Transcript Searching for Intelligent Life in the Universe Allen Telescope Array Announcements • HW • Read Ch.

Searching for
Intelligent Life in the Universe
Allen
Telescope
Array
Announcements
• HW
• Read Ch. 24: Life in the Universe
Outline
1) Life in Extreme Environments on Earth
2) Life in other solar systems
3) Search for extraterrestrial intelligence
4) The Drake Equation
5) Interstellar travel
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Prospects
for
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Life in the Universe
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The Universe:
• > 200 BillionGalaxies
•. 13.5 Billion Years Old
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Spiral Galaxies
Elliptical Galaxies
Each Galaxy has:
Each Galaxy:
~100 Billion Stars.
200 Billion Stars
Each Star is a Sun.
Most Stars have planets.
Laws of Physics and Chemistry
are the same
Everywhere in the Universe
Method to
Search for Earth-size Planets
Planet passes in front of the star, blocking its light.
Kepler-10 Light Curve
9
Kepler-10 Light Curve
Period = 45.29 days
10
Are there
Universal Laws of Biology ?
Is DNA the only Replicating Molecule ?
Intelligence:
Inevitable Result
of Evolution ?
Liquid Water:
Other mixers ?
Please vote
!
Is there Life in the Milky Way Galaxy?
Excluding Earth:
A)
B)
C)
D)
There is neither primitive nor intelligent life in our M.W. Galaxy. We are alone.
There is primitive life but not intelligence outside our Solar System.
There is primitive life both inside and outside the Solar System, but no intelligence.
I think there is intelligent life within our Milky Way Galaxy.
Only Known Site of Biology
In the Universe.
Need one more
example in our
Solar System
or beyond . . .
Life Began On Earth
3.8 Billion Years Ago
Earth: 4.6 Billion years old.
Life started fast here.
Does it routinely start elsewhere?
Is Intelligent Life
a Cosmic Imperative?
Earth is our only example.
Estimate Number of Earths in
Milky Way Galaxy
200 billion stars
>15% of all Stars
have planets .
Habitability may require
water in liquid form.
Too hot
(too close to star)
Just right.
Too cold
(too far)
``Search for habitable worlds . . .’’
Habitable Zone
Region around star
where Liquid water
can exist at the
surface.
. . . Temp = 0 - 100 C
Earth-sized planets are probably common.
But how common are
What conditions
are necessary
for life ?
One of the Least Hospitable Places on Earth:
Yellowstone National Park
• Boiling Geysers
• Freezing winter
• Sulfuric acid
Suitable for Life ?
Yellowstone
Pinwheel Geyser
Near Boiling:
T ~ 80 C
Each color
a different
species of
bacterium
Bacteria
Thrive
Water: Acidic
as battery acid
Yellowstone
Life at High Temperature
and High Acidity
Temp = 65 C
pH = 2
Yellowstone
Grand Prismatic Spring
Near Boiling:
T ~ 80 C
Each color
a different
species of
bacterium
Bacteria
Thrive
Yellowstone
Grand Prismatic Spring
Near Boiling:
T ~ 80 C
Each color
a different
species of
bacterium
Bacteria
Thrive
Yellowstone
Churning Cauldron
Boiling Temp
Yellowstone
Churning Cauldron
Algae
Near Boiling
Temperature,
pH = 2 :
Bacteria &
Algae Thrive
Corrosion
pH = 2
Life Thrives at:
Temp = 0 - 75 C
&
Wide Range of Acidity
Cyanidium Calderium
Lives at Temp > 65 C
Zygogonium sp.
Extremophiles Show that Life
• Tolerates heat or cold
• Thrives in acidic or alkaline environments
• Takes food from a variety of sources
• Copes with Intense Solar Radiation - - or none!
Liquid Water
Life
Primitive Life: Common in the Universe
February 5, 1996
Recipe for Microbial Life
 Planets
 Organic Molecules
 Water
 Energy - - Stars, Tidal, Geothermal
Molecular Biologists:
“Single-cell life is
common in the universe”.
Is our Milky Way Teeming
with Intelligent Life ?
30 Billion Planetary Systems
1/2 are older than Earth
What fraction have Intelligent Life ?
Pessimist: 1 in a Million
There
mustStars
be Thousands of Civilizations
200
Billion
In the Milky Way Galaxy. . .
