Hundreds of impacts every year still forming Mars craters

US astronomers say images from a spacecraft orbiting Mars suggest the Red Planet is still a target for cosmic impacts, experiencing hundreds each year. Scientists using images from NASA's Mars Reconnaissance Orbiter have estimated the planet is bombarded by more than 200 small asteroids or bits of comets each year, forming craters at least 12.8 feet across on average. Researchers using images from the University of Arizona-led HiRISE imaging instrument aboard the spacecraft, have identified 248 new impact sites on parts of the Martian surface in the past decade. The estimate of 200 impacts a year is a calculation based on the number found in a systematic survey of just a portion of the planet, they said. "It's exciting to find these new craters right after they form," UA researcher Ingrid Daubar said. "It reminds you Mars is an active planet, and we can study processes that are happening today." The objects striking Mars are typically no more than 3 to 6 feet in diameter; space rocks too small to reach the ground on Earth can cause craters on Mars because the Red Planet has a much thinner atmosphere, researchers said. The meteor that exploded over Chelyabinsk, Russia, in February was about 10 times bigger than the objects that are still creating fresh Martian craters, they said.