Planet Earth, commonly referred to as Earth, is a rocky planet in the Solar System of the Local Interstellar Cloud, which resides within the Orion–Cygnus Arm of the Milky Way Galaxy. At nearly 4.5 billion years old and 7,918 miles in diameter, it is the home world of the homo sapien sapiens species, the dominant and only sapient species on the planet and the only planet known to consist of intelligent lifeforms and civilization. The dominant species, humans, achieved the ability to leave their home planet technologically in 1969, landing humans on the Earth's only moon. By the Earth year of 2010, human beings landed on the nearest planet to the Earth, Mars, the first of an age of interplanetary and then interstellar travel.