The Drake Equation:
Number of Advanced Civilizations in the Galaxy
N = NSTAR fHab.Pl. fLife fIntel f Intel.Now
Let’s Estimate Values:
NSTAR
= Number of Stars in Milky Way Galaxy
fHab.Pl. =
fLife =
f
=
=
Fraction of stars with habitable planets
Fraction of planets on which life appears
=
=
Intel = Fraction of planets with life where Intelligence emerges
=
f Intel.Now =
fraction Surviving Today = L=Civ
L Civ = Lifetime of typical civilizations
/LStar
=
/5 billion years
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Non-Detections of
Intelligent Life in the Galaxy:
• Moon: No Alien Spacecraft, Crash Debris, Obelisk
• Mars: No sign of past visitors or colonies
• Earth: Lovely Planet for 4 Billion Years . . .
Yet, no Alien Settlement.
• 100’s of Telescopes: No Alien spacecraft spotted
• Night Sky: No Exotic Rocket Exhaust-gamma rays
• No Robotic Probes orbiting Solar System
• SETI: No Radio Signals in 40 years.
Where
Is
Everybody?
Did We Overestimate the Probability
of Intelligent Life in the Galaxy?
Aliens should already have wandered
here
If only by chance!
( Even ants eventually find your Kitchen.)
Where
Is
Everybody?
How Might Intelligent Life
Be Rare in the Galaxy?
Aliens should already have wandered
here
If only by chance!
( Even ants eventually find your Kitchen.)
Earths: A Lucky Amount of Water
is Needed for Intelligent Life
Earth is 0.06% water.
Water in Other Earths:
< 0.03%: Desert World
> 0.09%: Water World.
Delivery of Water to Earth
by Asteroids and Comets
Most Rocky Planets are
Water Worlds or Deserts
No Technological Life
Does Evolution Favor Intelligence ?
Paleontology:
• Walnut-size brains
• No tools
• Bird-like brains
200 Million Years of Dinosaur Evolution: A No-Brainer
Dinosaur Brain Mass:
150 Million Years of Evolution
Dinosaur brain mass:
Similar to birds and reptiles.
Smartest was the Troodon:
with Ostrich-size brains
Does Evolution Favor Intelligence?
Intelligence is not strongly favored .
Prediction:
1000 Civilizations in 5 Billion Years
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For contemporaneous civilizations,
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Their Lifetimes Must Overlap:
Need: Lifetime > 5 Million yr
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What is the
Typical Lifetime
of a Civilization ?
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Interstellar Travel
Long Travel Times
Speed of Light 300,000 km/sec
Light travels a distance of 1 “Light Year” in 1 Year
Speed of Modern Spacecraft : 10 - 4 Speed of Light
v = 10 - 4 Light-year/year
Nearest Star: Alpha Centauri d = 4 Light years
Travel Time to Alpha Centauri = . . .
t = d/v = 4 / 10-4
= 40,000 years
100,000 Light Years
Andromeda Galaxy: Near Twin of our Milky Way
Jon Stewart:
“ Only 35 light years away. That’s close
enough that we could pop over to borrow a
cup of sugar
assuming we didn’t need the sugar
for 700,000 years.”
Prediction:
1000 Civilizations in 5 Billion Years
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For contemporaneous civilizations,
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Their Lifetimes Must Overlap:
Need: Lifetime > 5 Million yr
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What is the
Typical Lifetime
of a Civilization ?
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SETI
Search for Extraterrestrial Intelligence
Where do you point your
Radio Telescopes ?
Habitable,Earth-Like Planets:
- Stare for weeks.
New:
Allen Radio Telescope Array:
Search for radio
transmissions.
Under construction at Mount
Lassen
Please vote again
!
Is there Life in the Milky Way Galaxy?
Excluding Earth:
A)
B)
C)
D)
There is neither primitive nor intelligent life in our M.W. Galaxy. We are alone.
There is primitive life but not intelligence outside our Solar System.
There is primitive life both inside and outside the Solar System, but no intelligence
I think there is intelligent life within our Milky Way Galaxy.
Summary
Lecture 23
• Planets are Common in the Universe
• Life Survives in Extreme Environments (but needs water)
• Detection of first Earth-Like Planets in 2-3 years
• Primitive Life:
G. Chin (GSFC)
Common
• Technological Life: Possibly Rare
Still Only One Precious Example