Answer:
Caloris basin, a huge circular region on Mercury surrounded by rings of mountains, appears to have been produced by an impact from a large asteroid or comet. This impact is estimated to have occurred about 3.8 billion years ago and was powerful enough to create a basin nearly 1,550 miles (2,500 km) in diameter. The impact also created a series of concentric rings of mountains around the basin, which rise to heights of over 1 mile (1.5 km) above the surrounding terrain. The Caloris basin is one of the largest and most prominent features on Mercury and provides important clues about the planet's geological history.