This picture shows NASA's Deep Space Network,
which searches the sky for radio signals.
Click on image for full size
Looking for Life's Garbage
Most forms of life leave behind evidence that they are there. Plants help make oxygen and use up carbon dioxide. Some creatures help make nitrogen. People leave behind smog, television signals, and garbage.
Scientists find life by looking for the things that creatures leave behind. Io, Titan, and maybe Triton show some of the things that creatures make, including molecules of oxygen and nitrogen.
Most planets and moons do not have the common garbage which life forms leave behind. This means that life does not seem to live there.
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