Download Lecture 32. Titan and its Atmosphere.

First Images from the Mars Reconnaisance Orbiter
(MRO)
Reached Mars on March 10
Now: turning elliptical orbit into
a more circular orbit.
First test images.
Craters (fresh/old?)
Gullies
Dunes
Begins collecting data in
November.
$720 million mission.
ESA Venus Express Went into Orbit
$260 million mission.
25th Anniversary of the First Shuttle Launch
Reflection in the news media over the Crew
Exploration Vehicle.
-lack of funds to accomplish
-costs over 1/5 of NASA’s budget
-requires significant transformation in NASA
Lecture 32. Titan and its Atmosphere.
reading: Chapter 8
Titan
Earth: 12,700 km
Mars: 6,800 km
Ganymede:5262 km
Moon: 3476 km
Largest Moon of Saturn - 5150 km.
Discovered by Christiaan Huygens in 1655.
Voyager 1 flyby in 1980.
In 2004, Cassini orbiter made close observations.
Jan 2005, Huygens probe landed on the surface.
Composition: ~50% water ice and ~50% rock
Similar composition as Ganymede & Callisto.
Density of water: 1.0 g/cm3
Titan/Callisto:
1.9 g/cm3
Earth:
5.5 g/cm3
May have a rocky core and a mantle of ice.
Rotates every 16 days, is in synchronous rotation.
Voyager found southern hemisphere to be brighter,
are seasonal differences in brightness.
Titan’s Atmosphere
Unique that it has a dense atmosphere of 1.6 bars and is mostly N2.
77-85% N2, 12-17% argon, 3-6% methane, 0.2% H2
Trace amounts of organic compounds:
ethane, propane, hydrogen cyanide, CO2, CO, acetylene
Organic compounds when methane undergoes photochemical
QuickTime™
and a
reactions from the faint
sunlight.
TIFF (Uncompressed) decompressor
Produces a thick smog,arehazy
neededatmosphere.
to see this picture.
Haze layer is ~300 km above the surface.
There are distinct layers in the haze.
Titan’s orbit is sometimes outside of Saturn’s magnetosphere.
Solar wind particles may ionize the atmosphere and cause
some of the photochemical reactions in the atmosphere.
Thick atmosphere obscures the surface in visible light.
false-color Voyager 1 image of haze layers
Voyager Observations
Atmosphere structure and dynamics determined by 2 instruments:
-radio occultation
How radio waves are scattered and bent as they pass through
the atmosphere determine the T and density of the atmosphere
-infrared spectroscopy
Different compounds absorb heat energy at different
wavelengths and vibrate. Measure how heat energy
from sunlight is absorbed (produces peaks and valleys in the spectrum).
Each compound has particular
fingerprint.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Voyager Observations, cont.
Voyager Observations, cont.
large number of hydrocarbons and N-containing compounds
Titan’s Surface
Surface temperature: -179˚C
Cold enough that methane (CH4) could be liquid.
Cold enough that ethane (CH3CH3) could also be liquid.
Thought there could be seas of liquid methane and ethane.
.
Freezing T
H2O
0˚C
NH3
-78˚C
CH4
-182˚C
CH3CH3 -183˚C
Boiling T
100˚C
-33˚C
-164˚C
-89˚C
at -179˚C, CH4 is solid/liquid/gas?
at -179˚C, CH3CH3 is solid/liquid/gas?
Titan’s Surface
So, if it is cold enough to liquify methane and ethane, why is there
lots of methane in the atmosphere??
Could be places where it is slightly warmer than -164˚C where liquid
methane can turn into gas, once in the atmosphere cooling would produce
clouds and then methane rain.
If there are regions where the surface is
<-183˚C (cools 4˚C)
you could have frozen mountains
of methane and ethane ice!
Why is Titan so cold??
at 9.6AU, sunlight is 100x weaker
Titan’s Surface
Hubble Space Telescope images:
Peered through the clouds using infrared light.
Observed dark and light regions on the surface.
Couldn’t really figure out what they were due to.
Methane/ethane Seas? Bright volcanic regions?
If Titan does have liquid seas,
they should experience tides just
like the Earth as it revolves around
Saturn!
Clouds
Scattered clouds.
Composed of methane, ethane, or simple organic compounds.
More complex organic compounds create the orange color.
Clouds change hourly, presumably deposit methane rain onto the surface.
Tholins
Polymer formed from uv irradiation of CH4 or CH3CH3.
Abundant on icy bodies in the solar system.
Coined by Carl Sagan
to describe unknown organic substances
obtained in Miller-Urey-type experiments using
gas mixtures found in Titan’s atmosphere.
Produce a thick orange goo.
When dissolved, they produce amino acids
with both handedness.
Polymers of C, H, and N.
Over 75 different compounds in it.
PAH family: benzene (1 ring), 2-4 rings
cyclic compounds with C and N: includes bases found in nucleic acids
How are Tholins Produced?
UV light causes
reactions to occur
high in the atmosphere
(photochemical
reactions)
Solid particles Tholins likely
rain down to the
surface.
Speculation: could be
km-deep deposits of
tholins on the surface.
Titan as a Model for Early Earth
Methane-rich, N2-rich atmosphere, lack of oxygen.
An early methane greenhouse helps solve Earth’s Faint Young Sun
Problem.
Photochemical reactions producing organic compounds.
Some think there could have been similar hazes on early Earth.
Hydrogen cyanide in the atmosphere - is a prebiotic compound in
the abiotic synthesis of amino acids.
Titan is soooo cold - chemical reactions proceed very sloooowly.
So fewer number of organic compounds are produced.
At -179˚C a chemical reaction will be 1042 times slower than at
room temperature!
Life on Titan?
Do you have the 5 thing needed to have life?
Properties of Water that are Important for Life
It is the “universal solvent” because it
can dissolve the most substances than any
other liquid.
Electrical charge differential helps it
dissolve ions, like sodium chloride.
Water molecules are attracted to each other creates surface tension
Water forms drops, capillary action allows water to be sucked up
plant roots and blood vessels
Water is a polar compound.
Water can also dissolve
Ions are needed for life!
uncharged organic
compounds, like sugars.
It is found in all three states
solid, liquid, gas on the
Earth
Methane and Ethane Liquids
Are hydrocarbons - so have a greasy nature.
Are non-polar compounds so they:
-don’t dissolve ions.
-don’t have much surface tension.
Lecture 33. Cassini-Huygens Mission.
reading: Chapter 8