Paper Martian wind and surface conditions during the night-time descent and

Pathfinder parachuted through the Martian nocturnal boundary layer during the northern hemisphere summer. Encased in airbags the lander bounced across the surface in darkness coming to a stop surrounded by a rugged terrain. Studying the motion of Pathfinder during its descent and landing offers a unique opportunity to study the Martian winds at night in the stable boundary layer. We simulate the atmospheric descent of Pathfinder using a trajectory model together with winds imported from a global climate model. The bouncing trajectory of the airbags was investigated using atmospheric pressure observations made during the landing and a Digital Terrain Map (DTM).Reconstruction of the parachute and airbag trajectories together with accelerometer data indicates that there was possibly strong wind shear in the nocturnal boundary layer prior to the firing of the braking rockets. This is unexpected from atmospheric models. Atmospheric pressure data and the DTM indicate the first airbag impact was on the side of a low hill north of the deployed lander. From this point our airbag model indicates the airbags would have bounced downhill towards the south by about one hundred metres and descended several metres in elevation before arriving on level ground where they would have slowed to a stop.We use modern observations and analytical tools to reconstruct the descent and landing of Pathfinder and provide information on the atmospheric and surface conditions during the night-time landing. In addition we provide clues to the behaviour of the nocturnal boundary layer on Mars.