Matching Items (5)

Self-Compression of Ceres-like Bodies Composed of Hydrated Silicates

Description

We model the self-compression of homogeneous, undifferentiated, Ceres-like bodies composed of various minerals and mineral-composites: antigorite, brucite, dolomite, lizardite and magnesite, plus mixtures which were the above minerals mixed with

We model the self-compression of homogeneous, undifferentiated, Ceres-like bodies composed of various minerals and mineral-composites: antigorite, brucite, dolomite, lizardite and magnesite, plus mixtures which were the above minerals mixed with ice Ih. All of the modeled clay/ice bodies had a final radius within 1% of RCeres, an average final density of ~2083 kg m-3 and central pressures of ~133 MPa. The smallest radius was from magnesite, which had a final compressed radius of ~0.88 RCeres, central pressure of ~212 MPa and final density of ~2955 kg m-3. The most significant change in radius was due to the zero-pressure density as the highest densities created the highest force of gravity and produced the smallest radii, yet zero-pressure densities that matched Ceres produced 0.99 RCeres bodies. It was found that the addition of ice, anywhere from 9.1-19.1%, did not affect the body a measurable amount as the inclusion of ice resulted in a lower density creating a lower force of gravity, decreased central pressure and less overall compression. Models that closely resembled Ceres had internal pressures of 133 MPa, which is not enough pressure to induce pore collapse or produce drastic changes due to K and K'. Porosity and the addition of ice in Ceres-like bodies is possible and cannot be ignored when using more complicated modeling techniques. Each mineral and mineral-composite produced unique overall results which allowed us to compare each mineral to Ceres, understand how it has compressed over time and how objects of such a size are affected by compression. Due to the small size, low force of gravity and high bulk moduli of the given minerals, Ceres-like bodies do not compress a considerable amount if they are in fact composed of hydrated silicates.

Contributors

Agent

Created

Date Created
  • 2015-12

Systematics of giant impacts in late-stage planet formation and active neutron experiments on the surface of Mars

Description

Part I – I analyze a database of Smoothed Particle Hydrodynamics (SPH) simulations of collisions between planetary bodies and use the data to define semi-empirical models that reproduce remant masses.

Part I – I analyze a database of Smoothed Particle Hydrodynamics (SPH) simulations of collisions between planetary bodies and use the data to define semi-empirical models that reproduce remant masses. These models may be leveraged when detailed, time-dependent aspects of the collision are not paramount, but analytical intuition or a rapid solution is required, e.g. in ‘N-body simulations’. I find that the stratification of the planet is a non-negligible control on accretion efficiency. I also show that the absolute scale (total mass) of the collision may affect the accretion efficiency, with larger bodies more efficiently disrupting, as a function of gravitational binding energy. This is potentially due to impact velocities above the sound speed. The interplay of these dependencies implies that planet formation, depending on the dynamical environment, may be separated into stages marked by differentiation and the growth of planets more massive than the Moon.

Part II – I examine time-resolved neutron data from the Dynamic Albedo of Neutrons (DAN) instrument on the Mars Science Laboratory (MSL) Curiosity rover. I personally and independently developed a data analysis routine (described in the supplementary material in Chapter 2) that utilizes spectra from Monte Carlo N-Particle Transport models of the experiment and the Markov-chain Monte Carlo method to estimate bulk soil/rock properties. The method also identifies cross-correlation and degeneracies. I use data from two measurement campaigns that I targeted during remote operations at ASU. I find that alteration zones of a sandstone unit in Gale crater are markedly elevated in H content from the parent rock, consistent with the presence of amorphous silica. I posit that these deposits were formed by the most recent aqueous alteration events in the crater, since subsequent events would have produced matured forms of silica that were not observed. I also find that active dunes in Gale crater contain minimal water and I developed a Monte Carlo phase analysis routine to understand the amorphous materials in the dunes.

Contributors

Agent

Created

Date Created
  • 2019

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Investigation into the geodynamics of planetary ice-ocean systems: application to Jupiter's icy moon Europa

