Sotheby’s, which is hosting the auction, estimates the sample bag, which was used by Neil Armstrong to collect soil samples on the Apollo 11 mission and still contains moon dust and small rocks, will sell for between $2 million and $4 million. The samples were the first ever collected from the moon.

It’s an exceptionally rare piece of history. Virtually everything from that historic mission is held by the Smithsonian, but a recent court ruling allowed this bag to be the only privately held artifact, says Sotheby’s.

Ironically, just three years ago, the Armstrong moon dust bag failed to find a bidder at a U.S. Marshall’s service auction. In 2015, it was bought as part of a lot, which sold for $995. The owner, curious about the piece, sent it to NASA to learn more about it. Tests at the space agency confirmed the debris inside was moon dust from the Apollo 11 landing site and the bag had made the flight with Armstrong and “Buzz” Aldrin.

Among the other items up for bids at the auction are the flown flight plan for Apollo 13 (with extensive annotations from the crew), which is expected to go for $30,000 to $40,000, and the records file for Russian Cosmonaut Yuri Gagarin, which may garner $50,000 to $80,000.