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PHYS 162 1
Life in the Universe
• 1 example of Life - Carbon-water based
• 1 example of “intelligence” which has been able to
communicate with other “intelligent” life for about 70 years
• intelligence= able to use Radio to send/receive messages
• chemical building blocks (amino acids, water) plentiful in
interstellar space
• Somehow about 1 billion years after the Earth formed,
bacteria appeared. All other life are probably descendants
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PHYS 162 2
Life – Carbon+Water based?
“Ammonia! Ammonia!”
@R. Grossman 1962 New Yorker
Carbon vs Silicon? NO
Water vs other liquid or
gas? Not sure but water
seems to be the best
medium in which
biochemistry takes place
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PHYS 162 3
Life on Earth
• about 4.5 billion years ago Earth
formed. About 1.5 billion years
after that simple bacteria
(prokaryote) appeared
• About 2 billion years after,
complex life (eukaryote)
appeared including algae which
though photosynthesis started
releasing oxygen
• atmosphere changed, probably
keeping warm enough so end of
“iceball Earth”??
Takes billions of years for
complex life to develop
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PHYS 162 4
Life on Earth
• appears as if all current life descended from same
ancestor
• all use DNA and RNA and amino acids
• all use ATP for storing/using energy
• amino acids come in both left-handed and right-
handed versions. All life uses left-handed
exclusively
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PHYS 162 5
Other Life in Solar System?
• there is, or has been, liquid water on Mars and
various moons of Jupiter (Europa, Ganymede,
Callisto) and Saturn (Titan, Enceladus) look for
signs of life.
• If ever find, is it of different origin then Earth’s? Say
right-handed amino acids show independent origin
• more info about Mars then anywhere else: both
meteors from Mars and the many landings on the
surface
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PHYS 162 6
Best Bet: Moons of Jupiter and Saturn
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PHYS 162 7
Life on Mars? • landings on the surface have not shown any evidence
• BUT 16 million years ago, an asteroid slammed into
Mars, Mars rock thrown into space, drifted, and landed in
Antarctica 13,000 years ago, results in 1996
• tell from Mars by chemical and gas composition
• possible indications (tubelike objects, hydrocarbons) of
bacteria fossils from 3.6 billion years ago
• no agreement among experts (in Chapter 5)
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PHYS 162 8
Extra Terrestrial Intelligence
• is there intelligent life on other planets?
Drake equation estimates possibility in our
galaxy
• can we try to communicate?
SETI = Search for Extra Terrestrial
Intelligence
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PHYS 162 9
Drake Equation
• N = number of “intelligent” civilizations in the Galaxy
• R* = rate at which solar type stars are formed
• fp = fraction of stars which have planets
• ne = number of planets suitable for life
• fl = fraction of planets where life arises
• fi = fraction of life that develops intelligence
• fc = fraction of intelligent life that communicates
• L = lifetime of communicating intelligence
LfffnfRN cilep
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PHYS 162 10
Possible Stars
Stars can’t be
• too large. Need lifetime more than 2 billion years
• too small. Need habitable region not too close to
star
• too old. Need heavy elements C,O,N in “young”
stars
• in binary system. Planet’s orbit complicated.
Temperature varies
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PHYS 162 11
Possible Planets
Planets can’t be
• too large or too small want atmosphere, and
probably want water
• too hot or too cold want temperature so water is
a liquid
• habitable zone about a star. For larger/hotter
stars this will be further away
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PHYS 162 12
Habitable Zone
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PHYS 162 13
Habitable Zone
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PHYS 162 14
Evolution of Intelligence
• How probable is the evolution from simple to complicated to
intelligent life?
• How probable is the development of technology?
NOT VERY
• dolphins do not need technology (and neither do some human
cultures)
• How did humans evolve?
opposable thumb
communication
slow and weak
tools technology in some cultures but not in others
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PHYS 162 15
Length of Survival of “Intelligence”
• for human culture, anyone’s guess. 100 to
100,000,000 years
• large asteroid
• environmental catastrophes (global warming,
ozone, insecticides)
• nuclear/biological war
• plague
Most species are extinct
• humans could also become uninterested in SETI
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PHYS 162 16
Asteroids, Comets and Meteors
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PHYS 162 17
Asteroids, Comets and Meteors
Meteor crater in
Yucatan, from
65,000,000 years ago
Meteor crater in
Arizona, from 50,000
years ago
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PHYS 162 18
Near Earth Asteroid Tracking NEAT
Look for and track all objects > 1 km in
diameter, close to Earth. ~1200 are “potentially
hazardous”
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PHYS 162 19
Near Earth Asteroids
(29075) 1950 DA is notable for having the highest known
probability of impacting Earth (between 0 and 0.33%). Would
happen on March 16, 2880. But orbit can change with time....
mass about 3
billion tons
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PHYS 162 20
Drake Equation – guess at values
• R* = rate at which solar type stars are formed 1 per year
• fp = fraction of stars which have planets 1
• ne = number of planets suitable for life 0.01 - 0.1 ??
• fl = fraction of planets where life arises 0.001 - 0.1 ?????
• fi = fraction of life that develops intelligence 0.0001 - 0.5 ???????
• fc = fraction of intelligent life that communicates 0.0001- 0.9 ??????
• L = lifetime of communicating intelligence 100 - 25,000 years ????
• N = # of “intelligent” civilizations in the Galaxy = 100 (optimistic)
• N = number of “intelligent” civilizations in the Galaxy = 1 (us
possibly realistic)
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PHYS 162 21
Communicating with ET
• send a spaceship
too slow. velocity is at most .001 times light speed so
more than 1000 years to nearest star
• send a radio/TV message (and listen for them)
travels at speed of light over a wide area
What frequency?
What message?
What direction? maybe in time have a list of found
Earth-like exoplanets
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PHYS 162 22
Communicating with ET spacecraft
• covers why
space travel
will always be
“slow”
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PHYS 162 23
Communicating with ET: spacecraft
• Pioneer 10+11 and
Voyager I+II launched
in 1973+1977
• Now beyond Pluto. Can
still communicate with
the Voyager crafts who
are at 117 AU from Sun
• contain plaques and
records for ET to find
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PHYS 162 24
• Pioneer plaque
• Voyager record includes “Hello”
in many languages, Richard
Nixon, and 90 minutes of music
from Javanese to Bach to Chuck
Berry
• SNL joke. first message from
aliens “send more Chuck Berry”
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PHYS 162 25
Communicating with ET: Radio
What frequency? Microwave is most quiet.
Maybe near one of water’s frequencies?
21 cm is the
Hydrogen
spin-flip
wavelength
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PHYS 162 26
Communicating with ET: Radio
What message? See movie Contact (from Carl
Sagan’s book). Signal sent in 1974
23 columns by 73 rows = 1679 bits (either 0 or 1)
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PHYS 162 27
numbers 1 to 10
elements H (1) C(6) N(7) O(8) P(15)
nucleotides (like phosphate and adenine)
DNA double helix including the number of
base pairs in human genome
human with height (left) and population (right)
9 planets plus Sun with Earth shifted
Arecibo telescope with diameter noted on
bottom