5. Fermi paradox
• Time for an intelligent species to colonize
galaxy: 106 years
Friday, February 13, 2009
6. Fermi paradox
• Time for an intelligent species to colonize
galaxy: 106 years
• Age of the Galaxy: 1010 years
Friday, February 13, 2009
7. Fermi paradox
• Time for an intelligent species to colonize
galaxy: 106 years
• Age of the Galaxy: 1010 years
• where are they?
Friday, February 13, 2009
15. USING PHOTOMETRY TO DETECT
EARTH-SIZE PLANETS
The relative change in brightness (ΔL/L) is equal to the relative areas
•
(Aplanet/Astar)
Jupiter: Earth or Venus
1% area of the Sun (1/100) 0.01% area of the Sun (1/10,000)
Small planets need ultra-precise photometry. Must be done with wide-
field CCD imager in space.
Friday, February 13, 2009
16. What have we learned from
planet searches so far?
Friday, February 13, 2009
17. Only high metallicity
stars have planets
FISCHER & VALENTI Vol. 622
lity
/Star
tirety
sical
ance
0.3 × Solar 3 × Solar
03). In addition, a Fig. 5.—Same results as Fig. 4, but divided into 0.1 dex metallicity bins. The
s been underway increasing trend in the fraction of stars with planets as a function of metallicity is
004). No planets well fitted with a power law, yielding the probability that an FGK-type star has a
gas giant planet: P( planet) ¼ 0:03½(NFe =NH )=(NFe =NH ) Š2:0 .
veys, suggesting
nets with orbital
ikely lower than)
Friday, February 13, 2009
18. Stars with planets are young.
The Sun may be one of the oldest stars with planets
– 37 –
s
net
pla
rs
ith
sta
rs w
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Sta
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Friday, February 13, 2009
23. What planets support life?
What kinds of planets can support life?
What fraction of planets that can support life do support life?
Friday, February 13, 2009
24. The Habitable Zone is the range of distances
from a star which allow a planet to support life
Friday, February 13, 2009
25. What are the minimal
conditions for life?
• How hot? • How radioactive?
• How cold? • How poisonous?
• How dry? • How much
pressure?
• How acid?
• How barren?
• How salty?
Organisms that push these limits are called
extremophiles
Friday, February 13, 2009
32. Atacama Desert
dryest place on earth
2 mm
decadal
precipitation
recent
discoveries
of life below
4 inches
Friday, February 13, 2009
33. Lifeless desert in Oceans
• Centers of oceans
have very little life.
• Plenty of liquid
water
• Plenty of sunlight
energy
• Missing some key
chemicals
– Phosphorus
Friday, February 13, 2009
34. Lessons from terrestrial life
• Life can exist with only a bare minimum of
ingredients:
– Liquid Water
– Some energy source
• Sunlight, Rocks, Geothermal energy
– Basic chemical ingredients
• Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus
Friday, February 13, 2009
35. Old Habitable Zone Theory
• If planet is too close to star, fries through
runaway greenhouse effect
• If planet is too far from star, freezes, can’t
support life.
Friday, February 13, 2009
36. New Habitable Zone Theory
• Many other factors besides distance from the Sun
help determine planetary climate
– Greenhouse effect
– Plate Tectonics
– Impacts (Early Earth atmosphere stripped)
– Tidal Heating (Io, Europa)
• Liquid water can be found in a variety of unlikely
environments
– Europa, Callisto, Ganymede
– Early Mars very wet, present Mars dry?
Friday, February 13, 2009
37. How many habitable planets will
actually be alive?
• Basic ingredients to make life are common
throughout the cosmos
• Look at History of Life on Earth
• Life began shortly after Earth cooled
• Suggests that Life is easy to make.
Friday, February 13, 2009
39. Basic ingredients of life
• Organic molecules detected in interstellar
space.
Friday, February 13, 2009
40. Basic ingredients of life
• Organic molecules detected in interstellar
space.
• Water (Ice) detected throughout galaxy,
solar system.
Friday, February 13, 2009
41. Basic ingredients of life
• Organic molecules detected in interstellar
space.
