This picture shows NASA's Deep Space Network, which searches the sky for radio signals.
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NASA/JPL

Looking for Life's garbage

Most forms of life leave evidence behind that they are there. Plants use up carbon dioxide and release oxygen. Some bacteria are known to release nitrogen into the environment. People leave behind smog, radio signals, and garbage.

Io, Titan, and perhaps Triton, show some of the waste products of life, including molecules of oxygen, nitrogen, or the more sophisticated hydrocarbons such as Polycyclic-Aromatic-Hydrocarbons (PAH's). These constituents are not present in the environments of most planets and moons.

This means that there is no evidence that sophisticated creatures are present.


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