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Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 46 for “"Comets"”.
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Studying Short-Period Comets and Long-Period Comets Detected by WISE/NEOWISE
… the mission, WISE serendipitously observed 160 comets, including 21 newly discovered objects. About 89 of the comets observed by WISE displayed a significant dust tail in the 12 and 22 μm (thermal emission) bands, showing a wide range of activity levels and dust morphology. Since the observed …
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Comets in the near-Earth object population
… NEO population consists of dormant or extinct comets. We identify comet candidates among NEOs using three criteria: the Jovian Tisserand parameter Tj < 3, comet nucleus-like spectral parameters (generally linear spectra which correspond to C, D, or P taxonomic types), and low (<0.075) albedos. …
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Sublimative torques as the origin of bilobate comets
… bilobate, suggesting that some process unique to comets is responsible for the formation of bilobate shapes. We examine a new mechanism for creating bilobate nuclei in Jupiter-family comets (JFCs), in which sublimative torques acting on a comet during its migration through the Centaur region spin …
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New Molecular Probes of Astronomical Sources (Interstellar Sources, Comets)
Three molecules were examined to evaluate their potential for refining the knowledge of astronomical molecular sources. The primary project involved HCO in interstellar molecular clouds. The observational results include the verification of the identity of interstellar HCO, the confirmation of the …
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Dynamical influences on the comets of the Oort Cloud
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1986.
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Forms and Rotational States of the Nuclei of Ecliptic Comets
… properties of the nuclei of Jupiter Family comets (JFCs), based on time-series observations. These data were collected in four observing runs; two using the 3.6m NTT in Chile, and two using the 2.5m INT on the island of La Palma. From the time-series photometry rotation rates and elongations …
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Centaur shapes and the origin of bilobate Jupiter-family comets
The bilobate shape distribution of Jupiter-family comets (JFCs) is of unconstrained origin. One theory is that JFC progenitors become bilobate in the Centaur region, where sublimation of volatiles from object surfaces may spin objects up beyond a critical limit and disrupt them. We examine models …
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The Effect of Dust in Small Bodies: A Sample of Jupiter Family Comets
… are not entirely decoupled, of Jupiter Family Comets 45P/Honda-Mrkos-Pajdusakov (45P/HMP) from Dec. 26, 2016 - Mar. 15, 2017, 41P/Tuttle-Giacobini-Kresak (41P/TGK) from Feb. 16, 2017 - May 23, 2017, and 46P/Wirtanen from Nov. 10, 2018 - Feb. 13, 2019, in visible wavelengths. During that time …
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The Effects of Fractal Molecular Clouds on the Dynamical Evolution of Oort Cloud Comets
… Oort Cloud (OC) is a roughly spherical cloud of comets surrounding the solar system, stretching from well beyond the orbit of Neptune, half way to the nearest star. This body of comets is interesting because it contains a record of the gravitational perturbations suffered by the solar system over …
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Near-IR Spectroscopic Analysis of the Primary Volatile Composition of Long and Short-Period Comets
<p>"Comets are among the most well-preserved objects that formed in the protosolar nebula ∼4.5 Gyr ago. Hence, they are important for understanding various aspects of the formation, evolution, and habitability of the solar system. Multiple primary volatiles (molecules directly sublimating into the …
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Constant Orbital Momentum Equilibrium Trajectories of a Gyrostat-Satellite
… possible transitions between relative equilbria. COMETs are a class of paths in SO(3) that a gyrostat-satellite may travel along that maintain a constant system angular momentum. The primary contributions of this dissertation are the introduction and analysis of COMETs and their application to the …
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Comet-asteroid differentiation using visible and near-infrared spectroscopy
Comets have historically been defined as objects that experience the formation of a "head" (coma) or "tail" as ice and other volatiles that comprise their chemical makeup vaporize when they near the sun. Comets can lose this ability to form a coma or tail, however, through a variety of dynamical …
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Bulk Properties and Evolution of Jupiter-Family Comet Nuclei
… time-series observations of Jupiter-family comets (JFCs). A method was developed that allows mutual absolute photometric calibration of data taken at different epochs with different instruments and results in absolute-calibration uncertainty of ∼0.02 mag. The method was applied to various …
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Comparison of sonographic lung comet evaluation by an experienced ultrasonographer and novice in a high-altitude environment
… of sonographic artifacts called lung comets. This study was designed to establish whether a novice sonographer can perform effective assessment of lung ultrasound comet scores in comparison to an experienced sonographer in a high-altitude environment. An acceptable limit of agreement …
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Decoding the history of the early solar system using comet volatile compositions
… directly from the nucleus) composition of comets via analysis of fluorescence emission in cometary comae. Sampling fluorescence emission from a suite of primary volatiles has become possible from state-of-the-art ground-based observatories.</p><p>An overarching goal of comet volatile …
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The origin and evolution of warm exozodiacal dust
… An alternative mechanism is inward scattering of comets, which spontaneously fragment to produce dust. I then develop a numerical model for the zodiacal dust produced by spontaneous fragmentation of Jupiter-family comets in the Solar System. This is able to produce enough dust to sustain the …
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Late accretion to the early Earth and rocky exoplanets
… collisions of planetesimals, asteroids and comets -- by-products of the primary stage of planet formation -- with the nascent planet. It is thought these impacts, delivering vast sums of energy, may have transformed surface environments -- melting Earth's primitive crust, and sterilizing the …
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EXOCOMETS AT LARGE ORBITAL RADII AND THEIR INWARD TRANSPORT IN DEBRIS DISCS
… rise to debris discs. Primitive asteroids and comets likely played a major role in the emergence of life on Earth through their delivery of volatiles early in the lifetime of our planet. Cometary impacts, therefore, could be a necessary condition for the emergence of life in exoplanets and the …
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Observations of Large Biologically Important Interstellar and Cometary Molecules
… importance of detecting large biomolecules in comets is that in doing so will tie together the chemistry in HMCs with cometary chemistry.
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Following Carbon's Evolutionary Path: From Nucleosynthesis to the Solar System
… planetary nebulae (PNe), molecular clouds and comets. The 12C/13C isotope ratio was measured in Galactic molecular clouds using the CN isotopologs. A gradient of 12CN/13CN was determined to be 12C/13C = 6.01 DGC +12.28, where DGC is distance from the Galactic center. The results of CN are in …
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