3 research outputs found
Upper limits for undetected trace species in the stratosphere of Titan
In this paper we describe a first quantitative search for several molecules
in Titan's stratosphere in Cassini CIRS infrared spectra. These are: ammonia
(NH3), methanol (CH3OH), formaldehyde (H2CO), and acetonitrile (CH3CN), all of
which are predicted by photochemical models but only the last of which
observed, and not in the infrared. We find non-detections in all cases, but
derive upper limits on the abundances from low-noise observations at 25{\deg}S
and 75{\deg}N. Comparing these constraints to model predictions, we conclude
that CIRS is highly unlikely to see NH3 or CH3OH emissions. However, CH3CN and
H2CO are closer to CIRS detectability, and we suggest ways in which the
sensitivity threshold may be lowered towards this goal.Comment: 11 pages plus 6 figure file
Detection of Propene in Titan's Stratosphere
The Voyager 1 flyby of Titan in 1980 gave a first glimpse of the chemical
complexity of Titan's atmosphere, detecting many new molecules with the
infrared spectrometer (IRIS). These included propane (C3H8) and propyne
(CH3C2H), while the intermediate-sized C3Hx hydrocarbon (C3H6) was curiously
absent. Using spectra from the Composite Infrared Spectrometer (CIRS) on
Cassini, we show the first positive detection of propene (C3H6) in Titan's
stratosphere (5-sigma significance), finally filling the three-decade gap in
the chemical sequence. We retrieve a vertical abundance profile from 100-250
km, that varies slowly with altitude from ~2 ppbv at 100 km, to ~5 ppbv at 200
km. The abundance of C3H6 is less than both C3H8 and CH3C2H, and we remark on
an emerging paradigm in Titan's hydrocarbon abundances whereby: alkanes >
alkynes > alkenes within the C2Hx and C3Hx chemical families in the lower
stratosphere. More generally, there appears to be much greater ubiquity and
relative abundance of triple-bonded species than double-bonded, likely due to
the greater resistance of triple bonds to photolysis and chemical attack.Comment: 16 pages; 4 figures; 1 table. Withdrawn due to journal polic