Earth has one natural satellite, the moon, and more artificial satellites than any other planet which are used for radio, television and other communication technologies. Gravity holds objects on Earth due to its atmosphere and depends on mass and distance from the center of Earth. The oceans cover around 75% of the planet's surface, and much of Earth's land was previously covered by forests and grasslands but is now mostly occupied by human settlements and infrastructure. Earth measures approximately 12,756 kilometers in diameter.