Thermally driven atmospheric escape: Monte Carlo simulations for Titan's atmosphere

Tucker, O. J.; Johnson, R. E.

doi:10.1016/j.pss.2009.06.003

Cited by 60 publications

(69 citation statements)

References 27 publications

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“…Debates within the atmospheric modeling community have argued whether H 2 escape is limited by the Jeans escape rate (Bell et al, 2010(Bell et al, , 2011 or is escaping at a significantly greater rate . Exospheric simulations using Direct Monte Carlo Simulation have found the H 2 escape rate to be consistent with Jeans escape (Tucker et al, 2009).…”

Section: Titanmentioning

confidence: 74%

Saturn Plasma Sources and Associated Transport Processes

Blanc

Andrews

Coates

et al. 2016

Plasma Sources of Solar System Magnetospheres

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Section: Titanmentioning

confidence: 74%

Saturn Plasma Sources and Associated Transport Processes

Blanc

Andrews

Coates

et al. 2016

Plasma Sources of Solar System Magnetospheres

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“…However, Tucker and Johnson (2009) found no evidence for slow hydrodynamic escape to act in Titan's exosphere. Using an Direct Simulation Monte Carlo (DSMC) model, they conclude that either the Strobel model is incorrect or the size of the Jeans parameter (which will be discussed later) is not sufficient to describe the deviations from Jeans escape.…”

Section: Titan's Exospherementioning

confidence: 86%

Titan’s atomic hydrogen corona

Hedelt¹,

Ito²,

Keller³

et al. 2010

Icarus

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Based on measurements performed by the Hydrogen Deuterium Absorption Cell (HDAC) aboard the Cassini orbiter, Titan's atomic hydrogen exosphere is investigated. Data obtained during the T9 encounter are used to infer the distribution of atomic hydrogen throughout Titan's exosphere, as well as the exospheric temperature.The measurements performed during the flyby are modeled by performing Monte Carlo radiative transfer calculations of solar Lyman-α radiation, which * Corresponding author, Tel. +33 557 776 127 ACCEPTED MANUSCRIPTis resonantly scattered on atomic hydrogen in Titan's exosphere. Two different atomic hydrogen distribution models are applied to determine the best fitting density profile. One model is a static model that uses the Chamberlain formalism to calculate the distribution of atomic hydrogen throughout the exosphere, whereas the second model is a particle model, which can also be applied to non-Maxwellian velocity distributions. The density distributions provided by both models are able to fit the measurements although both models differ at the exobase: Best fitting exobase atomic hydrogen densities of n H = (1.5 ± 0.5) · 10 4 cm −3 and n H = (7 ± 1) · 10 4 cm −3 were found using the density distribution provided by both models, respectively. This is based on the fact that during the encounter, HDAC was sensitive to altitudes above about 3,000 km, hence well above the exobase at about 1,500 km. Above 3,000 km, both models produce densities which are comparable, when taking into account the measurement uncertainty.The inferred exobase density using the Chamberlain profile is a factor of about 2.6 lower than the density obtained from Voyager 1 measurements and much lower than the values inferred from current photochemical models. However, when taking into account the higher solar activity during the Voyager flyby, this is consistent with the Voyager measurements. When using the density profile provided by the particle model, the best fitting exobase density is in perfect agreement with the densities inferred by current photochemical models.Furthermore, a best fitting exospheric temperature of atomic hydrogen in the range of T H = (150 − 175) ± 25 K was obtained when assuming an isothermal exosphere for the calculations. The required exospheric temperature depends on the density distribution chosen. This result is within the temperature range determined by different instruments aboard Cassini. The inferred temperature is close to the critical temperature for atomic hydrogen, above which it can escape hydrodynamically after it diffused through the heavier background gas.

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“…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. The structure of the CH 4 corona is of special importance because it is highly relevant to CH 4 escape from Titan, an issue that has caught extensive research interest over the past ten years and is still under debate Strobel 2009;Tucker & Johnson 2009;Bell et al 2010Bell et al , 2011Cui et al 2012;Schaufelberger et al 2012). The link between these two issues is the topic of Section 5.…”

Section: Introductionmentioning

confidence: 99%

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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Thermally driven atmospheric escape: Monte Carlo simulations for Titan's atmosphere

Cited by 60 publications

References 27 publications

Saturn Plasma Sources and Associated Transport Processes

Saturn Plasma Sources and Associated Transport Processes

Titan’s atomic hydrogen corona

The Structure of Titan’s N₂ and CH₄ Coronae

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Thermally driven atmospheric escape: Monte Carlo simulations for Titan's atmosphere

Cited by 60 publications

References 27 publications

Saturn Plasma Sources and Associated Transport Processes

Saturn Plasma Sources and Associated Transport Processes

Titan’s atomic hydrogen corona

The Structure of Titan’s N2 and CH4 Coronae

Contact Info

Product

Resources

About

The Structure of Titan’s N₂ and CH₄ Coronae