[When an asteroid strikes, it creates a crater with an uplifted core. This is similar to how a drop of water splashes upward from a transient crater when you drop a pebble in a pool (Image credit: NASA/Don Davis)]
Sydney: The world’s largest asteroid impact structure is buried deep under the Earth in southern New South Wales, Australia, researchers said based on many years of experience in asteroid impact.
When an asteroid strikes, it creates a crater with an uplifted core. This is similar to how a drop of water splashes upward from a transient crater when you drop a pebble in a pool.
“The Deniliquin structure, yet to be further tested by drilling, spans up to 520 kilometres in diameter”, a recent research published by The Conversation said.
“This exceeds the size of the near-300km-wide Vredefort impact structure in South Africa, which to date has been considered the world’s largest”, the researchers wrote in the journal.
The Vredefort impact structure is the largest verified impact structure on Earth. The crater, which has since been eroded away, was around 180–300 km (100–200 mi) across when it was formed.
The Australian continent and its predecessor continent, Gondwana, have been the target of numerous asteroid impacts. These have resulted in at least 38 confirmed and 43 potential impact structures, ranging from relatively small craters to large and completely buried structures, according to the research jointly carried by Andrew Glikson and Tony Yeates.
This central uplifted dome is a key characteristic of large impact structures. However, it can erode over thousands to millions of years, making the structure difficult to identify.
Such domes, which can slowly erode and/or become buried through time, may be all that’s preserved from the original impact structure. They represent the deep-seated “root zone” of an impact.
Between 1995 and 2000, Tony Yeates suggested magnetic patterns beneath the Murray Basin in New South Wales likely represented a massive, buried impact structure.
The Deniliquin structure, believed to be world’s largest known asteroid impact structure, has all the features that would be expected from a large-scale impact structure.
“For instance, magnetic readings of the area reveal a symmetrical rippling pattern in the crust around the structure’s core. This was likely produced during the impact as extremely high temperatures created intense magnetic forces”, the researchers claimed.
“A central low magnetic zone corresponds to 30km-deep deformation above a seismically defined mantle dome. The top of this dome is about 10km shallower than the top of the regional mantle”, they added.
The Deniliquin structure was likely located on the eastern part of the Gondwana continent, prior to it splitting off into several continents (including the Australian continent) much later.
“The impact that caused it may have occurred during what’s known as the Late Ordovician mass extinction event”, the researchers said.
It is also possible the Deniliquin structure is older than the Hirnantian event, and may be of an early Cambrian origin (about 514 million years ago). The next step will be to gather samples to determine the structure’s exact age.
“This will require drilling a deep hole into its magnetic centre and dating the extracted material”, Andrew Glikson wrote.
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