The Moon is about 4.6 billion years old. The Moon has a layered structure of crust, mantle, and core like the Earth. The outermost lunar crust has an average thickness of about 60-65 km. Below the crust to a depth of 1000 km is the lunar mantle, which accounts for most of the volume of the Moon. Below the mantle is the lunar nucleus, which has a temperature of about 1000 degrees and is likely to be in a molten state. The diameter of the Moon is about 3474.8 km, which is about 1/4 of the Earth and 1/400 of the Sun, and the distance from the Moon to the Earth is equivalent to 1/400 of the distance from the Earth to the Sun, so the Moon is as big as the Sun when viewed from the Earth. The volume of the Moon is about 1/49 of the Earth, and its mass is about 735 billion tons, which is about 1/81 of the Earth’s mass. The gravity on the Moon’s surface is about 1/6 of the Earth’s gravity.
The first man-made object to reach the Moon was the Soviet Union’s unmanned lander Luna 2, which crashed into the lunar surface on September 14, 1959. “Luna 2 took pictures of the back of the Moon on October 7 of the same year. “Luna 9, the first lander to make a soft landing on the Moon, returned photos taken from the lunar surface on February 3, 1966. “Luna 10 was successfully orbited on March 31, 1966, and became the first artificial satellite on the Moon.
On July 19, 1969, Neil Armstrong, commander of Apollo 11, the first man to set foot on the moon, left a 9-inch by 7-inch stainless steel plaque on the moon’s surface to commemorate the landing and to provide some information on how it might be discovered. The Apollo 11 astronauts left a 9-inch by 7-inch stainless steel plaque on the lunar surface to commemorate the landing and provide some information about other creatures that might have discovered it. Eugene Cernan was the last man to stand on the Moon, as a member of the Apollo 17 mission in December 1972.