The thermal structure of Titan’s upper atmosphere, I: Temperature profiles from Cassini INMS observations

Snowden, D.; Yelle, R. V.; Cui, Jun; Wahlund, J. E.; Edberg, Niklas J. T.; Ågren, Karin

doi:10.1016/j.icarus.2013.06.006

Cited by 80 publications

(110 citation statements)

References 91 publications

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“…This is in good agreement with previous results also obtained from the INMS data, but including a smaller set of Titan flybys (e.g., Cui et al 2009;Westlake et al 2011;Snowden et al 2013). The lowest temperature is encountered in T43 and the highest temperature in T104, the latter being a dayside Titan flyby that has not been analyzed in any existing works.…”

Section: Characterization Of the Mean Thermal State In Titan's Upper supporting

confidence: 92%

“…The solar-driven scenario has also been excluded for interpreting the thermal structure of Titan's upper atmosphere by various authors (Westlake et al 2011;Snowden et al 2013;Snowden & Yelle 2014). The drastic change in corona structure from T28 to T29, two consecutive flybys sampling roughly the same regions of Titan's atmosphere but separated by one Titan day (see Table 1), reveals a variability on relatively short timescales that could only be driven by Titan's highly variable plasma environment (Arridge et al 2011a).…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

“…Taking into account the extended nature of Titan's atmosphere (e.g., Müller-Wodarg et al 2000), we define the dayside subsample as including all flybys with SZA at CA below 110°, and the nightside subsample as SZA at CA beyond 10°. Analysis of the INMS data then reveals an average dayside temperature that is slightly lower than the average nightside temperature by about 4K, indicating that the variability in the thermal structure of Titan's upper atmosphere is unlikely to be driven by solar energy deposition (Snowden et al 2013). A multivariate regression analysis is also performed to parameterize the correlation between the derived neutral temperature and various geophysical parameters.…”

Section: Characterization Of the Mean Thermal State In Titan's Upper mentioning

confidence: 99%

“…We start with a brief description of INMS data reduction in Section 2. This is followed by an analysis of neutral temperature in Titan's upper atmosphere in Section 3, as an extension of numerous existing studies (e.g., Müller-Wodarg et al 2008;Westlake et al 2011;Snowden et al 2013). We then derive in Section 4 the characteristics of Titan's corona using the traditional kinetic model of Chamberlain (1963) to evaluate the possible existence of suprathermal N 2 and CH 4 populations.…”

Section: Introductionmentioning

confidence: 97%

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The Structure of Titan’s N₂ and CH₄ Coronae

Jiang

Cui

2017

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In this study, we analyze the structures of Titan's N 2 and CH 4 coronae using a large data set acquired by the Ion Neutral Mass Spectrometer (INMS) instrument on board Cassini. The N 2 and CH 4 densities measured from the exobase up to 2000km imply a mean exobase temperature of 146K and 143K, respectively, which is lower than the mean upper atmospheric temperature by 4 and 7K. This indicates that on average, Titan possesses a subthermal rather than suprathermal corona. A careful examination reveals that the variability in corona structure is not very likely to be solar driven. Within the framework of the collisionless kinetic model, we investigate how the CH 4 energy distribution near the exobase could be constrained if strong CH 4 escape occurs on Titan. Several functional forms for the CH 4 energy distribution are attempted, assuming two representative CH 4 escape rates of 1.2 10 25 s −1 and2.2 10 27 s −1. We find that the double Maxwellian and power-law distributions can reproduce the shape of the CH 4 corona structure as well as the imposed CH 4 escape rate. In both cases, the escape rate is contributed by a suprathermal CH 4 population on the high-energy tail, with a number fraction below 5% and a characteristic energy of 0.1-0.6eV per suprathermal CH 4 molecule. The coexistence of the subthermal CH 4 corona revealed by the INMS data and substantial CH 4 escape suggested by some previous works could be reconciled by a significant departure in the exobase CH 4 energy distribution from ideal Maxwellian that enhances escape and causes a noticeable redistribution of the corona structure.

