Announcement

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Announcement

• NO CLASS on Thursday, October 27
• Amos Yahil (instructor) will not hold his office
  hour on November 1
• Steve Gindi (TA) holds his office hours as usual
• The regular office hours are
• Amos Yahil Tu 11-12, ESS 461
• Tel [phone]
• Steve Gindi Th 3-4, Physics D-116
• Tel [phone]

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Search for Life in the Universe

• Chapter 6
• Life in the Solar System

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Outline

• Environmental Requirements for Life
• Elements
• Energy
• Water
• Exploring the Solar System
• Methods of Observation
• Telescopes
• Robotic Spacecrafts
• Biological Tour of the Solar System
• Moon and Mercury
• Venus
• Jupiter and Jovian Planets
• Small Moons, Asteroids Comets

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Elements

• Most common elements on Earth (96 total) O, C,
  H N
• After H and He, they are also the most common in
  the universe
• Planetessimals cannot be formed with H (except as
  H2O) and He
• C essential for long organic molecules
• Some organic compounds can only be formed in an
  atmosphere or an ocean
• Atmosphere and ocean are reasonable requirements

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Energy

• Sunlight
• Decreases as the inverse square distance
• Electrical
• Lightning in atmospheres
• Chemical
• Abundant, but needs mixing in atmosphere or
  liquid
• Earth plenty of water and atmosphere
• Mars and Venus still enough internal heat for
  surface or subsurface chemical reactions
• Jovian moons plenty of ice and tidal heating in
  the ones closest to the planets, e.g., Io and
  Europa

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Water

• Alternative liquids at colder temperatures
• Ammonia (NH3) -78?C ? -33 ?C
• Methane (CH4) -182?C ? -164 ?C
• Ethane (C2H6) -183?C ? -89 ?C
• Reactions slower at lower temperatures
• Density decreases with decreasing temperature
  below 4?C ? floating Ice
• Polar molecule dissolves chemicals better

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Methods of Observation

• Human exploration
• Greatest benefit
• Greatest danger
• Robotic spacecraft
• Close by observations
• Collect samples
• Leave a station
• Telescopes
• Ground based
• In orbit around the Earth

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Telescopes

• More light
• Large aperture
• Longer exposure
• Other wavelengths
• Long-term time dependence
• Imaging
• Sensitivity
• Resolution
• Spectroscopy
• Temperature from broad-band spectroscopy
• Temperature, density, pressure, velocity from
  spectral lines (absorption and emission)

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Robotic Spacecrafts

• Flyby
• Least energy ? lowest cost
• Gravitational boost to reach other planets
• Short duration
• Orbiter
• More energy ? higher cost
• Longer duration
• Probes and landers
• Probes death-throe information from orbiter
• Landers often capable of roaming
• Sample return
• Blast-off ? highest energy
• So far only from the Moon (Soviet Union)

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Moon and Mercury

• Small internal heat not important
• No atmosphere
• No liquids
• Moon may have ice at the bottom of polar craters
  that are perpetually in shadow
• Mercury
• Close to the Sun, so little original water
• Water from bombardments hard to keep
• High density giant early bombardment removed
  mantle and crust, where most water would have been

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Venus

• Hell of the Solar System
• Temperature 450?C (850?F)
• Pressure 90 atmospheres
• Atmosphere also contains concentrated sulfuric
  acid and other harmful chemicals
• Runaway greenhouse effect
• Atmosphere 96 CO2 because there is no way to
  remove it
• Oceans too hot today for liquid water
• Plate tectonics apparently none today
• Past life on Venus?
• Oceans around 4 byr ago?
• Maybe, but the evidence is gone
• Cratering shows the surface to be 1 byr old
  (volcanism)

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Jupiter and Jovian Planets

• Composition solar
• No solid surface
• Water at a depth 100 km
• Strong winds and vertical circulation no stable
  life at any layer of the atmosphere
• Large buoyant creatures could avoid circulation,
  but how would they be formed?
• Other Jovian planets (Saturn, Uranus and
  Neptune) same problems

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Small Moons, Asteroids Comets

• All too small to keep liquid water
• Comets (also Pluto and 2003 UB313, the 10th
  planet) in permanent freeze
• Complex organic molecules are found in both
  asteroids and comets
• Early life? no evidence, but not ruled out
• Small moons, e.g., moons of Mars similar to
  asteroids

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