FM9.2.05 — Unanticipated Physical Processes in ALICE Spectra of 67P/Churyumov-Gerasimenko

Date & Time

Aug 11th at 5:30 PM until 5:45 PM




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Author(s): Michael F. A'Hearn4, Jean-Loup Bertaux5, Lori M. Feaga4, Paul D. Feldman3, Joel Wm. Parker2, Eric R. Schindhelm2, Andrew J. Steffl2, S. Alan Stern2, Harold A. Weaver1

Institution(s): 1. Johns Hopkins University Applied Physics Laboratory, 2. Southwest Research Institute, 3. The Johns Hopkins University, 4. University of Maryland, 5. University of Versailles Saint Quentin en Yvelines

FUV spectra of comet 67P by the ALICE instrument on Rosetta show atomic emission-line ratios (of C, O, and H) that are very different from those seen in comets near the sun. These line ratios suggest that they are formed largely by prompt emission after electron impact dissociation of parent molecules rather than photo-dissociation, but other processes may also be involved. The primary molecules leading to these atomic emissions are likely H2O, CO2, CO, and O2, of which we only directly measure CO. As prompt emission, the atomic lines trace the column density of the parents. The CO is directly detected only in a small subset of our data, primarily over the southern limb, whereas most of our data at the time of writing are over the northern limb.
We will present constraints on the relative column densities from the line ratios and compare with column densities of CO and with results for other molecules as measured with other instruments on Rosetta. We expect that these results will change significantly by the autumnal equinox in mid-July when the now barely illuminated southern hemisphere enters its summer. We will also present our results on the FUV spectroscopy of the surface at selected locations and consider whether there are surface variations that might be correlated with the outgassing variations.