Much of the litter was left by NASA astronauts, who landed on the moon between 1969 and 1972 during the Apollo missions. Other pieces of trash are from unmanned space-exploration missions from the United States, Japan, Russia, India and Europe, NASA chief historian, William Barry told Live Science.
The significant weight of the moon junk belongs to heavy artifacts, such as “five moon ranger and lunar probes, that are still there,” Barry said.
The reason these objects were left on the moon was simply because “there wasn’t a lot of thought [about] ... bringing back unimportant equipment.
"The real concern was: Can we get the crew safely to the moon, can they get the samples they need and can we get them back in one piece?" Barry said.
But the moon trash has actually given NASA researchers another field to study--such as how the materials weather the conditions of radiation and the vacuum of space over time. Barry told Live Science that some objects on the moon are still being used--such as the laser-range reflector left there by the Apollo 11 crew.