A mysterious near perfect circle spotted in satellite imagery of Western Australia in 2007 was later confirmed to be a meteorite impact crater after scientific drilling and chemical analysis provided evidence of an iron meteorite strike.
Arthur Hickman a geologist with the Geological Survey of Western Australia, noticed the unusual circular feature while examining satellite images of the outback. The structure, located in the Pilbara region, measures about 260 metres (850 feet) across and has been informally named the Hickman Crater.
A study published in the Australian Journal of Earth Sciences found that the crater was likely created by an object roughly 10 metres in diameter. Researchers estimated that the impact excavated a crater that may have been around 80 metres deep and dated the structure to between 10,000 and 100,000 years ago.
Initial geological evidence suggested that the circular formation was unlikely to have been created by volcanic activity. However, researchers needed stronger evidence to establish its origin. In 2012, the Geological Survey of Western Australia working with Atlas Iron, carried out a scientific drilling project to examine the crater’s subsurface structure.
The drilling reached a depth of 64.7 metres through the crater floor. Researchers found that the upper 48.4 metres consisted largely of sediment deposited after the crater formed. Below that, between 55.1 and 64.7 metres, the drill core contained heavily fractured rhyolite, the original bedrock.
The most significant evidence came from chemical analysis of material within the crater. Researchers found platinum group element ratios that were more similar to those found in meteorites than in Earth’s continental crust. Elevated nickel concentrations provided further evidence that the impactor was an iron meteorite.
Scientists also examined why the crater lacked some of the intense shock features normally associated with meteorite impacts. One explanation is that the relatively small meteorite may have slowed considerably while travelling through Earth atmosphere. The reduced speed could have lowered the pressure generated during impact while still leaving enough energy to excavate a crater hundreds of metres wide.
The Hickman Crater is considered an important example of a relatively small and well preserved impact structure. The scientific drilling also provided researchers with a rare opportunity to examine the geological effects of a meteorite impact below the surface.
The discovery highlights how satellite imagery can reveal geological features that may remain difficult to identify from the ground. What initially appeared to be an unusual circular formation in Australia’s remote outback ultimately provided evidence of a meteorite collision with Earth thousands of years ago.