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

Abstract

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 × 1011g. 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.