Life in the Universe
Are We Alone?

May 14, 2011, jeb

OUTLINE Evolution in the Cosmos Life in the Solar System What is Life Is There Life on Earth - The ET Perspective Drake Equation Fermi Paradox - Where Are They? UFOs The Scientific Search We Discover Them - SETI They Discover US - CETI Carbon Chauvinism Search for Extrasolar Planets

Extraterrestrial Life

NO? YES? MAYBE?

We will now consider the question of Life in the Universe

Are we alone?
• Drake equation

The search for extraterrestrial life

• What are we looking for?

Attempts for us to discover them

• SETI

Attempts to help them discover us

• CETI

The UFO phenomenon

• Why do scientists generally find the evidence unconvincing?

Evolution in the Cosmos

Our understanding of life in the universe requires we understand how life evolved in the one place we know for sure it did - on the Earth

Life on Earth emerged as part of an evolutionary sequence:
• Particulate phase
• Galactic phase
• Stellar phase
• Planetary phase
• Chemical phase
• Biological phase
• Cultural phase

Life appeared on Earth about 3.5 billion years ago

Was this a unique event in the Universe?

Life in the Solar System

Carbon based

Liquid water essential

Metereorites often contain organic molecules

Lesson from Earth regarding the possibility for life in hostile, alien worlds
In recent years life-forms have been found on Earth living in extreme environments
• extremophiles
  • in superheated hydrothermal vents along the midocean ridge in the eastern Pacific Ocean
  • in frigid lakes buried deep under the Antarctic glaciers
  • in the dark, oxygen-poor and salt-rich floor of the Mediterranean Sea
  • in the mineral-rich superalkaline environment of California's Mono Lake
  • in hydrogen-rich volcanic darkness far below Earth's crust
• in many cases organisms evolve to create the energy they need


Three large bodies in the solar system besides the Earth are thought to have possibilities to harbor life:


• Titan, Saturn's largest moon
  • atmosphere of methane, ammonia and nitrogen
  • Cassini-Huygens probe into the Titan atmosphere indicates inhospitable conditions for Earth-like life
  
  
• Europa, Jupiter's moon
  • liquid water below the icy surface
  
  
• Mars
  • explored by Viking -> no life
  • meteorites from Mars reach Earth

What Is Life?

Living organisms
1. react to environment and heal
2. grow - produce energy from food
3. reproduce - pass along traits
4. evolve from generation to generation - adapt

These are guidelines
• Some nonliving entities might posses these properties
• Some living entities might not always display these properties

Case For Extraterrestrial Life

Assumption of mediocrity
1. Life on Earth depends on a few basic molecules
2. elements making these molecules are common to all stars
3. if same laws of science apply throughout the universe
   
   - life must have also originated elsewhere in the universe

Life started very early on Earth and therefore, we assume, it is easy to begin

• Earth cooled
• acquired water
• stage of volcanism
  • added chemicals to the sea
• then life
  About 3½ billion years ago (About 1 billion years after formation of Earth)

We expect other harbors of life have been around for many billions of years more

Case Against Extraterrestrial Life

Intelligent life on Earth - product of series of extremely fortunate accidents

Scientific Assumptions

Earth was once viewed as "center of the universe" with special status

Now, science views Earth as an insignificant speck in the vast universe

Origin of Life - Can It Happen Spontaneously?

Life - as we know it - is based on complex molecules built as carbon chains

The young Earth was a violent place
• Natural radioactivity, lightning, volcanism, solar ultraviolet radiation, meteoritic impacts
• all sources of large amounts of energy, needed to created complex molecules
• simple molecules (ammonia, methane, carbon dioxide, and water)
• complex molecules (amino acids and nucleotide bases)
• sequences of nucleotide bases form genes (parts of the DNA molecule)


Can these molecules be created in the lab?
• 1953 - Harold Urey and Stanley Miller
  • Mixed H₂O (water), CH₄ (methane), NH₃ (ammonia), CO₂ (carbon dioxide), and applied sparks
  • They found amino acids were formed - the basic building blocks of life

