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| Titel |
Complex organic chemistry in Titan’s stratosphere near the poles from Cassini/CIRS |
| VerfasserIn |
Athena Coustenis, Donald Jennings, Richard Achterberg, Panayiotis Lavvas, Conor Nixon, Georgios Bampasidis, F. Michael Flasar |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250139725
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| Publikation (Nr.) |
 EGU/EGU2017-3020.pdf |
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| Zusammenfassung |
| We witness since 2010 the appearance at Titan’s South pole of several trace species for the
first time, in particular for complex hydrocarbons such as HC3N and C6H6, observed
previously only at high northern latitudes. Moreover, since 2012 this situation has rapidly
evolved with a strong enhancement of some gases and condensates in the South pole
(Coustenis et al. 2010; 2016; Vinatier et al. 2015; Jennings et al. 2015). This is due to
the transition of Titan’s seasons from northern winter in 2002 to (late) northern
spring in 2012 and the advent of winter in the South pole. During this time, the
reversal of Titan’s main atmospheric circulation cell is expected to channel fresh
photochemical products from mid latitudes towards the South pole. Meanwhile, gases
transported north during the previous season remain concentrated around the North pole,
undergoing slow photochemical destruction. Following the northern winter, species
with longer chemical lifetimes should remain in the north for a little longer while
those with shorter lifetimes disappear, reappearing in the south. We will present an
analysis of spectra acquired by Cassini/CIRS at high resolution in nadir mode. We
investigate here latitudes poleward of 50∘S and 50∘N since the Southern Autumnal
Equinox. Subsidence gases that accumulate in the absence of ultraviolet sunlight,
increased quickly since 2012 and some of them may be responsible also for the haze
decrease in the north and its appearance in the south at the same time (Jennings et al.
2015). For some of the most abundant and longest-lived hydrocarbons the evolution
in the past years at a given latitude is not significant until mid-2013 (Coustenis
et al. 2016). But in more recent dates, these molecules show a dramatic trend for
increase in the south, by several orders of magnitude in some cases (as for C6H6 and
HC3N). The 70∘S and mid-latitudes show different behavior indicative of different
dynamical processes in and out of the polar vortex region. While the 70∘N data
show generally no change with a trend rather to a small decrease for most species
within 2014, the 70∘S results indicate a strong enhancement in trace stratospheric
gases after 2012. This is a strong indication of the rapid and sudden buildup of the
gaseous inventory in the southern stratosphere during 2013-2014, as expected as
the pole moves deeper into winter shadow. This finding applies both for nadir and
for limb spectra. Subsidence gases that accumulate in the absence of ultraviolet
sunlight, evidently increased quickly since 2012 and some of them may be responsible
also for the reported haze decrease in the north and its appearance in the south at
the same time (Jennings et al. 2015). We will describe here a search for complex
molecules predicted by photochemical models to exist in Titan’s stratosphere and not yet
observed at all or with Cassini (such as butane, acetonitrile, acrylonitrile, proprionitrile,
etc).
References: Coustenis, et al., Icarus 207, 461, 2010 ; Coustenis et al. 2016, Icarus, 270,
409, 2016 ; Jennings et al., ApJ 804, L34, 5, 2015; Vinatier et al. Icarus 250, 95,
2015. |
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