abstract: During the early Solar System many physiochemical processes were taking place that would shape the formation and evolution of rocky bodies. Growth of these rocky objects was rapid, with some growing to sizes of 10s – 1000s km (“planetesimals”) in the first few million years. Because these objects formed early, they contained sufficient 26Al (an isotope of Al with a short half-life of ~705,000 yrs) to heat the interiors to melting temperatures, resulting in the formation of the first igneous rocks in nascent Solar System. Depending on the size and time of accretion, some bodies experienced high degrees of melting (with some having global magma oceans) while others experienced lower degrees of partial melting, and yet others did not experience any melting at all. These varying degrees of heating and melting processes on early-formed planetesimals produced a variety of achondritic meteorite types. These achondrites have bulk compositions ranging from ultramafic to basaltic, with some rare types having more highly “evolved” (i.e., high-SiO2) compositions. Determining the detailed chronology of their formation with fine time resolution is key for understanding the earliest stages of planet formation, and there are high resolution chronometers that are ideally suited for this application. Three such chronometers (i.e., the 26Al-26Mg, 53Mn-53Cr, and 207Pb-206Pb chronometers) are the focus of this work. Based on investigations of these chronometers in several achondritic meteorites, the implications for the formation and evolution of planetesimals in the early Solar System will be discussed. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

To constrain the thermal histories of two complex L chondrite melt breccia samples (NWA 5964 and NWA 6580) we compare textures and chemical compositions of metal and sulfide to L melt rock (NWA 6454 and NWA 6579) and strongly shocked (shock stage S6) (NWA 4860) samples. The inferred thermal histories can be used to evaluate formation settings on the L chondrite parent body. The L melt samples probably formed as different melt units within warm but largely unmelted material relatively close to the surface of the parent body, and the same is true for the S6 sample, except it experienced less melting. The breccia samples likely formed deeper, below different impact craters, by the injection of shock melt into a cooler chondritic basement. Carbide grains in the melt breccias could have formed by a contact metamorphic process caused by heating of the chondritic basement in proximity to the melt. Within the melt regions of the various samples, inferred cooling rates are on the order of 1-10 °C/sec, whereas in the chondritic portions of the melt breccias, the inferred cooling rates are many orders of magnitude slower, ~1-100 °C/My. The complex intergrowths of metal and FeS (hereafter referred to as dendritic grains) within the melt are recording cooling rates above the metal-sulfide eutectic, while the metal grains outside of the melt regions are recording cooling rates at much lower temperatures. It is likely the melt regions in the breccias cooled substantially prior to coming to rest against the chondritic basement, and thereafter the melt-chondrite rocks cooled more slowly.

The isotopic ratios S33/S32, S34/S32 and S36/S32 of different forms of sulphur in a number of meteorites have been studied. The results obtained indicate that processes of chemical fractionation have occurred in some meteorites but that the isotopic composition of the total sulphur in a single meteorite is remarkably constant from meteorite to meteorite. The relationships between the S33, S34 and S36 isotope abundances indicate that variations in these abundances due to inhomogeneities in the processes of nucleo-synthesis are not detectable. Isotopic analysis of sulphur from the iron phase of the Clark County, Pinon and Tlacotepic meteorites has shown the presence of cosmic ray induced spallation S36 and S33. These spallation results are in reasonable agreement with predictions based on production rates of other nuclei. / Thesis / Doctor of Philosophy (PhD)

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Earth and Planetary Sciences, 1981. / Microfiche copy available in Archives and Science. / Vita. / Bibliography: leaves 45-49. / by Mark Joseph Lupo. / M.S.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography: leaves 60-63. / M.S.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography: leaves [108]-[112]. / Part 1. Some implications of the Yarkovsky effect on the orbits of very small asteroids.--Part 2. Stable retrograde orbits outside the sphere of influence. / Ph.D.

