Origin of small pits in martian impact craters

► A model for the formation of closely-spaced pits in martian impact craters is proposed. ► The mechanism relies on explosively degassed of steam from the pitted material. ► The high-speed escape of this steam is mainly through numerous vent pipes. ► The escaping steam and entrained clasts erodes the pipes to form pits at the surface. ► The low atmospheric pressure and gravity of Mars enhances the gas escape speed.