Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Moses, J. I.; Lellouch, E.; Bézard, Bruno; Gladstone, G. R.; Feuchtgruber, H.; Allen, Mark

doi:10.1006/icar.1999.6320

Cited by 149 publications

(239 citation statements)

References 162 publications

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“…∼6 × 10 5 cm −2 s −1 . This matches the (1 ± 0.5)×10 6 cm −2 s −1 value required to explain Saturn's upper atmosphere water vapor (Moses et al 2000;Ollivier et al 2000). Enceladus is thus the likely source of Saturn's external water, though an additional confirmation could be provided by the latitudinal distribution of H 2 O on Saturn.…”

Section: Discussion and Implications For The Source Of Water In Satursupporting

confidence: 78%

“…The similar H 2 O fluxes per unit area into the four giant planets and Titan (Feuchtgruber et al 1997;Coustenis et al 1998;Moses et al 2000), combined with the rather constant dust flux (∼3×10 −18 g cm −2 s −1 ) measured in interplanetary space beyond 5 AU (Landgraf et al 2002) have been regarded as evidence that micrometeoroids -interplanetary (IDPs) or interstellar -are the dominant source (Moses et al 2000). Along with the evidence that the H 2 O present in Jupiter's atmosphere results from the Shoemaker-Levy 9 1994 impact -and that CO in Jupiter, Saturn, and Neptune Cavalié et al 2010;Lellouch et al 2005) also result from ancient cometary impacts -our inference that Enceladus is a quantitatively viable source of Saturn's water clearly shifts the paradigm towards local or sporadic sources playing a more important role.…”

Section: Discussion and Implications For The Source Of Water In Saturmentioning

confidence: 82%

“…Furthermore, based on the Landgraf et al (2002) dust fluxes and accounting for the gravitational focusing by Saturn at Titan's distance, we have found that the micro-meteoritic flux into Titan is in the range (0.1−0.7) × 10 6 mol cm −2 s −1 , depending on micrometeoroid velocity (i.e. their origin and orbit -interstellar, Halley-type or Kuiper Belt-like -see Moses et al 2000). This is short of the required H 2 O flux into Titan by a factor 3−80.…”

Section: Discussion and Implications For The Source Of Water In Saturmentioning

confidence: 96%

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Direct detection of the Enceladus water torus withHerschel

Hartogh

Lellouch

Moreno

et al. 2011

A&A

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Cryovolcanic activity near the south pole of Saturn's moon Enceladus produces plumes of H 2 O-dominated gases and ice particles, which escape and populate a torus-shaped cloud. Using submillimeter spectroscopy with Herschel, we report the direct detection of the Enceladus water vapor torus in four rotational lines of water at 557, 987, 1113, and 1670 GHz, and probe its physical conditions and structure. We determine line-of-sight H 2 O column densities of ∼4 × 10 13 cm −2 near the equatorial plane, with a ∼50 000 km vertical scale height. The water torus appears to be rotationally cold (e.g. an excitation temperature of 16 K is measured for the 1113 GHz line) but dynamically excited, with non-Keplerian dispersion velocities of ∼2 km s −1 , and appears to be largely shaped by molecular collisions. From estimates of the influx rates of torus material into Saturn and Titan, we infer that Enceladus' activity is likely to be the ultimate source of water in the upper atmosphere of Saturn, but not in Titan's.

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Section: Discussion and Implications For The Source Of Water In Satursupporting

confidence: 78%

Section: Discussion and Implications For The Source Of Water In Saturmentioning

confidence: 82%

Section: Discussion and Implications For The Source Of Water In Saturmentioning

confidence: 96%

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Direct detection of the Enceladus water torus withHerschel

Hartogh

Lellouch

Moreno

et al. 2011

A&A

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“…From the Voyager 2 UVS occultations, Bishop et al (1990) inferred molar fractions of only 10 −12 for ethane and acetylene at 30 µbar, more than seven orders of magnitude too small. Since the photochemically produced C 2 H 2 and C 2 H 6 should vary by less than a factor of 3 between solar minimum and solar maximum (Moses et al 2000), photochemistry alone cannot produce a sufficiently large radiative cooling rate. This conclusion is supported by Marley and McKay (1999), who show that changing the C 2 H 2 and C 2 H 6 abundances by a factor of 10 does not affect the temperatures at 1-100 µbar.…”

