I'm bouncing around this thread calling out all the problems with space colonization as a solution to problems on Earth, and I'd like to give just one example of why terraforming Mars is, for all practical terms, completely impossible. And I'm going off the premise that terraforming is necessary to make Mars actually habitable for large groups of humans - the resource cost of self-contained spaces all over the planet would be far too high to make sense as a solution to living even on a degraded Earth.
Mars's atmosphere is 1/50th the density of the Earth's. Its current total mass is 2.5e+16 kg. To get it on par with Earth's (the reasonable threshold for habitability), we'd need to increase the mass of its atmosphere to 1.25e+18 kg. What's that number? That's 1,250,000,000,000,000,000 kg. Typically, the solution for providing Mars an atmosphere is to slam it with carbonaceous asteroids over and over until the endless collisions have formed a carbon-dense atmosphere from which we can start. Let's assume, generously, that 20% of the mass of an asteroid hitting a planet permanently becomes asteroid (that's very high but we're going with it to demonstrate the absurdity of this proposition). That means we'll need to bombard Mars with 6.25 x 10^18 kg of asteroids. Let's not worry about how many asteroids and assume we can do it with maximum efficiency. We just need to move asteroids from the closest portion of the belt to Mars. To do so we're ignoring the issues of: finding the asteroids (they are mostly very small), getting to the asteroids (they are very far apart), halting their momentum (they move very quickly), and developing the technology to move them (we don't have anything resembling a prototype for this). We're going to pretend we have a space station in the asteroid belt that keeps pace with Mars's orbit and always has something to launch. All we're looking for is the energy needed to transport that much mass that far.
The distance we need to cover in the most generous possible circumstance is 250 million km - about twice the distance from the Earth to the Sun. Converting kg to N will land us roughly around 5,625,000,000,000,000,000 N. To move that our 250M km is going to take 1.41026167125e+30 joules. Wow! That's a big number. What does it tell us? Well, annual global energy consumption is about 295167599999997700000 joules. That's 1/4,777,833,580 of the number we require to move suffficient atmospheric mass from the asteroid belt to Mars. So, if we reoriented every single ounce of energy on earth exclusively to building an atmosphere of sufficient mass (NOT COMPOSITION!!!) under impossibly optimistic conditions, it would take 4.7 billion years. Oh, and there would be 0 energy left over for human needs. Oh well!
When I say "terraforming Mars is impossible", this is what I mean.
(I did all this math myself so hopefully nothing's off)
I'm bouncing around this thread calling out all the problems with space colonization as a solution to problems on Earth, and I'd like to give just one example of why terraforming Mars is, for all practical terms, completely impossible. And I'm going off the premise that terraforming is necessary to make Mars actually habitable for large groups of humans - the resource cost of self-contained spaces all over the planet would be far too high to make sense as a solution to living even on a degraded Earth.
Mars's atmosphere is 1/50th the density of the Earth's. Its current total mass is 2.5e+16 kg. To get it on par with Earth's (the reasonable threshold for habitability), we'd need to increase the mass of its atmosphere to 1.25e+18 kg. What's that number? That's 1,250,000,000,000,000,000 kg. Typically, the solution for providing Mars an atmosphere is to slam it with carbonaceous asteroids over and over until the endless collisions have formed a carbon-dense atmosphere from which we can start. Let's assume, generously, that 20% of the mass of an asteroid hitting a planet permanently becomes asteroid (that's very high but we're going with it to demonstrate the absurdity of this proposition). That means we'll need to bombard Mars with 6.25 x 10^18 kg of asteroids. Let's not worry about how many asteroids and assume we can do it with maximum efficiency. We just need to move asteroids from the closest portion of the belt to Mars. To do so we're ignoring the issues of: finding the asteroids (they are mostly very small), getting to the asteroids (they are very far apart), halting their momentum (they move very quickly), and developing the technology to move them (we don't have anything resembling a prototype for this). We're going to pretend we have a space station in the asteroid belt that keeps pace with Mars's orbit and always has something to launch. All we're looking for is the energy needed to transport that much mass that far.
The distance we need to cover in the most generous possible circumstance is 250 million km - about twice the distance from the Earth to the Sun. Converting kg to N will land us roughly around 5,625,000,000,000,000,000 N. To move that our 250M km is going to take 1.41026167125e+30 joules. Wow! That's a big number. What does it tell us? Well, annual global energy consumption is about 295167599999997700000 joules. That's 1/4,777,833,580 of the number we require to move suffficient atmospheric mass from the asteroid belt to Mars. So, if we reoriented every single ounce of energy on earth exclusively to building an atmosphere of sufficient mass (NOT COMPOSITION!!!) under impossibly optimistic conditions, it would take 4.7 billion years. Oh, and there would be 0 energy left over for human needs. Oh well!
When I say "terraforming Mars is impossible", this is what I mean.
(I did all this math myself so hopefully nothing's off)