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Titan

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2nd largest satellite in Solar System (2575 km radius) Larger than Mercury (radius 2439 km) ... Cassini/Huygens will tell us much more! ... – PowerPoint PPT presentation

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Title: Titan


1
Titans Atmospheric Chemistry
  • Emily Schaller
  • GE/AY 132
  • March 2004

2
Titan Background Information
  • 2nd largest satellite in Solar System (2575 km
    radius)
  • Larger than Mercury (radius 2439 km)
  • Orbits Saturn at a distance of 21 Saturn radii
  • Rotation is tidally locked to Saturn period
    16 earth days
  • Thick atmosphere with a surface pressure of 1.5
    bar.
  • Main atmospheric constituents
  • N2 (90-97)
  • Methane (2-5)
  • Argon (0-6)
  • Assorted hydrocarbons nitriles (C2H2, C2H6,
    HCN,)
  • H2O (8 ppb), CO2 (10 ppb)

3
Titans Atmosphere
  • Photodissociation of CH4 and N2 ? haze particle
    production
  • Tholin particles fall to the surface and
    methane is lost
  • Methane requires replenishment (outgassing?)
  • Temperature profile is similar in shape to
    Earths with an inversion layer.
  • Methane is near triple point on Titan likely an
    active methane weather cycle

4
CO in Titans atmosphere
  • Reaction pathway for CO
  • H2O ? OH H
  • OH CH3 ? CO 2H2
  • OH CO ? CO2 H
  • ?10 ppm CO in atmosphere
  • Wong et al (2002) main reaction pathway for CO
  • H2O ? 2H O
  • O CH3 ? H2CO H
  • H2CO ? H2 CO
  • ?1.8 ppm CO in atmosphere

5
CO Infrared observations
  • CO first discovered from the 3-0
    rotation-vibration band at 1.6 mm (Lutz et al.
    1983)
  • Mixing ratio
  • 48 ppm (100 -32)

6
CO Infrared Observations
  • Absorbtion from the 1-0 vibrational band at 4.8
    mm. P10 to P19 lines are visible
  • Mixing ratio 32 /- 10 ppm

Lellouch et al. 2003
7
CO Millimeter Observations
  • Rotational Transition lines
  • 12CO (1 - 0), 115.271 GHz
  • 12CO (2 - 1), 230.538 GHz
  • 12CO (3 - 2), 345.796 GHz

Vo 230.5380 GHz
(Gurwell Muhleman 2000)
8
CO Mixing Ratios
Gurwell and Muhleman 2000
32 /- 10 4.8 um Lellouch et al 2003
9
What does this mean?
  • Consensus is CO has about four times the mixing
    ratio predicted by chemical modeling.
  • CO is not in equilibrium and must be being
    delivered by some other process
  • Meteorites (need CO/H2O .13) (Lara et al 1996)
  • Outgassing from interior of planet
  • Comets (one event every 100,000 years would do
    it) (Lellouch et al. 2003)
  • Combination of all processes

10
Cassini/VIMS Instrument
  • IR channel covers wavelength range 0.85-5.1 mm
    over 256 spectral bands.
  • Goals
  • Accessing the nature and distribution of
    atmospheric species and aerosols in Titans
    atmosphere.
  • It will map CO in Titans lower atmosphere.

11
Conclusions
  • CO is uniformly mixed in Titans atmosphere
  • CO Mixing ratio is 40 ppm
  • Chemical modeling predicts an equilibrium of only
    10 ppm or 1.8 ppm
  • Indicates that CO is not in steady state and is
    constantly being replenished
  • Replenishment could come from Meteors, Comets,
    Outgassing or combination
  • Cassini/Huygens will tell us much more!
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