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

Abstract

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.

11 pages, 8 figures, accepted for publication in the Astronomical Journal

References in corpus (7)

• Alice: The Rosetta Ultraviolet Imaging Spectrograph
• Measurements of the Near-Nucleus Coma of Comet 67P/Churyumov-Gerasimenko with the Alice Far-Ultraviolet Spectrograph on Rosetta
• Evolution of CO${}_2$, CH${}_4$, and OCS abundances relative to H${}_2$O in the coma of comet 67P around perihelion from Rosetta/VIRTIS-H observations
• The Fourth Positive System of Carbon Monoxide in the Hubble Space Telescope Spectra of Comets
• Seasonal changes of the volatile density in the coma and on the surface of comet 67P/Churyumov-Gerasimenko
• The Nature and Frequency of the Gas Outbursts in Comet 67P/Churyumov-Gerasimenko observed by the Alice Far-ultraviolet Spectrograph on Rosetta
• H${}_2$O and O${}_2$ Absorption in the Coma of Comet 67P/Churyumov-Gerasimenko Measured by the Alice Far-Ultraviolet Spectrograph on Rosetta

Cited by in corpus (10)

• A sublimated water atmosphere on Ganymede detected from Hubble Space Telescope observations
• Atomic carbon, nitrogen, and oxygen forbidden emission lines in the water-poor comet C/2016 R2 (Pan-STARRS)
• Ultraviolet Observations of Coronal Mass Ejection Impact on Comet 67P/Churyumov-Gerasimenko by Rosetta Alice
• Diagnostics of collisions between electrons and water molecules in near-ultraviolet and visible wavelengths
• Analysis of Hybrid Gas-Dust Outbursts Observed at 67P/Churyumov-Gerasimenko
• Ultraviolet Observations of Comet 96/P Machholz at Perihelion
• A photochemical model of ultraviolet atomic line emissions in the inner coma of comet 67P/Churyumov-Gerasimenko
• A link between the size and composition of comets
• Upper Limits for Emissions in the Coma of Comet 67P/Churyumov-Gerasimenko Near Perihelion as Measured by Rosetta's Alice Far-Ultraviolet Spectrograph
• Spatial Distribution of Ultraviolet Emission from Cometary Activity at 67P/Churyumov-Gerasimenko