Ion and neutral mass spectrometry of the isotopic composition of Titan's upper atmosphere: Implications for the atmospheric dynamics and photochemistry, and the evolution of the major species over geological time scales

dc.contributor.advisorShipley, Heather
dc.contributor.advisorWaite, Jack H.
dc.contributor.authorMandt, Kathleen E.
dc.contributor.committeeMemberMousis, Olivier
dc.contributor.committeeMemberYoung, David
dc.contributor.committeeMemberSharif, Hatim
dc.date.accessioned2024-02-12T15:39:57Z
dc.date.available2024-02-12T15:39:57Z
dc.date.issued2012
dc.descriptionThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.
dc.description.abstractThe atmosphere of Titan, Saturn's largest moon, is an analog for the Earth's atmosphere in the distant past when life first emerged, and may also be used to study the distant future when the abundance of water in the atmosphere may be reduced by photochemical loss processes associated with climate change. This Dissertation investigates the evolution of Titan's atmosphere utilizing measurements of the stable isotope ratios in molecular nitrogen and methane. The Cassini Ion Neutral Mass Spectrometer (INMS) measures the composition of the ionosphere and neutral atmosphere as it flies through the atmosphere, approaching altitudes as low as 950 km above the surface. INMS measurements of the <super>14</super>N/<super>15</super>N in N<sub>2</sub> as a function of altitude for 30 Titan flybys are compared, using a basic diffusion model, to the Huygens Gas Chromatograph Mass Spectrometer (GCMS) measurement of the <super>14</super>N/<super>15</super>N in N<sub>2</sub> on the surface. This comparison provides the input parameters needed to extrapolate the INMS measurements of <super>12</super>C/<super>13</super>C in CH<sub>4</sub> from the upper atmosphere to the surface where the ratio is within the range of expected primordial values. Although the <super>12</super>C/<super>13</super>C at Titan is close to the primordial value, escape and photochemistry fractionate the isotope ratio over time. This suggests that methane has been present in Titan's atmosphere for no more than one billion years. A cross-calibration of INMS ion densities with the electron densities measured by the Cassini Radio Plasma Wave Spectrometer (RPWS) constrains the energy response of INMS and provides a new approach for determining the densities of ions in Titan's ionosphere. These ion densities validate an updated coupled Ion-Neutral-Thermal model that constrains the fractionation of the nitrogen isotopes due to photochemistry. Modeling the evolution of the nitrogen isotopes over geological times scales based on chemistry and escape limits the initial <super>14</super>N/<super>15</super>N to a heavier ratio than the <super>14</super>N/<super>15</super>N observed in the Earth's atmosphere. The methodologies developed for this Dissertation are relevant not only to Titan, but also to Earth. They can be used to evaluate dynamics and photochemistry of the nitrogen isotopes in the upper atmosphere and to define future missions to study the composition of the Earth's thermosphere.
dc.description.departmentCivil and Environmental Engineering
dc.format.extent296 pages
dc.format.mimetypeapplication/pdf
dc.identifier.isbn9781267343956
dc.identifier.urihttps://hdl.handle.net/20.500.12588/4518
dc.languageen
dc.subjectAtmospheric evolution
dc.subjectMass Spectrometry
dc.subjectTitan
dc.subject.classificationAtmospheric sciences
dc.subject.classificationAtmospheric chemistry
dc.subject.classificationEnvironmental science
dc.titleIon and neutral mass spectrometry of the isotopic composition of Titan's upper atmosphere: Implications for the atmospheric dynamics and photochemistry, and the evolution of the major species over geological time scales
dc.typeThesis
dc.type.dcmiText
dcterms.accessRightspq_closed
thesis.degree.departmentCivil and Environmental Engineering
thesis.degree.grantorUniversity of Texas at San Antonio
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy

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