Without life, Earth's atmospherewould have no oxygen, so we're trying to look for...

Without life, Earth's atmosphere
would have no oxygen, so we're trying to look for gases
that don't belong, that might be attributed to life,
and we call them biosignature gases. [narrator] Searching for biosignatures
on other planets is really hard. We can't even see planets
outside our solar system. Stars are so much brighter than planets. It's like trying to see a firefly
in a spotlight. Today, we have a planet finding technique
called the transit technique