1. Final results of HDAC analysis
P. Hedelt(1), Y. Ito(2,3), H. U. Keller(2), R. Reulke(3), P. Wurz(4), H. Lammer(5), H. Rauer(1,6), L. Esposito(7)
Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Max Planck Institut für Sonnensystemforschung (MPS)
Japan Manned Space Systems Corporation, Tsukuba, Japan
Institut für Verkehrsforschung, Deutsches Zentrum für Luft- und Raumfahrt (DLR)
Abteilung für Weltraumforschung und Planetologie, Universität Bern
Institut für Weltraumforschung, Österreichische Akademie der Wissenschaften
Zentrum für Astronomie und Astrophysik, Technische Universität Berlin (TUB)
Laboratory for Atmospheric and Space Physics, University of Colorado

2. HDAC T9 measurement UVIS Team Meeting 2009 Pascal Hedelt
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3. Difference signal
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4. Radiative transfer modeling
Parameter variation:
Exosphere atomic hydrogen distribution:
Chamberlain model (Chamberlain, 1963)
Particle Monte Carlo model (Wurz & Lammer, 2003)
Exobase hydrogen density
Exospheric temperature
 Fit to data
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5. Exospheric densities Particle model H Chamberlain model CH4
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6. Density Variation Exobase densities in the literature
nH = 4.2x103 cm-3 (Yung, model)
nH = 8.0x103 cm-3 (Toublanc, model)
nH = 1.0x104 cm-3 (Broadfoot, et al data)
nH = 4.6x104 cm-3 (Garnier, et al model)
nH = 7.0x104 cm-3 (Krasnopolsky, et al model)
nH = 8.0x104 cm-3 (De la Haye, et al., model)
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7. Density Variation Chamberlain Model
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8. Density Variation Particle Model UVIS Team Meeting 2009 Pascal Hedelt
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9. Difference signal during c/a
Particle model
Chamberlain model
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10. Difference signal during ingress
Chamberlain model
Particle model
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11. Temperature Variation
Exosphere temperatures in the literature:
De la Haye et al. (2008):
152.8 ± 4.6 K (TA)
149.0 ± 9.2 K (TB)
157.4 ± 4.8 (T5)
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12. Temperature Variation
Exobase H density: 8x104 cm-3, Particle model profile
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13. Fit to data Best fitting density distribution using least squares fit:
Particle model: Exobase H density nH=9x104 cm-3
Chamberlain model: Exobase density nH=2x104 cm-3
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14. Fit to data: Chamberlain model
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15. Fit to data: Particle model
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16. Best fitting H profile Particle model Chamberlain model
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17. Comparison with measurement
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18. Comparison with measurement: Removing the background
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19. Summary & Conclusion Using HDAC data we are able to determine atomic
Good agreement between model and data
Exospheric temperature has no influence
 Best fit using Chamberlain model: nH,Exobase= 2.0x104 cm-3
validated for Earth only, static model
 Best fit using Particle MC model: nH,Exobase= 9.0x104 cm-3
validated for Mercury & Mars, dynamic model
From latest calculations (De la Haye, et al. 2007): nH,Exobase= 8.0x104 cm-3
 Good agreement with Particle model distribution
Background signal in HDAC data: about 12,000 cts (430 R)
Titan Lyman α dayside brightness: 179±10 R (Ajello, et al. 2008: 208 R) nightside brightness: 50±4 R (Ajello, et al. 2008: 80 R)
Using HDAC data we are able to determine atomic
hydrogen distribution in Titan’s exosphere!!!
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20. Outlook: T66 & T67
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21. Outlook: T66 & T67
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22. Thanks for your attention!
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24. Aims & Scope
Using HDAC data gathered during T9, the distribution of atomic hydrogen in Titans exosphere is investigated:
Calculate exospheric emission of resonantly scattered Hydrogen Ly-Alpha from Titan
Simulate HDAC measurement during the Cassini/Titan T9 encounter
Little is known about Titan‘s hydrogen exosphere
Vary input parameters
Determine exospheric parameters
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25. Radiative transfer model (1)
Apply Monte Carlo to solve RTE:
40,000,000 photons started at sunlit side of upper exosphere layer
Scattered by H (isotropically)
Absorbed by CH4
Trace until:
Absorbed by methane
Reach model boundaries
Store scattering positions + WL + Directions

26. Radiative transfer model (2)
Simulate T9 flyby:
Apply „splitting“ technique: Photons are emitted in direction of detector
Calculate transmission to detector
Apply HDAC absorption pattern

27. Density model description
Chamberlain model
Maxwellian velocity distribution at exobase
Use Liouville theorem to derive exospheric densities
Static contribution of ballistic/escaping orbits
Particle MC model
Dynamic MC approach, single particles started at exobase with random energy & ejection angle
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