ON THIS DAY (Sept 20)

On Sept. 20, 1970, the Soviet Union's Luna 16 moon probe landed on the moon to retrieve a soil sample. Four days later, it became the first robotic spacecraft to bring back a sample of lunar soil to Earth.

Luna 16 was the first robotic spacecraft to succeed in landing on the moon, scooping up a soil sample and returning it to Earth. Before Luna 16, the Soviet space program had tried and failed five times to yield a sample from the moon.

Overall, this was the third lunar sample brought to Earth. NASA's Apollo 11 and Apollo 12 missions had also brought back some rocks and soil from the moon. Luna 16 made a soft landing on the lunar surface in a mare known as "the Sea of Fertility," where it retrieved 101 grams of lunar dirt.