Our inventory of material from the early solar system includes large, igneous-textured inclusions in O chondrites, whose origin and relationship to their host meteorite is unclear. These inclusions occur in approximately 4% of O chondrites, and are mineralogically, petrographically, and chemically diverse. Petrographic and chemical data from 29 inclusions from 23 host meteorites were collected with optical light and scanning electron microscopy, allowing for the determination of major phase modal abundance and major element bulk chemistry. No correlation between any inclusion property and host meteorite type were found, but some trends were observed. Nine of the inclusions show strong evidence, such as radial variations in texture and chemistry, for having crystallized as a free-floating droplet in a space environment, and may share the same formation process as chondrules. One inclusion is almost certainly shock-melted material that intruded into the host material. Thirteen inclusions have bulk chemistry patterns that suggest the material was vapor fractionated; the remaining sixteen are essentially chondritic, i.e., unfractionated. Broadly, the data support the conclusions of Ruzicka et al. (1998, 2000), which divided large inclusions into Na-poor (vapor fractionated) and Na-rich (unfractionated) groups, suggesting at least two different origins. There is no evidence that any of the inclusions studied formed by igneous differentiation.

"July 2003." Includes bibliographical references (leaves 459-484) Electronic publication; full text available in PDF format; abstract in HTML format. Details the application of a medium frequency Doppler radar to observations of meteorites entering the Earth's atmosphere. Techniques were developed that verified system performance was to specification Electronic reproduction.[Australia] :Australian Digital Theses Program,2001. xx, 485 leaves : ill. ; 30 cm.

The discovery of Ni-, Cu-, and Zn-bearing Fe-sulfides from comet 81P/Wild 2 represents the strongest evidence, in the Stardust collection, of grains that formed in an aqueous environment. Crystalline sulfide assemblages from Wild 2 and the hydrothermally altered CI chondrite Orgueil were investigated. Structural and compositional characterizations of the sulfide grains from both collections reveal similarities. The Stardust samples include a cubanite (CuFe₂S₃) grain, a pyrrhotite [(Fe,Ni)₁₋ₓS]/pentlandite [(Fe,Ni)₉S₈] assemblage, and a pyrrhotite/sphalerite [(Fe,Zn)S] assemblage. Similarly, the CI-chondrite sulfides include individual cubanite and pyrrhotite grains, cubanite/pyrrhotite assemblages, pyrrhotite/pentlandite assemblages, as well as possible sphalerite inclusions within pyrrhotite grains. The cubanite is the low temperature orthorhombic form, which constrains temperature to a maximum of 210°C. The Stardust and Orgueil pyrrhotites are the 4C monoclinic polytype, which is not stable above ~250°C. The combinations of cubanite and pyrrhotite, as well as pyrrhotite and pentlandite, signify even lower temperatures. The crystal structures, compositions, and petrographic relationships of these sulfides constrain formation and alteration conditions. Taken together, these constraints attest to low-temperature hydrothermal processing. The hydrothermal conditions under which cubanite forms were investigated through thermodynamic modeling and experimental synthesis. A thermodynamic model for cubanite was developed to constrain its formation environment. Cubanite was synthesized under hydrothermal conditions consistent with those predicted for the CI-chondrite parent body. The similarity between Stardust and CI-chondrite sulfides suggest similar fluid conditions may have existed on the comet at some point in its history. The presence of cubanite in the Stardust collection has implications for large scale issues such as: heat sources in the comet-forming region; aqueous activity on cometary bodies; and the extent and mechanisms of radial mixing of material in the early nebula. The Wild 2 sulfides are most likely the products of low-temperature aqueous alteration and provide evidence of radial mixing of material from the inner solar system to the comet-forming region and possible secondary aqueous processing on the cometary body.

Small near-Earth asteroids (NEAs) (< 20 m) are interesting, because they are progenitors for meteorites in our terrestrial collection. The physical characteristics of these small NEAs are crucial to our understanding of the effectiveness of our atmosphere in filtering low-strength impactors. In the past, the characterization of small NEAs has been a challenge, because of the difficulty in detecting them prior to close Earth flyby. In this study, we physically characterized the 2 m diameter NEA 2015 TC25 using ground-based optical, near-infrared and radar assets during a close flyby of the Earth (distance 128,000 km) in 2015 October 12. Our observations suggest that its surface composition is similar to aubrites, a rare class of high-albedo differentiated meteorites. Aubrites make up only 0.14% of all known meteorites in our terrestrial meteorite collection. 2015 TC25 is also a very fast rotator with a period of 133 +/- 6 s. We combined the spectral and dynamical properties of 2015 TC25 and found the best candidate source body in the inner main belt to be the 70 km diameter E-type asteroid (44) Nysa. We attribute the difference in spectral slope between the two objects to the lack of regolith on the surface of 2015 TC25. Using the albedo of E-type asteroids (50%-60%) we refine the diameter of 2015 TC25 to 2 m, making it one of the smallest NEAs ever to be characterized.