1. OSIRIS Full Team Meeting -
Schloss Ringberg
Is the sublimation of icy grains detectable with the OSIRIS camera onboard Rosetta ?
A. Gicquel, J-B. Vincent, J. Agarwal, I. Bertini, X. Shi, H. Sierks and OSIRIS-MPS Team

2. Model of sublimation : Temperature and lifetime
Objectives : Study the sublimation of icy grains
Porosity = 0.5 a
Pure water ice : αice = 100 %
Dirty: H2O mixed with amonia and amorphous carbon
Two-layers
αice = 20 %
Three-layers
αice = 50 %
Temperature of grains as a function of size lifetime
Water
ice
AmorphousOlivine
Amorphous Carbon
Amorphous Olivine ri
Rotundi et al. 2015
Rh = 1.24AU - Solid
Rh = 4.0AU - Dashed
The temperature of grains is not particularly sensitive to the exact amount of “dirt” contamination within the ice

3. Sublimation Esub = H(T)Q(T)
Temperature determines the sublimation rate of the grain
Sublimation is assumed to occur throughout the porous material and not only from the surface of the spherical grain
Sublimation rate [kg s-1]
a is the radius of the grain
Pv is the vapor pressure
m is the molecular mass
SA is the correcting factor translating the surface area of the grain into the total sublimating area of the porous medium - The lifetime is strongly dependent of this parameter
Velocity [m s-1] v0(5 μm) = 80 m s v0(50 μm) = 30 m s-1
v0(500 μm) = 10 m s-1
Vincent et al in good agreement with the GIADA data (Della Corte et al. 2015)

4. Variation with the geometry of observations
2-Layer Grains
Sublimation detectable in the images for small and large grains
1.24 AU < Rh < 2.0AU
Sublimation ends at distances from the nucleus < 1 km up to 10km
Sublimation detectable in the images for small grains
Rh = 3.0AU
Sublimation ends at distances from the nucleus < 10 km
Sublimation not detectable in the images even for small grains
Rh = 4.0 AU
Sublimation ends at distances from the nucleus < 1000 km
a = 5 μm - Solid
a = 500 μm – Dashed
Rh = 1.24AU
Rh = 1.6AU
Rh = 2.0AU
Rh = 3.0AU
Rh = 4.0AU

5. Variation with the composition
Rh = 2.0AU
a = 5 μm – Solid
a = 50 μm – Dash-Dotted
a = 500 μm – Dashed
2-Layer
Dirty
Sublimation for 2-Layer Grains
Sublimation ends at distances from the nucleus < 2km up to 20km
Sublimation for Dirty Grains
Sublimation ends at distances from the nucleus < 5km up to 70km

6. \MTP016P\STP058_DUST_MON_005
WAC images – Visible Filter – Rh = 2.0AU – Observations during the equinox
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18
WAC_ T Z_ID30_ _F18 to
WAC_ T Z_ID30_ _F18
ΔS/C = 206 km
FOV = 44km x 44km
Resolution = 21 m /px
Binning: 1 x 1
Time between the 1st and the last image used in this analysis ≈ 16h15

7. WAC_2015-05-30T16.43.38.579Z_ID30_1397549200_F18 Coma Jet 3 2 1
Coma = mean(coma1+coma2+coma3)

8. WAC_ T Z_ID30_ _F18
I = Dβ
Coma: β = -0.74
Jet only (Jet-Coma):
β =
Fit of the jet’s curve
Dispersion (cone)
Sublimation of Dirty Grains
a = 5 μm – Solid
a = 50 μm – Dash-Dotted

9. T Z T Z T Z T Z
T Z T Z T Z
T Z T Z T Z T Z

10. T Z T Z T Z T Z
β = -0.78
β =
β = -0.73
β =
β = -0.74
β =
β = -0.70
β =
T Z T Z T Z
β = -0.67
β =
β = -0.66
β =
β = -0.69
β =
T Z T Z T Z T Z
β = -0.85
β =
β = -0.84
β =
β = -0.75
β =
β = -0.77
β =

11. Conclusion Slope of the jet much steeper than the coma
Brightness of the coma < β < (-0.74± 0.06)
Brightness of the jet < β < (-1.31± 0.57)
Slope of the jet much steeper than the coma
Good agreement with Lin et al 2015 (August – September 2014 – Hapi region)
Brightness slope after one full rotation is similar
Flat slope f the coma :
Characteristic of large-sized grains with an organic-rich composition
(Capaccioni et al 2015.)
Scale length of the jets ≈ 10km
Good agreement with Lin et al 2015 and our model of sublimation
Steep slope the grain :
Gain acceleration : Terminal speeds for micron-sized around 2km from the nucleus
Dispersion due to a cone : Reproduction of the curve before 4 km
Sublimation : Reproduction of the curve from 4 km to 10 km

12. π – DSMC (Direct Simulation Monte Carlo) DLL (Dynamic Link Library)
Future Work: π- DSMC DLL
π – DSMC (Direct Simulation Monte Carlo)
Study the gas-flow close to the nucleus
Simulate millions of molecules
Homogeneous gas flux
Dust particles with a zero velocity
3 forces acting on the grains :
drag force, gravity and radiative pressure
DLL (Dynamic Link Library)
Integrate the sublimation of icy grains in the gas flow:
model of sublimation
Study the effect of the additional gas on the dust trajectories