Carl Sagan's master for Voyager Golden Record up for auction at Sotheby's

The two reels are not much to look at and the quality of their audio recordings, while described to be "excellent," exists in other formats. Their pedigree, though, is unique, which may be why they are estimated to be worth more than 10 times their weight in gold — an appropriate figure given that they were used in the creation of perhaps the most iconic golden records in existence.

On Thursday (July 27), Sotheby's will offer famed astronomer Carl Sagan and award-winning documentary producer Ann Druyan's personal copy of the master recording for NASA's Voyager Golden Record, identical discs intended as audio-visual time capsule that are now farther away from Earth than any other human-made objects in history.

"The Voyager missions are among the greatest acts of exploration in history, and the undertaking of the Golden Record reflects the incredible optimism, fascination and humility when faced with the great unknown of the universe. Led by Ann Druyan and Carl Sagan, the production of the record was a monumental task and it is a great honor to offer their personal copy of this most profound and unique artifact," Cassandra Hatton, Sotheby's global head of science and popular culture, said in a statement.

Sotheby's estimates that the Golden Record reels will command $400,000 to $600,000 (the minimum bid is $300,000). They are listed as Lot 80, the final item in the auction house's upcoming Space Exploration sale in New York.

Related: Scientists' predictions for the long-term future of the Voyager Golden Records will blow your mind

Launched in 1977 on NASA's Voyager 1 and 2 probes, the Golden Record was designed to communicate to possible space-faring civilizations something about the diversity of life and the culture on Earth. The record held greetings in 59 languages, 115 images, the sounds of our planet (including the call of humpback whales) and 27 pieces from the world's musical traditions.

Druyan, working with her future husband Sagan, selected the audio. The sound essay, which is the contents of the two reels up for auction, included a rain forest noisy with life, a mother's first words to her baby and the rasping of a distant pulsar, as well as the music of Bach, Beethoven, Mozart, Chuck Berry, and Louis Armstrong.

"Bursting with the myriad sounds of life, Carl and I and our colleagues designed the Golden Record to be a testament to the beauty of being alive on Earth," said Druyan (Sagan died in 1996). "We hoped it would capture the richness and diversity of our world."

In addition to the two discs that are now in deep space, only six other records were made. Today, examples of those original gold-plated copper records can be seen on display at the Smithsonian and at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California,

The Golden Record has also been reproduced. In 1992, Warner New Media released a two CD/CD-ROM box set, which included the full contents of the original Voyager disc, as well as as copy of Sagan's book, "Murmurs of Earth: The Voyager Interstellar Record." To mark the 40th anniversary of the probes' launch in 2017, Ozma Records produced a box set with three, heavyweight translucent gold vinyl LPs and a digital code to access the visual content on the flown discs.

Sotheby's is auctioning what is believed to be the only recordings produced in the making in the flown Golden Record to ever be offered for sale.

"Almost half a century since their creation, these tapes, which have never been out of our possession since they were made, present a unique opportunity for a collector to obtain the only original version of the first object to cross the heliopause, that place where the solar wind gives way to the gales of interstellar cosmic rays — it may be the only thing that will live on after everything we know is gone," Druyan said.

The reels come with their original Columbia Recording Studios boxes, with each labelled by hand in blue ink. The two have total running times of 51 minutes, 38 seconds and 60 minutes, 49 seconds.

In addition to the Golden Record, Sotheby's July 27 Space Exploration sale also features a number of original labels removed from the exterior of the Apollo command modules after they splashed down from the moon (est. $6,000 to $60,000) and a Russian Sokol launch and entry suit (est. $40,000 to $50,000).

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