Life on Other Worlds?

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Life on Other Worlds?
0
Please pick up your transmitter and swipe your ID
2
The chemistry of all known life forms on Earth is
based on which essential element?

1. Hydrogen
2. Helium
3. Carbon
4. Oxygen
5. Iron

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The Physical Basis of Life
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All life forms on Earth, from viruses to complex
mammals (including humans) are based on carbon
(C) chemistry.
Carbon-based DNA and RNA molecule strands are the
basic carriers of genetic information in all life
forms on Earth.
This complex mammal contains about 30 AU of DNA.
The Tobacco Mosaic Virus contains a single strand
of RNA, about 0.1 mm long
4
Do we find evidence for carbon-based compounds
anywhere else than on Earth?

1. No
2. Yes, but only in the atmospheres of other
   terrestrial planets
3. Yes in the atmospheres of most planets (and
   moons) which have an atmosphere.
4. Yes On the surfaces of other planets and moons
   throughout the solar system.
5. 3 and 4.

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The basic building blocks of life
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• Simple carbon-based (organic) compounds are found
  not only in the solar system (on planets and
  moons), but also in interstellar space
• Methane
• Ethane
• Formaldehyde

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The Miller Experiment
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Miller Experiment in 1952 Simulating conditions
on Earth when life began 4 billion years ago
Water (oceans), primitive atmosphere gases
(hydrogen, ammonia, methane), and energy from
electric discharges (lightning).
Experiment produced some of the fundamental
building blocks of life amino acids, fatty
acids, ...
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Requirements of Life
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• Liquid water (for chemical reactions and as
  transport medium).

• Atmosphere (to avoid rapid vaporization of water
  gases needed for organic compounds)

• Moderate temperatures (keep water liquid avoid
  disintegration of organic compounds activate
  complex chemical reactions)

• Time for life to evolve from simple organic
  compounds into higher life forms several billion
  years.

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Geologic Time
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In geologic terms, higher life forms, in
particular mammals and humans, have evolved only
very recently.
Humans have existed for only 3 million years.
9
Do we have evidence for planets around other
stars?

1. No.
2. Yes, but only very few might have planets.
3. Yes, many (single) stars might have planets.

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Requirements for Life in Other Planetary Systems
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• Planetary systems are probably common.

11
Do you expect that virtually all stars will be
single, rather isolated stars like our sun?

1. Yes. Most stars should be single stars.
2. No. Stars form in clusters, so many stars could
   still be bound in small groups (double-,
   triple-star systems).
3. No. Stars form in clusters, so virtually all
   stars should still be bound in large groups of
   several hundreds to thousands of stars.

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Requirements for Life in Other Planetary Systems
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• Planetary systems are probably common.

About 50 of all stars in our Milky Way are
bound in double- or triple-star systems.

• Stable orbit around the star ? consider only
  single stars.

13
If we have a planet with a reasonable atmosphere,
water, and carbon-based compounds, could life
always evolve on them?

1. No, it needs to have seasons.
2. No, it needs to be at an appropriate distance
   from the star to provide reasonable temperatures.
   
3. No, it needs to be around a star that lives at
   least several billion years.
4. All of the above
5. 2. and 3.
6. Yes.

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Requirements for Life in Other Planetary Systems
0

• Planetary systems are probably common.

• Stable orbit around the star ? consider only
  single stars.

• Time for evolution ? consider only stars that
  live for several billion years.

• Moderate temperatures ? Life zone around the star

Orbit of Mars
Too cold
Orbit of Earth
Life zone
Orbit of Venus
Too hot
Sun
15
Are we alone? The Drake Equation
0
Lets try to estimate the number of civilizations
(Nc) in our Milky Way that are currently in a
state of their development that they are
intelligent, advanced enough, and willing to
communicate with us.
Factors to consider

• Number of stars in the Milky Way
• N 21011

• Fraction of stars with planets
• fp 0.01 0.5

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Factors to consider (contd.)
0

• Number of planets per star that lie in the life
  zone for longer than 4 billion years
• nLZ 0.01 - 1

Orbit of Mars
Too cold
Orbit of Earth
Life zone
Orbit of Venus
Too hot
Sun
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Factors to consider (contd.)
0

• Fraction of suitable planets on whith life
  actually begins
• fL 0.01 - 1

• Fraction of eco-systems in which a life form
  evolves to inteligence
• fI 0.01 - 1

• Fraction a stars life during which there is a
  communicative civilization
• FS 10-8 10-4

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The Drake Equation
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The number of technologically advanced
civilizations per galaxy that are currently able
and willing to communicating with others
Nc N fp nLZ fL fl FS
Most of the factors are highly uncertain.
Nc 210-5 2107
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What does it mean if Nc 210-5?

1. There are currently 210-5 communicating
   civilizations in the Milky Way.
2. There are currently 50,000 ( 1/210-5)
   communicating civilizations in the Milky Way.
3. If you take 210-5 galaxies, you can expect to
   find one communicating civilization in them.
4. If you take 50,000 galaxies, you can expect to
   find one communicating civilization in them.

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The Drake Equation
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Nc 210-5 2107
Possible results range from 1 communicative
civilization within a few dozen light years to
us being the only communicative civilization in
the Milky Way.
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So, whats the final word on the question Are
we alone in the Milky Way?

1. There is most likely no other communicative
   civilization in the Milky Way at this time.
2. There is a reasonable chance that there are a few
   other communicative civilizations in the Milky
   Way at this time.
3. There are probably thousands or even millions of
   other communicative civilizations in the Milky
   Way at this time.
4. We have no clue!

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