NASA's Perseverance rover has identified evidence that a 245-foot-thick stack of ancient rock on the rim of Jezero Crater was built by repeated asteroid impacts over billions of years. The rock sequence, called the "Broom Point member," dates to more than 3.9 billion years ago and represents one of the oldest terrains examined by a Mars rover. Findings published Wednesday in the Journal of Geophysical Research: Planets reveal six distinct rock types alternating between impact breccias and fine-grained pulverized dust, with glassy beads similar in size to those ejected by Earth's dinosaur-killing Chicxulub impact. The preservation of this ancient impact record on Mars provides insight into the early solar system's turbulent history in ways Earth's crust cannot, since plate tectonics have erased our own earliest geological record.
Scientists believe two major impacts shaped this landscape: the colossal collision that created the 1,200-mile-wide Isidis Basin tilted the original rock layers steeply, and a later impact that formed Jezero Crater fractured and uplifted them further. Perseverance collected two core samples -- "Bell Island" and "Main River" -- that could be returned to Earth by a future mission for precise dating of when these impacts occurred. Determining the timing of early Mars impacts would effectively reveal the impact history of the young Earth as well, since both planets experienced the same bombardment during the solar system's violent early period.