Wind driven capillary-gravity waves on Titan’s lakes: Hard to detect or non-existent?

Hayes, Alexander G.; Lorenz, Ralph D.; Donelan, Mark A.; Manga, Michael; Lunine, Jonathan I.; Schneider, Tapio; Lamb, Michael P.; Mitchell, J. Murray; Fischer, Woodward W.; Graves, S. D.; Tolman, Hendrik L.; Aharonson, O.; Encrenaz, P.; Ventura, B.; Casarano, D.; Notarnicola, Claudia

doi:10.1016/j.icarus.2013.04.004

Cited by 48 publications

(58 citation statements)

References 50 publications

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“…Barnes et al [15] used a time-resolved specular reflection across north polar Jingpo Lacus to constrain wave angles at that time to be less than 0.15°. All of these observations are consistent with Titan lakes that are as flat as a millpond at the time of the observations: entirely wave-free [12].…”

Section: Introductionsupporting

confidence: 81%

“…The wind velocity needed to generate such waves, along with the resultant wave frequencies, will necessarily be affected by Titan's alien gravity, atmospheric density, and liquid viscosity/surface tension (which are in turn a function of composition and temperature). Theoretical calculations [10][11][12] predict that the first waves to be incited on Titan when the winds break the threshold should occur with wavelengths between 2.8 cm and 3.2 cm. Hayes et al [12] show that these waves should be capillary-gravity waves -ones for which surface tension and gravity both contribute to the restoring force.…”

Section: Introductionmentioning

confidence: 99%

“…Theoretical calculations [10][11][12] predict that the first waves to be incited on Titan when the winds break the threshold should occur with wavelengths between 2.8 cm and 3.2 cm. Hayes et al [12] show that these waves should be capillary-gravity waves -ones for which surface tension and gravity both contribute to the restoring force. Initial laboratory experiments with kerosene in a wind tunnel [13] showed that waves on hydrocarbons are both larger than waves on water and form at lower wind speeds, at least under Earth gravity and atmospheric conditions.…”

Section: Introductionmentioning

confidence: 99%

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Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

et al. 2014

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Cassini/VIMS high-phase specular observations of Titan's north pole during the T85 flyby show evidence for isolated patches of rough liquid surface within the boundaries of the sea Punga Mare. The roughness shows typical slopes of 6°± 1°. These rough areas could be either wet mudflats or a wavy sea. Because of their large areal extent, patchy geographic distribution, and uniform appearance at low phase, we prefer a waves interpretation. Applying theoretical wave calculations based on Titan conditions our slope determination allows us to infer winds of 0.76 ± 0.09 m/s and significant wave heights of 2 +2 −1 cm at the time and locations of the observation. If correct, these would represent the first waves seen on Titan's seas, and also the first extraterrestrial sea-surface waves in general.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

et al. 2014

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“…8). The progressive seasonal increase in insolation that is occurring however has been predicted to power the onset of energetic processes 6,7,[9][10][11][12] and we argue that these anomalous features are the observation of transient features in the seas. The regional extent of the anomalous signal, which does not seem to derive from a single contiguous structure but rather from distinct features, is approximately 20 km by 20 km.…”

mentioning

confidence: 70%

“…Titan's northern hemisphere is transitioning from vernal equinox (August 2009) to summer solstice (May 2017) and it is plausible that the anomalous, transient features are an expression of the changing seasons. Waves were/are expected to form and become detectable as wind speeds in the northern hemisphere climb with the approach of summer 6,7,9,10 . Thermal perturbations could lead to the exsolution of gases from the liquid and/or sea floor that form bubbles and buoyantly rise to the surface.…”

mentioning

confidence: 99%

Transient features in a Titan sea

et al. 2014

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Titan's surface-atmosphere system bears remarkable similarities to Earth's, the most striking being an active, global methane cycle akin to Earth's water cycle 1,2 . Like the hydrological cycle of Earth, Titan's seasonal methane cycle is driven by changes in the distribution of solar energy 2 . The Cassini spacecraft, which arrived at Saturn in 2004 in the midst of northern winter and southern summer, has observed surface changes, including shoreline recession, at Titan's south pole 3,4 and equator 5 . However, active surface processes have yet to be confirmed in the lakes and seas in Titan's north polar region 6-8 . As the 2017 northern summer solstice approaches, the onset of dynamic phenomena in this region is expected 6,7,9-12 . Here we present the discovery of bright features in recent Cassini RADAR data that appeared in Titan's northern sea, Ligeia Mare, in July 2013 and disappeared in subsequent observations. We suggest that these bright features are best explained by the occurrence of ephemeral phenomena such as surface waves, rising bubbles, and suspended or floating solids. We suggest that our observations are an initial glimpse of dynamic processes that are commencing in the northern lakes and seas as summer nears in the northern hemisphere.Anomalous, bright features were detected in Titan's north polar sea, Ligeia Mare, by the Cassini Titan Radar Mapper 13 (RADAR) during the T92 synthetic aperture radar (SAR) pass (Fig. 1). Three preceding SAR observations (T25, T29 and T64) and a subsequent low-resolution SAR observation (T95) did not detect the anomalous features. The faint, grey spots in the circle of the T95 image are consistent with the speckle noise in the surrounding sea region and thus are not anomalous. Radar backscatter above the noise floor, however, was also detected during preceding T91 radar scatterometry-mode observations 13 but we argue that this signal may not have originated from the anomalies. Subsequent Visual and Infrared Mapping Spectrometer (VIMS) and Imaging Science Subsystem observations (T93 and T94) also did not detect the anomalies. These eight passes, constituting all of the highresolution observations up to the present of the region of the anomalous features, are shown in Fig. 1. In radar images, brightness is determined by the normalized radar cross-section (NRCS), the ratio of the radar energy backscattered to the receiver compared with that from an isotropic scatterer 14 . Dynamic processes such as waves 7 , suspended particles 3 , or bubbles 15 increase the NRCS. Such phenomena have not been confirmed in Titan's northern lakes and seas, which have a dielectric constant that indicates a methane-ethane composition and surface height variations of less than 1 mm (ref. 8). The progressive seasonal increase in insolation that is occurring however has been predicted to power the onset of energetic processes 6,7,9-12 and we argue that these anomalous features are the observation of transient features in the seas. The regional extent of the anomalous signal, which does not s...

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Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis

Zebker

Hayes

Janssen

et al. 2014

Geophysical Research Letters

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Cassini radar observations of the surface of Ligeia Mare collected during the 23 May 2013 (T91)Cassini flyby show that it is extremely smooth, likely to be mostly methane in composition, and exhibits no surface wave activity. The radar parameters were tuned for nadir-looking geometry of liquid surfaces, using experience from Cassini's only comparable observation, of Ontario Lacus on 21 December 2008 (T49), and also include coincident radiometric observations. Radar echoes from both passes show very strong specular radar reflections and limit surface height variations to 1 mm rms. The surface physical temperature at 80°N is 92 +/À 0.5 K if the sea is liquid hydrocarbon and the land is solid hydrocarbon, essentially the same as Cassini CIRS measurements. Furthermore, radiometry measurements over the surrounding terrain suggest dielectric constants from 2.2 to 2.4, arguing against significant surface water ice unless it is extremely porous.

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Wind driven capillary-gravity waves on Titan’s lakes: Hard to detect or non-existent?

Cited by 48 publications

References 50 publications

Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

Cassini/VIMS observes rough surfaces on Titan’s Punga Mare in specular reflection

Transient features in a Titan sea

Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis

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