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Planetary Science Seminar - spring-2024

Partitioning Coefficient of Ar in H2-H2O via Ab Initio Calculations

May 2, 2024
noon - 1 p.m.
Slichter Hall 3853

Presented By:

  • Bing Hong Chua - EPSS, UCLA
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In the recent decadal survey by the National Academy of Sciences, a Uranus Orbiter and Probe (UOP) is identified to be of top priority. One of the key science objectives is to determine the interior of the planet. To this effort, the ice:rock ratio remains a parameter yet to be determined. In theory, radioactive decay of potassium in a silicate interior produces Argon-40. If transported efficiently through the silicate core, across the middle ice-rich layer and into the hydrogen-rich atmosphere, a mass spectrometer (planned to be on board the UOP) will be able to detect Ar-40 concentrations. However, many questions still remain regarding the transport processes. In our work, we aim to investigate the partition coefficient of Ar between H2 and H2O to determine whether it preferentially moves into the hydrogen-rich atmosphere or remains in the ice-rich layer via ab initio molecular dynamics simulations. Three methods have been attempted with varying rates of success, and continuing work will be discussed. The results from this work will either support or undermine the possibility of utilizing Ar-40 measurements to shed light on the possibility of a silicate interior and constraints on the bulk silicate composition of the planet.

Modeling Mars Paleoclimate with a Topography Focused Approach

May 2, 2024
noon - 1 p.m.
Slichter Hall 3853

Presented By:

  • Max Parks - EPSS, UCLA
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Understanding the historical Martian climate is a crucial step in our exploration of the Red Planet. Orbital mapping indicates that liquid water once flowed across the surface of the Red Planet, but current understanding of the atmospheric mass of ancient Mars would prevent the stability of water in a liquid phase. Ancient Martian liquid water is hypothesized to require at least 1-2 bar of atmosphere, but there is no accepted mechanism for how Mars would have shed that much atmospheric mass. We propose to model a novel paleoclimate for Mars, in which extremely thick ice sheets might concentrate a smaller atmosphere to create local regions on Mars that could sustain liquid water on the surface, addressing the need for higher surface pressure without requiring atmospheric masses incongruous with current estimations of the ancient Martian climate.

Interaction between Channel Development and Thrust Tectonics on Charon

May 9, 2024
noon - 1 p.m.
Geology 4677

Presented By:

  • Hanzhang Chen and Travis Gilmore -
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New Horizons' flyby of the Pluto system revealed various landforms on the surface of Charon. Though a global extension model has been proposed, the observed landscape was not systematically studied. This study adopts geomorphological mapping, landscape filtering, and topography analysis to interpret the geologic evolution history of Charon's northern highlands. Based on the mapping and quantitative analysis, we propose that before global extension, out-of-sequence thrusting and syn-tectonic glaciation may also have shaped the landscape on Charon. We inferred the subsurface structure of the thrusts through fitting surface topography with an elastic dislocation model. The fitting results suggest the thrust dip of 25 to 30 degrees and the elastic thickness of the ice shell to be 30 to 45 km.

Aeolian Sandstone Scour

May 16, 2024
noon - 1 p.m.
3853 Slichter Hall

Presented By:

  • Alana Archbold - EPSS, UCLA
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Aeolian sandstones, known to be quality petroleum reservoir rocks, are partitioned by first-order bounding surfaces. Prior models of aeolian stratigraphy assume first-order bounding surfaces to be planar, however, that is not usually the case in nature. In this work, we model aeolian sandstone using field-realistic measurements that incorporate the stratification type and degree of scour on bounding surfaces. In addition to the model, we will investigate the relationship between scour along a bounding surface and the thickness of a set of cross-strata, as well as the relationship between scour and incidence angle. We use a differential GPS to output the location in space along the bounding surfaces of various outcrops of Jurassic Aeolian Sandstone to measure scour. At each GPS point, we will compare the stratification type with the dip direction to determine the paleo-wind incidence angle. Thus far, there appears to be a modest linear relationship between scour and set thickness when the scour is greater than 0.2 meters. More measurements and stratification data are still necessary for drawing a conclusion on this relationship and incorporating it into the model. We will be using a cellular automaton model called ReSCAL, to recreate our field measurements and observations. The model created will be an updated field-realistic adaptation of aeolian sandstone, and our investigations will be useful in studying paleoenvironments and estimating the distribution of hydrocarbons in these systems.

