WASHINGTON—Saying the ambitious new project would be a historic, once-in-a-generation leap forward in the annals of space exploration, NASA announced Friday its plan to put the moon on Mars by 2040. “Ever since we first sent a man to the moon half a century ago, the American people have been waiting for us to take the next step and send the moon to Mars,” said NASA administrator Bill Nelson, adding that within two decades, the famed image of Apollo 11 commander Neil Armstrong’s first footprint on the moon would be joined in the public consciousness by photos of the 1,500-mile-wide crater the moon was expected to leave on the Red Planet. “No space mission is without risks. The moon could descent too quickly and disintegrate on impact with the Martian surface, or it could, upon its return, fail to achieve the velocity needed to escape the gravity of Mars and make it back home to its orbit around the Earth. But should we succeed in our mission, it could open up many other opportunities for us, such as putting the Earth on Mars, putting Mars on Venus, and so on.” Nelson added that it might also one day be possible to build a colony on Mars that could be inhabited by hundreds of moons.