We’re lucky to live on a water world. More than 70% of the Earth’s surface is covered in water.
Earth is about 94 million miles from the Sun. That’s within the Goldilocks zone: the place in our solar system where a planet has just the right temperature for water to exist in oceans and rivers as a liquid and as ice in the north and south poles.
Earth also has an atmosphere more than 6,000 miles (9,650 kilometers) thick that’s filled with oxygen for us to breathe. This atmosphere, along with a huge magnet in the center of the Earth, helps protect us from the Sun’s harmful radiation, mostly solar wind and cosmic rays.
But the Moon hardly looks like a water world, or even a place with a few puddles. It has a worn-out internal magnet and an atmosphere so weak it’s virtually a vacuum. There are no clouds or rain or snow, just a sky that’s only the blackness of space, with a surface baked by the Sun. The Moon’s temperature reaches 273 degrees Fahrenheit (134 Celsius) by day and goes as low as -243 F (-153 C) at night.
