View Photo Gallery: The craft — one of twin spacecraft sent to explore distant planets — is approaching interstellar space.

When Johann Sebastian Bach composed the first movement of the Brandenburg concerto No. 2, he probably did not have the outermost reaches of space on his mind.

Then again, perhaps he did. One can never really know a person’s innermost thoughts — especially a virtuoso musician who has long since passed. Soon, however, the same may not be able to be said of interstellar space, which remains almost entirely a mystery to Earth-bound scientists.

Voyager 1, which has traveled the farthest from Earth of any man-made object, is approaching the edge of the heliopause, the boundary between the sun’s solar winds and the interstellar medium. It is impossible to know when, exactly, the craft will reach interstellar space, since it will be the first man-made object ever to travel that far from Earth. It is anticipated, however, that the craft will cross the boundary within the next few months or years, reaching the heliopause roughly 10 years after crossing the Termination Shock, which it did in 2004. Voyager 2 crossed the termination shock in 2007.

The Golden Record holds photographs, sounds and music compiled by a committee led by Carl Sagan. There is one aboard both Voyager 1 and 2. (NASA/JPL)

Electrical power aboard Voyager is supplied by three Radioisotope Thermoelectric Generators (RTGs). The fuel for the RTGs is plutonium-238 oxide. As the isotopic decay continues to give off less heat, systems aboard each craft have been powered down.

The thrusters, meanwhile, are fueled by hydrazine — a combination of nitrogen and hydrogen. Since there is no gravity in space, the thrusters do not need to run continually, meaning each craft is traveling roughly 30,000 miles per gallon of hydrazine. Both craft are expected to have enough power to operate until 2020, with Voyager 1 having enough hydrazine to power it through 2040, and Voyager 2 through 2034, Slate’s Brendan Koerner reports. The discrepancy is due to Voyager 2’s swing past Uranus and Neptune, which required it to burn more fuel. According to NASA, communication with Voyager could continue for another century — or even two — if it weren’t for the diminishing resources aboard the craft.

And then there is the Golden Record.

Both craft — each roughly the size of a compact vehicle — are equipped with a 12-inch, gold-plated copper phonograph record. The disc, compiled by a committee chaired by Cornell University professor and famed science popularizer Carl Sagan, contains 115 images and sounds from Earth, ranging from a tractor and a chimpanzee to crickets, frogs and even a kiss. There are greetings in 55 languages and a playlist of 27 songs.

The playlist, which you can listen to on, is a collection of music from all over the world, from Beethoven and Mozart to Solomon Island panpipes and Chuck Berry’s “Johnny B. Goode.” In a February 2010 report, the public radio program RadioLab interviewed the project’s creative director, Ann Druyan, who, over the course of the project, fell in love with Sagan. They were married in 1981.

Sagan died in 1996 at age 62.

"Whenever I'm down, " says Druyan, "I'm thinking: And still they move, 35,000 miles an hour, leaving our solar system for the great open sea of interstellar space."

Druyan and Sagan’s union is far from the only element of romance when it comes to Voyager. Even the final images sent back from the Voyager mission were sent from Voyager 1 on Valentine’s Day 1990.

But 35 years later, as Voyager approaches the edge of the sun’s influence, it begs the question, if we had it to do all over again — if you had it to do all over again — what would you put on the Golden Record? Would it even be a record? How would you equip Voyager?

After all, the data storage capacity aboard Voyager is less than that of the smallest iPod — roughly 68 kilobytes total on each craft.

So, who would make the cut? What technology would you use?

What message would you want to send from, in Sagan’s words, “The Pale Blue Dot” today and how would you propose to deliver it?

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