Brightness of Saturn's rings with decreasing solar elevation

Flandes, A.; Spilker, L. J.; Morishima, Ryuji; Pilorz, S.; Leyrat, C.; Altobelli, Nicolás; Brooks, S. M.; Edgington, S. G.

doi:10.1016/j.pss.2010.04.002

Cited by 26 publications

(24 citation statements)

References 29 publications

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“…We thus account for the contribution of the rings to the continuum emission. The A-B-C ring system brightness temperatures are computed in the wavelength range of our observations by interpolating the observational results obtained in the infrared with Cassini/CIRS (Flandes et al 2010) and at 2 cm with the Very Large Array (van der Tak et al 1999), accounting for the brightness temperature roll-off seen around 200 µm by Spilker et al (2003Spilker et al ( , 2005. We use the solar elevation as seen from the rings given in Table 1, and the optical depths of the different rings from Altobelli et al (2014) and Guerlet et al (2014).…”

Section: Radiative-transfer Modelmentioning

confidence: 99%

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

Cavalié

Hue

Hartogh

et al. 2019

A&A

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Context. The origin of water in the stratospheres of Giant Planets has been an outstanding question ever since its first detection by ISO some 20 years ago. Water can originate from interplanetary dust particles, icy rings and satellites and large comet impacts. Analysis of Herschel Space Observatory observations have proven that the bulk of Jupiter's stratospheric water was delivered by the Shoemaker-Levy 9 impacts in 1994. In 2006, the Cassini mission detected water plumes at the South Pole of Enceladus, placing the moon as a serious candidate for Saturn's stratospheric water. Further evidence was found in 2011, when Herschel demonstrated the presence of a water torus at the orbital distance of Enceladus, fed by the moon's plumes. Finally, water falling from the rings onto Saturn's uppermost atmospheric layers at low latitudes was detected during the final orbits of Cassini's end-of-mission plunge into the atmosphere. Aims. In this paper, we use Herschel mapping observations of water in Saturn's stratosphere to identify its source. Methods. Several empirical models are tested against the Herschel-HIFI and -PACS observations, which were collected on December 30, 2010, and January 2 nd , 2011 (respectively). Results. We demonstrate that Saturn's stratospheric water is not uniformly mixed as a function of latitude, but peaking at the equator and decreasing poleward with a Gaussian distribution. We obtain our best fit with an equatorial mole fraction 1.1 ppb and a half-width at half-maximum of 25˝, when accounting for a temperature increase in the two warm stratospheric vortices produced by Saturn's Great Storm of 2010-2011. Conclusions. This work demonstrates that Enceladus is the main source of Saturn's stratospheric water.

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Section: Radiative-transfer Modelmentioning

confidence: 99%

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

Cavalié

Hue

Hartogh

et al. 2019

A&A

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“…2. The temperatures of the rings were assumed to be 65 K for the A ring, 68 K for the B ring and 80 K for the C ring (e.g., Flandes et al 2010), with optical depths (τ) of 0.6, 2.0 and 0.1 for the A, B and C rings respectively (e.g., Colwell et al 2010). We used a simple formulation to estimate the ring emission spectrum (I em = B(T )(1 − exp(−τ/μ))), where B(T ) is the blackbody emission of each ring, and the parameter exp(−τ/μ) accounts for the viewing geometry (μ = sin(φ)) and optical depth (τ).…”

Section: Estimating Saturn's Ring Contributionmentioning

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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“…Because all Saturn's major moons are in relatively low inclination orbits with respect to Saturn's rotational equator, they can experience~29 year seasonal variations in concert with Saturn. Seasonal effects have been observed at Titan [Brown et al, 2010], at the rings [Horányi et al, 2009;Flandes et al, 2010], likely at Rhea and Dione [Teolis andWaite, 2011, 2012], and have been modeled the E ring [Juhász and Horányi, 2004]. If a critical atmospheric layer or a differentiated area near a moon's polar region is heated by insolation near one solstice or the other, some portion of its 28 M atmospheric population may experience changes (dissociation or photolysis, for example), attain escape velocity, and leave the moon.…”

Section: Discussion and Summarymentioning

confidence: 99%

Saturn suprathermal O₂⁺ and mass‐28⁺ molecular ions: Long‐term seasonal and solar variation

et al. 2013

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Suprathermal singly charged molecular ions, O2+ (at ~32 Da/e) and the Mass‐28 ion group 28M+ (ions at ~28 Da/e, with possible contributions from C2H5+, HCNH+, N2+, and/or CO+), are present throughout Saturn's ~4–20 Rs (1 Saturn radius, Rs = 60,268 km) near‐equatorial magnetosphere from mid‐2004 until mid‐2012. These ~83–167 keV/e heavy ions measured by Cassini's CHarge‐Energy‐Mass Spectrometer have long‐term temporal profiles that differ from each other and differ relative to the dominant water group ions, W+ (O+, OH+, H2O+, and H3O+). O2+/W+, initially ~0.05, declined steadily until equinox in mid‐2009 by a factor of ~6, and 28M+/W+, initially ~0.007, declined similarly until early‐2007 by a factor of ~2. The O2+/W+ decline is consistent with Cassini's in situ ring‐ionosphere thermal ion measurements, and with proposed and modeled seasonal photolysis of Saturn's rings for thermal O2 and O2+. The water ice‐dominated main rings and Enceladus plume depositions thereon are the two most likely O2+ sources. Enceladus' dynamic plumes, though, have no known long‐term dependence. After declining, O2+/W+ and 28M+/W+ levels remained low until late‐2011 when O2+/W+ increased, but 28M+/W+ did not. The O2+/W+ increase was steady and became statistically significant by mid‐2012, indicating a clear increase after a decline, that is, a possibly delayed O2+ “seasonal” recovery. Ring insolation is driven by solar UV flux which itself varies with the sun's 11 year activity cycle. The O2+/W+ and 28M+/W+ declines are consistent with seasonal ring insolation. No O2+/W+ response to the late‐2008 solar‐cycle UV minimum and recovery is evident. However, the O2+/W+ recovery from the postequinox baseline levels in late‐2011 coincided with a strong solar UV enhancement. We suggest a scenario/framework in which the O2+ observations can be understood.

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Brightness of Saturn's rings with decreasing solar elevation

Cited by 26 publications

References 29 publications

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

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

Saturn suprathermal O₂⁺ and mass‐28⁺ molecular ions: Long‐term seasonal and solar variation

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Brightness of Saturn's rings with decreasing solar elevation

Cited by 26 publications

References 29 publications

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

Herschel map of Saturn’s stratospheric water, delivered by the plumes of Enceladus

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

Saturn suprathermal O2+ and mass‐28+ molecular ions: Long‐term seasonal and solar variation

Contact Info

Product

Resources

About

Saturn suprathermal O₂⁺ and mass‐28⁺ molecular ions: Long‐term seasonal and solar variation