Luna 10 or Lunik 10 was a 1966 Soviet lunar robotic spacecraft mission in the Luna program. It was the first artificial satellite of the Moon, and any other body other than Earth and the Sun (in heliocentric orbit). Luna 10 conducted extensive research in lunar orbit, gathering important data on the strength of the Moon's magnetic field, its radiation belts, and the nature of lunar rocks (which were found to be comparable to terrestrial basalt rocks), cosmic radiation, and micrometeoroid density. Perhaps its most important finding was the first evidence of mass concentrations (called "mascons")—areas of denser material below the lunar surface that distort lunar orbital trajectories.

Wikipedia: https://en.wikipedia.org/wiki/Luna_10. Related NASA reference: https://nssdc.gsfc.nasa.gov/planetary/chronology.html#1966. Description adapted from Wikipedia contributors (CC BY-SA 4.0; https://creativecommons.org/licenses/by-sa/4.0/).