Mercury is the closest planet to the sun. We learned this in kindergarten. However, it is considered to be an extreme planet. It is also a rocky planet. Very little exploration and information is known about this planet. The planet has extreme temperatures. Obviously, it has very hot temperatures that are too difficult to even wrap your mind around it. However, their temperatures also change greatly.
This is why it is called an extreme planet. Due to this, it is impossible to send astronauts to Mercury to explore it. Therefore, it is considered to be inactive. There are many craters and rock on the planet. It is believed that this planet has volcanoes on it because of the remnants of lava have been detected.