NSF Award
1945950
The molecule carbon monoxide (CO) is a major large part of the cloud of surrounding material, or coma, around a comet nucleus. Comet activity seen at large distances from the Sun is often caused by CO. The amount of CO can differ by up to 5 times between comets. These large differences in CO can be clues to how the comet formed or how it has changed with time. These investigators will first use a large amount of comet spectra to study the activity of CO in two bright comets - Hale-Bopp and Hyakutake - and update an existing model for CO activity in comets. They will then use this model to learn how CO is made at greater distances from the Sun, and test the model with old and new telescopic observations of comets at different distances, and other objects that are in the outer Solar System. This research serves the national interest by promoting our understanding of what gases are in comets, what the comets' structures are like, and how they formed and changed through their lifetimes. Graduate and undergraduate students at the university where the lead investigator works will be observing, reducing and analyzing the comet spectra.<br/><br/>Carbon monoxide (CO) is a major contributor to comet comae, and often drives the activity of comets beyond 3 AU. Substantial evidence indicates that relative CO abundances can vary by factors of about 5 between comets. This variation could be an important clue to either differences in cometary formation or processing history. Gaseous emission spectra are key to unlocking mysteries of these comets, since super-volatile sublimation drives the observed cometary activity and spectra can be used to put physical and chemical constraints on nucleus models. The investigators will use a large dataset of mm-wavelength spectra of comets already in hand, and obtain new spectra with telescope time that is already secured. The project has three parts: 1) Determine excitation and collisional parameters for comae using maps of CO and other molecular emission in two bright comets (Hale-Bopp and Hyakutake), and a 1D-spherical hybrid kinetic/dusty gas hydrodynamic model. Test the model at larger heliocentric distances with new CO maps of comet 29P/Schwassmann-Wachmann 1 at about 6 AU. 2) Derive new CO production rates using the improved coma model with new data, and recalculate them for comets in the literature. 3) Study the newly-recalculated CO production rates for a group of distantly-active comets to help construct a new model of distantly-active comet nuclei. As part of this last task, the investigators will also compare the CO production rates in two long-period comets and two Centaurs to explore the importance of nucleus size and thermal evolution of CO in outer Solar System objects. Graduate and undergraduate students will be incorporated in the research to be conducted in observing, reducing and analyzing millimeter-wavelength spectroscopy of comets.
