1. Deep Impact observations by the scientific imaging system OSIRIS of the Rosetta mission
H.U. Keller, M. Küppers, L. Jorda, P. Gutierrez, S. Hviid, C. Barbieri, S. Fornasier, I. Bertini, L.-M. Lara, D. Koschny, J. Knollenberg, H. Sierks, N. Thomas, P. Lamy, H. Rickman6, R. Rodrigo, and the OSIRIS Team

2. Observations
OSIRIS:
Narrow Angle Camera (NAC)
Pixel scale at Tempel 1: 1,500 km
Filters used: orange (640), clear, red (744), near-IR (882), IR (990)
Wide Angle Camera (WAC)
Pixel scale: 7,800 km
Filters: OH, CN, Na, OI, UV and red continuum
Observations
Start: 23:45 on 28. June 2005
End: 15:00 on 14. July 2005
Total number of images: 2277
Best time resolution: ca. 1 image per minute with NAC
Unique data set of continuous observations with a large FOV and good photometric accuracy

3. Imaging geometry
Phase angle 69 º
Solar elongation 91º

4. Impact Geometry
Skyplane from Rosetta

5. Water
WAC OH filter

6. Water production by impact
Analysis
Observe the number of OH radicals within a virtual aperture centered on the nucleus until the radicals start to leave this aperture
The number of OH radials within an aperture is given by:
This analysis does not depend on the outflow velocity of the molecules!

7. Water produced by impact: 1.5 ± 0.5 1032 or 4.6 106 kg
Total amount of water
Water produced by impact: 1.5 ± or kg

8. Total amount of CN CN/H2O ratio ca. 3.3 10-3
Slight increase compared to pre impact ( )
CN parent lifetime seems to be larger
=> more HCN?

9. Brightness change after impact
Aperture = 2 px (3,000 km)

10. Brightness change - details

11. Brightness variation Within aperture of 2 px (3,000 km) radius:
Steep increase for 40 min
Level off until 90 min
Slow decrease afterwards over several days
Pre impact brightness reached after ca.1 week
Steep increase over 40 min due to:
Opacity of dust cloud – no, only about first minutes
Enhanced cometary activity out of crater – no, crater is too small
Fragmentation of particles due to sublimation – yes
Shoulder of slope caused by change in particle size (only large ones are left)
Dip in brightness slope at 200 s connected to crater formation

12. Dust from impact Post impact images minus pre impact image
OSIRIS images contain information about large particles

13. Dust - velocity distribution
Model with radiation pressure force yields:
Fastest dust particles:
ca. 400 m s-1
Bulk speed:
160 m s-1
Large particles with
10 m s-1
and slower are observed
See "Late Poster #33"
tonight from 18:00-19:15

14. Dust - β distribution Model with radiation pressure force yields:
β = ratio of radiation pressure to gravitation force
This can be converted to particle size and mass
Dispersion at least 2 orders of magnitude
See "Late Poster #33"
tonight from 18:00-19:15

15. Dust production
Brightness increase in orange filter corresponds to a reflecting surface of 33 ± 3 km2 assuming albedo A = 1 and isotropic scattering
Detailed modeling is required but preliminary estimates from velocity and β dispersions yield dust/ice ratio > 1 (possibly >>1)

16. Nucleus of Tempel 1 is an icy dirt ball
Summary
OSIRIS continuous observations over 17 days:
Strong brightness increase of dust, OH, CN emission
Water amount due to impact only kg
Dust at least as much, probably considerably more
CN/H2O ratio slightly enhanced over pre impact
Increase over 40 min explained by fragmentation
Dust outflow: bulk ca. 160, fastest ca. 400 m s-1
Variability up to 1 week => large particles
Cometary outbursts are not triggered by meteroids
Nucleus of Tempel 1 is an icy dirt ball

17. Dust to ice ratio
O’Keefe and Ahrens (1985) for crater radius of 30 m

18. Dust production
Brightness increase in orange filter corresponds to a reflecting surface of
33 ± 3 km2 with albedo A = 1
If only 1 μm particles with A = 0.05
=> kg (10% of water)
If a typical dust mass distribution exponent of -3.5 is assumed => dust/ice ratio is >10!
Crater radius is about 30 m for dust/ice ratio of 1
Detailed modeling is required but preliminary estimates make dust/ice ratio > 1 probable

19. CN brightness
WAC CN filter

20. 121.000 km Pre Impact +1 - +10 min +40 - +50 min +2h +6h +15h +22h

21. Long term variability NAC orange Aperture: 5 px (7500 km)
Brightness variations visible over 1 week in large aperture.
Caused by large fragments (?)

22. NAC dust observations
Aperture radius 3000 km
NAC orange filter