Isotopic evolution during Earth-Moon formation and general circulation in Jupiter's middle atmosphere
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Isotopic evolution during Earth-Moon formation and general circulation in Jupiter's middle atmosphere


This thesis is constructed around two distinct topics. The first is the formation history of the Earth and the Moon. The hafnium/tungsten (Hf/W) isotopic system can act as a chronometer for planets forming in the early solar system. To study possible planetary formation scenarios, I model the isotopic evolution of planetary embryos as they form rocky planets during collisions in N-body simulations. In Chapter 2, I show that the fast accretion timescales of the Grand Tack scenario require highly efficient re-equilibration of W to produce an Earth with observed mantle W isotope anomaly (excess of radiogenic tungsten compared to non-radiogenic). Such a high level of re-equilibration is not supported by fluid dynamic experiments, and this result suggests the Grand Tack scenario builds the Earth too quickly. The Earth and Moon share a very similar isotopic fingerprint: many chemical isotopes found in lunar rocks are nearly identical to ones found on Earth. It is particularly interesting that they also share a near-identical W isotope anomaly, because simply starting from similar material is not sufficient. This system evolves depending on the collision history of bodies, so the Earth and Moon sharing W isotopic values require an explanation. The canonical model of the Moon formation holds that it is mostly made up of material from Theia, the impactor into Earth. In Chapter 3, I apply the isotopic evolution model to the canonical Earth-Moon impact formation scenario. Using 242 N-body simulation results, I demonstrate the likelihood of forming an Earth and Moon with near-identical W isotope anomaly is less than 5%. This suggests that an alternate explanation for forming the Moon with Earth material may be necessary to explain the similarity in W isotope anomaly. The second topic is understanding the temperature, zonal wind, and general circulation that occurs in the middle atmosphere of Jupiter. The Voyager and Cassini spacecraft, along with many ground-based telescopic observations, have provided zonally averaged distributions of temperature, gaseous species, and haze particles in Jupiter’s upper troposphere and stratosphere. Measurements of wind speed are derived from cloud movement near the 0.5 – 1 bar pressure level, but we have no measurements of circulation in the stratosphere. Historical models of this region have used 2D linearized equations of motion and simple radiative calculations. In Chapter 4, I present a state-of-the-art 2D dynamical model of Jupiter’s middle atmosphere with realistic radiative transfer. A dynamical model with a simple frictional drag force, representing eddy forces that damp the mean zonal wind, is able to reproduce some of the small latitudinal temperature variations seen on Jupiter. However, none of the models tested were able to produce strong >5 K variations observed in the low-to-mid latitudes between 1 – 500 mbar. This suggests that localized wave forcing plays a dominant role in shaping the temperature distribution in the middle atmosphere of Jupiter. I also show that polar temperatures are strongly dependant on the chosen optical properties of stratospheric haze, and further work constraining haze opacity is needed to accurately model heating and cooling at the poles.

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