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Transcript
Friday March 17:
Assignment #1 will be handed back at end of today (also next
week). Average: 14/18 = 78%
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Assignment #1 solutions now on WebCT
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Assignment #2 due Friday, Mar 31
Monday March 20: Guest lecture from Dr. Martin Duncan, on
“The Kuiper Belt and Outer Solar System”
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Outer Planets and Moons Continued
Motivation:
Outer moons contain very exciting possibilities for life,
especially Europa, Enceladus, and Titan
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If life found in the outer solar system, it extends the habitable
zone, and the range of domains for which to search for life
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Titan may tell us a lot about what conditions were like when the
Earth was young
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Extrasolar planets are all “hot Jupiters”, so we should learn
more about these big planets
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Exploration of the Outer Planets
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Pioneer 10/11 (1970s)
Jupiter, Saturn
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Voyager 1/2 (1977-1989):
Jupiter, Saturn, Uranus, Neptune
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Galileo (1995-2003):
Jupiter and its moons
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Cassini/Huygens (2004-Present):
Life On (in?) Jupiter and Saturn
Pro
Organic chemistry very likely producing simple organic
compounds.
-- could more complex organic compounds also be
produced?
e.g. to explain cloud colours?
●
There is a region in atmosphere where temperature (27 C)
and pressure (few times Earth) allows liquid water to exist
as clouds
-- Jupiter has internal sources of heat, so temperatures
not so cold as one might think
-- water is available
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Con
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Ammonia toxic to most (but not all) LAWKI
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No solid surfaces to help concentrate and polymerize organics
Deep convection mixes upper and lower atmosphere on 300
year (or shorter) time scales
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-- extreme climate change on short
time scales
-- proto-life environs mixed down
to much different environment (higher T,
different chemicals)
Summary:
If life exists in/on Jupiter, it's probably in upper
atmosphere, where there are water clouds, reasonable
temperatures and pressures.
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Maybe there are “floaters”, balloon life-forms drifting
through the clouds? (Carl Sagan)
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Neither Jupiter or Saturn are seriously considered as
possible sites for life
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Saturn's Moons
Titan
Titan is Saturn's largest moon, like Ganymede in size and
composition. It's bigger than Mercury.
● Titan has a dense atmosphere, ~1.5x denser than Earth!
-- even though Titan 45x less massive than Earth, it's
cold enough (85K) to retain an atmosphere against
thermal escape
● Very interesting atmosphere! 97-98% N , 1-2% CH ,
2
4
traces of H2, CO, C2H6, C2H4, C2H2, H2O, CO2
-- Many complex chemical reactions happening
-- Photochemical reactions: Solar UV photons break up
CH4 and produce other hydrocarbons in atmosphere
-- Photochemical Smog: long-chain hydrocarbons
● Could even more complex organics be present? HCN is
starting point for some components of DNA; CO and CO2
makes formation of amino acids possible
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Could have rain or snowfall of organic material onto surface
There could be oceans of methane and ethane! Methane and
ethane would both be liquid at pressure and temperature (95K) of
Titan's surface
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However:
-- Earth-based radar data rule out deep, global oceans
-- Huygens did not see any evidence for liquid (later)
No evidence for surface liquid at present time (but probably
in the past-- later)
-- but still pretty exciting, and possibility of life in an ocean!
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This is very interesting organic chemistry even though it's not
LAWKI: organic compounds and maybe liquid solvent ...
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Cassini-Huygens Mission to Saturn and Titan
Arrived July 2004,
to spend 4 years
studying Saturn and
moons
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In Dec 2004,
Huygens probe
dropped onto Titan
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Both Cassini and
Huygens studying
surface, atmosphere
of Titan with several
instruments
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Cassini
Instruments
Optical Remote Sensing
Composite Infrared Spectrometer
Imaging Science Subsystem
Ultraviolet Imaging Spectrograph
Visible & IR Mapping Spectrometer
Fields, Particles and Waves
Cassini Plasma Spectrometer
Cosmic Dust Analyzer
Ion and Neutral Mass Spectrometer
Magnetometer
Magnetospheric Imaging Instrument
Radio & Plasma Wave Science
Microwave Remote Sensing
Radar
Radio Science
Huygens
Instruments
Atmospheric Structure
Instrument
Doppler Wind Experiment
Descent Imager/Spectral
Radiometer
Gas Chromatograph Mass
Spectrometer
Aerosol Collector and Pyrolyser
Surface-Science Package
Titan Pictures
Titan Science Results:
Nature, Vol. 438, 8 Dec 2005
Titan's Atmosphere
N2 and CH4 confirmed as main
species
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Must be geological source to
replenish CH4
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12C/13C
ratios show no evidence
for biota
Trace organic species (e.g.
cyanogen/ethane) found on surface
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14N depleted-- loss of 5x present
atmosphere
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Titan's Atmosphere: The Big Picture
Titan's Surface
Huygens landed on “soft, solid surface” like damp sand-probably mix of ice chips, precipitated aerosols, and liquid
methane.
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So methane cycle of rain and evaporation!
No evidence from Cassini or Huygens for large amounts
of liquid on the surface, but spectacular images of river
networks and drainage channels.
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So liquid methane has flowed on the surface in the
past-- how recently?
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Could be water ice on the surface-- unclear
Titan's Surface
Titan Summary
Chances for life on Titan are small:
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very cold on surface (95 K)
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little water
what energy source? Not much sunlight penetrates
clouds
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no evidence for biota
But:
complex organic chemistry on surface and in
atmosphere
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Saturn's Moon Enceladus:
Science, Vol 311, 10 Mar 2006
“Tiger Stripes”
Enceladus
Very active: south polar hot spot, deep canyons and thick
flows on surface, and plume of H2O, CO2, CH4, N2
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Heat source: likely tidal heating and heat retention
Source of plume: deep, gas-saturated ocean or deep
crustal pocket of water?
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Life habitat? Would be hard, as on Titan ...
Movie
Enceladus
Triton
Triton is Neptune's largest moon, similar to Pluto in
composition, about half size of Titan, probably captured
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Surface temperature only 37K (-235C)! Damn cold
Frozen Methane and either liquid/solid Nitrogen on
surface
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There is also a very thin atmosphere, about 16 millionths
that of Earth. The pinkish color of Triton, plus haze and
clouds in atmosphere tell us there is organic chemistry
happening on the surface (like in atmospheres of Jupiter
and Titan)
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Triton also very active: young surface, geysers up to
Summary of Outer Planets
No definite evidence for life on any of the outer planets or their
moons, similar to Mars
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However, some really interesting possibilities:
-- Jupiter's moon Europa
-- Saturn's moons Titan and Enceladus
-- Neptune's moon Triton (?)
-- and possibly atmosphere of Jupiter itself (maybe
Saturn?)
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Further exploration will be very exciting. Any signs of life in
the outer solar system will extend the habitable zone in size, and
will have huge implications for life on planets around other stars
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