this post was submitted on 27 Jul 2025
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But how much can be caught?
From the sun, the angular diameter of the earth (12,756 km wide, 149,000,000 km away) is something like 0.004905 degrees (or 0.294 arc minutes or 17.66 arc seconds).
Imagining a circle the size of earth, at the distance of the earth, catching all of the solar wind, we're still looking at something that is about 127.8 x 10^6 square kilometers. A sphere the size of the Earth's average distance to the sun would be about 279.0 x 10^15 square km in total surface area. So oversimplifying with an assumption that the solar wind is uniformly distributed, an earth-sized solar wind catcher would only get about 4.58 x 10^−10 of the solar wind.
Taking your 130 billion tons number, that means this earth-sized solar wind catcher could catch about 59.5 tons per day of matter, almost all of which is hydrogen and helium, and where the heavier elements still tend to be lower on the periodic table. Even if we could theoretically use all of it, would that truly be enough to meet humanity's mining needs?
Well there are a lot of factors defining how much usable material we could get, and how hard it would be to do it.
Yeah, about 98% of the sun is hydrogen and helium, with other elements making up the remaining 2%.
The machine used to generate the magnetic field would likely be a ring rather than plate, with the goal being to bend the trajectory of any matter that passes through the ring just a little. In effect it would work a lot like a lens, that could focus matter passing through it into a cone of trajectories, with collection happening at the point of the cone, possibly a point at a much higher in orbit. (This does introduce some complications in the different orbital speeds for the ring and collector, but without getting into it, there is a solution for that, it's not the hardest part of this idea)
And how much you can capture depends a lot on how close to the sun you can put your magnet field ring. If it's stationed closer to the sun it shrinks the size of the sphere you're trying to cover. So if your ring could survive at 0.2 AU from the sun (about half the distance of mercury's orbit), a ring of the same diameter would cover 25 times more area of the sphere than if it was stationed at 1 AU.
So your 59.5 tons collected turns into 1487.5 tons, 2% of which is 29.75 tons of usable material (which I'll be honest, is not great considering the magnitude of the construction project). It's probably a better deal if you're using the hydrogen towards fusion power, but it's still not great.
The good news is that it scales well, the larger you make the ring, the better your ratio of materials gathered vs materials needed to build the ring, which makes the optimal diameter of the ring about the same as the diameter of the sun. So... yeah, this is not a project in our immediate future.