Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible

Christa A. Hasenkopf, Melinda R. Beaver, Melissa G. Trainer, H. Langley Dewitt, Miriam Arak Freedman, Owen B. Toon, Christopher P. McKay, Margaret A. Tolbert

Research output: Contribution to journalArticle

39 Citations (Scopus)

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.

Original languageEnglish (US)
Pages (from-to)903-913
Number of pages11
JournalIcarus
Volume207
Issue number2
DOIs
StatePublished - Jun 1 2010

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early Earth
haze
Titan
optical property
refractive index
analogs
optical properties
aerosols
refractivity
Earth analogs
aerosol
laboratory
planetary atmosphere
planetary atmospheres
aerosol property
greenhouses
sunlight
floating
retrieval
cavity

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Hasenkopf, C. A., Beaver, M. R., Trainer, M. G., Langley Dewitt, H., Freedman, M. A., Toon, O. B., ... Tolbert, M. A. (2010). Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible. Icarus, 207(2), 903-913. https://doi.org/10.1016/j.icarus.2009.12.015
Hasenkopf, Christa A. ; Beaver, Melinda R. ; Trainer, Melissa G. ; Langley Dewitt, H. ; Freedman, Miriam Arak ; Toon, Owen B. ; McKay, Christopher P. ; Tolbert, Margaret A. / Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible. In: Icarus. 2010 ; Vol. 207, No. 2. pp. 903-913.
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Hasenkopf, CA, Beaver, MR, Trainer, MG, Langley Dewitt, H, Freedman, MA, Toon, OB, McKay, CP & Tolbert, MA 2010, 'Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible', Icarus, vol. 207, no. 2, pp. 903-913. https://doi.org/10.1016/j.icarus.2009.12.015

Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible. / Hasenkopf, Christa A.; Beaver, Melinda R.; Trainer, Melissa G.; Langley Dewitt, H.; Freedman, Miriam Arak; Toon, Owen B.; McKay, Christopher P.; Tolbert, Margaret A.

In: Icarus, Vol. 207, No. 2, 01.06.2010, p. 903-913.

Research output: Contribution to journalArticle

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AU - Hasenkopf, Christa A.

AU - Beaver, Melinda R.

AU - Trainer, Melissa G.

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AU - Toon, Owen B.

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AU - Tolbert, Margaret A.

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N2 - 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.

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Hasenkopf CA, Beaver MR, Trainer MG, Langley Dewitt H, Freedman MA, Toon OB et al. Optical properties of Titan and early Earth haze laboratory analogs in the mid-visible. Icarus. 2010 Jun 1;207(2):903-913. https://doi.org/10.1016/j.icarus.2009.12.015