The Drake equation states that:
where:
N is the number of
civilizations in our galaxy with which communication might be possible; and
R* is the average rate of
star formation in
our galaxy
fp is the fraction of those stars that have
planets
ne is the average number of planets that can potentially support
life per star that has planets
fℓ is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop
intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space.
This astronomer is saying
ne = 100 billion