# Is there enough material in the solar system to build a shell to enclose the sun?

Short answer: Yes, there is enough material in the solar system to build a shell enclosing the sun, but don’t count on it happening any time soon.

Long answer: Dyson spheres, which are shells that enclose stars and capture 100% of their energy output, are popular in sci-fi. On the Kardashev scale, which measures a civilization’s technological capacity, this sort of construction would make an alien species a “type II” civilization. But how feasible is it to actually build one? Is it even remotely possible for any species, perhaps one like us, to be a type II civilization?

Let’s do the math. If we took apart the planets for spare parts, how much matter would we have to work with?

Aside from the sun, the vast majority of the mass in the solar system is hydrogen in Jupiter. This is unfortunate for us because you can’t build something with a gas. Fortunately, the gas giants all have large rocky cores, likely similar in composition to the earth, which is made of iron, nickel, and rock. Jupiter’s core is about 25 times the mass of the earth. Saturn’s is about 15 earth masses. Uranus and Neptune together might give us 3 more earth masses of metal and rock. Altogether, combining the cores of the giant giants with the four inner planets, we get approximately 50 earth masses of metal and rock.

Imagine a square of earths, seven earths to a side. That’s approximately what we’ve got to work with. If we used it all to build a shell at the earth’s distance from the sun, it would be about 17 cm thick. And I’m not assuming this will be an efficient tool for gathering useful energy from the sun – I just want to build the shell.

Anyway, there is more than enough mass to build this shell, but matter isn’t the only raw material we need. To do this sort of cosmic construction project we also need energy to take apart the planets and move them around. The gravitational binding energy of Jupiter is immense – you could burn all the fossil fuels and nuclear power on earth and that wouldn’t even get you a trillionth of the energy you need to disassemble Jupiter.

Of course, if you already had a Dyson sphere, you could gather enough energy to build another one in just a few weeks. The problem is building that first one, so the only type II civilizations that can exist must have been born that way.

image credit: NASA via Wikimedia Commons

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