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Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible |
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| Authors: | Christa A Hasenkopf Melinda R Beaver Melissa G Trainer Miriam A Freedman Christopher P McKay |
| Institution: | a Department of Atmospheric and Oceanic Sciences, University of Colorado, Boulder, CO 80309, United States b Cooperative Institute for Research in the Environmental Sciences, University of Colorado, Boulder, CO 80309, United States c Department of Chemistry, University of Colorado, Boulder, CO 80309, United States d NASA Goddard Space Flight Center, Greenbelt, MD 20771, United States e Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, United States f Space Science Division, NASA Ames Research Center, Moffett Field, CA 94503, United States |
| Abstract: | Scattering and absorption of sunlight by aerosols are integral to understanding the radiative balance of any planetary atmosphere covered in a haze, such as Titan and possibly the early Earth. One key optical parameter of an aerosol is its refractive index. We have simulated both Titan and early Earth organic haze aerosols in the laboratory and measured the real and imaginary portion of their refractive index at λ = 532 nm using cavity ringdown aerosol extinction spectroscopy. This novel technique allows analysis on freely-floating particles minutes after formation. For our Titan analog particles, we find a real refractive index of n = 1.35 ± 0.01 and an imaginary refractive index k = 0.023 ± 0.007, and for the early Earth analog particles we find n = 1.81 ± 0.02 and k = 0.055 ± 0.020. The Titan analog refractive index has a smaller real and similar imaginary refractive index compared to most previous laboratory measurements of Titan analog films, including values from Khare et al. (Khare, B.N., Sagan, C., Arakawa, E.T., Suits, F., Callcott, T.A., Williams, M.W. 1984]. Icarus 60, 127-137). These newly measured Titan analog values have implications for spacecraft retrievals of aerosol properties on Titan. The early Earth analog has a significantly higher real and imaginary refractive index than Titan analogs reported in the literature. These differences suggest that, for a given amount of aerosol, the early Earth analog would act as a stronger anti-greenhouse agent than the Titan analog. |
| Keywords: | Titan Spectroscopy Experimental techniques Photochemistry |
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