Venus' strange rotation was likely triggered by a high-velocity, moon-sized impactor

Venus' bizarre and extraordinarily slow retrograde rotation on its axis has long puzzled planetary scientists. But in a new paper presented at the recent European Geosciences Union General Assembly in Vienna, the authors argue that their models indicate a high-angle, moon-sized, high-velocity impactor likely triggered Venus' strange 248-day rotation. And it probably happened within the first 50 million years of Venus' formation.