Searching for Life Beyond The Solar System

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Searching for Life Beyond The Solar System
Dr. Victoria Meadows NASA Astrobiology
Institute Spitzer Science Center/California
Institute of Technology
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Life Beyond Our Solar System

• There are countless suns and countless earths
  all rotating around their suns in exactly the
  same way as the seven planets of our system. We
  see only the suns because they are the largest
  bodies and are luminous, but their planets remain
  invisible to us because they are smaller and
  non-luminous. The countless worlds in the
  universe are no worse and no less inhabited than
  our Earth.
• - GIORDANO BRUNO (1584)

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What Is Astrobiology?

• Astrobiology is the scientific study of life in
  the universe, its past, present and future.
• Astrobiology seeks to answer three questions
• How does life begin and develop?
• Does life exist elsewhere in the universe?
• What is lifes future on Earth and beyond?
• Astrobiology is an interdisciplinary science
• combines biology, chemistry, geology, astronomy,
  planetary science, paleontology, oceanography,
  physics, and mathematics to answer these
  questions.

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Where would we start the search for life outside
our Solar System?
First, find a habitable world
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What Is a Habitable World?

• A world that can maintain liquid water on its
  surface

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Challenges Separating Planet and Star

• In the visible, they dont give off their own
  light
• They are VERY far away, which makes them very
  faint
• They are lost in the glare of their star

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Learning About the Planet

• We will not be able to see details on it
• Everything we learn will be disk-averaged.
• The signs of life must be a global and on the
  surface
• Our interpretation is only as good as how deep we
  can see!

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Learning About Distant Worlds
Radio
Infrared
Visible
Ultra- Violet
X-Ray
Gamma Rays
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Greenhouse Warming
Teffective Tsurface Greenhouse
Venus -43C 470C 513C Earth -17C 15C 32C Mars -55C -50C 5C
? 37 C ? 520 C
A planets greenhouse effect is at least as
important in determining that planets surface
temperature as is its distance from the star!
After Table 9.1, Bennet, Shostak, Jakosky, 2003
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So Many Planets

• 211 planets known beyond our Solar System!
• But theres ONE problem

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Too Big!

• These planets are mostly giant planets
• Small, rocky, Earth-like terrestrial planets
  around good parent stars are still very difficult
  to find.
• A handful of M lt 10 Earth masses known
• Recent discovery of Gl 581c, gt 5.1 Mearth

R. Hasler
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How can we tell if a planet is inhabited?
DEAFENING SILENCE!
Without direct contact with an alien
civilization, or travelling to the nearest solar
system, our best chance for finding life in the
Universe is to look for global changes in the
atmosphere and surface of a terrestrial planet.
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Signs of Life

• Astronomical Biosignatures are global-scale
  photometric, spectral or temporal features
  indicative of life.
• Earth shows us that life can provide global-scale
  modification of
• A planets atmosphere
• A planets surface
• A planets appearance
• over time
• Biosignatures must always be identified in the
  context of the planetary environment
• e.g. Earth methane and Titan methane

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Signs of Life Atmosphere
O3
CH4
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Signs of Life Surface
Reflectivity
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Signs of Life Time
NOAA-CMDL
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A Diversity of Worlds
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A Diversity of Worlds in Space
Circularity
Star-Planet Distance
Water Content
Wet
Dry
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and Time
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Earths Around Other Stars
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Active M Star Planets
N2O
Earth-like planets around M stars with similar
surface fluxes can produce simultaneous strong
signatures of O2 or O3 and CH4, CH3Cl or N2O.
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Early Earth-like Planets
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Modern Earth 355ppm CO2
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Proterozoic 0.1PAL O2 100ppm CH4 15 decrease in
ozone column depth
Segura, Krelove, Kasting, Sommerlatt,Meadows,Crisp
,Cohen
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Archean N2 99.8 2000ppm CO2 1000ppm CH4 100ppm
H2
Karecha, Kasting, Segura, Meadows, Crisp, Cohen
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High CO2 Early Earth-like Planet
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High CO2 Early Earth-like Planet
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The Coevolution of Photosynthesis with the
Atmosphere On Extrasolar Worlds
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Why Are Plants Green?
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Terrestrial Planet Finders
Terrestrial Planet Finder
NASA
Direct detection of planets Launch ?
Darwin ESA
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http//vpl.ipac.caltech.edu http//planetquest.jp
l.nasa.gov