A meteor that exploded over Antarctica around 430,000 years ago was “entirely destructive over a large area”, according to a new study documenting the discovery of 17 particles left over from the blast. Recovered from the summit of a mountain called Walnumfjellet, the rare fragments indicate that the space rock must have been at least 100 meters (330 feet) in diameter, and collided with the ground at high velocity.
What’s peculiar about this event, however, is that the meteor in question was not large enough to leave an impact crater, yet was sufficiently bulky to reach the Earth without simply burning up in the atmosphere. Reporting their findings in the journal Science Advances, the study authors describe the impact as a rare “intermediate touchdown event”, in which a “jet of melted and vaporized meteoritic material” was able to reach the surface, causing serious damage but lacking the density required to generate a crater.
The discovery of the particles is something of a wonder in itself, given that the largest was less than half a millimeter in size. Using scanning electron microscopy, the researchers found the fragments to be made up of mostly iron and olivine, with high nickel content. This matches the composition of certain meteorites, confirming that the particles were of extra-terrestrial origin.
The tiny pieces of space rock also contained oxygen isotopes that are characteristic of Antarctic ice, suggesting that they obtained these upon impact with the surface, rather than by burning up in the air. This implies that when the meteorite exploded, vaporized material was sent hurtling to the ground at high speed, where it condensed as it mixed with the Antarctic ice sheet.
What’s more, the resulting condensation spherules were found to be highly similar in their chemical composition to spherules left over from two other touchdown events that occurred over Antarctica around 430,000 years ago. Based on this observation, the researchers speculate that these particles were all produced by the same exploding asteroid, suggesting that the impact sent out a plume of debris that spanned a huge area.
As such, the study authors conclude that meteoritic explosions of this size have the potential to generate blast effects causing strong overpressures over areas up to 100,000 square kilometers (38,610 square miles), while also producing enough thermal radiation to spark fires over an area of 10 to 1,000 square kilometers (3.86 to 386.1 square miles) wide.
In a statement, study author Matthias van Ginneken explained that “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.”