Description

The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with

The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with distinct surface composition suggests past/present geophysical activity with implications for habitability. In this body of work, I propose a hypothesis for material transport from the ocean towards the surface via a convecting ice-shell. Geodynamical modeling is used to perform numerical experiments on a two-phase water-ice system to test the hypotheses. From these models, I conclude that it is possible for trace oceanic chemistry, entrapped into the newly forming ice at the ice-ocean phase interface, to reach near-surface. This new ice is advected across the ice-shell and towards the surface affirming a dynamical possibility for material transport across the ice-ocean system, of significance to astrobiological prospecting. Next, I use these self-consistent ice-ocean models to study the thickening of ice-shell over time. Europa is subject to the immense gravity field of Jupiter that generates tidal heating within the moon. Analysis of cases with uniform and localized internal tidal heating reveal that as the ice-shell grows from a warm initial ocean, there is an increase in the size of convection cells which causes a dramatic increase in the growth rate of the ice-shell. Addition of sufficient amount of heat also results in an ice-shell at an equilibrium thickness. Localization of tidal heating as a function of viscosity controls the equilibrium thickness. These models are then used to understand how compositional heterogeneity can be created in a growing ice-shell. Impurities (e.g. salts on the surface) that enter the ice-shell get trapped in the thickening ice-shell by freezing. I show the distribution pattern of heterogeneities that can form within the ice-shell at different times. This may be of potential application in identifying the longevity and mobility of brine pockets in Europa's ice-shell which are thought to be potential habitable niches.

Contributors

Agent

Created

Date Created
  • 2017

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Shock metamorphism in ordinary chondrites: constraining pressure and temperature history

Description

Shock metamorphism in meteorites constrains the impact histories of asteroids and planets. Shock-induced high-pressure (HP) minerals can provide more precise estimates of shock conditions than shock-induced deformation effects. In this

Shock metamorphism in meteorites constrains the impact histories of asteroids and planets. Shock-induced high-pressure (HP) minerals can provide more precise estimates of shock conditions than shock-induced deformation effects. In this research, I use shock features, particularly HP minerals, in ordinary-chondrite samples to constrain not only shock pressures but also the pressure-temperature-time (P-T-t) paths they experienced.

Highly shocked L5/6 chondrites Acfer 040, Mbale, NWA 091 and Chico and LL6 chondrite NWA 757 were used to investigate a variety of shock pressures and post-shock annealing histories. NWA 757 is the only highly shocked LL chondrite that includes abundant HP minerals. The assemblage of ringwoodite and majoritic garnet indicates an equilibration shock pressure of ~20 GPa, similar to many strongly shocked L chondrites. Acfer 040 is one of the only two chondrite samples with bridgmanite (silicate perovskite), suggesting equilibration pressure >25 GPa. The bridgmanite, which is unstable at low-pressure, was mostly vitrified during post-shock cooling. Mbale demonstrates an example of elevated post-shock temperature resulting in back-transformation of ringwoodite to olivine. In contrast, majoritic garnet in Mbale survives as unambiguous evidence of strong shock. In these two samples, HP minerals are exclusively associated with shock melt, indicating that elevated shock temperatures are required for rapid mineral transformations during the transient shock pulse. However, elevated post-shock temperatures can destroy HP minerals: in temperature sequence from bridgmanite to ringwoodite then garnet. NWA 091 and Chico are impact melt breccias with pervasive melting, blackening of silicates, recrystallization of host rock but no HP minerals. These features indicate near whole-rock-melting conditions. However, the elevated post-shock temperatures of these samples has annealed out HP signatures. The observed shock features result from a complex P-T-t path and may not directly reflect the peak shock pressure. Although HP minerals provide robust evidence of high pressure, their occurrence also requires high shock temperatures and rapid cooling during the shock pulse. The most highly shocked samples lack HP signatures but have abundant high-temperature features formed after pressure release.

Contributors

Agent

Created

Date Created
  • 2016

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Trans-Neptunian and exosolar satellites and dust: dynamics and surface effects

Description

Solar system orbital dynamics can offer unique challenges. Impacts of interplanetary dust particles can significantly alter the surfaces of icy satellites and minor planets. Impact heating from these particles can

Solar system orbital dynamics can offer unique challenges. Impacts of interplanetary dust particles can significantly alter the surfaces of icy satellites and minor planets. Impact heating from these particles can anneal away radiation damage to the crystalline structure of surface water ice. This effect is enhanced by gravitational focusing for giant planet satellites. In addition, impacts of interplanetary dust particles on the small satellites of the Pluto system can eject into the system significant amounts of secondary intra-satellite dust. This dust is primarily swept up by Pluto and Charon, and could explain the observed albedo features on Pluto's surface. In addition to Pluto, a large fraction of trans-neptunian objects (TNOs) are binary or multiple systems. The mutual orbits of these TNO binaries can range from very wide (periods of several years) to near-contact systems (less than a day period). No single formation mechanism can explain this distribution. However, if the systems generally formed wide, a combination of solar and body tides (commonly called Kozai Cycles-Tidal Friction, KCTF) can cause most systems to tighten sufficiently to explain the observed distributions. This KCTF process can also be used to describe the orbital evolution of a terrestrial-class exoplanet after being captured as a satellite of a habitable-zone giant exoplanet. The resulting exomoon would be both potentially habitable and potenially detectable in the full Kepler data set.

Contributors

Agent

Created

Date Created
  • 2013