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Project Progress

During this period, NASA Postdoctoral Fellow Dr. Lucas Paganini has initiated a robust means for quantitative detections of sulfur compounds at submillimeter and infrared (IR) wavelengths by means of quantum fluorescence models. These achievements will enable new measurements of the content of hydrogen sulfide in comets. Studies of cometary diversity can be extended significantly by measuring H₂S simultaneously with other parent volatiles (organics, nitriles, and water). This will ultimately enhance our knowledge about the dynamical distribution and evolution of cometary volatiles in the Solar System, and provide further insights on their relation with interstellar ices and/or the protosolar nebula at the time when comets formed.

To this end, NASA scientists Dr. Lucas Paganini (NPP Fellow, PI), Dr. Michael Mumma and Dr. Geronimo Villanueva (Co-I’s); and Dr. Alexandre Faure (Collaborator), Laboratoire d’Astrophysique de Grenoble; were awarded 20 hours observing time with the ESO’s sub-millimeter and far-IR Herschel Space Observatory for their proposed investigation “Analysis of OPR and D/H of hydrogen sulfide in comets: Testing the natal origin and constraining the place of formation of pre-cometary ices in the protoplanetary disk.” (This achievement represents 1 out of 14 proposals around the world awarded (OT1) observation time for Solar System exploration objects with the Herschel Observatory.) This investigation will target cosmogonic parameters in bright comets during the 2011–2012 observation period, through measurements of the nuclear spin temperature in H₂S (via the ortho-para ratio, or OPR) and enrichment of its deuterated isotopologue (HDS). These parameters will constrain the temperature of formation of sulfur species, and will test the role of various processes in their production (e.g., ion-molecule, neutral-neutral gas reactions, and gas-grain heterogeneous chemistry). In addition, simultaneous observation of a water emission line will aid the retrieval of accurate abundances H₂S/H₂O and HDS/H₂O.

In addition to his work on the determination of sulfur content in comets, Dr. Paganini has worked on and improved current analysis tools and pipelines for data processing of infrared observations by our group. He has also collaborated extensively on astronomical observations and presentation in scientific conferences of comet 103P/Hartley 2, the target of NASA’s EPOXI Mission to understand the wide diversity of morphology and topography of cometary nuclei; comet 10P/Tempel 2, and comet C2003/K4 (LINEAR). This collaboration has resulted in two ApJ papers (Mumma et al., 2011; and Meech et al., 2011), and a third publication submitted to Icarus (Paganini et al., 2011).