• Water (Ice) detected throughout galaxy,
solar system.
• The basic chemical ingredients of life are
common throughout the galaxy.
Friday, February 13, 2009
42. Organic Molecules in interstellar
space
• Amino Acids
• Nucleic Acids
• Soot
Friday, February 13, 2009
43. Given the right ingredients, how
easy is it to make life?
34
Friday, February 13, 2009
47. Conclusion from oldest life
• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.
Friday, February 13, 2009
48. Conclusion from oldest life
• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.
• 3.8 billion years ago, many
fewer impacts.
– Earth became inhabitable.
Friday, February 13, 2009
49. Conclusion from oldest life
• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.
• 3.8 billion years ago, many
fewer impacts.
– Earth became inhabitable.
• Oldest life on Earth 3.8 billion
years old.
Friday, February 13, 2009
50. Conclusion from oldest life
• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.
• 3.8 billion years ago, many
fewer impacts.
– Earth became inhabitable.
• Oldest life on Earth 3.8 billion
years old.
• Life formed on Earth as soon
as Earth could support life.
Friday, February 13, 2009
51. Conclusion from oldest life
• Earth was not habitable until
3.8 billion years ago.
– Too many impacts melted
surface.
• 3.8 billion years ago, many
fewer impacts.
– Earth became inhabitable.
• Oldest life on Earth 3.8 billion
years old.
• Life formed on Earth as soon
as Earth could support life.
• Life is easy to form?
Friday, February 13, 2009
57. Biomarkers in atmosphere
• Earth’s atmosphere shows
strong signals of two biogenic
molecules
– Oxygen
• Produced by plants
– Methane
• Produced by Cows
Friday, February 13, 2009
58. Biomarkers in atmosphere
• Earth’s atmosphere shows
strong signals of two biogenic
molecules
– Oxygen
• Produced by plants
– Methane
• Produced by Cows
• Normally, methane burns in
Oxygen
– Natural Gas
Friday, February 13, 2009
59. Biomarkers in atmosphere
• Earth’s atmosphere shows
strong signals of two biogenic
molecules
– Oxygen
• Produced by plants
– Methane
• Produced by Cows
• Normally, methane burns in
Oxygen
– Natural Gas
• Two can only exist in
combination because both
being produced by life.
Friday, February 13, 2009
63. Lessons from Extremophiles
• Complex life on Earth restricted to narrow
range of habitats.
– Not in Antarctica, too cold, dry
– Not inside rocks, nothing to eat, breath
– Not inside geothermal vents, too hot
– Not in clouds, too heavy
– Not in driest deserts, too dry
Friday, February 13, 2009
65. Formation of Oxygen Atmosphere
• Life begins to saturate
atmosphere with
Oxygen
• Oxygen kills off life
• Oxygen combines with
rock
• Life comes back,
makes more oxygen
• Oxygen kills off life
• Process continued for
800 million years.
Friday, February 13, 2009
66. Lessons from formation of life
• Complex multicellular life did not evolve until
recently.
– Cambrian Explosion 600 Mya.
• Complex life could not have evolved without
Oxygen atmosphere.
• Complex life more fragile than simple life.
• Complex life difficult to evolve.
Friday, February 13, 2009
67. Lessons from Mars
• Planetary climates
can change
• Complex life (if it
ever existed) likely
wiped out today.
• Simple life could
have survived.
Friday, February 13, 2009
68. Answer to Fermi
Paradox?
• Sun may be among the first stars to have
planets
• Life may be common
• Complex life may be rare
• Complex life may take a long time to form
• We may be alone?
Friday, February 13, 2009
69. Intelligent life
• No information how • Search for Extraterrestrial
common intelligent life is. Intelligence: SETI
– Cannot be federally funded
– Took most of history of
by congressional mandate
earth to evolve an
earthworm. – Now part of NASA’s
Astrobiology Institute
• Definition of Intelligent life:
– Just another means to
Ability to operate radio
search for life
transmitters
– Privately Funded SETI
• Search for intelligent life institute
by searching for radio
transmission
Friday, February 13, 2009