Life on Giant Planets

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Life on Giant Planets Their Moons
Stephen Eikenberry 12 March 2019 AST 2037
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• much larger than terrestrial planets
• not solid - gaseous
• all have rings
• all have many moons

The Jovian Planets
Jupiter
Jupiter, Saturn, Uranus, Neptune
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• Jupiter
• Named after the most powerful Roman god
• third-brightest object in the night sky (after
  the Moon and Venus)
• Atmospheric bands are very different than inner
  planets
• Many moons four largest called Galilean Moons

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• Saturn
• Named after the father of Jupiter in Greco-Roman
  mythology
• Almost twice Jupiters distance from the Sun
• Similar banded atmosphere
• Uniform butterscotch hue
• Many moons
• Spectacular ring system

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• Uranus
• Discovered by William Herschel in 1781
• Named after father of Saturn
• Barely visible to naked eye
• Featureless atmosphere
• Deviations in the expected orbit of Uranus
  pointed to the possibility of another planet
  influencing its motion

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• Neptune
• There had to be another planet influencing
  Uranus
• 1845 - John Adams determined the planets mass
  and orbit
• 10 months later - Urbain Leverrier,
  independently came up with the same result
• 1846 - Johann Galle found the new planet Neptune
  
• Cannot be seen with naked eye
• Bluish Jupiter atmosphere

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• Space Craft Exploration of Jovian Planets
• Voyager 1and 2 left Earth in 1977
• reached Jupiter in March and July of 1979
• Used Jupiters strong gravity to send them on to
  Saturn - gravity assist
• Voyager 2 used Saturns gravity to propel it to
  Uranus and then on to Neptune
• Studied planetary magnetic fields and analyzed
  multi-wavelength radiation
• Both are now headed out into interstellar space!

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• Space Craft Exploration of Jovian Planets
• Galileo - launched in 1989 and reached Jupiter
  in December 1995
• Gravity assists from Venus and Earth
• Two components atmospheric probe and orbiter
• Probe descended into Jupiters atmosphere
• Orbiter went through moon system

• Cassini mission to Saturn
• Studying Saturns moon Titan in much the same
  way as Galileo studied Jupiter

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• Jovian Planet Properties
• Most of their mass is Hydrogen and Helium light
  elements low densities
• High surface gravity allows their atmospheres to
  retain these light elements
• Dense compact core at the center
• But, NO SOLID SURFACE gaseous atmosphere
  becomes denser (eventually liquid) at core
• Differential Rotation outer regions rotate
  slower than inner regions

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Jovian planets - axis tilt and magnetic fields

• Uranus has the most inclined rotational axis -
  extreme seasons!
• All appear to have strong magnetic fields - rapid
  rotation and liquid conductive cores or mantles

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• Jupiters Atmosphere
• Two main features colored bands and Great Red
  Spot
• molecular hydrogen 86
• helium 14
• small amounts of methane, ammonia, and water
  vapor

• Darker colored belts lie atop downward moving
  convective cells
• Lighter zones are above upward moving cells
• Belts are low-pressure, Zones are high pressure
• As on Earth, wind moves from high to low
• But rotation causes wind patterns to move
  East/West along equator
• Temperature difference between bands is main
  reason for color difference

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Jupiters Atmosphere

• Haze lies at the upper edge of the troposphere
• Thin layer of white ammonia clouds 125 150 K
• Colored clouds below that

• Warmer - 200 K
• clouds are mostly droplets or crystals of
  ammonium hydrosulfide
• At deeper levels, clouds of water ice or water
  vapor

The Galileo probe survived for about an hour
before being crushed at this altitude.
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• Weather on Jupiter
• Main weather feature Great Red Spot!
• swirling hurricane winds
• has lasted over 300 years!
• diameter twice that of Earth
• rotates with planets interior
• the spot appears to be confined and powered by
  the zonal flow

Smaller storms look like white ovals (this one is
over 40 years old)
Why do the storms last so long? On Earth,
hurricanes lose power when then come upon land No
continents on Jupiter nothing to stop them once
they start
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• Saturns Atmosphere
• molecular hydrogen 92.4
• helium 7.4
• traces of methane and ammonia

• Layer of haze
• Troposphere contains 3 cloud layers
• Overall temperature is cooler than Jupiter
• Atmosphere thickness is 3 times that of Jupiter
  (caused by lower surface gravity on Saturn)
• Thicker clouds result in less varied visible
  colors

• ammonia ice
• ammonium hydrosulfide ice
• water ice

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• Weather on Saturn
• Computer enhanced image shows bands, oval storm
  systems, and turbulent flow patterns like those
  seen on Jupiter

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• Atmospheres of Uranus and Neptune
• molecular hydrogen 84
• helium 14
• methane 2 (Uranus) 3 (Neptune)

