Download Chapter 29: Life in the Universe

Chapter 29: Life in the
Universe
Does life exist beyond Earth?
In our own solar system?
Does intelligent life exist?
How can we search for life?
March 21, 2006
Astronomy 2010
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The Case for Life Beyond
Earth
There are billions of galaxies in the
universe, and the typical galaxy
contains billions of stars: 1018 stars!
Planets have been found around many
nearby stars; planet formation seems to
be a natural result of star formation.
Even if life is rare, there is a strong
possibility that it occurred more than
once.
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The Copernican Principle
“There is nothing special about our
place in the universe”
Copernicus proposed a model for the
solar system with planets orbiting the
Sun.
Later we discover that the Sun is not
the center of the Milky Way, nor is the
Milky Way the center of the universe.
The atoms of which we’re made
comprise just a fraction of the stuff of
the universe.
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Astrobiology
“The study of the origin, distribution, and
ultimate fate of life in the universe.”
Combines astronomers, biologists,
chemists, geologists, …
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How to Search for Life
A basic search for life should include the
simplest form of single celled life.
Can we find some requirements for life
that will narrow a search?
Water (can something take its place?)
Energy source: light or chemical
Chemistry: organic compounds or
alternate
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Organic Molecules
Life on Earth is based on organic
molecules: carbon-based molecules
with hydrogen, nitrogen, oxygen, or a
few other elements.
Organic molecules have been found in
clouds of interstellar gas and dust!
Starting from these organic molecules,
chemists formed amino acids in a
simple apparatus that mimics the
conditions of Earth 4 billion years ago.
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Extremophiles
Biologists have discovered that life can
exist in rather extreme environments:
Hot springs where the water temperature is
close to 100ºC.
Frozen for thousands of years in Antarctic
ice, and able to reanimate when thawed.
Living without light near deep
sea vents called
“black smokers”.
Living in high acidity
environments like the Rio Tinto.
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Biomarkers
To search for life around other stars, we
should look for something distinctive of
life: biomarkers.
The simultaneous presence of oxygen
and methane is a clear biomarker.
Unfortunately the Earth didn’t have much
free oxygen for much of the time that life
existed.
An indisputable signal is still being
sought.
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Habitable Zone
The Habitable zone is the region around a
star where a planet with liquid water could
exist.
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Could There Be Life on Mars?
Or Europa?
Or Encelades?
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Intelligent Life
Of course, electromagnetic signals from
extra-terrestrial life would be a very
clear signature.
SETI: Search for Extra-Terrestrial
Intelligence
Scientists scan many radio frequencies
searching for non-random signals.
The latest idea is to search for brief
signals in visible light.
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Listening for Signals from
Intelligent Life
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The Drake Equation
“Predicts” number of civilizations we
could detect signals from in galaxy, N:
R* = rate of star formation (about 10/year)
fp = fraction of stars with planets
ne = number of Earth-like planets / system
fl = fraction of them where life develops
fi = probability that intelligence evolves
fc = prob. that advanced civilization evolves
L = lifetime of advanced technology
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The Drake Equation
If we take:
R* = 10/year
fp = 1.0
ne = 1.0
fl = 0.1
fi = 1.0
fc = 1.0
then N = L, or the number of detectable
intelligent civilizations equals the length of
time that such civilizations survive.
Our civilization has been at this stage since
about 1900, or 100 years.
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Sending Signals
We have sent several space probes on
voyages out of our solar system.
These probes carry plaques with
information about us, in case they are
intercepted by other intelligent life.
Kind of like a note in a bottle.
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Discussion Question
Should we actively try to send signals to
any extra-terrestrial life that may be out
there? Please consider what the
consequences could be.
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