Dr. Harrington and colleagues are developing a linked series of 3D hydrodynamic and chemical models for the impact, plume blowout, and plume flight/splash phases of the Shoemaker-Levy 9 (SL9) events. These models include tracer particles, whose temperature (T) and pressure (p) histories will drive chemical and grain models. Chemical and grain results will be re-inserted into the splash model to calculate realistic light curves and impact-site images. A prior grant (Phase 1) has been focused on impact modeling, and the first of several papers is in publication. This award will be used for modeling the blowout and plume flight/splash phases, and to perform preliminary chemical modeling. Spectroscopic (and more chemical) modeling is contemplated for future work, so the current models calculate the necessary data to drive those models.
With this award, Dr. Harrington and his colleagues will create the first self-consistent, observationally-constrained model of a large impact and its aftermath. The model is required for full interpretation of the puzzling SL9 data, and will yield basic information about Jupiter's atmosphere and comet composition. Several investigations will be carried out with the models, which run on a cluster supercomputer constructed with a prior award. The models will test theories for the expanding rings seen by the Hubble Space Telescope. Each theory depends on different fundamental Jovian parameters, some unmeasured, such as an elevated oxygen abundance. The composite model will distinguish among the competing theories by replicating each one's physics and determining whether it both couples to the impact energy and produces synthetic images that match the HST observations. These researchers will adjust the viscosity in the splash model until the outer part of the plume re-entry shock matches the expanding infrared rings. The project will test the hypothesis that the plumes had a strong density enhancement at their maximum velocity that produced the expanding infrared rings and the third precursor and flare in the infrared light curves. This vanguard makes stronger re-entry shocks, which increase the damage a given-sized terrestrial impactor could produce. Existing SL9 chemical models only do a moderate job of matching observations, particularly for sulfur: models produce oxidized sulfur (and carbon), but only reduced sulfur was observed. With realistic T and p histories (including multiple shocks) driving the models, the researchers expect to improve the match to data dramatically. They will address whether a comet with heterogeneous composition is required to produce the sulfur results. Models run with Saturnian conditions will make predictions that may aid Cassini data interpretation and will determine whether Earth-based observers should have seen evidence of such frequent impacts.
This is the first observationally-constrained 3D radiative-hydrodynamic-chemical model of all phases of a cometary impact. The models and model grids will be archived with the Planetary Data System so that they will be quickly available for use in planning observations of the next impact, be it 10 or 500 years from now. The models will make predictions for Cassini. Several observers hold SL9 main event spectra that they cannot interpret. A model of this sophistication is required to drive a line-by-line, slant-path radiative transfer code to produce synthetic spectra for comparison to observations; this task is contemplated for a follow-on proposal. Since this is the only ongoing atmospheric SL9 modeling effort, it is important if the significant remaining puzzles are to be solved. Public interest in impacts is high, so results will appear in both the scientific literature and in popular science magazines. ***
