Diatomic Sulfur in Jupiter Family Comets
The first astronomical detection of diatomic sulfur (S2) was in comet IRAS-Araki-Alcock in 1983 using the IUE satellite (A’Hearn et al. 1983) and it has since been remotely detected in 3 other comets. All four remote S2 detections have come from objects originating from the Oort cloud, and the only detection in an object originating from the Kuiper Belt was taken in situ by the Rosetta mass spectrometer at 67P/Churyumov-Gerasimenko (Calmonte et al. 2016). As many compositional differences have been observed between Kuiper Belt and Oort Cloud objects, there is no compelling reason to assume that S2 ought to be present in similar abundances in both populations. Observations of three Jupiter Family Comets (252P/LINEAR, 45P/Honda–Mrkos–Pajdušáková and 46P/Wirtanen) were conducted using the DeVeny Spectrograph on the Lowell Discovery Telescope (formerly the Discovery Channel Telescope) between 2016 and 2018, ranging from 3000 to 4000 Å. Geocentric distances were all under 0.1 AU, yielding a spatial resolution on the order of 60 km/arcsec. S2 is believed to sublimate directly from the surface of the nucleus, and the short lifetime (approximately 450 seconds) prior to photodissociation means that high spatial resolution, and thus a very low geocentric distance, is needed to search for the molecule. The observing geometry is therefore relatively rare, and another similar opportunity will not present itself for nearly another decade. Preliminary results indicate the presence of several unexplained emission features in the spectra of both 46P and 252P. Work is ongoing to ascertain whether those features match those expected by the fluorescence model (Reylé and Boice, 2003) or if another yet-unidentified molecule has been detected.
This work is supported by NASA’s Solar System Observations Program grant 80NSSC18K0856 and the Marcus Cometary Research Fund.