 Both craters were previously believed to have the same age, 290 ± 20 million years (Permian period), promoting the long-held idea that they formed simultaneously.According to this doublet impact crater theory initially proposed by Michael R. Dence and colleagues in 1965, the impactors may have been gravitationally bound as a binary asteroid, a suggestion also made by Thomas Wm.Hamilton in a 1978 letter to "Sky & Telescope" magazine in support of the then-controversial theory that asteroids may possess moons (such as, for example, asteroid 243 Ida with its satellite Dactyl).