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 signs that they are there. Plants help make oxygen and 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, seem to include the things that creatures make.
Most planets and moons do not have signs that life has lived there, which means that they are probably lifeless.
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