Life in the Universe
What is Life?
• “Life is what dies when you stomp on it”
-Dave Barry
• Simple definitions all fail
– Moves? Grows? Feeds? Reproduces?
• Best definitions focus on:
– Self-organizing, complexity, adaptation
– Information coding
– Feedback (homeostasis)
DNA
• Deoxyribonucleic acid
• Total length of human DNA in a single cell is
about a meter
• A human body contains about 20 trillion
cells
• The total length of DNA in a human body is
thus 20 trillion meters, or twenty billion
kilometers, the circumference of the orbit
of Pluto.
Prebiotic Evolution
• The basic molecules of organic chemistry are
easily made
• The first self-replicating molecule was almost
certainly not DNA
• DNA assembles from simpler materials all the
time
• Many likely candidates
• Clay minerals as templates?
Plants and Animals
• CO2 + H2O + Energy = Sugars, Starches, etc.
+ O2 (toxic waste)
• 12CO2 + 11H2O --> C12H22O11(Sucrose) + 12O2
• O2 is actually toxic (even to us!)
• Idea: Take the sugars and starches (from
somebody else) combine it with the waste
O2, and get the energy back
Planetary Habitable Zones
• Primarily in the Liquid Water Zone
• Can’t be too warm
– Water Vapor in upper atmosphere broken down
by solar UV and charged particles
(photodissociation)
– Hydrogen escapes to space
– Too hot planets will quickly lose all their water
• Freezing not so much of a problem
Reasons to be a "Carbon
Chauvinist".
• Carbon is abundant in the Universe
• Carbon can bond to four neighboring atoms
• Carbon can bond to other carbon atoms,
sharing one, two, or three electrons
• These properties make it possible to form a
vast array of organic molecules
• No other element has these properties
Reasons to be a ”Water Chauvinist".
• Water stays liquid over a wide range of
temperatures.
• Water is very abundant in the Universe
• Water is a polar or asymmetrical molecule. It
attracts ions easily, making it a good
transporter of nutrients
• It does not dissolve organic molecules (so we
do not dissolve in our own cell fluids)
Alternate Biologies?
• Ingredients need to be abundant in Universe
• Need solids to maintain structure
• Need liquids or gases to transport nutrients
and wastes
• Need source of energy
• High temperatures destroy complex molecules
– Also solid state electronics
– Why your computer has a fan
Alternate Biologies?
• Silicon? Earth’s crust is 27% Si
– If silicon biology is possible, why not here?
– Silicon doesn’t bond to itself well
– C + O = gas, Si + O = quartz
– CO2 dissolves in water, SiO2 doesn’t
• (SiH4 and SiF4 are gases, however)
• Alternatives to water?
– Ammonia? Polar like water
– Methane? Not polar
– Hydrogen peroxide?
Alternate Biologies?
• Nitrogen or Phosphorus?
– Can form complex molecules
– Both rarer in universe than carbon
• Arsenic?
– Alternative to phosphorus
– Even rarer in Universe
• Chlorine
– Alternative to oxygen?
– Rarer in Universe than oxygen
Alternate Biologies?
• Sulfur?
– Not likely as alternative to carbon
– Can be alternative to oxygen – even on earth
• We cannot design a probe to look for
“alternative biology” because we just don’t
know what to look for.
Earth’s Alternative Biologies
• Extremophiles: organisms that thrive under
extreme temperature, pressure, or chemical
conditions
• Many of Earth’s simplest organisms are
extremophiles
• Extremophile domain is a bigger target
– We’re more likely to find planets inhabitable by
extremophiles than planets suitable for humans
Tolerance Ranges
Alternative Biology on Earth (GFAJ-1)
The Role of Phosphorus
Arsenic-Eating GFAJ-1
• Not “arsenic based” life
– Organic structures built of carbon
• More than merely able to utilize arsenic
• Can apparently replace P with As
– Up till now, P considered absolutely essential
• Seems to build As into DNA instead of P
• What about Si?
Life on Early Earth
• Oldest minerals: 4.4 b.y.
• Oldest rocks: 4.2 b.y.
• Probably no life until Late Heavy
Bombardment over (3.8 b.y.)
– Large impacts would sterilize Earth
• Liquid water as far back as we can see
• Life by 3 b.y.
Life on Early Earth
• Faint Early Sun
– Sun 4 b.y. ago was 70% as bright as today
– We have liquid water throughout Earth history
– Probably thick greenhouse atmosphere
• How life originated?
