The haze and methane distributions on Neptune from HST-STIS spectroscopy

Erich Karkoschka, Martin G Tomasko

Research output: Contribution to journalArticle

60 Citations (Scopus)

Abstract

We analyzed a data cube of Neptune acquired with the Hubble STIS spectrograph on August 3, 2003. The data covered the full afternoon hemisphere at 0.1. arcsec spatial resolution between 300 and 1000. nm wavelength at 1. nm resolution. Navigation was accurate to 0.004. arcsec and 0.05. nm. We constrained the vertical aerosol structure with radiative transfer calculations. Ultraviolet data confirmed the presence of a stratospheric haze of optical depth 0.04 at 370. nm wavelength. Bright, discrete clouds, most abundant near latitudes -40° and 30°, had their top near the tropopause. They covered 1.7% of the observed disk if they were optically thick. The methane abundance above the cloud tops was 0.0026 and 0.0017. km-am for southern and northern clouds, respectively, identical to earlier observations by Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Dowling, T.E., Baines, K.H., Limaye, S.S., [2001b]. Icarus 149, 459-488). Aside from these clouds, the upper troposphere was essentially clear. Below the 1.4-bar layer, a vertically uniform haze extended at least down to 10 bars with optical depth of 0.10-0.16/bar, depending on the latitude. Haze particles were bright at wavelengths above 600. nm, but darkened toward the ultraviolet, at the equator more so than at mid and high latitudes. A dark band near -60° latitude was caused by a 0.01 decrease of the single scattering albedo in the visible, which was close to unity. A comparison of methane and hydrogen absorptions contradicted the current view that methane is uniformly mixed in latitude and altitude below the ∼1.5-bar layer. The 0.04 ± 0.01 methane mixing ratio is only uniform at low latitudes. At high southern latitudes, it is depressed roughly between the 1.2 and 3.3-bar layers compared to low-latitude values. The maximum depression factor is ∼2.7 at 1.8 bars. We present models with 2° latitude sampling across the full sunlit globe that fit the observed reflectivities to 2.8% rms.

Original languageEnglish (US)
Pages (from-to)780-797
Number of pages18
JournalIcarus
Volume211
Issue number1
DOIs
StatePublished - Jan 2011

Fingerprint

Neptune (planet)
haze
Neptune
methane
spectroscopy
tropical regions
optical thickness
wavelength
wavelengths
optical depth
tropopause
globes
equators
mixing ratios
distribution
troposphere
hemispheres
albedo
navigation
polar regions

Keywords

  • Atmospheres, Composition
  • Atmospheres, Structure
  • Neptune
  • Neptune, Atmosphere
  • Spectroscopy

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

The haze and methane distributions on Neptune from HST-STIS spectroscopy. / Karkoschka, Erich; Tomasko, Martin G.

In: Icarus, Vol. 211, No. 1, 01.2011, p. 780-797.

