04-03-11 The scars of impacts on Mars

ESAs Mars Express has returned new images of an elongated impact crater in the southern hemisphere of Mars.Located just south of the Huygens basin,it could have been carved out by a train of projectiles striking the planet at a shallow angle.The large Huygens basin (not visible in the main image but seen in the wider contextual image) is about 450 km in diameter and lies in the heavily cratered southern highlands.In this area there are many impact scars but none perhaps are more intriguing than the elongated craters.One of these craters is seen in this new image,which covers an area of 133 x 53 km.The scene was captured on 4 August 2010 and the smallest objects distinguishable by the camera are about 15 m across.This unnamed elongated crater sits just to the south of the much larger Huygens basin.It is about 78 km in length,opens from just under 10 km wide at one end to 25 km at the other,and reaches a depth of 2 km.Impact craters are generally round because the projectiles that create them push into the ground before the shockwave of the impact can explode outwards.So why is this one elongated? The clue comes from the surrounding blanket of material,thrown out in the initial impact.This ejecta blanket is shaped like a butterflys wings,with two distinct lobes.This hints that two projectiles,possibly halves of a once-intact body,slammed into the surface here.