Hello, SFIA audio listeners. In this month's Nebula exclusive, big alien theory,

we're asking the reason alien civilizations might be rare is because most aliens are huge.

To hear it and every episode early and ad-free, plus hours of bonus content,

check out go.nebola.tv slash Isaac Arthur and use my code, Isaac Arthur.

We often discuss our future in the asteroid belt, and the glorious civilizations we might

one day build there.

However, it is but a pale shadow of its larger twin, the Kuiper Belt, out of the edge of

the solar system.

When I was a kid, we were first beginning to seriously discuss the possibility that the

asteroid belt might be as important to settling space as the Moon, Mars, or Venus.

And indeed I think it's more critical to settling in solar system than Mars or Venus are, and

second only to the Moon.

However, if the asteroid belt is the gateway to colonizing our solar system,

it is the Kipel belt outpass Neptune that represents the gateway to the galaxy, and today

we'll discuss why that is and what that future looks like. In order to do that, we first

need to say what the Kuiper belt is. The Kipel belt is a region out past the orbit

of Neptune of many unattached minor planets and icy objects orbiting our Sun.

We typically define it as a donut or tourist-shaped region stretching from 30 to 50 astronomical

units, also known as A-U, where one A-U is the distance of Earth from the Sun. As such, it contains

a larger value in it than the entire inner solar system. The name is in honor of Gerard Kuyper,

the astronomer who discovered two of the bigger moons of Neptune and Uranus, and also helped

identify landing sites on our own moon for the Apollo missions.

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