Letter to the Editor
Detection of C2H4 in Neptune from ISO/PHT-S observations
B. Schulz 1,
Th. Encrenaz 2,
B. Bézard 2,
P.N. Romani 3,
E. Lellouch 2 and
S.K. Atreya 4
Received 27 July 1999 / Accepted 6 September 1999
The 6-12 µm spectrum of Neptune has been recorded with the PHT-S instrument of the Infrared Space Observatory (ISO) at a resolution of 0.095 µm. In addition to the emissions of CH4, CH3D and C2H6 previously identified, the spectrum shows the first firm identification of ethylene C2H4. The inferred column density above the 0.2-mbar level is in the range (1.1-3)1014 molecules cm-2. To produce this low amount, previous photochemical models invoked rapid mixing between the source and sink regions of C2H4. We show that this requirement can be relaxed if recent laboratory measurements of CH4 photolysis branching ratios at Lyman are used.
Key words: planets and satellites: general planets and satellites: individual: Neptune infrared: solar system
Send offprint requests to: B. Schulz (firstname.lastname@example.org)
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© European Southern Observatory (ESO) 1999
Online publication: September 24, 1999