Large impact events and atmospheric evolution on the terrestrial planets.

Persistent Link:
http://hdl.handle.net/10150/184649
Title:
Large impact events and atmospheric evolution on the terrestrial planets.
Author:
Grinspoon, David Harry.
Issue Date:
1989
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
This dissertation is an exploration of the effects of the collision of large asteroids and comets on the atmosphere of the Earth and Earthlike planets. The first task undertaken is the characterization of the impact rates in the inner solar system during the present time, and during the first billion years of Solar System history when the flux was changing rapidly. Once defined, these fluxes are used to model the long term cumulative effect of multiple impacts on planetary atmospheres. The implications of cometary impacts on evolution of the water and deuterium abundances on Venus are examined. The short lifetime of water on Venus suggests that the water abundance is in a quasi-steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. Results are presented of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D/H ratio. The stochastic variability of each of these quantities is shown to be large. Water on Venus is likely to be in a near steady state mediated by large comet impacts. The early history of water on the planet has been obscured by a history of random impacts. A study of the effects of impact-generated dust clouds on the primitive Earth leads to the conclusion that such clouds were significant perturbers of the early climate. The Earth was shrouded by an optically-thick dust cloud for ≈ 150-250 m.y. During this time the surface temperature was equal to the planetary equilibrium temperature unless significant heating by impacts or surface heat flow existed beneath the dust cloud. An admixture of a few per cent of organic materials in the cloud may have significantly lowered the planetary bond albedo, thereby raising the equilibrium temperature. The epoch of continuous dust shrouding was followed by a period of stochastically intermittent dust clouds occuring at greater intervals as the early intense bombardment subsided towards the present day flux.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Planets -- Atmospheres.; Meteorites.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Planetary Sciences; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Lewis, John S.

Full metadata record

DC FieldValue Language
dc.language.isoenen_US
dc.titleLarge impact events and atmospheric evolution on the terrestrial planets.en_US
dc.creatorGrinspoon, David Harry.en_US
dc.contributor.authorGrinspoon, David Harry.en_US
dc.date.issued1989en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThis dissertation is an exploration of the effects of the collision of large asteroids and comets on the atmosphere of the Earth and Earthlike planets. The first task undertaken is the characterization of the impact rates in the inner solar system during the present time, and during the first billion years of Solar System history when the flux was changing rapidly. Once defined, these fluxes are used to model the long term cumulative effect of multiple impacts on planetary atmospheres. The implications of cometary impacts on evolution of the water and deuterium abundances on Venus are examined. The short lifetime of water on Venus suggests that the water abundance is in a quasi-steady-state balance between loss by escape and replenishment by infall. In addition, the observed deuterium-to-hydrogen ratio on Venus is consistent with a steady state and does not necessarily imply a past water excess. Results are presented of a model incorporating a stochastic cometary source and nonthermal escape of hydrogen that produces the observed water abundance and D/H ratio. The stochastic variability of each of these quantities is shown to be large. Water on Venus is likely to be in a near steady state mediated by large comet impacts. The early history of water on the planet has been obscured by a history of random impacts. A study of the effects of impact-generated dust clouds on the primitive Earth leads to the conclusion that such clouds were significant perturbers of the early climate. The Earth was shrouded by an optically-thick dust cloud for ≈ 150-250 m.y. During this time the surface temperature was equal to the planetary equilibrium temperature unless significant heating by impacts or surface heat flow existed beneath the dust cloud. An admixture of a few per cent of organic materials in the cloud may have significantly lowered the planetary bond albedo, thereby raising the equilibrium temperature. The epoch of continuous dust shrouding was followed by a period of stochastically intermittent dust clouds occuring at greater intervals as the early intense bombardment subsided towards the present day flux.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectPlanets -- Atmospheres.en_US
dc.subjectMeteorites.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePlanetary Sciencesen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorLewis, John S.en_US
dc.contributor.committeememberHubbard, Williamen_US
dc.contributor.committeememberStrom, Robert G.en_US
dc.contributor.committeememberMiller, Walter B.en_US
dc.contributor.committeememberVemulapalli, Krishnaen_US
dc.identifier.proquest8915959en_US
dc.identifier.oclc702151433en_US
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