Today, some 40 years after moon dust brought back from the Apollo 11 mission went missing, it has been recovered.

The moon dust was discovered at a St. Louis auction house and returned to the Johnson Space Center in Houston this week.

"It's a speck — the size of a fingertip," said David Kols of Regency-Superior auction house, where the dust had been placed for sale. "But it's lunar material, and since we're not going back to the moon in my lifetime or yours, that makes it worth a lot to some people."

The U.S. Attorney's office in St. Louis, which announced the recovered moon dust on Thursday, said that investigators with the National Aeronautics and Space Administration (NASA) believed the dust had come from the film cartridge of a camera used by astronauts on humanity's first trip to the moon in 1969.

The dust was lifted from the cartridge using a 1-inch (2.5 cm) piece of clear tape. Somehow, it reached the black market and was sold in 2001, NASA investigators believe, to a German collector who cut up the tape into tiny slivers, rather than return it to the U.S. government.

When investigators from both NASA and the U.S. Attorney's office noticed moon dust listed for sale in St. Louis, they shut down the transaction with the cooperation of the auction house and the seller. The widow trying to sell the dust — her name was not released — said she didn't know where her late husband had purchased it. She "immediately and graciously agreed to relinquish it back to the American people," the U.S. Attorney's office said.

The auction house had estimated its value at between $1,000 and $1,500.