The Solar System

The Inner Solar System

What is Mercury’s history?

Astronomers think that Mercury, like the moon, was originally made of liquid rock and that the rock solidified as the planet cooled. Some meteorites hit the planet during the cooling stage and formed craters. Other meteorites, however, were able to break through the cooling crust. The impact caused lava to flow up to the surface and cover over older craters, forming the plains.


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