The North Polar Basin, more commonly known as the Borealis Basin, is a large basin in the northern hemisphere of Mars that covers 40% of the planet.[1][2] Some scientists have postulated that the basin formed during the impact of a single, large body roughly 2% the mass of Mars, having a diameter of about 1,900 km (1,200 miles).[1][3] However, the basin is not currently recognized as an impact basin by the IAU. The basin is one of the flattest areas in the Solar System, and has an elliptical shape.[1][2] Chryse Planitia, the landing site of the Viking 1 lander, is a bay that opens into this basin.