Voyager ultraviolet stellar occultation measurements of the composition and thermal profiles of the Saturnian upper atmosphere

Festou, M. C.; Atreya, S. K.

doi:10.1029/gl009i010p01147

Cited by 57 publications

(60 citation statements)

References 10 publications

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“…A recent reanalysis of the Voyager occultations (Vervack et al, 2005 1 ) suggests that T ∞ at 30 • latitude may be closer to ∼550 K. However, for the purposes of this study we will continue to consider the published results of Smith et al (1983) and Festou and Atreya (1982). We will, however, discuss the implications of the reanalysis upon our results.…”

Section: Introductionmentioning

confidence: 68%

“…The horizontal band in Fig. 6 represents the 800 K at 4 • N measurement of Festou and Atreya (1982) in the same way. The vertical bands on both of Figs.…”

Section: Exploring Parameter Spacementioning

confidence: 99%

“…To compare the available observations with the model-derived temperatures it is, of course, necessary to associate each measurement with specific grid points within the model. In the case of the spacecraft occultation data we associate the measured exospheric temperatures of 400 K at 30 • N (Smith et al, 1983) and 800 K at 4 • N (Festou and Atreya, 1982) with the model-derived temperatures at the topmost pressure level and at the appropriate latitude. In the case of the ground-based spectroscopic measurements we assume that the observed emission is associated with the peak of the ionosphere, and that this in turn is, approximately, spatially coincident with the peak of q h .…”

Section: Exploring Parameter Spacementioning

confidence: 99%

“…We find that the form of the topside heating profile is particularly important in determining exospheric temperatures. We compare our results to exospheric temperatures from Voyager occultation measurements (Smith et al, 1983;Festou and Atreya, 1982) and auroral H + 3 temperatures from ground-based spectroscopic observations (e.g. Miller et al, 2000).…”

Section: Introductionmentioning

confidence: 99%

“…Smith (chriss@apl.ucl.ac.uk) performed by the Voyager spacecraft (Smith et al, 1983;Festou and Atreya, 1982) and ground-based infrared spectroscopic measurements of H + 3 temperatures in the polar regions of the planet (Miller et al, 2000). The Voyager solar occultation experiment (Smith et al, 1983) returned an exospheric temperature of T ∞ ∼420 K at a latitude of 30 • N. In contrast, the stellar occultation experiment (Festou and Atreya, 1982) gave a value of T ∞ ∼800 K at 4 • N. In the decades since Voyager there has been considerable debate over the relative validity of these results. For a detailed analysis of the advantages and disadvantages of occultation measurements, and a discussion of the Smith et al (1983) and Festou and Atreya (1982) measurements at Saturn, we refer the reader to the excellent review by Smith and Hunten (1990).…”

Section: Introductionmentioning

confidence: 99%

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Polar heating in Saturn's thermosphere

et al. 2005

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Abstract.A 3-D numerical global circulation model of the Kronian thermosphere has been used to investigate the influence of polar heating. The distributions of temperature and winds resulting from a general heat source in the polar regions are described. We show that both the total energy input and its vertical distribution are important to the resulting thermal structure. We find that the form of the topside heating profile is particularly important in determining exospheric temperatures. We compare our results to exospheric temperatures from Voyager occultation measurements (Smith et al., 1983;Festou and Atreya, 1982) and auroral H + 3 temperatures from ground-based spectroscopic observations (e.g. Miller et al., 2000). We find that a polar heat source is consistent with both the Smith et al. determination of T ∞ ∼400 K at ∼30 • N and auroral H + 3 temperatures. The required heat source is also consistent with recent estimates of the Joule heating rate at Saturn (Cowley et al., 2004). However, our results show that a polar heat source can probably not explain the Festou and Atreya determination of T ∞ ∼800 K at ∼4 • N and the auroral H + 3 temperatures simultaneously.

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Section: Introductionmentioning

confidence: 68%

“…The horizontal band in Fig. 6 represents the 800 K at 4 • N measurement of Festou and Atreya (1982) in the same way. The vertical bands on both of Figs.…”

Section: Exploring Parameter Spacementioning

confidence: 99%

Section: Exploring Parameter Spacementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Polar heating in Saturn's thermosphere

et al. 2005

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Coupling between atmospheric layers in gaseous giant planets due to lightning‐generated electromagnetic pulses

et al. 2014

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Atmospheric electricity has been detected in all gaseous giants of our solar system and is therefore likely present also in extrasolar planets. Building upon measurements from Saturn and Jupiter, we investigate how the electromagnetic pulse emitted by a lightning stroke affects upper layers of a gaseous giant. This effect is probably significantly stronger than that on Earth. We find that electrically active storms may create a localized but long‐lasting layer of enhanced ionization of up to 103 cm−3 free electrons below the ionosphere, thus extending the ionosphere downward. We also estimate that the electromagnetic pulse transports 107 J to 1010 J toward the ionosphere. There emissions of light of up to 108 J would create a transient luminous event analogous to a terrestrial “elve.”

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The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

2018

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In the present paper we have modeled diffuse auroral emissions, which have been observed at lower latitudes as compared to the main auroral arc at Saturn. It is generally accepted that these emissions are generated by precipitation of hot population of magnetospheric electrons on the closed field lines. We have considered the pitch angle diffusion by electrostatic electron cyclotron harmonic waves as the mechanism to diffuse trapped electrons into the atmospheric loss cone. Electrons are thereby precipitated into the atmosphere and excite the neutral atmospheric constituents producing auroral emissions. Calculation of ultraviolet emission intensities has been performed at two L‐shells 5.35 and 7.0. Observed hot electron distribution functions and observed electrostatic electron cyclotron harmonic wave characteristics have been used in the study. Intensities of Lyman‐alpha emission from excitation of atomic H and Lyman‐alpha produced from dissociative excitation of H2 have been calculated, obtaining the values 20.1 R (1.8 R) and 1.6 kR (0.29 kR), respectively, for both L‐shells 7.0 (5.35).Further, intensities of Lyman and Werner bands of H2 are also calculated. These have the values 7.50 kR (1.43 kR) and 7.52 kR (1.49 kR), respectively, for L‐shells 7.0 (5.35). It is observed that the volume excitation rates of these four excitations peak at an altitude of about 2,000 km. From the range‐energy relation in H2 gas it is estimated that the electrons producing these excitations should have energies less than about 250 eV.

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Voyager ultraviolet stellar occultation measurements of the composition and thermal profiles of the Saturnian upper atmosphere

Cited by 57 publications

References 10 publications

Polar heating in Saturn's thermosphere

Polar heating in Saturn's thermosphere

Coupling between atmospheric layers in gaseous giant planets due to lightning‐generated electromagnetic pulses

The Generation of Saturn's Aurora at Lower Latitudes by Electrostatic Waves

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