Learning from SL9: Realistic Modeling, Phase 2

AST 0606809 harringtondr。哈林顿和他的同事正在为苏梅克-列维9号（SL9）事件的撞击、羽流喷出和羽流飞行/飞溅阶段开发一系列三维流体动力学和化学模型。这些模型包括示踪粒子，其温度(T)和压力(p)历史将驱动化学和颗粒模型。化学和颗粒结果将被重新插入到飞溅模型中，以计算真实的光曲线和撞击点图像。先前的一笔拨款（第一阶段）集中在影响建模上，几篇论文中的第一篇已经发表。该合同将用于模拟井喷和羽流飞行/飞溅阶段，并执行初步的化学建模。光谱学（以及更多的化学）建模将用于未来的工作，因此目前的模型计算驱动这些模型所需的数据。有了这个奖项，哈林顿博士和他的同事们将创建第一个自一致的、受观测约束的大撞击及其后果模型。该模型需要全面解释令人费解的SL9数据，并将提供有关木星大气和彗星组成的基本信息。这些模型将在一台由事先拨款建造的集群超级计算机上运行，并将进行几项研究。这些模型将检验哈勃太空望远镜观测到的膨胀环的理论。每一种理论都依赖于不同的木星基本参数，有些是无法测量的，比如氧丰度的升高。复合模型将通过复制每一个理论的物理特性，并确定它是否都与撞击能量相耦合，并产生与HST观测相匹配的合成图像，从而区分出相互竞争的理论。这些研究人员将调整飞溅模型中的粘度，直到羽流再入冲击的外部部分与膨胀的红外环相匹配。该项目将验证这样一个假设，即羽流在其最大速度下密度增强，从而产生膨胀的红外环，以及红外光曲线上的第三个前体和耀斑。这个先锋队制造了更强的重返冲击，这增加了给定尺寸的地面撞击可能产生的伤害。现有的SL9化学模型只能适度地匹配观测值，特别是对于硫：模型产生氧化硫（和碳），但只观察到还原硫。有了真实的T和p历史（包括多次冲击）驱动模型，研究人员希望显著改善与数据的匹配。他们将讨论是否需要一颗具有异质成分的彗星来产生硫的结果。在土星条件下运行的模型将做出预测，这可能有助于卡西尼号数据的解释，并将确定地球上的观测者是否应该看到如此频繁撞击的证据。这是第一个观测受限的彗星撞击所有阶段的三维辐射-流体动力学-化学模型。这些模型和模型网格将与行星数据系统一起存档，以便能够迅速地用于规划下一次撞击的观测，无论是10年还是500年后。这些模型将对卡西尼号进行预测。一些观测者持有无法解释的SL9主事件光谱。需要这种复杂的模型来驱动逐行倾斜路径辐射传输代码，以产生与观测结果比较的合成光谱；这项任务将作为后续提案加以考虑。由于这是唯一正在进行的大气SL9建模工作，因此如果要解决剩余的重要难题，这一点很重要。公众对影响的兴趣很高，因此结果将出现在科学文献和大众科学杂志上

AST 0606809HarringtonDr. 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.***