apollo 11 training
Neil Armstrong holds a bag while Edwin "Buzz" Aldrin practices scooping up a lunar sample during training. NASA

A piece of space exploration history will be sold in July due to a mistake made in 2015 that landed a pouch that once held moon rocks in private hands. The pouch, used during the Apollo 11 mission to the moon to collect lunar rocks and dust, will be sold at the auction that will be part of Sotheby’s Space Exploration sale. The bag is expected to sell for $2 million to $4 million at the July 20 auction during the anniversary of the lunar mission.

Read: A Slice Of The First Meteorite That Ever Hit Someone Sold For Thousands

The bag never permanently made it to a museum like most of the artifacts from the historic moon landing. The unassuming white pouch was up for auction at a small auction house a few times in 2014 but failed to attract any bids. Then in 2015 it was listed again, which is when the current owner purchased it. The owner, Nancy Carlson, paid just $995 for the white pouch. Little did she know the dust inside wasn’t ordinary old dirt; it was lunar material, Sotheby’s said.

She sent the pouch to NASA for further information on the dust in the bag, which was verified to be moon dust left over from the Apollo 11 mission. Astronaut Neil Armstrong had placed 500 grams of material from the surface of the moon in the bag to bring back to Earth during the historic first mission, Sotheby’s said. A number printed on the inside of the bag matched with that of the bag listed on the stowage list for the Apollo 11 mission. This confirmed not only that the bag was used during a lunar landing, but that it was used during the historic first lunar landing.

In December, a judge ruled the bag legally belonged to Nancy Carlson, the woman who purchased it at the 2015 auction, and not NASA. The bag was found at the home of Max Ary a curator who was convicted of stealing in 2006 and was subsequently auctioned to help pay off the restitution, Space.com reported.

Read: 13 Amazing Images From The First Lunar Landing

Earlier this month a slice of a meteorite was auctioned off online as part of the “Deep Impact: Martian, Lunar and Other Rare Meteorites” online auction at Christie’s. The slice of meteorite that was sold for thousands came from the first meteorite ever known to hit a person. The space rock was no bigger than a quarter and looks like an average stone, but the story compelled bidders.

Other items that will be up for auction during Sotheby’s “Space Exploration” event will include signed photos and emblems from astronauts, maps and engineering models. The materials come from both the U.S. and Soviet space programs. The auction will be the first space-themed auction Sotheby’s has hosted since the 1990s.