7 Places to Visit in the Solar System

Caloris Basin, Mercury

About 4 billion years ago, the inner solar system was being cleared of the remaining debris left over from its formation. During this period, which is called the Late Heavy Bombardment, a large asteroid like those that created the “seas” on the Moon crashed into the planet Mercury and formed the Caloris Basin, one of the largest such features in the solar system with a diameter of 1,550 km (960 miles). The interior of the basin is filled with high ridges and deep fractures that radiate outward from the center.

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