How do people know where the Moon came from? Scientists think the Moon formed when an object about the size of Mars crashed into the young Earth, and Moon rocks brought back by Apollo match Earth rocks very closely in their chemistry, a clue about how the Moon formed. The young Moon was melted to great depth in a global "magma ocean." As it cooled, the lighter, less-dense rock floated upward toward the top. Deeper down, the Moon's core has two parts: a solid inner core inside a fluid (molten) outer core.

The rocks came from six landings. People have landed on the Moon on six Apollo missions: Apollo 11, 12, 14, 15, 16 and 17, and the Apollo astronauts brought back 842 pounds (382 kilograms) of Moon rocks and soil. The surface is a record too. The Moon has a rocky surface covered with craters, which were made when space rocks crashed into it. Lunar soil, called regolith, is pulverized rock, and it was made by countless meteorite impacts over geologic time. The Moon has so little air that a footprint left there can last for centuries or longer.

The dark patches tell a different story. The Moon's dark patches are called maria, a Latin word meaning seas. The Moon's dark maria are giant impact basins that were later flooded with lava; the flows were laid down over billions of years, and some of the youngest flows are about 1.2 billion years old. The Moon had erupting volcanoes long ago, but its volcanoes are quiet today. Dark lava plains called maria cover much of the near side of the Moon but are almost missing from the far side.

Galileo used a telescope to see that the Moon has mountains and craters and is not smooth. The first known drawing of the Moon made through a telescope was by Thomas Harriot, dated July 26, 1609, a few months before Galileo's drawings.

The Soviet Luna 2 was the first spacecraft to reach the surface of the Moon, but it made a hard-impact crash landing, and the impact destroyed the spacecraft. The Soviet Luna 9 lander transmitted the first photographs taken from the surface of the Moon.

Some clues need instruments. Apollo 11 astronauts left a mirror array (a retroreflector) on the Moon, and scientists on Earth bounce laser pulses off it to measure the distance to the Moon. That distance changes as the Moon moves on an oval orbit: on average about 363,300 km (225,700 miles) at its closest and about 405,500 km (252,000 miles) at its farthest.

There is also water ice on the Moon, hidden in dark craters near the poles where the Sun does not shine. Data from India's Chandrayaan-1 spacecraft, which orbited the Moon in 2008 and 2009, gave direct evidence of it.

Until a Soviet spacecraft flew past in 1959, nobody had seen the far side of the Moon. The far side of the Moon never faces Earth, so a spacecraft working there needs a relay satellite to send messages to Earth. As of November 2026, China's Chang'e-6 mission brought back 1,935.3 grams of Moon samples from the far side, the first samples ever returned from there.

Words to know

• regolith: moon soil
• magma: melted rock
• molten: melted
• retroreflector: light-bouncing mirror
• pulverized: ground to dust