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Haze and clouds in Plutos atmosphere
Pascal Rannou, Franck Montmessin Service
d'Aéronomie/IPSL, Université Versailles-St-Quentin
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Observation of Pluton with a stellar occultation
I0
I (1 - D M (?r /2) dn/dr)-1I0
M (2 ? Rp / H )1/2 ?r susceptibility of
molecules n(r) concentration in molecules
D
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Elliott et al. (2003)
Sicardy et al. (2003)
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Sicardy et al. (2003)
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TI/I0 (1 - D M (???r /2) dn/dr)-1
e-????? The refraction can be estimated to about
0.1, then the extinction by the layer is
inferred using ??(? ) - ln (1 - D M (???r
/2) dn/dr) T
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Tholins Khare et al. (1984) ??eff 0.3






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Tholins Khare et al. (1984) ??eff 0.3
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Is it possible to have such large aerosols and
such a thick haze on Pluto ? And what if Pluto
aerosols are fractal ? Comparison with Titan
- FO _at_ Pluton 0.11 FO _at_ Titan - XCH4 0.1
to 2 times XCH4 on Titan (Strobel et al.,
1996) - HPLUTO HTITAN 40 - 50 km (T/g
cst) - Same mean molecular mass 28 10-3
kg/mole - Pressure pressure _at_ detached haze of
Titan (0.1 to 1.0 Pa) (Sicardy et al., 2003) -
How to estimate the aerosol production rate on
Pluto ?
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Microphysical model of aerosol (Cabane et al.,
1992, 1993)
Macromolecules produced in a narrow altitude zone
(z0 20 km) with a production rate (mass /
surface /time) P.
d C(r, z,t) ? C(r,z,t)/?t sed. dt ?
C(r,z,t)/?tdiff. dt ? C(r,z,t)/?tcoag. dt
Sedimentation and diffusion
Altitude
Coagulation
Particle radius
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Cabane et al. (1993)
?lmfp gtgt r
Spherical (Df3)
Fractal (Df2)
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Parameters for Pluto haze layer Spherical
particles / fractal particles Production rate
noted Q, a factor of P0 3.5 10-13
kg/m2/s Production zone z0 between 100 and 600
km (Monomer radius function of z0- NOT A FREE
PARAMETER) Coagulation with charged particles (c
in e-/m) Molecular mass 28 a.m.u Condition
T (z) 100 K, P (z35 km) 0.5 Pa (cf. Sicardy
et al., 2003) Tan. opacity (??(? )) for z35 km
(that is R1180 35 1215 km) (cf. Elliott et
al., 2003, Sicardy et al., 2003)
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Haze on Pluto The extinction layer due to
aerosols, even fractal, is unlikely We would
need aerosol production rate 10 times larger
than those used for Titan !! Hypothesis the
extinction layer could be rather due to clouds
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Clouds on Pluto Temperature profile unknown
below about 30 km ! Surface temperature at about
40K Unknow composition (Nitrogen minor species
as carbon monoxide and methane) Temperature
gradient in troposphere Dry adiabatic ???
-0.56098 K/km S1 with Tsurf36 K ???
-0.083 K/km
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• Cloud model of Pluton (based on Mars and Titan
  model)
• Two species CO and N2
• Nucleation/condensation collapse of the main
  atmosphere
• Temperature profile with a troposphere ( ???
  -0.083 K/km), a surface temperature 36 K and a
  stratosphere at 110 K
• Wettability of CO ice and N2 ice on aerosols gt
  0.9
• Drop as large as 1 mm are possible
• Work under progress

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