
7. Oct 8, 2012

### Pkruse

In the past and I think also currently, the people stongly supporting space mining and investing in it are looking at the very small amount of material they could bring back as an interesting novelty and a very small side benefit to their main objective. Sales pitches to potential investors speak of processing, manufacturing, sale, and use of products and commodities in space without ever bringing it to Earth. They are also very confident that once their system is in place they could also redirect an asteroid that is on a collision course with Earth. One company working toward this is already profitable because they have found funding to research what it would take to deflect an asteroid. They are also getting NASA funding to figure out how to make fuel and water for a Mars mission. Also a concern bringing in money is how to build a radiation shield for long term human space flight.

8. Oct 8, 2012

### VegaMan

Interesting. Thanks for the insight everyone. i didnt really think about the fact that the amount of mass in the asteroid belt was less than 1% of the earth's mass.

9. Oct 12, 2012

### Vodkacannon

It's a good thing the moon isn't getting closer to us by centimeters each year!