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

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

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-1 v0(50 μm) = 30 m s-1 v0(500 μm) = 10 m s-1 Vincent et al. 2013 in good agreement with the GIADA data (Della Corte et al. 2015)

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

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

\MTP016P\STP058_DUST_MON_005 WAC images – Visible Filter – Rh = 2.0AU – Observations during the equinox WAC_2015-05-31T04.16.49.508Z_ID30_1397549200_F18 WAC_2015-05-30T18.43.38.561Z_ID30_1397549400_F18 WAC_2015-05-31T06.58.22.461Z_ID30_1397549600_F18 WAC_2015-05-31T07.28.22.464Z_ID30_1397549700_F18 WAC_2015-05-30T18.13.39.551Z_ID30_1397549300_F18 WAC_2015-05-31T04.46.49.472Z_ID30_1397549300_F18 WAC_2015-05-30T17.13.38.508Z_ID30_1397549900_F18 WAC_2015-05-30T15.43.38.487Z_ID30_1397549400_F18 WAC_2015-05-30T17.43.38.509Z_ID30_1397549600_F18 WAC_2015-05-30T16.13.39.463Z_ID30_1397549100_F18 WAC_2015-05-30T16.43.38.579Z_ID30_1397549200_F18 WAC_2015-05-30T15.43.38.487Z_ID30_1397549400_F18 to WAC_2015-05-31T07.28.22.464Z_ID30_1397549700_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

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

WAC_2015-05-30T16.43.38.579Z_ID30_1397549200_F18 I = Dβ Coma: β = -0.74 Jet only (Jet-Coma): β = - 1.29 Fit of the jet’s curve Dispersion (cone) Sublimation of Dirty Grains a = 5 μm – Solid a = 50 μm – Dash-Dotted

2015-05-30T15.43.38.487Z 2015-05-30T16.13.39.463Z 2015-05-30T16.43.38.579Z 2015-05-30T17.13.38.508Z 2015-05-30T17.43.38.509Z 2015-05-30T18.13.39.551Z 2015-05-30T18.43.38.561Z 2015-05-31T04.16.49.508Z 2015-05-31T04.46.49.472Z 2015-05-31T06.58.22.461Z 2015-05-31T07.28.22.464Z

2015-05-30T15.43.38.487Z 2015-05-30T16.13.39.463Z 2015-05-30T16.43.38.579Z 2015-05-30T17.13.38.508Z β = -0.78 β = - 1.15 β = -0.73 β = - 1.43 β = -0.74 β = - 1.29 β = -0.70 β = - 1.74 2015-05-30T17.43.38.509Z 2015-05-30T18.13.39.551Z 2015-05-30T18.43.38.561Z β = -0.67 β = - 1.41 β = -0.66 β = - 1.32 β = -0.69 β = - 1.31 2015-05-31T04.16.49.508Z 2015-05-31T04.46.49.472Z 2015-05-31T06.58.22.461Z 2015-05-31T07.28.22.464Z β = -0.85 β = - 1.06 β = -0.84 β = - 1.13 β = -0.75 β = - 1.31 β = -0.77 β = - 1.32

Conclusion Slope of the jet much steeper than the coma Brightness of the coma -0.66 < β < -0.85 (-0.74± 0.06) Brightness of the jet -1.75 < β < -1.13 (-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

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