No, the moon is not a big ball of gas. The moon is rocky and consists of silicate rocks and metals like potassium, uranium, thorium, magnesium, iron, and titanium. It is believed that the moon was formed about 4.5 billion years ago as a result of a collision between the Earth and a Mars-sized body called Theia. The impact ejected material into orbit around the Earth, which eventually merged to form the moon.