– Cold earth: improves chemical stability
– Hot Earth: speeds up chemical reactions
– Use minerals as templates?
You can buy the exact number
and proportion of atoms to make
a human for only a few dollars.
• You can buy the exact number and proportion of
atoms to make a Lexus from a junkyard for only a
few dollars, too
• If you want to talk about the exact arrangement
of the atoms, the price goes up sharply.
• Buying the exact organic molecules that make up
a human would cost millions of dollars, and many
cannot yet be synthesized at all
Galactic Habitable Zone?
Planetary Habitable Zones
The Ultimate Long-Term Forecast
• Slow warming trend for the next billion
years
• Increasing humidity
• CO2 decrease leads to extinction of plants?
• Boiling and evaporation of the oceans
Surviving on a Warming Earth
• Higher organisms stop reproducing around 50C
• There will be no place cool to hide
• Possible evolutionary strategies
– Ultra sturdy heat resistant molecules
– Concentrated solutions to raise boiling point
– Retreat underground where pressure and boiling
point higher
– Pressurized cells
– Ultimate limit 150-200 C?
Surviving on a Warming Earth
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•
•
•
Plants need > 10 ppm CO2
Animals and plants die around 50 C
Micro-organisms can tolerate 130 C +
But biology seems to like heat and we have
a billion years to experiment
– Pressurized cells?
– Anti-boiling fluids?
– Problem is breakdown of organic molecules
– 150 - 200 C (300-380 F) max?
The Oreo Model of Life History
Micro-organism
Earth (0-3 billion
years)
Multicellular Earth
(3-5 billion years)
Micro-organism
Earth (5-6 billion
years)
“The white creamy
middle”
The Drake Equation
“A wonderful way to organize our
ignorance”
- Jill Tarter
The Drake Equation
Number of Intelligent Civilizations =
Number of Stars in the Galaxy (400 billion)
x Fraction of Stars with Planets (1/4?)
x Number of suitable planets per star (0.1?)
x Fraction of planets where life appears (1/2??)
x Fraction of planets with intelligence (???)
x Fraction of planets with technology (????)
x Fraction of planet’s life with technology
(??????)
So Where Are They?
• Populations expand exponentially
• It would take an exponentially-growing
civilization only a few million years to fill
the Galaxy, even at sub-light speeds
• 2 to the 40th power is over a trillion
• If it takes 10,000 years for a colony to
achieve interstellar travel, 40 doubling
times is only 400,000 years.
• So why aren’t they all around us?
Is There A Problem?
• Alien psychology? We barely understand
humans!
• Why did it take us so long to develop
technology?
• Maybe we’re first?
• Maybe we’re unique?
Other Stuff For the Drake Equation
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•
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Jupiter Stabilizes Solar System?
Jupiter lessens impact bombardment
Moon stabilizes Earth’s axial tilt
Earth’s magnetic field deflects cosmic rays
Liquid Water Zone is narrow and changes with
time as stars brighten
• Center of the Galaxy Deadly?
What if we succeed?
Some Features of Culture Shock
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•
•
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Loss of Faith in Beliefs and Institutions
Xenophobia
Over-Dependence, Copying
Nihilism
Models for Alien Encounters
• Star Trek?
– We’re OK, they’re OK (Klingons sort of, Romulans
not so much)
• War of the Worlds? (Also the Borg)
– We’re food (or in the way)
• Watership Down?
– We’re irrelevant
Why Would Aliens Want Earth?
• If they can freely travel in space:
– Water from icy bodies and comets
– Hydrocarbons and organic molecules from gas
giants and frozen methane
– Oxygen from silicates and water
– Metals from asteroids
– Unlimited size solar collectors close to Sun for
Energy
• We are not likely to be
– A threat
– A source of anything useful
Why Would Aliens Want Earth?
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A Planet to Live On
Convenient working conditions
Lithophile Elements
Hydrothermal ores
Organic materials
It probably won’t be about us
– Not that it will make it any easier
“Wonderful,
just
wonderful.
So much for
instilling them
with a sense
of awe.”
“Matthews,
we’re getting
another one
of those
strange ‘awblah-es-panyol’ sounds.”
“’Take me to
your stove?’
You idiot, give
me that book
back!”
