The Caloris Basin
The Caloris Basin is the biggest feature on the exterior of Mercury. It is also one of the greatest influential basins in the solar system.
It was created by a gigantic meteorite smashing into Mercury’s exterior during the early creation of the solar system, almost four billion years ago.
Astronomers have been able to perceive only half of the pit; the other half was hiding in the dark when Mariner 10 flew by the planet. The Caloris Basin is around 960 miles (1,540 km) wide.