For only the second time in history, someone will be able to purchase pieces of the moon ― legally that is.

Three tiny rocks, the only known documented pieces of the moon in private hands, are hitting the auction block next month. The out-of-this-world soil is expected to fetch $700,000 to $1 million, according to auction house Sotheby’s.

An unmanned Soviet spacecraft brought the lunar samples back to Earth in 1970. After that, the USSR presented them to the widow of former Soviet space program director Sergei Pavlovich Korolev as a gift.

Sotheby's This lunar material is in a display case with viewing lenses.

Korolev was a rocket engineer; aircraft and spacecraft designer; and mastermind of the Soviet space program in the 1950s and ’60s. He died unexpectedly before the samples could be gifted to him.

The rocks, which will headline Sotheby’s Space Exploration auction scheduled for Nov. 29, fetched $442,500 when they were first sold in 1993, according to CNN.

“It was the first time a piece of another world had ever been offered for sale to the public,” Sotheby’s said of that sale. “It remains to this day, the only known legal sale of moon rocks to have ever occurred. We look forward to once again offering this tremendously rare and historic artifact to the public.”

Bettmann via Getty Images The USSR gave the moon rocks to the widow of Soviet space program director Sergei Pavlovich Korolev, following his death.

Lunar material is typically not available for purchase, at least legally. (In one case in 2011, a woman tried to sell a moon rock for $1.7 million, but the buyer was an undercover agent.)

The U.S. government considers lunar material from the Apollo missions to be government property, though a few pieces have been given as gifts to foreign governments. But this is a Soviet sample, and according to Sotheby’s, the rock “is the only known, documented lunar sample to have been gifted to a private individual.”