On Terra? Probably a few millions, tourists coming and going. In the Solar System? Around 1 trillion [1]. Living on a planet is the worst thing you can do as an

On Terra? Probably a few millions, tourists coming and going. In the Solar System? Around 1 trillion [1]. Living on a planet is the worst thing you can do as an advanced civilization: little or nothing to do against common occurrences such as hurricanes and regolith-quakes, or even, on a long enough time scale, gamma-ray bursts. Thankfully, as the unwise, mere LUCA [2] spacetime unattended consequences that we are, we are not an advanced civilization. [1] https://en.wikipedia.org/wiki/O%27Neill_cylinder https://en.wikipedia.org/wiki/O%27Neill_cylinder [2] https://en.wikipedia.org/wiki/Last_universal_common_ancestor https://en.wikipedia.org/wiki/Last_universal_common_ancestor