The closest planet to the sun, Mercury is also the smallest planet in the solar system! Hot and barren with hardly any atmosphere, its rocky surface is covered in craters. Exploratory missions to Mercury have revealed evidence that it once had extremely active volcanoes on its surface! Subscribe to FreeSchool: https://www.youtube.com/user/watchfreeschool?sub_confirmation=1 Visit us on Facebook: https://www.facebook.com/watchFreeSchool Check our our companion channel, FreeSchool Mom! https://