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.

Our future lies among the stars, and many

challenges must be overcome to reach them. One of those challenges is making sure all ships

don't crash into our own garbage littering orbit. People often discuss if our future

spaceships will be built down here or up in orbit,

and as we discussed a couple months back in our episode Starship factories, it's just as likely

they'll be built deeper out in space and inside contained dockyards.

Here, fragile ships under construction don't have to worry about tiny bits of space debris

hitting them or the construction crews, who also don't have to worry that any lost nut

or bolt or sliver of metal will drift off into space and strike someone moving on a different

orbital path like a bullet.

And this is the danger of orbital debris.

Things orbit our planet faster the lower they are, and that low

orbital region is also the most valuable being close to Earth, but they are crisscross at

different speeds, and with those different speeds, varying by as much as thousands of miles or

kilometers per hour. Any tiny fragment of material, the size of a P, you collide with, carries energy comparable

to what we use for heavy machine guns, designed for tearing lightly armored vehicles or

structures apart.

What they do to people in spacesuits or tissue paper-thick spacecraft walls is devastating,

...