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

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

To hear it and every episode early and add free, plus hours of bonus content, check out

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

This episode is brought to you by Brilliant.

We hope to one day send spaceships to distant stars and settle the worlds around them,

but first, we had to find the systems and planets which are habitable.

So today we'll be asking how we go about surveying the galaxy for places we might want

to settle or ensuring we have the information we need to best prepare any expeditions

to the area.

Now principally, we tend to be thinking in terms of our telescopes back here on or around

Earth, but we have three basic approaches for garnering information in the context

of sending ships, and that's only one of them. If we can settle a system, that means we

have ships to get people and gear are there, so that also means we can get probes there for a flyby,

or probes and scouts there for in-depth looks. Fly-by is represented their own category because

of how spaceflight works. It takes immense energy to get a ship up to interstellar speeds,

but the same energy is required to slow it down upon arrival, and even more energy to get

that probe up to speed while also carrying its slowdown fuel. Thus two identical probes,

one doing a flyby and one traveling and halting a system, have different speeds. The flyby

probe can move twice as fast as the one planning to stop, and that matters a lot more expecting

centuries of flight time to even nearby star systems. The flyby probe can't get as much done in a given system, but it can get there faster,

and it can probably carry several additional systems that allow for a wider variety of information

...