Human footprint in space: What are we emitting from earth?

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Offline rjpakes

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Dear all,

I'm doing some research on a SciFi short story I'm thinking of writing - the rough concept is that a human-like race is trying to hide it's existence from "prying" alien races surrounding their solar system. What technologies should they avoid using? Radio waves are the obvious answer - but is there anything else? I heard that nuclear detonations also leave a footprint traveling through space?

Any help will be greatly appreciated, I'm far from a physicist myself, but a big enthusiast nonetheless and would hate to write something a person with a scientific background would laugh at.

Obvious things I've already considered:

- no major city lights
- no space flight/satellite technologies (GPS)
- no wireless broadcasting (TV/Radio)

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Offline RD

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« Last Edit: 16/11/2015 23:45:51 by RD »

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Offline rjpakes

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Thanks! This also gives me an idea - If they're extra paranoid, I presume they'd need to avoid building larger structures reflecting sunlight - like aluminum rooftops of factories and the like...

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Offline RD

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Thanks! This also gives me an idea - If they're extra paranoid, I presume they'd need to avoid building larger structures reflecting sunlight - like aluminum rooftops of factories and the like...

A reflection from the surface of Earth could be from water, so not necessarily proof of human habitation.

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Offline Colin2B

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No cities, they tend to be hotter than surroundings.
Of course you could always concrete over your planet.
and the misguided shall lead the gullible,
the feebleminded have inherited the earth.

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Offline rjpakes

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Thanks - I guess something like an infrared scan would reveal the heat of a city? What do you mean by "concrete over your planet"? Some sort of planetary Dyson sphere?

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Offline evan_au

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It depends what you are trying to hide.

For an alien at the distance of Pluto, it would be fairly easy to tell that Earth has an oxygen-rich (unstable) atmosphere, hinting at the presence of life. This alone may trigger a closer look by curious aliens. Hiding the signal would almost take a Dyson sphere.

If you want to hide advanced technology without going entirely back to the bronze age, you could communicate via medium wave and shortwave radio; the ionosphere reflects it back to Earth.

Higher frequencies (such as used by TV, FM radio and radar) go straight through the ionosphere into space, giving away the presence of a technological society.

If you want an internet, optical fibers work at high speeds, and don't emit telltale signals.

But really, why would your average alien be interested in anything happening on Earth?
- We see a lot of "Hot Jupiter" exoplanets; for aliens from these worlds, Earth is too cold and too small, and doesn't have enough atmosphere.
- On the other hand, aliens from the Oort cloud comets would find Earth much too hot and heavy.