Upper limits for undetected trace species in the stratosphere of Titan

Titan is the only moon with a substantial atmosphere, the only other thick N2 atmosphere besides Earth's, the site of extraordinarily complex atmospheric chemistry that far surpasses any other solar system atmosphere, and the only other solar system body with stable liquid currently on its surface. The connection between Titan's surface and atmosphere is also unique in our solar system; atmospheric chemistry produces materials that are deposited on the surface and subsequently altered by surface‐atmosphere interactions such as aeolian and fluvial processes resulting in the formation of extensive dune fields and expansive lakes and seas. Titan's atmosphere is favorable for organic haze formation, which combined with the presence of some oxygen‐bearing molecules indicates that Titan's atmosphere may produce molecules of prebiotic interest. The combination of organics and liquid, in the form of water in a subsurface ocean and methane/ethane in the surface lakes and seas, means that Titan may be the ideal place in the solar system to test ideas about habitability, prebiotic chemistry, and the ubiquity and diversity of life in the universe. The Cassini‐Huygens mission to the Saturn system has provided a wealth of new information allowing for study of Titan as a complex system. Here I review our current understanding of Titan's atmosphere and climate forged from the powerful combination of Earth‐based observations, remote sensing and in situ spacecraft measurements, laboratory experiments, and models. I conclude with some of our remaining unanswered questions as the incredible era of exploration with Cassini‐Huygens comes to an end.

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“…o Nixon et al [2013a] (at 225 km). p Nixon et al [2010] (3 upper limits at 25 ∘ S). q Teanby et al [2006] (3 upper limit at 50 ∘ N).…”

Section: Temperature Structurementioning

confidence: 99%

Titan's atmosphere and climate

2017

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“…For spectra in which C 6 H 6 or HC 3 N were not detected, we estimated the 2-σ upper limit on their mixing ratios following the methodology described in Nixon et al (2010).…”

Section: Molecular Gas Volume Mixing Ratio Profile Retrievalsmentioning

confidence: 99%

Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

Mathé

Vinatier

Bézard

et al. 2020

Icarus

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The Cassini/Composite InfraRed Spectrometer (CIRS) instrument has been observing the middle atmosphere of Titan over almost half a Saturnian year. We used the CIRS dataset processed through the up-to-date calibration pipeline to characterize seasonal changes of temperature and abundance profiles in the middle atmosphere of Titan, from mid-northern winter to early northern summer all around the satellite. We used limb spectra from 590 to 1500 cm −1 at 0.5-cm −1 spectral resolution, which allows us to probe different altitudes. We averaged the limb spectra recorded during each flyby on a fixed altitude grid to increase the signal-to-noise ratio. These thermal infrared data were analyzed by means of a radiative transfer code coupled with an inversion algorithm, in order to retrieve vertical temperature and abundance profiles. These profiles cover an altitude range of approximately 100 to 600 km, at 10-or 40-km vertical resolution (depending on the observation). Strong changes in temperature and composition occur in both polar regions where a vortex is in place during the winter. At this season, we observe a global enrichment in photochemical compounds in the mesosphere and stratosphere and a hot stratopause located around 0.01 mbar, both linked to downwelling in a pole-to-pole circulation cell. After the northern spring equinox, between December 2009 and April 2010, a stronger enhancement of photochemical compounds occurred at the north pole above the 0.01-mbar region, likely due to combined photochemical and dynamical effects. During the southern autumn in 2015, above the South pole, we also observed a strong enrichment in photochemical compounds that contributed to the cooling of the stratosphere above 0.2 mbar (∼300 km). Close to the northern spring equinox, in December 2009, the thermal profile at 74 • N exhibits an oscillation that we interpret in terms of an inertia-gravity wave.

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“…17. Data from the first two MIRLMPAIR observations have been analyzed to search for new gas species, and although none were detected, stringent upper limits were placed on the abundances that can be used to constrain photochemical models [6].…”

Section: Mirlmpairmentioning

confidence: 99%

Designing infrared observations of Titan's atmosphere with Cassini CIRS

Nixon

Ansty

Flasar

et al. 2012

2012 IEEE Aerospace Conference

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In this paper we describe the technical implementation of infrared observations of Titan using the Cassini Composite Infrared Spectrometer (CIRS). Due to the distributed operations model of Cassini, instrument teams such as CIRS are responsible for spacecraft pointing during their own observations. We describe the principal factors driving and constraining observation design, and then provide details of the eight standard observation types resulting, followed by a discussion of several later 'evolved' types. We then show some sample science results, and finally conclude with a mention of continuing challenges to CIRS Titan observation design.

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Upper limits for undetected trace species in the stratosphere of Titan

Cited by 43 publications

References 57 publications

Titan's atmosphere and climate

Titan's atmosphere and climate

Seasonal changes in the middle atmosphere of Titan from Cassini/CIRS observations: Temperature and trace species abundance profiles from 2004 to 2017

Designing infrared observations of Titan's atmosphere with Cassini CIRS

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