The collision of comet Shoemaker‐Levy 9 with Jupiter: Detection and evolution of HCN in the stratosphere of the planet

We report submillimeter heterodyne observations of Jupiter taken with the JCMT during and after the infall of Comet Shoemaker‐Levy 9 into the planet. We detected the J = 4 ‐ 3 and J = 3 ‐ 2 rotational transitions of HCN in emission at many of the impact sites. Measurements suggest for fragment G a mixing ratio of ∼ 5 × 10 −8 above the 0.5‐mbar pressure level and a total HCN mass of 6 × 10 11 g. Subsequent observations, made in September and November 1994, reveal that HCN is still present but that the lines now appear in absorption. This results from a cooling of the stratospheric thermal profile between July and September. Chemical implications of the observed persistence of HCN in the Jovian stratosphere for over 6 months are discussed.