Upper limits for PH3 and H2S in Titan’s atmosphere from Cassini CIRS

We have searched for the presence of simple P and S-bearing molecules in Titan’s atmosphere, by looking for the characteristic signatures of phosphine and hydrogen sulfide in infrared spectra obtained by Cassini CIRS. As a result we have placed the first upper limits on the stratospheric abundances, which are 1 ppb (PH3) and 330 ppb (H2S), at the 2-σ significance level.

► We have searched in Cassini CIRS infrared spectra for signatures of PH3 and H2S. ► We find no evidence for either gas in the stratosphere at 0.3 mbar. ► 2-σ upper limits on abundance are 1 ppb (PH3) and 330 ppb (H2S). ► These gases may still be present at lower levels, released from clathrate hydrates.