H2O and O2 absorption in the coma of comet 67P/Churyumov–Gerasimenko measured by the Alice far-ultraviolet spectrograph on Rosetta. (8th June 2017)

• Record Type: Journal Article
• Authors: Keeney, Brian A.; Stern, S. Alan; A'Hearn, Michael F.; Bertaux, Jean-Loup; Feaga, Lori M.; Feldman, Paul D.; Medina, Richard A.; Parker, Joel Wm.; Pineau, Jon P.; Schindhelm, Eric; Steffl, Andrew J.; Versteeg, M.; Weaver, Harold A.
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 469(2017)Supplement 2
• Page Start: S158
• Page End: S177
• Publication Date: 2017-06-08
• Subjects: comets: individual: 67P -- ultraviolet: planetary systems; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stx1426
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We have detected H2 O and O2 absorption against the far-UV continuum of stars located on lines of sight near the nucleus of Comet 67P/Churyumov–Gerasimenko using the Alice imaging spectrograph on Rosetta . These stellar appulses occurred at impact parameters of ρ = 4–20 km, and heliocentric distances ranging from R h = − 1.8 to 2.3 au (negative values indicate pre-perihelion observations). The measured H2 O column densities agree well with nearly contemporaneous values measured by VIRTIS-H. The clear detection of O2 independently confirms the initial detection by the ROSINA mass spectrometer; however, the relative abundance of O2 /H2 O derived from the stellar spectra (11–68 per cent, with a median value of 25 per cent) is considerably larger than published values found by ROSINA. The cause of this difference is unclear, but potentially related to ROSINA measuring number density at the spacecraft position while Alice measures column density along a line of sight that passes near the nucleus.