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.nebula.tv slash Isaac Arthur and use my code, Isaac Arthur.

The galaxy has many stars orbited by many planets, and many of these are orbited by

immense icy moons, but could others have oceans on their surface, or even life?

In the early 24th millennia, a colony arc fleet arrived around Cygnus X1, a black hole super giant binary 7,200 light years from Earth, where they had used the black hole to

permit them to decelerate down from a high fraction of light speed.

This had become a common way of seeding regions of the galaxy to send out massive fleets

propelled by enormous pushing beams to distant black holes, where they could use the powerful

gravity of the object to slow down with little to no fuel.

Of course a black hole already very close to a blue super giant just waiting to go

bang is not an ideal place to set up your civilization, and a rough place to break a fleet

at, so they plan to complete their maneuver then drift over to a nearby system in which

Astrius, a G1 Sun, just a bit brighter than our own, was orbited by some planets, including an

immense gas giant named Zephyr that dwarfs even Jupiter.

From here they would set up their Alpha Base, where they could resupply and from which

splinters of the fleet could radied out from this new hub of Humanities Galactic expansion.

As the vanguard of the fleet completed

their maneuvers around Cygnus X1 and left the region of mass of radiation and lighting

around the binary, they turned their telescopes on the Astria-Zephyr system to learn more details

of its minor planets. They soon saw a beautiful oceanic moon around Zephyr, which they nicknamed Aquarius.

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