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Measurements of the helium 584 Å airglow during the Cassini flyby of Venus |
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| Authors: | J-C Gérard J Gustin B Hubert GR Gladstone LW Esposito |
| Institution: | aLaboratoire de Physique Atmosphérique et Planétaire, Université de Liège, 17, allée du 6 août, B5c, B-4000 Liège, Belgium;bSouthwest Research Institute, P.O. Drawer 28510, 6220 Culebra Road, San Antonio, TX 78238-5166, USA;cLaboratory for Atmospheric and Space Physics, University of Colorado, Campus Box 392, Boulder, CO 80309-0392, USA |
| Abstract: | The helium resonance line at 584 Å has been observed with the UltraViolet Imaging Spectrograph (UVIS) Extreme Ultraviolet channel during the flyby of Venus by Cassini at a period of high solar activity. The brightness was measured along the disk from the morning terminator up to the bright limb near local noon. The mean disk intensity was ∼320 R, reaching ∼700 R at the bright limb. These values are slightly higher than those determined from previous observations. The sensitivity of the 584 Å intensity to the helium abundance is analyzed using recent cross-sections and solar irradiance measurements at 584 Å. The intensity distribution along the UVIS footprint on the disk is best reproduced using the EUVAC solar flux model and the helium density distribution from the VTS3 empirical model. It corresponds to a helium density of 8×106 cm−3 at the level of where the CO2 is 2×1010 cm−3. |
| Keywords: | Venus Helium density Airglow Cassini Flyby Radiative transfer |
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