Class 23 - Titan

Reading: One purpose of this class is to use Titan to review the course content. So, the reading is class notes - Classes 1 to 22.

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Latest images - "backside" - Natural light, 938nm methane window, false color composite

Basic Properties

E.g. Table of Titan properties

a=9.5 AU, R=2575 km, g=1.36 m/s2, Vesc=2.6 km/s

P=Po exp -(z/H) where H=kT/mg ~19 km and Po=1.5 Bars

To=95K, <m>=28 amu

Po=no kTo -> no= 10^26 m-3 ( 4 x earth)

rho=no <m> = 5.4 kg m-3 (1.2 x earth)

Mc = rho H = 10^5 kg m-2 (10 x earth)


NOTE: We do not know the Argon abundance - critical for understanding the origin of the atmosphere - nor the isotope abundances....

Altitude Structure - Layers

WHY this profile? Heat budget

Adiabatic lapse rate = g/cp - at the very bottom, where non-adiabatic processes are important

Non-adiabatic processes: latent heat, absorption, radiation, scattering...

If you want to look at the surface at what wavelengths do you look?

Determination of composition comes from high-resolution spectroscopy such as this:

Detection of water in the upper atmosphere - shows water being brought into the upper atmosphere by comets. Similar argument for CO2 and CO.

Solar flux = So / (a in AU)^1/2 - divide by 4 to get average over planet - at Titan F=1368/(4 x 9.5^2)=3.8 W m^-2

Tequilibrium = To (1-A)^1/4 / (a in AU)^1/2 where To= (So/4 sigma)^1/4 = 280K (for So=1368 W m^-2)

Visible Albedo A=0.27 -> Eeq=83K


NOTE: Because of all the scattering there are few shadows - permanently heavily overcast - this is what it looks like:


Methane photochemistry:

Methane photochemistry with nitrogen:

Here's the "lite" version:

Prebiotic chemistry???

Latitude distribution - seasonal?

Sources, Losses & Recycling

Source of Titan's atmosphere?

Losses of Titan's atmosphere?


Methane is recycled in a similar way to water in the Earth's atmosphere through the hydrological cycle......

French version...

Ideas of how organic raindrops develop and grow as thy slowly drop.....

Fat raindrops (up to centimeter) caused by slow descent.


Dave Grinspoon's version - with biology....

Source of these "warm underground lakes"?

 In upper atmosphere UV dissociates CH4



Meteorology / Dynamics


NOTE: Persistent longitudinal variations and significant temporal variations - cloud outburst

Eccentricity of Saturn = 0.056 = 5.6% (compare with Earth = 1.7%).

Looking at the solar flux over the year we see a similar asymmetry that we saw at Mars due to the orbital eccentricity.

Units of Watts m^-2 at outer atmosphere



Here's the picture overview