When a Stream of Cosmic Debris Struck the Earth

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A research team including members of Freie Universität Berlin has found traces of an ancient meteor explosion above the Antarctic / Re-assessment of asteroid threat

No 058/2021 from Apr 01, 2021

An international research team has discovered that a huge meteor exploded over the Antarctic ice plateau around 430,000 years ago. The team, which included geoscientist Professor Lutz Hecht from Freie Universität Berlin and the Berlin Museum für Naturkunde, investigated space particles known as "condensation spherules" that were found on top of Walnumfjellet (WN) in the Sør Rondane Mountains in eastern Antarctica. These unusual findings indicate that it was not a large lump of meteoritic stone that struck the Earth, but rather a stream of melted and vaporized meteoritic material. The particles that were discovered are believed to derive from an asteroid of around 100 meters in diameter, which entered the Earth’s atmosphere at immense speed but exploded before reaching the planet’s surface. The findings of the team’s research were published in the highly selective journal Science Advances at the end of March this year.

This research demonstrates just how much destructive power may be contained in even a relatively small or medium-sized meteor. If an asteroid of this size were to hit the Earth or explode over its surface, says Professor Hecht, it could destroy an area of several hundred square kilometers. The damage caused would far outweigh what happened after the famous Tunguska event that took place over the eponymous region in Siberia in 1908. Then, a small meteorite exploded some way above Earth’s surface, yet the pressure waves emanating from the explosion uprooted over 60 million trees. The meteor strike in Antarctica 430,000 years ago has been described as an "intermediate touchdown event" by experts from the research team. The meteorite fell to Earth as a stream of debris made up of condensation spherules, so it had greater impact than an airburst, where the meteorite explodes and melts in the atmosphere. But it had a lesser effect than an "impact cratering event," in which a single, large meteoritic rock creates a crater when it hits the Earth. The researchers were able to analyze some of the cosmic spherules, and based on their chemical composition, there’s no doubt of their extraterrestrial origin, explains Hecht. The professor specializes in the petrology and geochemistry of impactites and meteorites, and his team investigated the material samples using an electron beam microprobe. Overall, the team’s research findings clearly show the need for a re-assessment of the threat to the Earth posed by medium-sized asteroids. The threat is real and should be taken seriously.