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

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

Imaging geometry Phase angle 69 º Solar elongation 91º

Impact Geometry Skyplane from Rosetta

Water WAC OH filter

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!

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

Total amount of CN CN/H2O ratio ca. 3.3 10-3 Slight increase compared to pre impact (1.6 10-3) CN parent lifetime seems to be larger => more HCN?

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

Brightness change - details

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

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

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

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

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)

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 4.6 106 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

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

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 => 4.4 105 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

CN brightness WAC CN filter

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

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

NAC dust observations Aperture radius 3000 km NAC orange filter