Titan’s Photochemical Model: Oxygen Species and Comparison with

Triton and Pluto

Vladimir Krasnopolsky

• Initial data: N2 and CH4 densities near the surface• Products: vertical profiles of 83 neutral

species and 33 ions from 0 to 1600 km

Main Features• The only after-Cassini model of coupled neutral and ion

chemistry• Hydrocarbon chemistry is extended to C12H10 • Radiative transfer using the Huygens data and a code for

the aggregate particles• Ion chemistry is extended to C10H11

+ • Ambipolar diffusion and escape of ions• Involves effects of magnetospheric electrons, protons,

and cosmic rays• The number of reactions is reduced to 415 with column

rates for each reaction

Calculated extinction by haze using the Huygens data, refractive indices from Khare84, and a

code for aggregate particles

Ionization by solar EUV, magnetospheric electrons, protons, and cosmic rays

Calculated absorption of solar EUV and UV on Titan (λ in nm)

Oxygen species formed by meteorite H2O and magnetospheric O+

Production of haze (100 m/Byr total)

Calculated and observed ionospheric profiles

Three bodies with N2-CH4 atmospheres: Titan, Triton, and Pluto

• Titan 1.5 bar, Triton 40 μbar, Pluto 15 μbar. Why are they so different?

• Titan at 10 AU, Triton at 30 AU, Pluto at 30-50 AU• Titan T = 94 K, Triton T = 40 K, Pluto T = 38 -29 K• Titan N2 is completely in the atmosphere, and N2

is in surface ice on Triton and Pluto

Triton: mostly atomic composition (Krasnopolsky and Cruikshank 1995)

Pluto: molecular composition. [N]Triton/[N]Pluto ≈ 104 (Krasnopolsky and Cruikshank 1999)

Triton’s ionosphere: atomic ions, emax = 3x104 cm-3 (Krasnopolsky and Cruikshank 1995)

Pluto’s ionosphere: molecular ions, emax = 800 cm-3 (Krasnopolsky and Cruikshank 1999)

Why are Triton and Pluto so different?Conclusion: Triton still keeps

Voyager-type chemistry