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Transcript
Life in the Universe
Astronomy 115
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
• Carbon dioxide and water in the presence
of an energy source can make sugars
6 CO2 + 6 H2O + energy C6H12O6 (glucose) + 6 O2
• O2 is actually toxic (even to us!)
• Metabolism: Take the sugars and starches
(from yourself or somebody else) combine
it with the waste O2, and get the energy
back to make different molecules
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)
The Role of Phosphorus
DNA requires
phosphorus to link itself
Adenosine triphosphate
(ATP) is an energy transport
molecule in all organisms
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 are more rare in universe than carbon
• Arsenic?
– Alternative to phosphorus
– Even more rare in universe
• Chlorine
– Alternative to oxygen?
– More rare 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)
Mono Lake, California, a highly saline lake
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
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?
Planetary Habitable Zones
Also known as the
“Goldilocks zone”
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 50°C
• 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
•
•
•
•
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
Life in the Universe
• What are the odds of intelligent life
elsewhere in the Universe?
• How many communicating civilizations
are there in the Milky Way?
• How do you guess?
• How do you guess the number of
jellybeans in a jar?
• Break the problem down into things you
can guess.
The Drake Equation
N  R *  f p  n e  fl  fi  fc  L
N = Number of communicating
civilizations in our galaxy right now.
And what about the rest?
Star Formation Rate: R*
N  R *  f p  n e  fl  fi  fc  L
• There are 100 billion stars in the Milky
Way.
• The Milky Way is 10 billion years old.
R* = 100 billion stars/10 billion years
R* = 10 */year
Fraction with Planets: fp
N  R *  f p  n e  fl  fi  fc  L
• What fraction of stars have planets?
• Extrasolar planet research since 1995:
–
–
–
–
539 confirmed planets
414 planetary suystems
55 multi-planet systems
1 star has six
fp = 1/20
Number of Earths: ne
N  R *  f p  n e  fl  fi  fc  L
• How many habitable planets are there
in each of these planetary systems?
• Habitable zone: water should be a
liquid
• Depends on star.
– No O or B
– No M
– No binaries
ne = 1
Fraction with life: fl
N  R *  f p  n e  fl  fi  fc  L
• On what fraction of habitable planets does
life evolve?
• Look at our Solar System.
• 3 planets in habitable zone, life has evolved
on 1 (or maybe 2).
fl = ?
Fraction with intelligence: fi
N  R *  f p  n e  fl  fi  fc  L
• What fraction of life bearing planets
have life evolve to intelligence?
• Is intelligence inevitable?
fi = ?
Fraction that communicate: fc
N  R *  f p  n e  fl  fi  fc  L
• What fraction of intelligent civilizations
become technological enough that we
could communicate?
• Is technology inevitable?
• Desirable?
fc = ?
Lifetime: L
N  R *  f p  n e  fl  fi  fc  L
• How long does a civilization last?
• Do we have time to communicate with
them?
• For us: L = 75 years!
L = ? years
What’s the Answer?
N  R *  f p  n e  fl  fi  fc  L
•
•
•
•
•
•
•
•
R* = 10 */year
fp = 1/20
ne = 1
fl = ?
fi = ?
fc = ?
L = ? year
N = _____  # of technological
civilizations in Milky Way, right now.
Let’s Put It All Together!
Nic = R* Pp Pe N e PL PI Lic
R* = 0.9 stars / yr
Pp = 0.1 - 0.5 fraction with appropriate planets
Pe = 0.3
fraction with planets in CHZ
N e = 0.1-1
number of planets in the CHZ
PL = 0.5 fraction that develop life
PI = 0.2 -1 fraction of these that develop intelligence
Lic = 50 -10 9 yrs
lifetime of intelligence
(
Nic = ( 0.9stars / yr ) ( 0.1 - 0.5) ( 0.3) ( 0.1-1) ( 0.5) ( 0.2 -1) 50 -10 9 yrs
1ö
æ 1
\ N ic = ( 0.00027 - 0.068) Lic ~ ç
L
è 3700 15 ÷ø ic
1 9
10 = 108 civilizations
15
1
"Worst Case" N ic =
50 = 0.02 civilizations
3700
"Best Case" N ic =
)
But space is vast
• Milky Way is a giant cylinder (disk).
– Radius = 15000 pc
– Thickness = 1000 pc
• Volume = p(Radius)2 x Thickness
• V = 7 x 1011 pc3 = 700 billion cubic
parsecs!
