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

Emission features and Filters OSIRIS Wide Angle Camera

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)

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

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

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

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) O2 25-60%. 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

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

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?

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

Rosetta’s 1st distant excursion Median stacked images OI OH Log scale. NH CN

NAC Gas observations

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

NAC NIR: continuum

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

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

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

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