Search for sulfur-bearing species as remnant of cometary impact on Neptune

We present the results of CS, OCS, H2CS, H2S, SO, C3S and SO2 observations in Neptune׳s stratosphere performed in 2010 and 2013 with the Atacama Sub-millimeter Telescope Experiment 10-m telescope in submillimeter wavebands. Several authors have suggested that CO in Neptune׳s stratosphere has an external origin and may be due to a previous large cometary impact. To investigate the effects of such impacts, we have conducted new observations to search for various sulfur-bearing species, which are possible remnant gases from the impacts. The CS molecule was likely to be found because CS was observed in Jupiter׳s stratosphere at least five years after the cometary impact event that occurred in 1994. No sulfur-bearing species was clearly detected in Neptune׳s upper stratosphere, and their upper limit abundances relative to oxygen were lower than that of both Jupiter׳s atmosphere observed after the SL9 event and small solar system bodies. From the cometary origin viewpoint, the depletion of sulfur-bearing species found here may be due to their removal from the gas phase by processes such as condensation.