Why is a meteorite black outside?
Many fresh meteorites have a thin, dark coat. It tells the story of their fiery fall.
When a space rock rushes into Earth's air, it is going very fast. The air in front of it gets squashed and becomes extremely hot.
The outside of the rock gets so hot that it melts. The melted rock is blown away, again and again, as it falls.
High in the air, the rock slows down. The glowing stops. The last thin layer of melted rock cools and hardens into a dark coat.
That coat is called a fusion crust. It is usually thinner than a coin. On a fresh meteorite it is often black, and can be shiny or dull.
The fall through the air takes only a few seconds, so the heat does not have time to soak into the middle. Inside, the rock stays as cold as space. Most meteorites are not hot when they land.
Over many years, rain and air can turn a fusion crust brown and rusty.
Some meteorites have shallow dents on the outside that look like thumbprints in clay. They form as the surface melts away during the fall.