Transcript Saturn`s Titan

Homework 9 is due
Tuesday, Nov. 23, 5:00 pm
Enceladus
Titan
Titan
Titan
 Huygens spacecraft
landed on surface
 Cassini spacecraft
has made several
close flybys
 2nd largest moon
 Only moon with a
substantial atmosphere
Saturn’s Titan
 atmosphere denser than Earth’s
but very cold (100K) and composed
mostly of N2 and methane (CH4)
 Completely enshrouded in smoglike clouds
 Methane acts like water (liquid).
 Few craters on the surface.
 Surface eroded by liquids
 Methane/Ethane lakes
View from Cassini Spacecraft during Flyby
Huygens Probe
On the surface!
“Rocks” of ice?
View from Huygens Spacecraft during descent to surface
Sunlit side
Looking through
the atmosphere
Thick
atmosphere
with
photochemical
hydrocarbon
“smog”
Hubble view at
wavelengths that
penetrate atmosphere
Physical Characteristics
• Size
– Among moons, second only to Ganymede (measured
by surface, not atmosphere)
• Mass
– Almost double that of our Moon
– Density: 1.9 gm/cm3  equal mixture of rock and ice
– Thought to be differentiated: rocky core of silicates
with a crust of water ice
Surface
• Gross features:
– Few impact craters  surface 130-300 Myr old
– Tectonics: thin features for hundreds of miles
• Cryo-volcano:
– 30 km volcano observed on Titan, including caldera
inside
– Magma would be mainly CH4 & H2O
– Energy?: tidal heating or radioactivity
• Erosion:
– Huygens saw round ice pebbles
– Sinuous channels: liquids
– East-west dunes near equator with sharp western
boundaries: super-rotating winds
Dunes
Earth
Titan
Possible Earthlike Processes
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Tectonics
Weather, including rain (methane)
Erosion by winds and liquids
Formation of complex organic compounds
Greenhouse effect
Volcanism (molten water, not rock)
But: all at a much lower temperature
Atmosphere
• Pressure: 1.5 bar
• Surface temperature: 180C (-290F)
• Composition: 9298%
N2 + 26% methane
(CH4)
• Constantly smoggy: UV
breaking up CH4 into
radicals
• Radicals combine to
form complex
hydrocarbons: C2H6,
C2H2, HCN, C6H6
Why does Titan have an atmosphere while
the larger Ganymede does not?
• At Saturn’s distance from the Sun, the protosolar nebula was
much colder that at Jupiter.
• Ammonia (NH3), methane (CH4) & ethane (C2H6) ices could
condense at Saturn’s distance, but not at Jupiter, where only
water ices condensed.
• Moons formed at Saturn could have significant amount of
methane, ethane, ammonia - this provided molecules for UV
interactions to form atmosphere
• Comets and asteroids hit at a smaller velocity (~ half the
energy), so collisional losses were smaller.
• NH3 (ammonia) broken up by UV radiation into N2 and H2. H2
escaped, and N2 stayed behind
• Expect similar process for CH4 (methane)
• CH and CH2 products of CH4 breakup help form larger organic
molecules, e.g., C2H6
• Why are we still seeing CH4?
– Possible reservoir of CH4 and/or C2H6.
– Rain or drizzle of CH4 and/or C2H6
 CH4C2H6 Ocean?
• Cassini: no global ocean, but many (relatively) small lakes, and
observed a number of clouds
River gully?
Coastline?
Hydrocarbon
lakes
Cold Life?
• Liquid methane - ethane (CH4C2H6):
– Chemical reaction rates orders of magnitude slower
– Poorer solvents than water
– No density anomaly: liquids freeze completely
– But it’s a liquid
• Saving graces:
– UV forms organic molecules in the upper atmosphere,
which sink to the CH4C2H6 lakes and the surface
– Comet or asteroid impacts can create pockets of
water lasting thousands of years?
– Underground water ocean heated by radioactivity?
?
Enceladus
Enceladus
is small
It was not
considered
a moon of
particular
interest,
until this
image was
obtained by
Cassini
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!?
“tiger stripes”
Ice Plumes from Enceladus
Area of plumes is much
warmer than surroundings evidence of subsurface
reservoir of liquid water
Liquid water + energy source + chemicals
life?
Uranus
Neptune
anything of interest?
Named moons of Uranus
Cordelia
Ophelia
Bianca
Cressida
Desdemona
Juliet
Portia
Rosalind
Belinda
Puck
Miranda
Ariel
Umbriel
Titania
Oberon
Caliban
Sycorax
Prospero
Setebos
Stephano
Trinculo
Moons of Uranus
No large moons, nothing of
particular interest as far as
the search for life
Moons of Neptune
One location of interest
• Neptune’s Triton
– 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.
Very unlikely location for life
Solar system beyond Saturn
• Decline of probability of life
– Main factor is temperature
– Europa  Ganymede  Callisto  Titan  Enceladus ?
• Triton
– Retrograde rotation  capture
– Uneven surface:
• Cantaloupe terrain, Smooth parts, Frost deposits?, Wind
streaks
– Few impact craters  recent geological activity (10100 Myr)
• Pluto and remaining moons
– Too cold and too small
– But, amino acids seen in meteorites
Time to reach for the stars!