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 add free, plus hours of bonus content,

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

Whether it's Javan 4 or Endor from Star Wars or Pandora from Avatar, science fiction

has shown us many planets with life that were actually moons.

But as science begins showing us our first real exo moons, we may discover that some already

have life on them, or may make good candidates

for future settlement.

Earth has one of the largest moons in the solar system, and the only moon of significance

around a rocky planet. Indeed, our moon is five or six times more massive than Pluto,

while Jupiter and Saturn's largest moons each have

nearly half the mass of Mercury. Now, the reality is that our solar system is probably not a

very representative example of what there is out in the universe. Indeed, Earth's moon has long been

suspected of being particularly anomalous, and possibly a critical factor in why Earth has life. But with the

exception of our moon around our planet, which may or may not be bizarre in galactic terms,

we have every reason to think that a planet as big as Jupiter could have moons which are

fully as big as Earth. We have even found thousands of planets bigger than Jupiter, most

of them warmer and closer

to their star than Jupiter.

Now that's probably not the norm either, any more than 7 feet or 2 meter tall humans would

be, but they sure are easy to spot in a crowd.

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