More recent experiments
• Produced amino acids, complex sugars, and nucleotide bases
• protein-like microspheres
  • Similar to ancient cells found in fossils, with many features needed for life
  • But not true life
  • no DNA
• Still no life
  • This step is a mystery
  • But research continues

Possible Alternate Origin of Life on Earth

Rather than life emerging from primordial soup on Earth
• Initial organic material produced in interstellar space and came to Earth as interplanetary dust and with meteors
• NASA tested this hypothesis with modern version of Urey-Miller experiment, using ultraviolet radiation to simulate energy from newborn stars
  • Found oily, hollow droplets rich in organic molecules


Studies during last visit of Halley's Comet and passage of other comets, such as Hale-Bopp
• large amounts of organic material detected


A small fraction of meteorites found on surface of Earth contain organic compounds
• Murchison Meteorite
  • Found soon after landing in Australia in 1969
  • contains large amounts of amino acids and other organic material

Did life arrive from Outer Space?

MAYBE - BUT WE DON'T KNOW

History of Life on Earth

A Timeline of Life's Evolution

Is There Life on Earth? - The ET Perspective

Or how easy would it be to detect life on Earth from distant worlds?

Mass of the Earth = 6x10²⁷ grams
Mass of the atmosphere = 5x10²¹ grams
Biological material on surface of Earth = few x 10¹⁷ grams

THEREFORE

Life = 0.01% of the atmosphere


(10^-10 of the Earth)

"Biological Rust"
• very small effect
  Ref: Shklovskii and Sagan - page 248

Drake Equation

1961 - A small group of astrophysicists (including Carl Sagan) gathered at the National Radio Astronomy Observatory, Green Bank, WV


• Frank Drake presented his equation
  
  
  • to estimate the number of technological civilizations that presently exist in the Milky Way
    
    
    

    N = R_*f_pn_ef_ef_if_cL

    N = the number of civilizations in our galaxy with which communication might be possible
    (Note: This original form is a little different from the textbook)

Conclusion - Extraterrestrial Life Looks Common

	OPTIMISTIC	PESSIMISTIC
R* = rate of star formation in the Milky Way	10/yr	1/yr
fp = fraction of stars with planets	1	0.4
ne = # of habitable planets/star	0.1	0.1
planet in habitable zone;     system in galactic habitable zone;     cannot include binary systems
fe = fraction with life evolved	1	1
fi = fraction where life develops intelligence	1	1
fc = fraction which choose to communicate and develop advanced technology	1	0.1
L = lifetime of such civilizations	108yr.	102yr.
N	108	4

However
Suppose we require conditions like the Earth, since this is the only example of life we know

	OPTIMISTIC	PESSIMISTIC
R* - Only G stars will do	.15/yr	.005/yr
fp - must be single star - near supernova?	.3	very small
Ne - must have continuously habitable zone	.2	very small
fe - special conditions required like large moon	.5	very small
fi - moving to land may require tidal pools	1	very small
fe - periodic ice ages may be required	1	very small
fd - how can we predict civilizations desire to communicate	1	very small
L - civilizations may only search for life	106	102
N	4,500	very small

Fermi Paradox - Where Are They?

Fermi Paradox

Enrico Fermi pondered extraterrestrial life


• He thought it would take about 10,000,000 years to colonize the Milky Way
• We haven't seen them - Why? - This is the Paradox of Fermi
  
  
  1. Perhaps civilizations are content to stay at home
  2. Perhaps it takes longer
  3. Perhaps it has happened but we are not aware of it

UFOs

Claims of sightings and journeys None strongly substantiated Occam's Razor Fundamental principle in science - "the simplest explanation that satisfies all the evidence is the best". Many sightings are explained by optical illusions Many sightings turn out to be fraud No sign that extraterrestrials want to contact authorities - like the U.S. President Occam's Razor leads to the conclusion that reported UFO's are not extraterrestrial life



Of course, we know some people take UFOs very seriously

The Scientific Search

• We are looking for intelligent, advanced life since we assume primitive life is too difficult to detect
  
  
• We assume that intelligent life wants to communicate
  
  
• Two avenues for discovery
  
  
  1. We discover them
     SETI - search for extraterrestrial intelligence
     
     
  2. They discover us
     CETI - communication with extraterrestrial intelligence

We Discover Them (SETI)

SETI - search for extraterrestrial intelligence

What should we look for?