Arthur C. Clarke’s Laws
• The only way to test the limits of the possible is
by going beyond them into the impossible
• When an elderly but distinguished scientist says
something is possible, he is probably right. When
he says something is impossible, he is very likely
wrong
• Any sufficiently advanced technology
is indistinguishable from magic
No Point in Hiding
• At Radio Frequencies, Earth is brighter than
the Sun
• Our Radio signals are now 70+ light years
out
• From our signals, aliens could determine:
– Length of our day and year
– Size of Earth, Distance from Sun
– Probable mass and gravity
– Draw a crude map of Developed World
Mapping Earth by Radio
Our Views of Aliens
• Post World-War II
– “Savior Model”
– “Hostile Aliens” - Eat or Enslave
• Science Source of Fascination and Fear
– Winning World War II
– Nuclear War
• Similarity with Westerns
– We’re the Good Guys
– Fighting off Hostile Threats
Our Views of Aliens Evolve
• 1960’s: “Hostile Alien” films and Westerns
both decline
• We’re Not Always the Good Guys
– Historical Revision of Frontier
– “Spaghetti Westerns”-Dark and satirical
– Civil Rights Movement
– Vietnam
• Star Trek, 1967
– Enlightened, Optimistic Future
Variations
• Humans as Helpers: E.T.
• Encounter as Wonder: Close Encounters of
the Third Kind
• Encounter as Dreary: Contact
• Swashbuckling: Star Wars
• Satire: Men In Black
• Return to Hostile Aliens
– Star Trek Spinoffs (The Borg, the Dominion)
– Independence Day
SETI@Home
http://setiathome.ssl.berkeley.edu/
Back Door to Area 51
What Really Happened to the
Aliens
Going to the Stars
Visiting Other Star Systems
• Time problem
– @ 10%c, 43 years to Alpha Centauri
– @ 90%c, 4.8 years to Alpha Centauri
– Missions need to be ultra reliable
– Missions need to be totally autonomous
• Energy problem
– @ 10%c, a 10-ton probe needs 1000 Mt
– @ 90%c, a 10-ton probe needs 250,000 Mt
How Do We Get There?
• Problem with rockets is just moving all that fuel
• Solar Sail
– Very low acceleration using sunlight
– Speed up using laser or microwave beams
• Orion Design
– “How I learned to stop worrying and love The
Bomb”
– Used in movie Deep Impact
– Only known technology capable of accelerating
large masses to high speeds
Looking A Little Further Ahead
• Bussard Ramjet
– Use large collector or magnetic fields to scoop
particles out of interstellar space
– Use nuclear reactor to accelerate particles and
generate thrust
– If we master fusion, we could use the particles
(mostly hydrogen) as fuel
Going There In Person
• Low speed = Low Energy = One-Way Trip
• High speed = High Energy = Return Trip
(Nearby Stars Only)
• Life Support
– Static Life Support Practical Only For Small Crew,
Short Trip
– Hibernation or Suspended Animation?
– Long Voyages Will Need To Be Self-Sustaining
Answer to Population Growth?
• In 50 years we have sent less than 500
people into space (A few thousand counting
multiple trips)
• In 50 years we have established zero
extraterrestrial colonies
• Earth’s Population Growing at 250,000/day
• That’s Madison today, Louisville tomorrow,
then Newark, Orlando, Tacoma…
• …Just to keep up.
Time Dilation
• Requires speeds >50% c to be important
• Makes a difference only to those on the trip
• Might be useful in terms of making trips
within a human lifetime
• Irrelevant to Earth
Life Support and Star Travel
• Radiation Shielding
– Becomes critical at high speeds
• Food, Oxygen, Water
– Recycle biologically
– Biosphere II Experience
– Not as Easy as Often Envisioned
– Inevitable Losses
– Needs to be almost perfect
• Energy
The Psychological Factor
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Humans are Very Adaptable
How Big Does Crew Need to Be?
Intellectual Stimulation, Variety
How to Maintain Commitment?
OK, We’re Here. Now What?
• Exploration versus Colonization
• Exploration
– Can use Lander and Living Module
– Medical and Biochemical Issues
• Colonization
– Will Need Functional Shuttle System
– Will Need Broad Range of Expertise
– Will Need To Be Able to Make or Repair High
Technology
Terraforming
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Eliminate Dangerous Organisms
Introduce Earth Organisms
Domesticate Local Organisms
Alter Biochemistry
Increase Water Supply
Increase Oxygen Supply
Eliminate Toxic Chemicals
Modify Greenhouse Effect
Moral Issues