How far to the neighbors?
• If there are 100 civilizations in 700
billion cubic parsecs, then:
– 1 civilization in every 15 billion cubic
parsecs
• Imagine every civilization surrounded
by a bubble in which it is alone.
R
• V = 15 billion cubic parsecs
R
• R = 3 kpc
• Distance between civilizations:
3 kpc = 9000 ly (optimistically)!
How Can We Know?
• How can we tell if there are
extraterrestrial civilizations?
• Go visit. Is this practical?
• Look for visitors? Is there evidence?
• Look, or listen, for signals from E.T.
SETI
•
•
•
•
•
Search for Extraterrestrial Intelligence
Several organized searches over the last 30 years.
Use a radio telescope to try to detect signs of E.T.
Why?
The Earth floods space with radio waves.
–
–
–
–
TV
Radio
Cellular phones
etc
E.T. FM
• Most natural radio sources are
broadband.
• Radio stations are narrowband.
Tuning the Dial
• Nearly all searches have been looking for
extremely narrow radio signals.
– But there are millions and billions of
frequencies to listen to.
– And millions and billions of stars
• Concentrate on nearby sun-like stars.
– No luck.
• Point in the sky randomly.
– No luck yet. But you can help.
[email protected]
•
•
•
•
•
•
•
Receiver piggybacks on Arecibo telescope.
Constantly searches as telescope observes.
Millions of channels (frequencies).
Thousands of hours.
Lots of data.
Needs lots of computer power.
Your power;
http://setiathome.ssl.berkeley.edu/
[email protected]
“Is there anybody out there?”
We have made three
attempts to
communicate.
1. The Arecibo broadcast
to Hercules Cluster.
The Voyager Record Club
Voyagers 1 and 2 contain a plaque and a
record.
Voyagers 1 and 2
• Greetings 55 languages
• 115 images
• Music
Sumerian"May all be well."
Arabic"Greetings to our friends in the stars. We wish
that we will meet you someday."
Urdu"Peace on you. We the inhabitants of this earth
send our greetings to you."
Italian"Many greetings and wishes."
Ila (Zambia)"We wish all of you well."
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?
The Ming Dynasty (15th Century)
1405-1435 Chinese vessels
sailed through Indian Ocean.
Under Admiral Zheng He, the
Chinese established tributary
and trade relations throughout
the region.
After the 7th grand expedition in 1435, the Chinese
abandoned sea trade and exploration. Junks were
broken down and left to rot, and it became a crime to
build a vessel with more than two masts.
Why? We do not know.
Rise of the land-oriented bureaucracy?
Rise of expensive internal canal projects?
Rise of inward-looking neo-Confucianism?
Search the Solar System for Alien Artifacts
(for instance, 2001, A Space Odyssey)
Look for spacecraft and/or Von Neumann Machines (selfreplicating probes) in Earth orbit, the Moon, the Asteroid Belt,
etc. Nothing so far.
Search Biological Systems for "Messages"
A stable, "non-functioning" section of our DNA could carry a coded
message. After all, coded information is precisely what DNA is all
about. The Human Genome Mapping Project is COMPLETED. To
my knowledge, there has been no such message detected.
Eyewitness Accounts & Memory
What we “see” is often not really there (Lowell’s “canals”)
People can be convinced during questioning to “remember”
things that did not happen (many recent sexual abuse
allegations)
People lie
People like to play tricks
People tend to “want to believe”
People don’t like to change their minds
People don’t like to admit when they are wrong
People make up things when they do not understand*
PEOPLE ARE HUMAN
Some claim to see UFOs in artwork
Flying Saucer or a
common motif ??
Aliens in Spacecraft?
Actually depict the
Sun & Moon
Want to learn more?
Lenticular
clouds
Unidentified Flying Objects (UFOs)
Most people equate UFO with alien craft
The term “unidentified” actually means unidentified
Reports of UFOs go back centuries
Prior to invention of airplanes, UFOs tended to look like
zeppelins
“Flying Disks” reported by Kenneth Arnold in 1945 while
flying airplane near Mt. Rainier - this is where the “modern
era” began - aliens now operate flying saucers, not flying
cigars!
What aliens “looked like” also varies from culture to
culture and one era to another.
Global mass communication has changed this….