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Section: Characterization Of the Mean Thermal State In Titan's Upper supporting

confidence: 92%

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

Section: Characterization Of the Mean Thermal State In Titan's Upper mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

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The Structure of Titan’s N₂ and CH₄ Coronae

Jiang

Cui

2017

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“…The chemical composition of Titan's atmosphere is similar to Earth's nitrogen-dominated atmosphere and both 9 planets feature a distinct stratosphere. Titan's atmosphere is unique within the Solar System because it is so cold and extends to such high altitude, with evidence that upper atmospheric temperature is influenced by both magnetospheric plasma (external influence) (Westlake et al, 2011) and atmospheric waves (internal) (Hinson and Tyler, 1983), causing it to change rapidly (Snowden et al, 2013;Snowden and Yelle, 2014). Yet the existence of Titan's atmosphere appears relatively stable.…”

Section: Temperature Structurementioning

confidence: 99%

Science goals and mission concept for the future exploration of Titan and Enceladus

Tobie¹,

Teanby²,

Coustenis³

et al. 2014

Planetary and Space Science

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Saturn's moons, Titan and Enceladus, are two of the Solar System's most enigmatic bodies and are prime targets for future space exploration. Titan provides an analogue for many processes relevant to the Earth, more generally to outer Solar System bodies, and a growing host of newly discovered icy exoplanets. Processes represented include: atmospheric dynamics, complex organic chemistry, meteorological cycles (with methane as a working fluid), astrobiology, surface liquids and lakes, geology, fluvial and aeolian erosion, and interactions with an external plasma environment. In addition, exploring Enceladus over multiple targeted flybys will give us a unique opportunity to further study the most active icy moon in our Solar System as revealed by Cassini and to analyse in situ its active plume with highly capable instrumentation addressing its complex chemistry and dynamics. Enceladus' plume likely represents the most accessible samples from an extra-terrestrial liquid water environment in the Solar system, which has far reaching implications for many areas of planetary and biological science. Titan with its massive atmosphere and Enceladus with its active plume are prime planetary objects in the Outer Solar System to perform in situ investigations. In the present paper, we describe the science goals and key measurements to be

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Density waves in Titan's upper atmosphere

Cui

Yelle

et al. 2014

JGR Space Physics

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Analysis of the Cassini Ion Neutral Mass Spectrometer data reveals the omnipresence of density waves in various constituents of Titan's upper atmosphere, with quasi‐periodical structures visible for N2, CH4,29N2, and some of the minor constituents. The N2 amplitude lies in the range of ≈4%–16%with a mean of ≈8%. Compositional variation is clearly seen as a sequence of decreasing amplitude with increasing scale height. The observed vertical variation of amplitude implies significant wave dissipation in different constituents, possibly contributed by molecular viscosity for N2but by both molecular viscosity and binary diffusion for the others. A wave train with near horizontally propagating wave energy and characterized by a wavelength of ≈730 km and a wave period of ≈10 h is found to best reproduce various aspects of the observations in a globally averaged sense. Some horizontal and seasonal trends in wave activity are identified, suggesting a connection between the mechanism driving the overall variability in the background atmosphere and the mechanism driving the waves. No clear association of wave activity with magnetospheric particle precipitation can be identified from the data.

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The thermal structure of Titan’s upper atmosphere, I: Temperature profiles from Cassini INMS observations

Cited by 80 publications

References 91 publications

The Structure of Titan’s N₂ and CH₄ Coronae

The Structure of Titan’s N₂ and CH₄ Coronae

Science goals and mission concept for the future exploration of Titan and Enceladus

Density waves in Titan's upper atmosphere

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The thermal structure of Titan’s upper atmosphere, I: Temperature profiles from Cassini INMS observations

Cited by 80 publications

References 91 publications

The Structure of Titan’s N2 and CH4 Coronae

The Structure of Titan’s N2 and CH4 Coronae

Science goals and mission concept for the future exploration of Titan and Enceladus

Density waves in Titan's upper atmosphere

Contact Info

Product

Resources

About

The Structure of Titan’s N₂ and CH₄ Coronae

The Structure of Titan’s N₂ and CH₄ Coronae