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First extreme and far ultraviolet spectrum of a Comet Nucleus: Results from 67P/Churyumov-Gerasimenko

S.A. Stern 1 L.M. Feaga 2 E. Schindhelm 1 A. Steffl 1 J.Wm. Parker 1 P.D. Feldman 3 H.A. Weaver 4 Michael F. A'Hearn 2 J. Cook 1 Jean-Loup Bertaux 5
1 SwRI - Southwest Research Institute [Boulder]
2 Department of Astronomy [College Park]
3 JHU - Johns Hopkins University
4 APL - Johns Hopkins University Applied Physics Laboratory [Laurel, MD]
5 IMPEC - LATMOS
LATMOS - Laboratoire Atmosphères, Milieux, Observations Spatiales
Abstract : We used the Alice spectrograph onboard the Rosetta comet orbiter spacecraft to observe the surface of comet 67P/Churyumov-Gerasimenko in the extreme and far ultraviolet (EUV/FUV) from 700-2050 Å in mid-August 2014. These observations were before significant EUV/FUV coma signatures were observed by Alice. The resulting coadded spectrum has high signal to noise and reveals: (1) a very FUV-dark surface with (2) a blue spectral slope and (3) no evidence of significant H2O ice absorption in the FUV. We fit the measured reflectance spectrum with a model including 99.5% tholins, 0.5% H2O-ice, and a neutral darkening agent. Since we could not find any natural material with sufficiently low EUV/FUV reflectance, we interpret the low I/F as evidence of a fluffy, light-trapping surface. We interpret the blue spectral slope as consistent with a surface consisting primarily of tholins, though it may alternatively be the result of Rayleigh scattering by fine particles in the regolith.
Keywords : Comets Ultraviolet Surfaces
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https://hal-insu.archives-ouvertes.fr/insu-01145221
Contributor : Catherine Cardon <>
Submitted on : Thursday, April 23, 2015 - 3:06:58 PM
Last modification on : Friday, January 10, 2020 - 3:42:29 PM

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S.A. Stern, L.M. Feaga, E. Schindhelm, A. Steffl, J.Wm. Parker, et al.. First extreme and far ultraviolet spectrum of a Comet Nucleus: Results from 67P/Churyumov-Gerasimenko. Icarus, Elsevier, 2015, 256, pp.117-119. ⟨10.1016/j.icarus.2015.04.023⟩. ⟨insu-01145221⟩

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