Abstract Using MESSENGER Mercury Dual Imaging System data, we produced three new maps of Sibelius Crater, Mercury. Geomorphological and spectral maps were combined into a single hybrid map containing units associated with ejecta deposits, crater floor landforms and impact melt ponding. Spatial measurement of these units shows that ∼50% of the mapped melt pond area lies within a large, degraded impact crater (crater B), beyond the significantly lower northern Sibelius rim, with a potential melt flow to a smaller, degraded impact structure further north (crater C). Freshly processed spectral data from the eight-colour Map Projected Multispectral Reduced Data Record data highlight the emplacement of multiple uplifted ejecta units with distinct spectral properties. A new, high-resolution digital elevation model was created to help define and analyse crater floor uplift features and disrupted crater rims and to create detailed cross-sections. These illustrate a proposed location of B's central uplift structure exposed in the northern wall slopes of Sibelius. Small features at the limit of visibility, such as a groove possibly associated with a rolling or sliding mega-boulder and lobate melt flow on the crater floor with accompanying channel opening, are highlighted for future investigations by BepiColombo's instruments once it reaches orbit.

ABSTRACT Numerical models of meteorite delivery from impacts on the Moon have demonstrated that the impact event forming the lunar crater Tycho (~85 km diameter; ca. 109 Ma age) would have delivered considerable amounts of ejected material to Earth. The ejecta, containing lunar Ti- and V-rich chrome spinels, would have been distributed globally and admixed with seafloor sediments over a few meters of a typical marine stratigraphic interval. In order to locate such ejecta, samples weighing ~12–25 kg each, with one-meter spacing were extracted over an ~30 m interval of the deep-sea formed Calera Limestone, Albian and Aptian age (ca. 103–117 Ma), from the Pacifica Quarry, south of San Francisco. The limestone samples were leached in acids and residues searched for possible lunar Ti-rich chrome-spinel grains. In a total of 689 kg of limestone, 1154 chrome-spinel grains were found. Of these, 319 contain >0.45 wt% V 2 O 3 , of which 227 originate from equilibrated ordinary chondrites. The majority of the other 92 grains with >0.45 wt% V 2 O 3 are most likely from different types of achondritic meteorites. Among these, we found eleven particularly Ti-rich chrome-spinel grains. The elemental abundances of these grains were compared with chrome spinel from lunar, howardite-eucrite-diogenite (HED) and R-chondritic meteorites. This showed that only one of these grains could potentially be of lunar origin. The bulk of the other grains likely originate from HED meteorites based on oxygen isotopic analysis of similar grains in previous studies. Grains with TiO 2 >10 wt%, common among lunar spinels are not found, further supporting an HED source for the Ti-rich grains. In summary, Albian and Aptian strata in the Pacifica quarry do not likely record any major lunar impact event. Either the timing of the impact is located within a ca. 110–114 Ma unconformity in the middle part of the section or the impact is likely older than the interval searched.

ABSTRACT This thesis embraces and expands upon a century of research into disparate geological enigmas, offering a unifying catastrophic explanation for events occurring during the enigmatic mid-Pleistocene transition. Billions of tons of “Australasian tektites” were dispatched as distal ejecta from a target mass of continental sediments during a cosmic impact occurring ca. 788 ka. The accepted signatures of a hypervelocity impact encompass an excavated astrobleme and attendant proximal, medial, and distal ejecta distributions. Enigmatically, the distal tektites remain the only accepted evidence of this impact’s reality. A protracted 50 yr search fixated on impact sites in Southeast Asia—the location of the tektites—has failed to identify the requisite additional impact signatures. We postulate the missing astrobleme and proximal/medial ejecta signatures are instead located antipodal to Southeast Asia. A review of the gradualistic theories for the genesis and age of the “Carolina bay” landforms of North America finds those models incapable of addressing all the facts we observe. Research into 57,000 of those oriented basins informs our speculation that they represent cavitation-derived ovoid basins within energetically delivered geophysical mass surge flows emanating from a cosmic impact. Those flows are seen as repaving regions of North America under blankets of hydrated impact regolith. Our precisely measured Carolina bay orientations indicate an impact site within the Laurentide ice sheet. There, we invoke a grazing regime impact into hydrated early Mesozoic to late Paleozoic continental sediments, similar in composition to the expected Australasian tektites’ parent target. We observe that continental ice shielded the target at ca. 788 ka, a scenario understood to produce anomalous astroblemes. The ensuing excavation allowed the Saginaw glacial lobe’s distinctive and unique passage through the Marshall Sandstone cuesta, which encircles and elsewhere protects the central region of the intracratonic Michigan Basin. Subsequent erosion by multiple ice-age transgressions has obfuscated impact evidence, forming Michigan’s “Thumb” as an enduring event signature. Comprehensive suborbital modeling supports the distribution of distal ejecta to the Australasian tektite strewn field from Michigan’s Lower Peninsula. The mid-Pleistocene transition impact hypothesis unifies the Carolina bays with those tektites as products of an impact into the Saginaw Bay area of Lake Huron, USA. The hypothesis will be falsified if cosmogenic nuclide burial dating of Carolina bay subjacent stratigraphic contacts disallows a coeval regolith emplacement ca. 788 ka across North America. We offer observations, interdisciplinary insights, and informed speculations fitting for an embryonic concept involving a planetary-scale extraterrestrial impact.

ABSTRACT Suborbital analysis (SA) is presented here as the study of ballistics around a spherical planet. SA is the subset of orbital mechanics where the elliptic trajectory intersects Earth’s surface at launch point A and fall point B , known as the A -to- B suborbital problem, both launch and fall points being vector variables. Spreadsheet tools are offered for solution to this problem, based on the preferred simplified two-body model. Although simplistic in top-level description, this problem places essential reliance on reference frame transformations. Launch conditions in the local frame of point A and rotating with Earth require conversion to the nonrotating frame for correct trajectory definition, with the reverse process required for complete solution. This application of dynamics requires diligent accounting to avoid invalid results. Historic examples are provided that lack the requisite treatment, with the appropriate set of solution equations also included. Complementary spreadsheet tools SASolver and Helix solve the A -to- B problem for loft duration from minimum through 26 h. All provided spreadsheet workbook files contain the novel three-dimensional latitude and longitude plotter GlobePlot. A global ejecta pattern data set calculated using SASolver is presented. As visualized through GlobePlot, SASolver and Helix provide solutions to different forms of the A -to- B problem, in an effort to avoid errors similar to the historic misstep examples offered as a supplement. Operating guidelines and limitations of the tools are presented along with diagrams from each step. The goal is to enable mechanically valid interdisciplinary terrestrial ejecta research through novel perspective and quality graphical tools, so others may succeed where 1960s National Aeronautics and Space Administration researchers did not.