The Process of Tholin Formation in Titan's Upper Atmosphere

Waite, J. H.; Young, D. T.; Cravens, T. E.; Coates, A. J.; Crary, F. J.; Magee, B.; Westlake, J. H.

doi:10.1126/science.1139727

Cited by 618 publications

(653 citation statements)

References 27 publications

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“…As outlined in section 2, we have employed an empirical chemical production of H 2 given by P H 2 = 1.15 × L CH 4 , which is loosely based upon the measurements of heavy hydrocarbon C:H ratios made by INMS [Waite et al, 2007;Westlake et al, 2012]. This scheme liberates significantly more H 2 than the original scheme of Bell et al [2010a], and we now examine the implications of this added H 2 production on T-GITM simulated H 2 densities and mixing ratios.…”

Section: The Impacts Of H 2 Chemistrymentioning

confidence: 99%

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Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N2, CH4, H2, 40Ar, HCN, and the major stable isotopic ratios of 14N/15N in N2. We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×1011 CH4 m−2 s−1 and 1.08 ×1014 H2 m−2 s−1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here.

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Section: The Impacts Of H 2 Chemistrymentioning

confidence: 99%

“…an analysis of the Cassini INMS heavy hydrocarbon data by Waite et al [2007] and Westlake et al [2012], which indicate that the heavy hydrocarbons have a carbon to hydrogen ratio of roughly 1:1.7. This 1:1.7 C to H ratio suggests that 1.15 H 2 molecules are liberated for every CH 4 molecule consumed by chemistry.…”

Section: Introductionmentioning

confidence: 99%

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

et al. 2014

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“…The relationship between these ions and the heavy positive ion population was discussed by Waite et al (2007). They suggested that nitrogen and methane in Titan's high atmosphere would be acted on by sunlight and magnetospheric particles forming heavier but relatively simple species by dissociation and )) is not yet understood; but it may be the poorer sensitivity of IBS, or different chemical pathways for positive and negative ions.…”

Section: (D ) Negative Ions: An Unexpected Feature In Titan Encountersmentioning

confidence: 99%

Interaction of Titan's ionosphere with Saturn's magnetosphere

Coates

2008

Phil. Trans. R. Soc. A.

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Titan is the only Moon in the Solar System with a significant permanent atmosphere. Within this nitrogen-methane atmosphere, an ionosphere forms. Titan has no significant magnetic dipole moment, and is usually located inside Saturn's magnetosphere. Atmospheric particles are ionized both by sunlight and by particles from Saturn's magnetosphere, mainly electrons, which reach the top of the atmosphere. So far, the Cassini spacecraft has made over 45 close flybys of Titan, allowing measurements in the ionosphere and the surrounding magnetosphere under different conditions. Here we review how Titan's ionosphere and Saturn's magnetosphere interact, using measurements from Cassini low-energy particle detectors. In particular, we discuss ionization processes and ionospheric photoelectrons, including their effect on ion escape from the ionosphere. We also discuss one of the unexpected discoveries in Titan's ionosphere, the existence of extremely heavy negative ions up to 10 000 amu at 950 km altitude.

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“…Extrapolation of the INMS measurements (limited to mass up to 100 Da) and of CAPS data, strongly suggests that high-molecular-weight species (up to several 1,000 Da) may be present in the ionosphere. These new data-if confirmedrevolutionize the understanding of the organic processes occurring in Titan's atmosphere, with a strong implication that ionospheric chemistry plays a role in the formation of complex organic compounds in Titan's environment, which was predicted [3] but whose extent was not envisioned before [2,51].…”

Section: A Complex Prebiotic-like Chemistrymentioning

confidence: 60%

“…The direct analysis of the ionosphere by the INMS instrument during the closest Cassini flybys of Titan shows the presence of many organic species, in spite of the very high altitude (1,100-1,300 km) [51]. Extrapolation of the INMS measurements (limited to mass up to 100 Da) and of CAPS data, strongly suggests that high-molecular-weight species (up to several 1,000 Da) may be present in the ionosphere.…”

Section: A Complex Prebiotic-like Chemistrymentioning

confidence: 99%

TandEM: Titan and Enceladus mission

et al. 2008

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International audienceTandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (Montgolfière) and possibly several landing probes to be delivered through the atmospher

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The Process of Tholin Formation in Titan's Upper Atmosphere

Cited by 618 publications

References 27 publications

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

Interaction of Titan's ionosphere with Saturn's magnetosphere

TandEM: Titan and Enceladus mission

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