• advanced civilization is very likely to develop radio communication, as we have, so we should look for such signals

Suppose they were trying to communicate - what frequency would they choose?

• Popular guess among scientists
  - 21 cm spin-flip line of hydrogen
      (1420 MHz)
  because hydrogen is the simplest atom in the universe and the 21 cm wavelength is a simple emission of hydrogen
  The entire band of wavelengths around 21 cm is an interesting part of spectrum and is known as the water hole

Searches at or near 21 cm (1420 MHz)

1960 - Frank Drake
1. tau Ceti G type 11 light years away
   • very much like the sun - No SIGNAL
2. epsilon Eridani K type 11 light years away
   • BIG SIGNAL
   • turned out to be airplane
   • then nothing

1973 - Zuckerman and Palmer
• surveyed 600 nearest sun-like stars
  • no signal of life

Late 1990's - Project Phoenix using sophisticated computer controls to investigate millions of channels simultaneously
• Still no sign of life

They Discover Us (CETI)

CETI - communication with extraterrestrial intelligence
1. We have been beaming radio signals to outerspace now for more than 70 years
   • Howdy Doody, I Love Lucy, etc.
   • (sign of intelligent life? - maybe)

   closest stars ( Centauri) are about 4 light years away and since radio signals travel at the speed of light, Centauri has been receiving these signals for about 70 years
   roughly 1,000 stars have now been exposed to this emission
   

2. Maybe we need to signal them more directly
   Big Question - should we?
   No,
   they will be much more advanced and view us as primitive life
   they may choose to exploit us, enslave us, or EAT US
   Yes,
   if they are so advanced
   • they can teach us a lot
   • help solve problems
     • population explosion
     • energy shortage
     • world of wars
   besides their distance is probably so great that we need not worry about their coming here

1974 - Arecibo - Puerto Rico
message from people on Earth beamed at globular cluster M13 (many stars) - distance 24,000 light years
1679 bits of information (0000001010101000000000000101......
only factors of 1679 are 23 and 73 (1679 = 23 x 73)

The Arecibo message consists of seven parts
1. The numbers one (1) through ten (10)
2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA)
3. The formulas for the sugars and bases in the nucleotides of DNA
4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA
5. A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth
6. A graphic of the Solar System
7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish

Placed messages aboard space vehicles
• Pioneer
• Voyager

We assume these messages will be interpreted correctly if received

Carbon Chauvinism

Usual assumption of SETI is that life is based on carbon chemistry, like on Earth
• WHY?
  1. We know it works
     • example - Earth
  2. Basis element must be plentiful
     • no exotic elements like Ytterbium or Gadolinium
  3. Chemistry must form long chains to pass information like with DNA
     only possibilities are Silicon and Carbon (ref: Rood and Trefil)

Why Not Silicon?

1. We don't have an existence proof - like for carbon
2. Life on Earth is based on molecules containing millions of atoms (DNA)
   This is required to pass the enormity of information:
   • blue or brown eyes
   • male or female
   • short or tall
Silicon
• Room temperature
  30-40 atoms maximum
• At -200^oC, long chains form - but other problems like Nitrogen is a liquid and reactions slow down

Search for Extrasolar Planets

Hundreds of planetary systems beyond the Solar System have now been discovered
Discussed in last lecture

Conclusion

• It is easy to imagine that life exists on distant worlds
  
  
• Efforts have been underway on Earth for many years to detect extraterrestrial intelligence
  
  
• If we do someday "make contact," our view of the universe will be changed forever

The SETI Institute