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Is There Life Beyond Earth?
Section 6
• How many students got an “A” in marking
period 2 in 8th grade science?
• What information would you need to figure
this out?
• How many homerooms are there in 8th
• How many students in each homeroom?
• How many possible grades are there?
– A, B, C, D, F 5 possible grades (20% A)
How many intelligent alien
civilizations do you think exist?
• Drake equation-an attempt to estimate
the number of extraterrestrial civilizations
in our galaxy with which we might come in
N = N* fp ne fl fi fc fL
• The equation can really be looked at as a
number of questions
N = N* fp ne fl fi fc fL
• N, the number of communicating civilizations
in the galaxy.
• N* represents the number of stars in the Milky
Way Galaxy
• fp is the fraction of stars that have planets
around them
• ne is the number of planets per star that are
capable of sustaining life
• fl is the fraction of planets in ne where life
• fi is the fraction of fl where intelligent life evolves
• fc is the fraction of fi that communicate
• fL is fraction of the planet's life during which the
communicating civilizations live
Try the Drake Equation
• What was the number of communicating
civilizations in the galaxy that your class
came up with?
• ___________
• Exploring Outside of our Solar System
• (2 clips)
– Exoplanets
– Aliens
SETI Program
• SETI — the Search for Extraterrestrial
• The Mission of the SETI Institute is to explore,
understand and explain the origin, nature and
prevalence of life in the universe
– Earth Science: The Universe
• Clip: Searching for Extraterrestrial Life (3min)
Why Complex Life May Be Rare
• The Rare Earth Hypothesis argues that life on Earth
required an improbable combination of astrophysical and
geological events and circumstances
• Some conditions that a planet needs for complex life to
– Habitable zone
the necessary existence of liquid water requires that the
temperature of the planet be neither too high nor too low.
– A central star of the right character
– Planetary system: Inner and Outer Planets
• Need a large Jupiter-sized planet to keep asteroids away
– Size of planet -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.
– Large moon- keeps the climate stable
– Chemistry of the atmosphere
Life on Earth
All living things:
Are made up of one or more cells
Take in energy and use it to grow and
Give off waste
The “Goldilocks” Conditions
• Life exists on Earth…No one knows
whether life exists anywhere other than
• Earth has:
– Liquid water
– Suitable temperature range
– Atmosphere for living things to survive
• Scientists call these favorable conditions
the “Goldilocks” conditions
Extreme Conditions
• Scientists have discovered living things in places
where it was once believed that life could not
• Examples:
• Giant tubeworms in the deep ocean
• Single-celled organisms in hot springs
• Tiny life-forms inside solid rock
• These discoveries show that the range of
conditions in which life can exist is much
greater than scientists once thought
• We have found organisms that can survive
in conditions without water, in extreme
heat, extreme cold, and extreme acidity
Life on Mars?
• Spacecraft have found regions on the
surface of Mars that look like streambeds
with crisscrossing paths of water
• Life requires water so scientists
hypothesize that Mars may have once had
conditions for life to exist
Video clips
minutes/main3994925.shtml (entire segment10minutes)
• Inner Solar System: Mars
Clips (5 min total):
– Mars Global Surveyor Explores Evidence of Water on
– Mars Odyssey Searches for Water and Ice
– 2003: Mars Express, Beagle II, Spirit Rover, and
Opportunity Lander
Life on Europa?
• One of Jupiter’s moons explored by Voyager spacecraft
• Europa has a smooth, icy crust with giant cracks
• Similar patterns occur in the ice crust over Earth’s Arctic
• Scientists hypothesize that there is a liquid ocean under
Europa’s ice-the water could be kept liquid by heat
coming from inside Europa
Water on Saturn’s Moon?
• Images from NASA’s Cassini spacecraft
indicate that one of Saturn’s moons,
Enceladus, may contain pockets of liquid
water below its icy crust
Water on Saturn’s Moon
• Liquid water geyers make Enceladus a
very exciting place to look for life
• Unknown heat sources inside Enceladus
melt ice into deposits of subsurface water
and under pressure, these water pockets
burst through the icy crust
The white streaks in this image are
backlit geysers of water ice, rising
hundreds of miles into space from
Enceladus’s dark disc
Most Recent Discovery:
Water Ice on the Moon
• In 2009, a NASA probe
on India’s lunar orbiter
discovered 600 million
metric tons (158 billion
gallons) of water ice in 40
craters at the Moon’s
North Pole.
• In 2009, NASA crashed
two probes into the
Moon’s South Pole and
there was significant
amounts of water in the
debris cloud