Answered: Factor What It Represents Possible…

Astronomy

1st Edition

ISBN:9781938168284

Author:Andrew Fraknoi; David Morrison; Sidney C. Wolff

Publisher:Andrew Fraknoi; David Morrison; Sidney C. Wolff

Chapter30: Life In The Universe

Section: Chapter Questions

Problem 31E: Think of our Milky Way Galaxy as a flat disk of diameter 100,000 light-years. Suppose we are one of...

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Question

The Drake equation In 1961 astronomer Frank Drake
developed an equation to try to estimate the number of
extraterrestrial civilizations in our galaxy that might be

able to communicate with us via radio transmissions. Now
largely accepted by the scientific community, the Drake
equation has helped spur efforts by radio astronomers to
search for extraterrestrial intelligence. Here is the equation:

NC = N # fp # ne # fl
# fi
# fc # fL
OK, it looks a little messy, but here’s what it means:So, how many ETs are out there? That depends; values
chosen for the many factors in the equation depend on
ever-evolving scientific knowledge and one’s personal
guesses. But now, some questions.
a) What quantity is calculated by the first product, N # fp?
b) What quantity is calculated by the product, N # fp # ne # fl
?
c) What probability is calculated by the product fl
# fi?
d) Which of the factors in the formula are conditional
probabilities? Restate each in a way that makes the
condition clear.

Factor
What It Represents
Possible Value
N
Number of stars in the Milky Way Galaxy
200–400 billion
fp
Probability that a star has planets
20%-50%
Number of planets in a solar system capable
of sustaining earth-type life
ne
1? 2?
fi Probability that life develops on a planet
with a suitable environment
1%-100%
fi
Probability that life evolves intelligence
50%?
fe
radio communication
Probability that intelligent life develops
10%-20%
fi Fraction of the planet's life for which the
civilization survives
1
1,000,000
Number of extraterrestrial civilizations
Ne
in our galaxy with which we could
communicate
?

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