1. Rosetta/OSIRIS observations of gas in the inner coma of 67P
Dennis Bodewits, Mike A’Hearn, Luisa Lara, Fiorangela La Forgia, Joerg Knollenberg, Monica Lazzarin, Zhong-Yi Lin, and the OSIRIS team

2. Emission features and Filters
OSIRIS Wide Angle Camera

3. Gas: OSIRIS and Ground based
Very different physical environment: Inner coma of weakly active comet
Different filter set
Distance S/C to 67P is 5 – 1000 km; corresponds to FOV of 1 – 200 km.
1 arcsec ~ 200 km at 0.3 AU -> resolving inner coma is rare
(However HST/WFC has IFOV = 0.04 arcsec/pix!)
Can be sampled with spectroscopy (e.g DeCock et al. 2014)

4. Rh (AU) -2.47 -2.12 -1.88 -1.66 -1.51 -1.34 Bodewits et al. 2016
Explain Pinhole, ghosts, shapemodel.
-1.51
-1.34
Bodewits et al. 2016

5. Production Rates derived from surface brightness
ROSINA/COPS H2O
Fougere et al. 2016
0.1% * ROSINA/COPS H2O
H2O from OI
H2O from OH
NH3 from NH
HCN from CN
Haser model and photo processes

6. Production Rates derived from surface brightness
ROSINA/COPS H2O
Fougere et al. 2016
0.1% * ROSINA/COPS H2O
H2O from OI
H2O from OH
NH3 from NH
HCN from CN
Why did both drop?
Haser model and photo processes + acceleration + quenching & transport of OI

7. What drives excess emission?
Combination of different parents, processes, and emission from other species in the filter passbands
Parents:
CO2 <10%, CO <1% (abundances sunward side)
O %. Good that O2 and H2O are coupled.
Cannot explain orders of magnitude difference nor OH
Processes
Recombination of H2O+, sputtering of water ice, prompt emission: yield not enough
Dissociative electron impact excitation can explain OH emission.
e- + CO2 may explain OI emission
Contaminating species:
OH+ in NH filter; from electron impact on H2O
CO2+ in CN filter (weaker); from electron impact on CO2

8. Nothing is what it seems?
Deep Impact closer to HB.

9. What changed in April 2015?
While Q ~ rh-4, all surface brightnesses drop
rh < 1.88 AU
Q(H2O) < 1027 mol/s
Higher local densities in coma:
Increased opacity for UV light so less electrons produced
Increased quenching of OI excited states
Electrons are kept cold (<10 eV) by collisions with gas
Transition to physical regime as we know it from the ground?
For Halley, this occurred around 10,000 km. Observable?

10. Rosetta’s 1st distant excursion 2015/9/27, D=1011 km, R=1.36 AU, res 0.41 km/pix
OSIRIS
100 km

11. Rosetta’s 1st distant excursion Median stacked imagesOI OH
Log scale. NH CN

12. NAC Gas observations

13. CN emission in NAC HYDRA NIR Fe2O3 CN (1,0) & (2,1) C2 NH2 OI
Line ratios may be completely different for different excitation processes!
CN (3,0) & (4,1)
CN (1,0) & (2,1) C2
NH2 OI
CN (2,0) & (3,1)
Fink 2009

14. NAC NIR: continuum

15. Fe2O3 minus hydra
Good subtraction, definitely different morphology. Real or scattering?

16. Hydra minus NIR
Poor subtraction, morphology similar to dust. Need to vary color.

17. NUV minus NIR
Poor subtraction due to color differences NIR/NUV.

18. Summary
Light in OSIRIS narrowband filters from different species and due to different processes than expected
OSIRIS samples a regime that is only occasionally accessible from the ground
Clear changes in the physical environment were seen at Q~1e27/s at 2AU from the Sun
Scale of regimes depends on activity as well: can we study this from the ground?
OI line ratios and profiles (McKay)
Compare ions and neutrals (Spectroscopy)
HST Narrow Band imaging (CN)
NAC data work in progress
Need help with interpretation