Research output: Contribution to journalArticle

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abstract = "We analyzed a data cube of Neptune acquired with the Hubble STIS spectrograph on August 3, 2003. The data covered the full afternoon hemisphere at 0.1. arcsec spatial resolution between 300 and 1000. nm wavelength at 1. nm resolution. Navigation was accurate to 0.004. arcsec and 0.05. nm. We constrained the vertical aerosol structure with radiative transfer calculations. Ultraviolet data confirmed the presence of a stratospheric haze of optical depth 0.04 at 370. nm wavelength. Bright, discrete clouds, most abundant near latitudes -40° and 30°, had their top near the tropopause. They covered 1.7{\%} of the observed disk if they were optically thick. The methane abundance above the cloud tops was 0.0026 and 0.0017. km-am for southern and northern clouds, respectively, identical to earlier observations by Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Dowling, T.E., Baines, K.H., Limaye, S.S., [2001b]. Icarus 149, 459-488). Aside from these clouds, the upper troposphere was essentially clear. Below the 1.4-bar layer, a vertically uniform haze extended at least down to 10 bars with optical depth of 0.10-0.16/bar, depending on the latitude. Haze particles were bright at wavelengths above 600. nm, but darkened toward the ultraviolet, at the equator more so than at mid and high latitudes. A dark band near -60° latitude was caused by a 0.01 decrease of the single scattering albedo in the visible, which was close to unity. A comparison of methane and hydrogen absorptions contradicted the current view that methane is uniformly mixed in latitude and altitude below the ∼1.5-bar layer. The 0.04 ± 0.01 methane mixing ratio is only uniform at low latitudes. At high southern latitudes, it is depressed roughly between the 1.2 and 3.3-bar layers compared to low-latitude values. The maximum depression factor is ∼2.7 at 1.8 bars. We present models with 2° latitude sampling across the full sunlit globe that fit the observed reflectivities to 2.8{\%} rms.",
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N2 - We analyzed a data cube of Neptune acquired with the Hubble STIS spectrograph on August 3, 2003. The data covered the full afternoon hemisphere at 0.1. arcsec spatial resolution between 300 and 1000. nm wavelength at 1. nm resolution. Navigation was accurate to 0.004. arcsec and 0.05. nm. We constrained the vertical aerosol structure with radiative transfer calculations. Ultraviolet data confirmed the presence of a stratospheric haze of optical depth 0.04 at 370. nm wavelength. Bright, discrete clouds, most abundant near latitudes -40° and 30°, had their top near the tropopause. They covered 1.7% of the observed disk if they were optically thick. The methane abundance above the cloud tops was 0.0026 and 0.0017. km-am for southern and northern clouds, respectively, identical to earlier observations by Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Dowling, T.E., Baines, K.H., Limaye, S.S., [2001b]. Icarus 149, 459-488). Aside from these clouds, the upper troposphere was essentially clear. Below the 1.4-bar layer, a vertically uniform haze extended at least down to 10 bars with optical depth of 0.10-0.16/bar, depending on the latitude. Haze particles were bright at wavelengths above 600. nm, but darkened toward the ultraviolet, at the equator more so than at mid and high latitudes. A dark band near -60° latitude was caused by a 0.01 decrease of the single scattering albedo in the visible, which was close to unity. A comparison of methane and hydrogen absorptions contradicted the current view that methane is uniformly mixed in latitude and altitude below the ∼1.5-bar layer. The 0.04 ± 0.01 methane mixing ratio is only uniform at low latitudes. At high southern latitudes, it is depressed roughly between the 1.2 and 3.3-bar layers compared to low-latitude values. The maximum depression factor is ∼2.7 at 1.8 bars. We present models with 2° latitude sampling across the full sunlit globe that fit the observed reflectivities to 2.8% rms.

AB - We analyzed a data cube of Neptune acquired with the Hubble STIS spectrograph on August 3, 2003. The data covered the full afternoon hemisphere at 0.1. arcsec spatial resolution between 300 and 1000. nm wavelength at 1. nm resolution. Navigation was accurate to 0.004. arcsec and 0.05. nm. We constrained the vertical aerosol structure with radiative transfer calculations. Ultraviolet data confirmed the presence of a stratospheric haze of optical depth 0.04 at 370. nm wavelength. Bright, discrete clouds, most abundant near latitudes -40° and 30°, had their top near the tropopause. They covered 1.7% of the observed disk if they were optically thick. The methane abundance above the cloud tops was 0.0026 and 0.0017. km-am for southern and northern clouds, respectively, identical to earlier observations by Sromovsky et al. (Sromovsky, L.A., Fry, P.M., Dowling, T.E., Baines, K.H., Limaye, S.S., [2001b]. Icarus 149, 459-488). Aside from these clouds, the upper troposphere was essentially clear. Below the 1.4-bar layer, a vertically uniform haze extended at least down to 10 bars with optical depth of 0.10-0.16/bar, depending on the latitude. Haze particles were bright at wavelengths above 600. nm, but darkened toward the ultraviolet, at the equator more so than at mid and high latitudes. A dark band near -60° latitude was caused by a 0.01 decrease of the single scattering albedo in the visible, which was close to unity. A comparison of methane and hydrogen absorptions contradicted the current view that methane is uniformly mixed in latitude and altitude below the ∼1.5-bar layer. The 0.04 ± 0.01 methane mixing ratio is only uniform at low latitudes. At high southern latitudes, it is depressed roughly between the 1.2 and 3.3-bar layers compared to low-latitude values. The maximum depression factor is ∼2.7 at 1.8 bars. We present models with 2° latitude sampling across the full sunlit globe that fit the observed reflectivities to 2.8% rms.

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