An attempt to detect changes in the Sun's luminosity during the last glaciation by applying the Poynting-Robertson effect to cosmic spherules from a dated deep-sea core

Abstract

In previous papers by Parkin, Sullivan & Bull and Parkin, the Poynting-Robertson effect was applied to iron-type cosmic spherules, from two North Pacific cores, in the hope of proving that cosmic spherules existed as round bodies in space. It was assumed that they were produced as melt-droplets in asteroidal collisions. The outcome was unsatisfactory because better methods of measuring spherule density were required. If this was done, it was realized that it might be possible to detect changes in the Sun's luminosity. The present work is a further development. Density measurement is now highly accurate, and only iron spherules undamaged in atmospheric flight are accepted. Both iron and stony spherules have been extracted from a dated (δ18O stage boundaries) Kastenlot core, from the North Atlantic at ∼41°N, 23°W. This 174 cm ≈125 ka core covered the period of the last glaciation but, unfortunately, several sections were missing, one at a critical time. In a plot of the product Dδ (diameter D, density δ) for pristine-looking iron spherules against their time of arrival, the points are mainly confined within a wedge, and seemingly form lines with slopes roughly parallel to the edge of the wedge. By applying the Poynting-Robertson effect, it is suggested that very large iron meteorites impacted Mars, each line denoting an impact. The accompanying stony spherules are thought to be molten ejecta of Martian rock. Because of marine corrosion, the densities of stony spherules are meaningless; however, their sizes are useful if a common density of 3 g cm−3 is assumed, in space. To my eye, the sloping lines have bends which match the variations in δ18O. This would mean that the Sun began to dim more markedly at ∼40 ka than previously, and reached a minimum at ∼20 ka. It then rapidly brightened, perhaps to more than the present-day luminosity. The data are too crude to warrant any estimate of luminosity. Numerous iron and stony spherules have been extracted from a single section 54 to 62 cm down another Kastenlot core from the North Atlantic, at ∼26°N, 31°W. This slowly sedimenting, carbonate-free core is not dated; but perhaps 54 cm ≈210 ka. This section shows that irons and stones are ejected together at a collision; and an iron spherule accompanies a stony one during Poynting-Robertson spiralling, if they have the same Dδ value.