Abstract
FIFTEEN years ago, it was found1 that Saturn has a very different thermal infrared (7–13 (μm) brightness distribution from that observed at visible wavelengths. Single-detector scans of Saturn at 11.7 μm (ref. 1) showed emission increasing strongly towards the south pole, which was attributed in part to 12-μm ethane (C2H6) emission in the upper atmosphere of Saturn, enhanced by an atmospheric temperature inversion. Subsequently, it was confirmed that the observed brightening in ethane was concentrated towards the pole, and was not simply a general limb-brightening effect2. A similar brightening has been seen in the vibrational ν4 band of methane near 7.8 μm3 and in the hydrogen (3–1) pressure induced rotational line near 17.0 μm. Here we present observations of the stratospheric infrared emission structure on Saturn made using a 58×62 pixel imaging array camera system at 7.8, 11.6 and 12.4 μm. The high-spatial-resolution (1.3-arcsec full width at half maximum) global images show a variety of new features including a narrow equatorial belt of enhanced emission at 7.8 μm, a prominent symmetrical north polar hotspot at all three wavelengths, and a mid-latitude structure which is asymmetrically brightened at the east limb. These results confirm the polar brightening and reversal in position predicted by recent models4,5 for seasonal thermal variations of Saturn's stratosphere.
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