FUV Spectral Signatures of Molecules and the Evolution of the Gaseous Coma of Comet 67P/Churyumov–Gerasimenko

Paul Feldman (1) , Michael F. A'Hearn (2) , Jean-Loup Bertaux (3) , Lori M. Feaga (2) , Brian A. Keeney (4) , Matthew M. Knight (2) , John Noonan (4) , Joel Wm. Parker (4) , Eric Schindhelm (5) , Andrew J. Steffl (4) , S. Alan Stern (4) , Ronald J. Vervack (6) , Harold A. Weaver (6)

1 Department of Physics and Astronomy [Baltimore]
2 Department of Astronomy [College Park]
3 PLANETO - LATMOS
4 Department of Space Studies [Boulder]
5 Ball Aerospace and Technologies Corp.
6 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]

The Alice far-ultraviolet imaging spectrograph onboard Rosetta observed emissions from atomic and molecular species from within the coma of comet 67P/Churyumov–Gerasimenko during the entire escort phase of the mission from 2014 August to 2016 September. The initial observations showed that emissions of atomic hydrogen and oxygen close to the surface were produced by energetic electron impact dissociation of H₂O. Following delivery of the lander, Philae, on 2014 November 12, the trajectory of Rosetta shifted to near-terminator orbits that allowed for these emissions to be observed against the shadowed nucleus that, together with the compositional heterogeneity, enabled us to identify unique spectral signatures of dissociative electron impact excitation of H₂O, CO₂, and O₂. CO emissions were found to be due to both electron and photoexcitation processes. Thus, we are able, from far-ultraviolet spectroscopy, to qualitatively study the evolution of the primary molecular constituents of the gaseous coma from start to finish of the escort phase. Our results show asymmetric outgassing of H₂O and CO₂ about perihelion, H₂O dominant before and CO₂ dominant after, consistent with the results from both the in situ and other remote sensing instruments on Rosetta.

Domaines: Planète et Univers [physics]

Paul Feldman, Michael F. A'Hearn, Jean-Loup Bertaux, Lori M. Feaga, Brian A. Keeney, et al.. FUV Spectral Signatures of Molecules and the Evolution of the Gaseous Coma of Comet 67P/Churyumov–Gerasimenko. The Astronomical Journal, 2018, 155 (1), pp.art. 9. ⟨10.3847/1538-3881/aa9bf2⟩. ⟨insu-01662711⟩