NASA reveals a strange spider-shaped crater left behind by an ancient impact

Spider Crater has puzzled geologists for decades after it was first spotted in the 1950s. It's about 13 km by 11 km in size and is located in the remote Kimberley region of Western Australia. The features of the crater are characterized by a network of ridges that spread out from a central point, giving it a distinctive spider-like appearance, unlike most impact craters.

A volcanic origin was one of the first explanations considered for the structure, but its unusual features remained difficult to explain. The answer, however, came in the late 1970s when the shatter cones were found. These are a rare type of fan-shaped fracture that forms under extreme shock pressures associated with an impact.

On September 20, NASA's Landsat 9 satellite captured a fresh image of the crater, where the distinct pale ridges radiating out from the central mound are visible. This distinctive shape can be said to be a record of the impact that occurred hundreds of millions of years ago.

The giant impact left behind an unusual shape

Spider Crater doesn't look at all like the classic circular bowl that is usually expected from a meteorite impact. The central pattern is about 4 km across, and the ridges that give it its name are all sandstone, which makes the crater more resistant to erosion when compared to the other rocks around it.

The distinct spider pattern is believed to be the remnant of a central uplift. When a large body impacts the ground, the resulting shock wave travels through the rock, and the floor of the crater can briefly rebound, pushing material upwards from a central mound. That mound is what the Spider Crater is.

Subsequent wind and water slowly eroded the softer rock strata, leaving the more resistant sandstone ridges standing up. It is worth noting that the spider shape didn't form as a clean pattern during the initial meteorite impact. Its development happened over the course of time as erosion stripped away various layers of the rock. It can be said to be a heavily modified version of the original impact structure.

Geologists found evidence of an ancient impact

The Spider Crater's unusual appearance left its origins a matter of debate for decades. Some researchers proposed volcanic origins, but the discovery of shatter cones provided evidence that it was an impact structure.

Researchers went on to look at the shocked quartz and zircon crystals in the sandstone. These materials can record the extreme pressures associated with an impact, and by looking at the shock features in the lab, researchers can investigate details about the impact event, including the meteorite's angle of approach.

So far, the exact age of the Spider Crater is not known. Estimates from the rocks in the area put the impact somewhere in the range of the late Precambrian period, approximately 900 million to 600 million years ago. This happened long before complex animals became widespread, when the Earth's environments and continents looked vastly different from what they are today.

The new NASA image gives a much clearer picture of the general shape of the crater. Further field observation and laboratory analyses could help scientists better understand its origins and how it formed.

The Spider Crater is also a good example of how it can be difficult to identify ancient impact sites, as they may not always remain obvious circular depressions. Erosion can completely wipe out the obvious form of a crater, leaving only fragments of its original internal structure visible. In the case of the Spider Crater, the distinct surviving ridges make the ancient impact structure recognizable, even from space.

Sources: NASA, Wiley, Taylor & Francis Online

Affiliate links on Cult of Mac may earn us and our partners a commission.