FEROCIOUS asteroid bombardments on Mars could have triggered scalding rain and flash floods that carved out the planet’s giant river valleys billions of years ago. Mars must have been wet in the past for these valleys to have formed. The big question has always been how the planet could ever have been warm enough for this rain to fall. Asteroids impacts could be the answer.
Mars lies around 75 million kilometres farther from the Sun than Earth does and average temperatures today are about -50 °C. But 3.5 billion years ago, asteroids regularly bombarded the planet. A single impact would…
