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Reassessing the threat to Earth from medium-sized asteroids

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Touchdown Impact
Press release,

A research team of international space scientists, led by Dr. Matthias van Ginneken of the University of Kent's School of Physical Sciences and including the Museum für Naturkunde Berlin has published new evidence of a meteorite impact in the journal Science Advance. The impact occurred 430,000 years ago in the region of the Antarctic ice sheet. The extraterrestrial material was studied in the research laboratories of the Museum für Naturkunde Berlin using an electron beam microprobe and served as the data basis for the international research work.

Extra-terrestrial particles (condensation spherules) recovered on the summit of Walnumfjellet (WN) within the Sør Rondane Mountains, Queen Maud Land, East Antarctica, indicate an unusual touchdown event where a jet of melted and vaporised meteoritic material resulting from the atmospheric entry of an asteroid at least 100 m in size reached the surface at high velocity. This type of explosion caused by a single-asteroid impact is described as intermediate, as it is larger than an airburst, but smaller than an impact cratering event.

“The chondritic bulk major, trace element chemistry and high nickel content of the debris demonstrate the extra-terrestrial nature of the recovered particles”, says Prof. Lutz Hecht, professor of Impactpetrology and head of the microanalytic lab at the Museum für Naturkunde Berlin. Their unique oxygen isotopic signatures indicate that their interacted with oxygen derived from the Antarctic ice sheet during their formation in the impact plume.

The findings indicate an impact much more hazardous that the Tunguska and Chelyabinsk events over Russia in 1908 and 2013, respectively.This research, published by Science Advances, guides an important discovery for the geological record where evidence of such events in scarce. This is primarily due to the difficult in identifying and characterising impact particles. The study highlights the importance of reassessing the threat of medium-sized asteroids, as it likely that similar touchdown events will produce similar particles. Such an event would be entirely destructive over a large area, corresponding to the area of interaction between the hot jet and the ground.

Dr van Ginneken said: "To complete Earth’s asteroid impact record, we recommend that future studies should focus on the identification of similar events on different targets, such as rocky or shallow oceanic basements, as the Antarctic ice sheet only covers 9% of Earth’s land surface. Our research may also prove useful for the identification of these events in deep sea sediment cores and, if plume expansion reaches landmasses, the sedimentary record. While touchdown events may not threaten human activity if occurring over Antarctica, if it was to take place above a densely populated area, it would result in millions of casualties and severe damages over distances of up to hundreds of kilometres."

The extra-terrestrial particles (condensation spherules) examined in this study were found during the 2017-2018 Belgian Antarctic Meteorites (BELAM) expedition based at the Belgian Princess Elisabeth Antarctic station and funded by the Belgian Science Policy (Belspo).

Publication: A large meteoritic event over Antarctica ca. 430 ka ago inferred from chondritic spherules from the Sør Rondane Mountains.M. van Ginneken - University of Kent; S. Goderis, F. Van Maldeghem, P. Claeys, B. Soens - Vrije Universiteit Brussel; N. Artemieva - Planetary Science Institute and Russian Academy of Sciences; V. Debaille - Université Libre de Bruxelles; S. Decrée - Belgian Geological Survey and Royal Belgian Institute of Natural Sciences; R. P. Harvey, K. Huwig - Case Western Reserve University; L. Hecht - Museum für Naturkunde Berlin and Freie Universit.t Berlin; F. E. D. Kaufmann - Museum für Naturkunde Berlin; S. Yang, M. Humayun - National Highste Magnetic Field Laboratory und Department of Earth; M. J. Genge - Imperial College London. Science Advances

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