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Name: _____________________________________________________________________________ Period: __________________________
Is There Life Beyond Earth?
Note Guide
1) How many intelligent alien civilizations do you think exist?
a) ___________________________-an attempt to estimate the number of extraterrestrial
civilizations in our galaxy with which we might come in contact
b) N = N* fp ne fl fi fc fL
c) The equation can really be looked at as a number of questions.
2) N = N* fp ne fl fi fc fL
a) N, the number of communicating civilizations in the galaxy
b) N* represents the number of stars in the Milky Way Galaxy
c) fp is the fraction of stars that have planets around them
d) ne is the number of planets per star that are capable of sustaining life
e) fl is the fraction of planets in ne where life evolves
f) fi is the fraction of fl where intelligent life evolves
g) fc is the fraction of fi that communicate
h) fL is fraction of the planet's life during which the communicating civilizations
3) Try the Drake Equation Yourself
a) What was the number of communicating civilizations in the galaxy that your
class came up with? _________________________
4) SETI Program
a) SETI — _______________________________________________________________________________
b) The Mission of the SETI Institute is to explore, understand and explain the
origin, nature and prevalence of life in the universe.
5) Why Complex Life May Be Rare
a) The _______________________________________ argues that life on Earth required an
improbable combination of astrophysical and geological events and
b) Some conditions that a planet needs for complex life to exist:
1. ____________________________ - the necessary existence of liquid water
requires that the temperature of the planet be neither too high nor too
2. _________________________________________________________________________________
3. ___________________________________________________________________________: Need
a large Jupiter-sized planet to keep asteroids away
4. _______________________________________________________: if its mass is too large,
the planet will become a gaseous planet with an atmosphere made
essentially of hydrogen and helium. In such conditions, the chemical
reactions of life cannot occur. If it is too small, it will not be able to
maintains an atmosphere.
5. _____________________________: keeps the climate stable.
6. ___________________________________________________________________________________
6) Life on Earth
a) All living things:
1. ____________________________________________________________________________________
2. ____________________________________________________________________________________
3. ____________________________________________________________________________________
4. ____________________________________________________________________________________
7) The “Goldilocks” Conditions
a) Life exists on Earth…No one knows whether life exists anywhere other than
b) Earth has:
1. Liquid _______________
2. Suitable _________________________________
3. __________________ for living things to survive
c) Scientists call these favorable conditions the ____________________________.
8) Extreme Conditions
a) Scientists have discovered living things in places where it was once believed
that life could not exist:
b) Examples:
1. _______________________________________________________________________________
2. _______________________________________________________________________________
3. _______________________________________________________________________________
c) These discoveries show that the range of conditions in which life can exist is
much __________________ than scientists once thought.
d) We have found organisms that can survive in conditions without _______________,
in extreme ______________, extreme ______________, and extreme _____________________.
9) Life on Mars?
a) Spacecraft have found regions on the surface of Mars that look like
___________________with crisscrossing paths of ___________________.
b) Life requires water so scientists hypothesize that Mars may have once had
conditions for ______________ to exist.
10) Life on Europa?
a) One of _________________ moons explored by Voyager spacecraft.
b) Europa has a smooth, ________________crust with giant cracks.
c) Similar patterns occur in the ice crust over Earth’s __________________________.
d) Scientists hypothesize that there is a liquid _______________ under Europa’s icethe water could be kept liquid by heat coming from inside Europa.
11) Water on Saturn’s Moon?
a) Images from NASA’s Cassini spacecraft indicate that one of Saturn’s moons,
_______________________, may contain pockets of liquid water below its icy crust.
b) Liquid water_________________ make Enceladus a very exciting place to look for
c) Unknown heat sources inside Enceladus melt ___________ into deposits of
subsurface water and under __________________, these water pockets burst
through the icy crust.
12) Most Recent Discovery: Water Ice on the Moon
a) In 2009, a NASA probe on India’s lunar orbiter discovered 600 million metric
tons (158 billion gallons) of water ice in 40 _______________ at the Moon’s
b) In 2009, NASA ________________ two probes into the Moon’s _____________________
and there was significant amounts of ________________ in the debris cloud.