Matching Items (5)
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- All Subjects: astrobiology
- All Subjects: stellar evolution
- Creators: Desch, Steven
- Status: Published
Description
As the detection of planets become commonplace around our neighboring stars, scientists can now begin exploring their possible properties and habitability. Using statistical analysis I determine a true range of elemental compositions amongst local stars and how this variation could affect possible planetary systems. Through calculating and analyzing the variation in elemental abundances of nearby stars, the actual range in stellar abundances can be determined using statistical methods. This research emphasizes the diversity of stellar elemental abundances and how that could affect the environment from which planets form. An intrinsic variation has been found to exist for almost all of the elements studied by most abundance-finding groups. Specifically, this research determines abundances for a set of 458 F, G, and K stars from spectroscopic planet hunting surveys for 27 elements, including: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, and Hf. Abundances of the elements in many known exosolar planet host stars are calculated for the purpose investigating new ways to visualize how stellar abundances could affect planetary systems, planetary formation, and mineralogy. I explore the Mg/Si and C/O ratios as well as place these abundances on ternary diagrams with Fe. Lastly, I emphasize the unusual stellar abundance of τ Ceti. τ Ceti is measured to have 5 planets of Super-Earth masses orbiting in near habitable zone distances. Spectroscopic analysis finds that the Mg/Si ratio is extremely high (~2) for this star, which could lead to alterations in planetary properties. τ Ceti's low metallicity and oxygen abundance account for a change in the location of the traditional habitable zone, which helps clarify a new definition of habitable planets.
ContributorsPagano, Michael (Author) / Young, Patrick (Thesis advisor) / Shim, Sang-Heon (Committee member) / Patience, Jennifer (Committee member) / Desch, Steven (Committee member) / Anbar, Ariel (Committee member) / Arizona State University (Publisher)
Created2014
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 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.
ContributorsAllu Peddinti, Divya (Author) / McNamara, Allen Keith (Thesis advisor) / Garnero, Edward (Committee member) / Desch, Steven (Committee member) / Zolotov, Mikhail (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2017
Description
Stellar mass loss has a high impact on the overall evolution of a star. The amount<br/>of mass lost during a star’s lifetime dictates which remnant will be left behind and how<br/>the circumstellar environment will be affected. Several rates of mass loss have been<br/>proposed for use in stellar evolution codes, yielding discrepant results from codes using<br/>different rates. In this paper, I compare the effect of varying the mass loss rate in the<br/>stellar evolution code TYCHO on the initial-final mass relation. I computed four sets of<br/>models with varying mass loss rates and metallicities. Due to a large number of models<br/>reaching the luminous blue variable stage, only the two lower metallicity groups were<br/>considered. Their mass loss was analyzed using Python. Luminosity, temperature, and<br/>radius were also compared. The initial-final mass relation plots showed that in the 1/10<br/>solar metallicity case, reducing the mass loss rate tended to increase the dependence of final mass on initial mass. The limited nature of these results implies a need for further study into the effects of using different mass loss rates in the code TYCHO.
ContributorsAuchterlonie, Lauren (Author) / Young, Patrick (Thesis director) / Shkolnik, Evgenya (Committee member) / Starrfield, Sumner (Committee member) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
I present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially habitable exoplanets. The main grid is composed of 904 tracks, for 0.5-1.2 M_sol at scaled metallicity values of 0.1-1.5 Z_sol and specific elemental abundance ratio values of 0.44-2.28 O/Fe_sol, 0.58-1.72 C/Fe_sol, 0.54-1.84 Mg/Fe_sol, and 0.5-2.0 Ne/Fe_sol. The catalog includes a small grid of late stage evolutionary tracks (25 models), as well as a grid of M-dwarf stars for 0.1-0.45 M_sol (856 models). The time-dependent habitable zone evolution is calculated for each track, and is strongly dependent on stellar mass, effective temperature, and luminosity parameterizations. I have also developed a subroutine for the stellar evolution code TYCHO that implements a minimalist coupled model for estimating changes in the stellar X-ray luminosity, mass loss, rotational velocity, and magnetic activity over time; to test the utility of the updated code, I created a small grid (9 models) for solar-mass stars, with variations in rotational velocity and scaled metallicity. Including this kind of information in the catalog will ultimately allow for a more robust consideration of the long-term conditions that orbiting planets may experience.
In order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. It is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. This catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars.
In order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. It is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. This catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars.
ContributorsTruitt, Amanda Rosendall (Author) / Young, Patrick (Thesis advisor) / Anbar, Ariel (Committee member) / Desch, Steven (Committee member) / Patience, Jennifer (Committee member) / Shkolnik, Evgenya (Committee member) / Arizona State University (Publisher)
Created2017
Description
This project focuses on using Neutral Gas and Ion Mass Spectrometer (NGIMS) density data for carbon dioxide, oxygen, carbon monoxide, and nitrogen during deep dip campaigns 5, 6, and 8. Density profiles obtained from NGIMS were plotted against simulated density profiles from the Mars Global Ionosphere-Thermosphere Model (MGITM). Averaged temperature profiles were also plotted for the three deep dip campaigns, using NGIMS data and MGITM output. MGITM was also used as a tool to uncover potential heat balance terms needed to reproduce the mean density and temperature profiles measured by NGIMS.
This method of using NGIMS data as a validation tool for MGITM simulations has been tested previously using dayside data from deep dip campaigns 2 and 8. In those cases, MGITM was able to accurately reproduce the measured density and temperature profiles; however, in the deep dip 5 and 6 campaigns, the results are not quite the same, due to the highly variable nature of the nightside thermosphere. MGITM was able to fairly accurately reproduce the density and temperature profiles for deep dip 5, but the deep dip 6 model output showed unexpected significant variation. The deep dip 6 results reveal possible changes to be made to MGITM to more accurately reflect the observed structure of the nighttime thermosphere. In particular, upgrading the model to incorporate a suitable gravity wave parameterization should better capture the role of global winds in maintaining the nighttime thermospheric structure.
This project reveals that there still exist many unknowns about the structure and dynamics of the night side of the Martian atmosphere, as well as significant diurnal variations in density. Further study is needed to uncover these unknowns and their role in atmospheric mass loss.
This method of using NGIMS data as a validation tool for MGITM simulations has been tested previously using dayside data from deep dip campaigns 2 and 8. In those cases, MGITM was able to accurately reproduce the measured density and temperature profiles; however, in the deep dip 5 and 6 campaigns, the results are not quite the same, due to the highly variable nature of the nightside thermosphere. MGITM was able to fairly accurately reproduce the density and temperature profiles for deep dip 5, but the deep dip 6 model output showed unexpected significant variation. The deep dip 6 results reveal possible changes to be made to MGITM to more accurately reflect the observed structure of the nighttime thermosphere. In particular, upgrading the model to incorporate a suitable gravity wave parameterization should better capture the role of global winds in maintaining the nighttime thermospheric structure.
This project reveals that there still exist many unknowns about the structure and dynamics of the night side of the Martian atmosphere, as well as significant diurnal variations in density. Further study is needed to uncover these unknowns and their role in atmospheric mass loss.
ContributorsRobinson, Jenna (Author) / Desch, Steven (Thesis director) / Hervig, Richard (Committee member) / School of Earth and Space Exploration (Contributor) / School for the Future of Innovation in Society (Contributor) / School of International Letters and Cultures (Contributor) / Barrett, The Honors College (Contributor)
Created2019-05