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5-µm Spectroscopy of Saturn with the IRTF

• Nancy Chanover (New Mexico State U.)
• Gordon Bjoraker David Glenar (NASA/GSFC)
• Tilak Hewagama (U. Maryland)
• Kevin Baines (JPL)

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Observed Saturn with SpeX and CSHELL at the same
time that the Cassini spacecraft has targeted
observations of Saturns atmosphere.

• The spectral coverage afforded by SpeX and CSHELL
  fills in an important gap between the wavelength
  sensitivity of Cassinis VIMS and CIRS
  spectrometers
• Saturns 5.0-5.4 µm spectrum contains absorption
  features of NH3 and PH3 that are indicative of
  cloud structure

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CSHELL Results

• At 5 µm thermal emission originates from
  Saturn's deep atmosphere (4-bar level) and is
  attenuated by cloud layers of varying thicknesses.

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SpeX Results

• SpeX data were used to build up an image cube
  between 2.5 and 5.5 µm
• Both SpeX and Cassini/VIMS images at 5.1 µm show
  interesting cloud structure in Saturns southern
  hemisphere that is not evident at shorter
  wavelengths.

Image of Saturns southern hemisphere at 5.05 µm
derived from SpeX observations
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Interpretation

• The pressure level of Saturns clouds was derived
  from CSHELL spectra by modeling the strength and
  width of ammonia (NH3) and phosphine (PH3)
  absorption lines
• Saturns Equatorial Zone appears to have a
  massive cloud near 3 bars in addition to the NH3
  cloud at 0.5 bars that is evident at optical
  wavelengths.
• The SpeX data show that the physics changes
  abruptly between 4.7 µm, which is dominated by
  reflected sunlight, and 5.1 µm, which is
  primarily thermal emission.