Download Moons of the Outer Solar System

Life Outside the
Habitable Zone?
Astrobiology Workshop
June 27, 2006
Terrestrial Planet Region:
Quick Review
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MERCURY
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MOON
X
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Terrible Extremes of Temperature
No Atmosphere, UV, Cosmic Rays
Little or No Volatiles, No Liquids
Been There, Done That
VENUS
Absurdly High Temperatures
No or Little Water
Young Surface  No Fossil Record

MARS
Evidence for Liquid Water in Past
Possible Environments for Life to Survive?
Volatiles and Water Present Now
X
X
?
Terrible Extremes of Temperature
No Atmosphere, UV, Cosmic Rays
Little or No Volatiles, No Liquids
Gas and Ice Giant Planets:
Interiors
Gas Giant Planets
Ice Giant Planets
Jupiter’s Interior:
More Detail
XXXXX
Gas and Ice Giant Planets: Atmospheres
Gas and Ice Giant Planets:
Prospects for Life?
Prospects for Life?
• There are ingredients for organic chemistry, and
• Atmospheric layers exist with roughly Earth-like
Temperature & Pressure;
• But there are no solid surfaces (except ice crystals) and
no liquid water (except very deep in Uranus and
Neptune),
• Violent winds and convective turbulence would mix any
life-bearing gas quickly over extremes of T & P.
• Although the sunlight is very weak,
• Internal heat is available.
• They are very difficult to explore!
What about Moons of Planets?
For instance, the Galilean
Satellites of Jupiter
Io
Europa
Ganymede
Callisto
Moons of the Outer Solar System:
Jupiter’s Io
Moons of the Outer Solar System:
Jupiter’s Europa
Moons of the Outer Solar System:
Io and Europa
Jupiter’s Io
 Is the most volcanic object in the Solar System
due to
 Tidal heating caused by the gravitational tug of
war it experiences from Jupiter and its sister
Galilean satellites.
Jupiter’s Europa
 Has similar but weaker tidal heating,
 Has a young cracked water ice crust perhaps only
a few kilometers thick, and
 May have a warm ocean of liquid water below the
crust.
 Could there be life?
Tidal Forces:
Tides Raised on Earth by the Moon
The misaligned bulges
exert a small force on
the Moon that increases
the size of its orbit, while
friction in the bulges slows
the Earth’s rotation.
Tidal forces are
difference forces.
Tidal Heating of a Moon:
Tides Raised by a Planet on its Moon
Tidal heating occurs because
Io and Europa’s orbits are
Eccentric.
The orbits stay eccentric due
to a three-way orbital resonance
among the three moons Io,
Europa, and Ganymede.
Effects of Tidal Interactions
Rotation
 Rotation of moons become synchronized with their
orbits.
 They keep the same face toward the planet.
 The rotation of the planet is slowed down.
Orbits
 Orbits of moons mostly evolve outward.
Internal “Tidal Heating”
 Eccentric orbits lead to periodic flexing of the moon’s
shape which heats the interior.
 Orbital resonances with other moons can maintain
eccentric orbits and tidal heating.
Roche Radius
Roche Radius
 Objects held together by
their own gravity are
shattered inside the
Roche Radius (about 2
Planet Radii).
 This is where most giant
planet rings are.
 Comet SL9 was tidally
disrupted within the
Roche Radius of Jupiter
and destroyed
Why doesn’t the
Space Shuttle get
disrupted? Why
don’t we get
disrupted?
Tidal Disruption:
Comet Shoemaker Levy 9
Moons of the Outer Solar System:
Saturn’s Enceladus
Saturn’s Enceladus
Small icy moon (500 km)
in diameter
Young, crater-free
surface regions with like
those on Europa
Orbit resonance with
Dione
South polar hot spot and
ice plumes
Thin “atmosphere” of
water vapor
Subsurface ocean!?
Moons of the Outer Solar System:
Saturn’s Enceladus
Ice Plumes from Enceladus
Surface Temperatures on
Enceladus
Moons of the Outer Solar System:
Saturn’s Titan
Saturn’s Titan
The atmosphere is
denser than Earth’s but
very cold (100K) and
mostly CH4 and N2
It is completely
enshrouded in smog-like
clouds
Methane acts like water
there.
There are few craters on
the surface.
Surface eroded by liquids
but no oceans.
Moons of the Outer Solar System:
Titan’s Atmosphere
Moons of the Outer Solar System:
Saturn’s Titan
Moons of the Outer Solar System:
Movie of Huygen’s Decent
Show the movie outside
the ppt if there is time:
http://saturn.jpl.nasa.gov/multimedia
Moons of the Outer Solar System:
“The Dunes of Titan”
Moons of the Outer Solar System:
Neptune’s Triton
Neptune’s Triton
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Extremely cold (< 40K)
objects made from
volatile materials produce
icy volcanism.
Huge geysers of
nitrogen!
Pluto and the Kuiper Belt
Objects may look and act
similarly.
Comparative Planetology:
Lessons Learned
Surfaces of Planets (or Moons)



Location, location, location…
Size matters (for retaining an atmosphere).
The star matters.
Overall, However

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There is an incredible diversity of worlds!!!
Warm pockets or oceans of liquids plus organics may
exist in a variety of environments outside the classic
Habitable Zone.
Even on Earth not all life requires starlight for an
energy source. Sources of potentially life-giving energy
may exist even in the cold outer reaches of our own
and other planetary systems.
Beyond the Solar System
Do We Live in a “Life-Friendly” Universe?

Water and Carbon Chemistry are Everywhere!
• Hydrogen, Oxygen, Carbon, Nitrogen
– 1st, 3rd, 4th, and 6th most abundant elements
• Organic Chemistry is found in

– Interstellar gas clouds, comets, meteorites, outer planet
and moon atmospheres
Physical Laws
• Copasetic Time Scales
– Expansion rate of the Universe & stellar lifetimes
compatible with time to evolve complex life
• Abundant Materials
– Even small changes in physical constants would cause
little hydrogen or carbon to exist
• Huge Diversity of Environments