Luna 24 sample of lunar soil. Luna 24 was the last in the Soviet Luna program of unmanned moon probes. It was the third Luna mission (after Luna 16 and Luna 20) to retrieve samples from the surface of the Moon. Luna 24's sample was from the Mare Crisium (Sea of Crisis). 170 grams of lunar soil was successfully returned to the Earth on 22 August 1976. Parts of the sample were shared with NASA in December 1976. Studying these samples helps reveal the conditions present in the early solar system when the Moon and Earth were forming. Studying these samples also provides evidence of lunar weathering processes.