Section: Cooling By Radiationmentioning

confidence: 99%

Uranus after Solstice: Results from the 1998 November 6 Occultation

Young

Bosh

Elliot

et al. 2001

Icarus

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We observed a stellar occultation of the star U149 by Uranus from Lowell Observatory and the IRTF on Mauna Kea on November 6, 1998. The temperatures derived from isothermal fits to the Lowell lightcurves are 116.7 ± 7.9 K for immersion, and 124.8 ± 15.5 K for emersion. The secular increase in temperature seen during the period 1977-1983 has reversed. Furthermore, the rate of decrease (≥1.2 K/yr) cannot be explained solely by radiative cooling. Although the temperature structure of Uranus' upper atmosphere may be related to seasonal effects (e.g., the subsolar latitude) or local conditions (e.g., diurnally averaged insolation), these observations suggest nonradiative influences on the temperature, such as adiabatic heating/cooling or thermal conduction.

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“…The Sub-millimeter Wave Astronomy Satellite (SWAS) and Infrared Space Observatory (ISO) determined the stratospheric abundances of exogenicallysupplied H 2 O Bergin et al 2000;Moses et al 2000b), and a combination of IRAM (Institut de Radio Astronomie Millimétrique) millimetric measurements and JCMT (James Clerk Maxwell Telescope) sub-millimetre observations have been used to investigate the distribution of CO in Saturn's stratosphere (Cavalié et al 2008(Cavalié et al , 2009(Cavalié et al , 2010. Spatially-resolved Cassini observations between 10-200 cm −1 have been used to map Saturn's PH 3 (Fletcher et al 2007a(Fletcher et al , 2009a, determine the abundance of CH 4 (Fletcher et al 2009b) and place new upper limits on the abundances of the hydrogen halides (Teanby et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

Fletcher

Swinyard

Salji

et al. 2012

A&A

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Aims. We provide an extensive new sub-millimetre survey of the trace gas composition of Saturn's atmosphere using the broad spectral range (15-51 cm −1 ) and high spectral resolution (0.048 cm −1 ) offered by Fourier transform spectroscopy by the Herschel/SPIRE instrument (Spectral and Photometric Imaging REceiver). Observations were acquired in June 2010, shortly after equinox, with negligible contribution from Saturn's ring emission. Methods. Tropospheric temperatures and the vertical distributions of phosphine and ammonia are derived using an optimal estimation retrieval algorithm to reproduce the sub-millimetre data. The abundance of methane, water and upper limits on a range of different species are estimated using a line-by-line forward model. Results. Saturn's disc-averaged temperature profile is found to be quasi-isothermal between 60 and 300 mbar, with uncertainties of 7 K due to the absolute calibration of SPIRE. Modelling of PH 3 rotational lines confirms the vertical profile derived in previous studies and shows that negligible PH 3 is present above the 10-to 20-mbar level. The upper tropospheric abundance of NH 3 appears to follow a vapour pressure distribution throughout the region of sensitivity in the SPIRE data, but the degree of saturation is highly uncertain. The tropospheric CH 4 abundance and Saturn's bulk C/H ratio are consistent with Cassini studies. We improve the upper limits on several species (H 2 S, HCN, HCP and HI); provide the first observational constraints on others (SO 2 , CS, methanol, formaldehyde, CH 3 Cl); and confirm previous upper limits on HF, HCl and HBr. Stratospheric emission from H 2 O is suggested at 36.6 and 38.8 cm −1 with a 1σ significance level, and these lines are used to derive mole fractions and column abundances consistent with ISO and SWAS estimations a decade earlier.

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Photochemistry of Saturn's Atmosphere II. Effects of an Influx of External Oxygen

Cited by 149 publications

References 162 publications

Direct detection of the Enceladus water torus withHerschel

Direct detection of the Enceladus water torus withHerschel

Uranus after Solstice: Results from the 1998 November 6 Occultation

Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

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