BIOROBIN HAGUE
T he largest confirmed crater in the Solar System is the one that lies beneath Utopia Planitia, a huge plain in the northern hemisphere of Mars. With a diameter of 3,300 kilometres (2,050 miles), this huge and shallow basin must have been created by the force of a wide impactor and would have had a devastating effect on Mars at the time. But the Utopia impact happened roughly 4 billion years ago, and later geological activity has done a lot to hide it. The basin was only confirmed in 2001 using satellite maps of Martian topography. Far more easily identified as an impact basin is Hellas Planitia, an oval depression in the Red Planet’s southern hemisphere some 2,300 kilometres (1,429 miles) across. What’s more, these same maps revealed that a vast swathe of the northern hemisphere of Mars, around 10,600 kilometres (6,587 miles) across at its widest, is notably depressed and flat compared to the rest of the planet. Some geologists have suggested that the entire north polar basin is also an impact structure – if confirmed, it would dwarf anything else in the Solar System.