Stellar Occultations by Saturn Observed by Cassini VIMS: Imaging Mode Subset
Abstract
During Cassini's 13 years in orbit around Saturn, the Visual and Infrared Mapping Spectrometer (VIMS) performed over 100 stellar occultation experiments on the planet, covering a wide range of latitudes and seasons. The principal goals of observing Saturn stellar occultations with VIMS were to obtain temperature-pressure profiles of the planet's stratosphere through inversion of light curves, and to obtain vertical profiles of hydrocarbon abundance in the upper stratosphere with which to test photochemical and eddy-diffusion models such as those of Moses et al. (2000) and Moses and Greathouse (2005). Methane in Saturn's upper atmosphere is photolyzed by UV light into higher order hydrocarbons, which diffuse downwards to regions with higher temperature and pressure where they are broken back down into methane (Strobel 1969). This carbon cycle is driven by UV insolation, and is therefore a function of latitude, season, and ring shadowing. VIMS did most of its experiments in occultation mode, but a small subset (9) were done in imaging mode. These imaging-mode data probe deeper into the atmosphere (~50 mbar vs ~10 mbar), but sacrifice temporal resolution for the ability to track the star after it is refracted out of the single pixel observed in occultation mode. In the imaging-mode data we directly measure the bending angle of the ray of starlight through Saturn's atmosphere and can correlate this with the attenuation of the starlight. The latter should be a function of the former assuming no other sources of opacity (e.g. aerosol hazes). We test this assumption in the region of Saturn's stratosphere that the occultation-mode dataset probes (~1-10 mbar). We can also measure when the refractive bending exceeds the single pixel of the occultation-mode data so that we can better disentangle the effects refraction from the effects of atmospheric attenuation in the occultation-mode dataset.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P13B3513F
- Keywords:
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- 5704 Atmospheres;
- PLANETARY SCIENCES: FLUID PLANETS;
- 5729 Ionospheres;
- PLANETARY SCIENCES: FLUID PLANETS;
- 6255 Neptune;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6293 Uranus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS