Spaceborne Radar Images Suggest Chain of Impact Craters

Radar images of the Earth taken by the Spaceborne Imaging Radar C/X-band Synthetic Aperture Radar (SIR-C/X-SAR) have revealed two craters close to a previously known impact site called Aorounga, located in northern Chad, a country in central Africa. "The Aorounga craters are only the second chain of large craters known on Earth, and were apparently formed by the break-up of a large comet or asteroid prior to impact. With ground confirmation, this second chain will provide valuable data on the nature and origin of small bodies that cross Earth's orbit," said Adriana Ocampo, a geologist at NASA's Jet Propulsion Laboratory, Pasadena, CA. "The two new craters are the first impact craters discovered in SIR-C data," said Dr. Kevin Pope, a SIR-C team member from Geo Eco Arc Research in La Canada Flintridge, CA. "That shows the power of the SIR-C instrument, because these craters are highly eroded and buried by wind-blown sand. They are hard to see even if you are standing on the ground." Ocampo and Pope suggest that the impact sites were caused by an comet or asteroid that broke up before impact. It is estimated that the craters are nearly 360 million years old, placing them in a time period of mass biological extinction. Although the impacts are not large enough to cause the extinction, they may have contributed to it. Similar series of craters have appeared on Jupiter's moon, Callisto.