The “Greys” (Close Encounters
of the 3rd Kind)
Roswell
Object crashes in June 1947 on
Brazel’s ranch
Debris collected & brought to nearby
Army Air Corps Base
Base press officer releases report of
“crashed discs”
Legend grows of alien bodies set to
Wright Field in Dayton
Recently, at the request of Congressman H. Shiff (R-NM), the US
General Accounting Office released all records relating to Roswell.
They indicate:
1. no evidence for a cover-up
2. no evidence for a UFO
3. no evidence for alien bodies
Crash debris identified by Columbia & NYU as theirs part of Project Mogul (now declassified) - balloon-borne
microphones to listen for Soviet nuclear tests.
Project Blue Book - 1965
Because some UFOs might actually be aircraft belonging to hostile countries
(read: USSR), the US Air Force launched a study to try to identify all such
sightings as best as they could. The breakdown:
Identification
Number of Sightings
Astronomical events (Venus)
Aircraft
Satellites
Hoaxes, Imagination, etc.
Insufficient Data
Weather Balloons
(still being processed)
UNIDENTIFIED
Percentage of Total
245
210
152
126
85
36
17
16
The 16 unidentified cases are just that - unidentified
26.7%
23.7%
17.1%
14.2%
9.6%
4.1%
1.9%
1.8%
The Alien Autopsy Film
First aired by Fox as a true documentary in 1995. But:
1. Autopsy not carried out using methods of the profession
2. Examiner does not handle instruments properly
3. Anticontamination suits are bogus
4. Injuries inconsistent with crash
5. Warning signs used did not exist until 20 years later (OSHA)
6. Organs have no connective tissue!!
Etc.
Kent Jeffrey, co-founder of the International Roswell Initiative, along
with many other UFO supporters, claim that the film is a hoax.
1998 - Fox “reveals” the film as a hoax in subsequent airing!
Crop Circles
These patterns of crushed grass began to appear in England in the 1980's. Since then,
they have been seen on other places, and the patterns have become more complex.
Explanations given:
•Alien landing sites - it was 'impossible" for any human to do this
•Wind vortices (totally absurd for the complex patterns seen)
•Hoaxes
In 1991 David Bower and Dave Chorley claimed responsibility for starting the crop
circle craze. They demonstrated live on BBC TV exactly how they did it. Since then,
others have been caught in the act.
Apparently aliens have force fields &
invisibility (i.e. the motion picture Signs),
travel interstellar distances and/or cross
“dimensions” but have to navigate by making
drawings in corn fields??
Crop circles have become a form of art…
For more visit this site.
Also http://www.circlemakers.org/
The “Face” on Mars
Richard C. Hoagland The monuments of Mars: A City on the
Edge of Forever (1987) claims the feature is artificial
Viking vs. MGS
“Happy Face” on Mars!
Other Stuff For the Drake Equation
•
•
•
•
•
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?
Galactic Habitable Zone?
Civilizations: Type +
• Type I+
– Able to restructure planets
• Type II+
– Able to restructure solar systems
• Type III+
– Able to restructure galaxies
• Type +
– Able to restructure Universe
Other Things We Might Do
Detection of Massive Engineering
Projects- Astroengineering
Freeman Dyson
Dyson Sphere -A sphere with a
radius of 1 AU will have a
temperature of approximately 300K,
and radiate strongly near 12 m
wavelength.
An examination of sources
detected in the infrared survey
of the sky made by the IRAS
satellite yielded no sources that
could be definitively labeled as
coming from such a structure.
IRAS
Civilizations: Type • Type I– Able to manipulate objects on their scale
• Type II– Able to manipulate genes, transplant and replace parts of
themselves
• Type III– Able to manipulate molecules, create new materials
• Type IV– Able to manipulate atoms, create nanotechnologies and
artificial life
Civilizations: Type – (contd.)
• Type V– Able to manipulate atomic nuclei
• Type VI– Able to manipulate elementary particles of
matter and create new states of matter
• Type – Able to manipulate space and time
Which Path Shall Our Species Take?
• Rat Race Strategy (RRS)
– Short Term Gain
– Self Interest
– Competition
• Evolutionarily Stable Strategy (ESS)
– Cooperation
– Great Foresight
– Great Altruism
Which path should we take ?
– Longevity
What if we succeed?
Some Features of Culture Shock
•
•
•
•
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 raw materials)
• 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?
•
•
•
•
•
•
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.”
“’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
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
•
•
•
•
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
•
•
•
•
•
•
•
•
•
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