Apollo 8 in 1968 was the first crewed mission to orbit the Moon, and in 1969, astronaut Neil Armstrong became the first person to walk on the Moon. In all, people have landed on the Moon on six Apollo missions: Apollo 11, 12, 14, 15, 16 and 17. The astronauts brought back 842 pounds (382 kilograms) of Moon rocks and soil.
Apollo 11, the mission that first landed people on the Moon, lifted off on July 16, 1969. Neil Armstrong and Buzz Aldrin landed on the Moon in Eagle, while Michael Collins stayed in orbit in the command module Columbia. Armstrong flew the last part of the landing partly by hand and set Eagle down in the Sea of Tranquility, and as he stepped onto the Moon, he said, "That's one small step for man, one giant leap for mankind."
People had studied the Moon, which is about 2,160 miles (3,475 kilometers) across, long before anyone carried a rock home from it. 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, and Galileo used a telescope to see that the Moon has mountains and craters and is not smooth. The Moon has a rocky surface covered with craters, which were made when space rocks crashed into it, and its dark patches are called maria, a Latin word meaning seas.
On Apollo 17, Eugene Cernan and Harrison Schmitt spent just over 22 hours outside on the Moon's surface, and near the rim of Shorty Crater, Schmitt spotted orange soil. Lunar soil, called regolith, is pulverized rock that 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 young Moon was melted to great depth in a global magma ocean, and as it cooled, the lighter, less-dense rock floated upward toward the top. Later, the Moon's dark maria formed: they are giant impact basins that were flooded with lava, and the flows were laid down over billions of years, with some of the youngest flows about 1.2 billion years old. The Moon had erupting volcanoes long ago, but its volcanoes are quiet today.
The two faces of the Moon are not alike. Dark lava plains called maria cover much of the near side of the Moon but are almost missing from the far side. The Moon's crust is thicker on the far side than on the near side, by up to about 12 miles, and scientists do not yet fully understand why it is so uneven.
Scientists think the Moon formed when an object about the size of Mars crashed into the young Earth. Moon rocks brought back by Apollo match Earth rocks very closely in their chemistry, a clue about how the Moon formed. Moon rocks also hold only small amounts of the volatile elements, the ones that vaporize when heated, and compared with Earth, the Moon is depleted in them.
Seismometers left by Apollo astronauts recorded 28 shallow moonquakes between 1969 and 1977. The Moon is also slowly shrinking as its hot interior cools, and scientists link this shrinking to cracks in the crust called thrust faults and to some moonquakes.
Beneath the surface, the Moon has a very small core, and the core has two parts: a solid inner core inside a fluid, molten outer core. There are also lunar mascons, hidden concentrations of extra mass under the Moon's surface, which formed when huge impacts dug out basins on the ancient Moon, according to an analysis of GRAIL gravity data.
The Apollo astronauts also left a mirror array on the Moon. Scientists on Earth bounce laser pulses off it to measure the distance to the Moon, and the mirrors are still used today to track its orbit. As of November 2026, no one has walked on the Moon since Apollo 17 left in December 1972, but the mirrors are still at work.
Words to know
- regolith: Moon soil
- maria: dark plains
- volatile: easily vaporized
- seismometers: quake detectors
