Every Type Of Moon Explained In 17 Minutes

The Moon. Earth's moon is about 2,159 miles across and sits an average of 238,000 miles away. It looks calm and gray, but it has no atmosphere to soften anything. In direct sunlight the surface reaches around 250 degrees F. In shadow it drops to minus 280, and the line between the two is sharp. One step can take you from one extreme to the other. A full day on the Moon lasts about 29 Earth days, so once the sun goes down, the night lasts two weeks. If you were caught on the surface when night fell, your suit's heaters would run continuously, draining power faster than they could hold the cold back. The dust would already be a problem before that. Lunar dust is jagged, never weathered by wind or water, and it clings to everything and scratches through seals. Your joints would grind. Your visor would haze over. And there is no air to carry sound, so all of it would happen in complete silence. Europa. Europa is one of Jupiter's largest moons, about 1,940 miles across. From the outside it's a smooth ball of ice, cracked with long reddish lines. Underneath that ice is an ocean of liquid saltwater, holding more water than every ocean on Earth combined. The surface temperature is around minus 260 degrees F, cold enough that the ice behaves like solid rock. The ocean stays liquid because Jupiter's gravity squeezes the moon constantly, and that squeezing generates heat deep inside. If you stood on the surface, the bigger danger wouldn't be the cold. It would be the radiation. Jupiter throws out a field so intense that an unshielded human on Europa's surface would receive a lethal dose in about a day. Your electronics would fail first. Then the radiation would start breaking apart the cells in your body, faster than they could repair. And below your feet, separated by miles of ice you could never dig through, the ocean that might hold life would keep moving in the dark, completely out of reach. Io. Io is another large moon of Jupiter, about 2,260 miles across, and it is the most volcanically active object in the solar system. It has hundreds of active volcanoes. Some of them blast plumes of sulfur and molten rock 250 miles into space. The surface is yellow and orange and black, constantly repaved by eruptions, with lava lakes that never cool. The reason is the same gravity that feeds Europa's ocean, but here it's far stronger. Jupiter and the other moons pull on Io from different directions, flexing its interior until the rock melts. If you landed on Io, the ground would not be stable. The surface shifts as the volcanoes reshape it. The air, what little there is, is sulfur dioxide, and it would freeze onto your suit as frost while the ground beneath you stayed hot enough to melt metal. The radiation from Jupiter is even worse here than on Europa. You'd be cooked from above and below at the same time, standing on a world that never stops erupting.