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.

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 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.

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