Diffusivity-Free Turbulence in Laboratory Core Convection Experiments

May 16, 2024
noon - 1 p.m.
3853 Slichter Hall

Presented By:

  • Jewel Abbate - EPSS, UCLA
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Convection in Earth’s liquid iron outer core is predicted to be in a regime of rapidly rotating turbulence. In this regime, the turbulent flow is unaffected by viscous and thermal diffusion, and is thus called “diffusivity-free.” Since theoretical scalings for this regime first arose in the ‘60s, researchers have strived to validate them in laboratory settings. Typical experiments, in which convection is driven by a heat flux through no-slip boundaries, have not been able to achieve this scaling due to the highly diffusive nature of physical boundaries. It has been postulated that diffusive boundary effects can become negligible at extremely high Rayleigh numbers (i.e. very strong buoyancy forcing), which are a challenge to reach in most settings. Here, we explore an alternative method. We show for the first time that diffusivity-free geophysical convective turbulence can be realized in liquid metal laboratory experiments conducted within the so-called oscillatory regime. Oscillatory convection exclusively arises in low Prandtl number fluids (i.e. liquid metals) and is driven entirely by the temperature gradient in the fluid bulk, and is therefore independent of the boundary layers. Achieving the theoretical diffusivity-free scalings in desktop-sized laboratory experiments provides the validation necessary to extrapolate and predict flow parameters in planets and stars.

Electrical and Thermal Conductivity of Iron-enriched Basal Magma Oceans

May 23, 2024
noon - 1 p.m.
3853 Slichter Hall

Presented By:

  • Francis Dragulet - EPSS, UCLA
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The Earth’s earliest magnetic field may have originated in a basal magma ocean, a layer of silicate melt surrounding the core that could have persisted for billions of years. Recent studies show that the electrical conductivity of liquid with a bulk silicate Earth composition exceeds 10,000 S/m at basal magma ocean conditions, surpassing the threshold for dynamo activity. Over most of its history, the basal magma ocean is more enriched in iron than the bulk silicate Earth, due to iron’s incompatibility in the mineral assemblages of the lower mantle. Using ab-initio molecular dynamics calculations, we examine how iron content affects the silicate dynamo hypothesis. We investigate how the electrical conductivity of silicate liquid changes with increasing the iron fraction Fe/(Fe+Mg), up to Super-Earth pressures and temperatures. We also compute the electronic contribution to the thermal conductivity, to evaluate convective instability of basal magma oceans. Finally, we apply our results to model the thermal and magnetic evolution of Earth's basal magma ocean over time.

Thermal and Illumination Environment of Lunar Pits and Caves

May 23, 2024
noon - 1 p.m.
3853 Slichter Hall

Presented By:

  • Tyler Horvath - EPSS, UCLA
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Since their discovery in 2009, lunar collapse pits have been popular candidates for future lunar exploration as they could offer astronauts and their equipment protection from the hazards present on the surface (e.g. micrometeorites, harmful solar radiation, high energy particles, etc.). It has also been theorized that these features yield a more tolerable thermal environment roughly equal to the average surface temperature (~260 K at the equator), opposed to the typical ~300 Kelvin diurnal temperature variation that brings long periods of extreme cold and heat to the surface. However, no formal analysis had been conducted prior to our study. Here we focus on the Mare Tranquillitatis pit, one of the largest known lunar collapse pits with a confirmed overhang that may lead to an extended cave as well as exposed stratigraphy of mare lava flows that may be used to study the Moon's geological history. Using remotely sensed temperatures from the Diviner Lunar Radiometer Experiment and computational thermal models, we are able to understand in great detail the thermal environment of the Mare Tranquillitatis Pit. We importantly find that subsurface voids (i.e. caves) with a collapse pit behave as natural blackbody cavities that are diurnally stable at 17 °C, a result that strongly supports pits and caves as highly desirable environments for long term inhabitants of the lunar surface.