Abundance of methane gives these planets their
blue color Methane absorbs longer wavelength
light (red) and reflects short wavelength light
(blue)
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Weather on Uranus and Neptune

• Uranus
• Few clouds in the cold upper atmosphere
  featureless
• Upper layer of haze blocks out the lower, warmer
  clouds

• Neptune
• Upper atmosphere is slightly warmer than Uranus
  (despite its further distance from Sun)
• More visible features (thinner haze, less dense
  clouds lie higher)
• Storms Great Dark Spot
• Seen in 1989 gone in 1994

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Internal Structures models that fit the data
Metallic hydrogen is like liquid metal
Uranus/Neptune
Saturn
Jupiter

• Increasing temperature and pressure deeper in
  core
• Jupiter bulges at radius (7 larger)
• Saturn less assymetric larger core same basic
  overall structure on a smaller scale
• Uranus/Neptune have a high density slush below
  cloud level - compressed water clouds

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• Internal Heating
• Primordial Heat
• Generation of Heat
• Effect of internal heating - raises the
  temperature of the interior and atmosphere to
  higher values than expected from the Suns
  heating alone

-Jupiters heat source results from strong
heating during formation by the collapse of
material onto the core
-Saturn generates some heat due to the
gravitational contraction of helium gas
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• Life on the Giant Planets?
• We see lots of life chemicals! (Water,
  methane, etc.)
• Lightning observed too
• Similar to early Earth atmosphere (?)
• Expect complex hydrocarbons (Urey-Miller) (?)
• At some depth, have warm temps (300K)
• But these temps at high pressure
• Methane is not a sign of life here just a sign
  of LOTS of free hydrogen, some carbon, relatively
  little oxygen
• No solid surface no oceans, no tidal pools, no
  clay matrix in short, no (Earth-like) places
  for life formation

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• Life on the Giant Planets?
• What about gas matrix life? (i.e. no solid
  surface, but life in the air)
• Wind speed turbulence problem try to put
  together a house of cards outdoors in a hurricane
• Thats easier than forming life in Jupiters
  atmosphere!
• Convection
• Causes any chemicals from warm lower layers to
  rise
• This gives exposure to solar UV radiation, which
  breaks it down

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• Does this mean NO life here?
• Nope
• Floater possibility
• But, this is pure speculation

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Moons

• Almost all moons in the Solar System orbit the
  Jovian planets
• Jupiters 4 major moons are the Galilean
  satellites Io, Europa, Callisto, and Ganymede
• Jupiter has 100s of smaller moons

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Io

• Innermost Galilean satellite
• Reddish color
• Smooth young surface
• Extreme volcanic activity
• Interior tidally heated by Jupiter ( Europa)

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Io Tidal Heating
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Europa

• Second Galilean satellite
• Whitish, highly-reflective color
• Smooth surface with patterns similar to ice caps
  on Earth
• Young surface
• May be a liquid waterworld with ice crust

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Life on Europa?

• Possible view of Europan ocean
• Note thermal segregation

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Life on Europa?

• Europa seabed may resemble black smoker
  environment on Earth (!)
• Probably little O2 in the water (where would it
  come from?)
• But anaerobic bacteria are the basis for life in
  Earth vents (even if larger life O2-dependent)
• NASA developing preliminary plans for a
  drilling/submarine exploration mission

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Callisto Ganymede

• Rock/ice moons
• Evidence for some glacial flows

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Saturns Titan

• Largest moon
• Smooth surface due to thick atmosphere (!)
• Infrared images show evidence for continents
  beneath

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Titans Surface
Lakes of liquid hydrocarbon imaged from orbit via
Cassini T 85K (probably ethane/methane) Huygens
lander mission in 2006
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Titans Surface
Lakes of liquid hydrocarbon imaged from orbit via
Cassini Huygens lander mission in 2006
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Life on Titan?

• Solid/liquid phase environment similar to
  Earths surface
• Totally different chemicals and temp ranges
  will not be H2O-based like on Earth
• But still a possibility

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Neptunes Triton

• Largest Neptunian moon
• Retrograde orbit
• Orbital tilt 20-degrees
• Could indicate KBO origin ??

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Other moons
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Enceladus

• Saturn moon
• Water here too?

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Enceladus

• Saturn moon
• Water here too?

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Summary

• The Giant Planets lack solid surfaces and have
  extreme wind speed, turbulence and convection in
  their atmospheres
• Still .. we cannot rule out life there
  (floaters?)
• Moons such as Europa and Enceladus may have
  liquid water oceans with Earth-like temperatures
  and geothermal vents these may be promising
  places to search for life
• The moon Titan has a thick atmosphere and
  (apparently) lakes/rivers of liquid hydrocarbons
  temps are COLD, but we can imagine some
  low-temperature, slow-reaction life developing
  here too (?)