Antarctica – Researchers have found evidence of an asteroid explosion over Antarctica more than 2.5 million years ago, according to a report published in Earth and Planetary Science Letters. This explosion is considered to be the oldest known midair detonation documented in the geologic record. The analysis of rock fragments found in the continent’s ice led the researchers to this discovery.
Asteroids or comets that have impacted the surface of Earth or other rocky bodies typically leave behind prominent craters. However, evidence of some objects disintegrating in midair before reaching the ground is scarce. These midair explosions, or airbursts, can cause massive destruction at altitudes ranging from a few to several tens of kilometers. The kinetic energy of the incoming object results in an impact plume, a whirlpool of pressure disturbances and heat.
In 2013, a roughly 20-meter asteroid broke up high over Chelyabinsk, Russia, causing a shockwave that shattered thousands of windows. Another catastrophic airburst occurred in Tunguska, Siberia, in 1908, during which a boulder about three times as large as the Chelyabinsk body flattened a forest covering over 2,000 square kilometers. The recent study of rock fragments in Antarctica suggests that a midair explosion from an asteroid might have occurred 2.3 million to 2.7 million years ago.
The research team analyzed 116 tiny rock fragments found within Antarctica’s ice. The minerals dominating the rock composition, olivine and spinel, were found to be chemically consistent with ordinary chondrite, a type of asteroid. The precise ratio of different forms of oxygen in the rocks confirmed that they were produced in an airburst whose impact plume interacted with the ice and then reached the surface.
Jason Pearl, a physicist at Lawrence Livermore National Laboratory in California, who was not involved in the research, commented that sizable chunks of extraterrestrial material bombarding Earth occur roughly every 50 to 500 years. This raises the possibility that there are more examples of such midair explosions present in the geologic record. Matthias van Ginneken, a cosmochemist at the University of Kent in England involved in the study, also believes that further research will reveal more airbursts in the geologic record.