: Two craters lying about 16 km apart in Sweden are evidence of a double asteroid impact that occurred some 458 million years ago, say Jens Ormo of the Center for Astrobiology in Madrid, Spain, and colleagues. The researchers presented their findings at the 45th Lunar and Planetary Science Conference
being held this week in the Woodlands, Texas. Binary asteroids form from a single asteroid that spins so fast that it ejects material, which then forms a small moon. As many as 15% of near-Earth asteroids are binaries, and about 3% of Earth’s impact craters may be the result of a direct hit by a binary pair. To date the craters and ascertain that they were formed simultaneously, Ormo’s team used biostratigraphy
to study fossil creatures contained in the rock strata.