Evidence for a Polar Ethane Cloud on Titan

Griffith, C. A.; Penteado, P.; Rannou, P.; Brown, R. H.; Boudon, Vincent; Baines, K. H.; Clark, R. N.; Drossart, P.; Buratti, B. J.; Nicholson, P.; McKay, C. P.; Coustenis, A.; Negrão, A.; Jaumann, R.

doi:10.1126/science.1128245

Cited by 166 publications

(158 citation statements)

References 32 publications

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“…2c). A discrete ordinates radiative transfer calculation with 32 streams is used (Griffith et al 2006), which adopts the opacity profile derived by the Huygens probe (Tomasko et al 2008a(Tomasko et al , 2008b al. 1991) indicate that only ∼10% of the surface insolation, ∼0.037 W m Ϫ2 (roughly the amplitude of seasonal insolation variations at tropical latitudes), is available for evaporation and convection.…”

Section: Titan's Tropospheric Humiditymentioning

confidence: 99%

Titan's Tropical Storms in an Evolving Atmosphere

Griffith

McKay

Ferri

2008

ApJ

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The Huygens probe landed in a damp lake bed fed by fluvial channels, indicative of past rainfall. Such washes, interspersed with vast dunes, are typical of Titan's tropical landscape. Yet, Cassini-Huygens measurements reveal a highly stable tropical atmosphere devoid of deep convective storms, and the formation of washes in dune fields is not understood. Here we examine the effects of seasonal variations in humidity, surface heating, and dynamical forcing on the stability of Titan's troposphere. We find that during the probe landing, the middle troposphere was weakly unstable to convection, consistent with the tenuous cloud detected at 21 km. Yet the tropical atmosphere, at any season, is too stable to produce deep convective storms. Convection in the tropics remains weak and confined to altitudes below ∼30 km, unless the humidity is increased below 9 km altitude. Solar heating is insufficient to significantly humidify the tropical atmosphere. The large polar lakes are seasonably stable, and the methane column abundance measured by Huygens typical of the tropical atmosphere. Our study indicates the presence of distinct polar and equatorial climates. It also suggests that fluvial features in the tropics do not result from recent seasonal rainstorms, and thereby supports other origins such as geological seepage, cryovolcanism, or a wetter climate in the past.

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Section: Titan's Tropospheric Humiditymentioning

confidence: 99%

Titan's Tropical Storms in an Evolving Atmosphere

Griffith

McKay

Ferri

2008

ApJ

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“…Numerous cloud features have also been detected from ground-based observations (e.g. Griffith et al 2000) and Cassini observations (Griffith et al 2005(Griffith et al , 2006Porco et al 2005). Even though some of the observed features have been speculated to be indicative of cryovolcanic activities (Roe et al 2005), most of the observed features can be understood in the framework of the general circulation model of Titan's atmosphere (Rannou et al 2006;Rodriguez et al 2007) and do not require any particular activity on Titan's surface.…”

Section: Observational Constraints On the Evolution Of Titan And Its mentioning

confidence: 95%

Evolution of Titan and implications for its hydrocarbon cycle

Tobie

Choukroun

Grasset

et al. 2008

Phil. Trans. R. Soc. A.

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Measurements of the carbon and nitrogen isotopic ratios as well as the detection of 40 Ar and 36 Ar by the gas chromatograph mass spectrometer (GCMS) instrument on board the Huygens probe have provided key constraints on the origin and evolution of Titan's atmosphere, and indirectly on the evolution of its interior. Those data combined with models of Titan's interior can be used to determine the story of volatile outgassing since Titan's formation. In the absence of an internal source, methane, which is irreversibly photodissociated in Titan's stratosphere, should be removed entirely from the atmosphere in a time-span of a few tens of millions of years. The episodic destabilization of methane clathrate reservoir stored within Titan's crust and subsequent methane outgassing could explain the present atmospheric abundance of methane, as well as the presence of argon in the atmosphere. The idea that methane is released from the interior through eruptive processes is also supported by the observations of several cryovolcanic-like features on Titan's surface by the mapping spectrometer (VIMS) and the radar on board Cassini. Thermal instabilities within the icy crust, possibly favoured by the presence of ammonia, may explain the observed features and provide the conditions for eruption of methane and other volatiles. Episodic resurfacing events associated with thermal and compositional instabilities in the icy crust can have major consequences on the hydrocarbon budget on Titan's surface and atmosphere.

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“…As on Earth, the clouds on Titan are varied in origin. Cassini has variously seen convective "thunderstorm" clouds (but without the thunder; [45]), fog [23], lake-effect clouds [22], and polar ethane clouds [46]. All of these clouds have different optical depths and heights, and evolve with time.…”

Section: Task 22amentioning

confidence: 99%

AVIATR—Aerial Vehicle for In-situ and Airborne Titan Reconnaissance

et al. 2011

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We describe a mission concept for a stand-alone Titan airplane mission: Aerial Vehicle for In-situ and Airborne Titan Reconnaissance (AVI-ATR). With independent delivery and direct-to-Earth communications, AVI-ATR could contribute to Titan science either alone or as part of a sustained Titan Exploration Program. As a focused mission, AVIATR as we have envisioned it would concentrate on the science that an airplane can do best: exploration of Titan's global diversity. We focus on surface geology/hydrology and lower-atmospheric structure and dynamics. With a carefully chosen set of seven instruments-2 near-IR cameras, 1 near-IR spectrometer, a RADAR altimeter, an atmospheric structure suite, a haze sensor, and a raindrop detector-AVIATR could accomplish a significant subset of the scientific objectives of the aerial element of flagship studies. The AVIATR spacecraft stack is composed of a Space Vehicle (SV) for cruise, an Entry Vehicle (EV) for entry and descent, and the Air Vehicle (AV) to fly in Titan's atmosphere. Using an Earth-Jupiter gravity assist trajectory delivers the spacecraft to Titan in 7.5 years, after which the AVIATR AV would operate for a 1-Earthyear nominal mission. We propose a novel 'gravity battery' climb-then-glide strategy to store energy for optimal use during telecommunications sessions. We would optimize our science by using the flexibility of the airplane platform, generating context data and stereo pairs by flying and banking the AV instead

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Evidence for a Polar Ethane Cloud on Titan

Cited by 166 publications

References 32 publications

Titan's Tropical Storms in an Evolving Atmosphere

Titan's Tropical Storms in an Evolving Atmosphere

Evolution of Titan and implications for its hydrocarbon cycle

AVIATR—Aerial Vehicle for In-situ and Airborne Titan Reconnaissance

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