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 ad-free, plus hours of bonus content, check out

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

Ganymede is an enormous moon, larger than any other we've found, including our own,

and may one day be the centerpiece of wider human settlements around Jupiter.

Colonizing Jupiter's moon Ganymede presents a fascinating mix of opportunities and challenges that we'll be exploring today.

As a basic background, Ganymede is the largest moon in our solar system, roughly parallel

in size to Saturn's largest moon Titan, which is slightly

wider if we include Titan's tall atmosphere, but if we just go by distance the surface,

Ganymede is a bit wider than Titan and also modestly denser and more massive.

Indeed, it is bigger than even Mercury, but being a good deal less dense is a little to half of

the planet Mercury's mass and a quarter of the mass of Mars.

It is also twice as massive as our own moon, though because it is less dense, gravity

is a bit lower on Ganymede, 14.6% of Earth normal compared to the moon's 16.6%.

In this regard, we tend to think it is very like our own moon, only without the proximity

to Earth, or the Sun, so it's often a less discussed colonization option than the major

planets, or even moons like Titan with its thick atmosphere, or Europa with its subsurface oceans.

But Ganymede has some unique characteristics that make it an interesting target for colonization

efforts.

Today we'll make the case for Ganymede by first reviewing some of the key advantages and

challenges associated with such an endeavor.

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