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Speaker 1: This Day in History Class is a production of iHeartRadio.

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Speaker 1: Hello and Welcome to This Day in History Class, a

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Speaker 1: show that rockets through history one day at a time.

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Speaker 1: I'm Gabeluesier, and in this episode we're talking about the

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Speaker 1: early days of the Voyager space program. NASA's first attempt

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Speaker 1: to explore the far reaches of our Solar System and beyond.

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Speaker 1: The day was August twentieth, nineteen seventy seven, a NASA

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Speaker 1: rocket launched the Voyager two space probe from Cape Canaveral, Florida.

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Speaker 1: Despite its name, Voyager two was actually the first of

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Speaker 1: two probes to be launched that year on a so

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Speaker 1: called Grand Tour of the outer planets. Its twin spacecraft

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Speaker 1: would launch about two weeks later, on September fifth, and

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Speaker 1: because that one was scheduled to reach Jueupiter and Saturn

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Speaker 1: before Voyager two, it was given the designation Voyager one.

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Speaker 1: Both probes were meant to take advantage of a rare

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Speaker 1: alignment of the Solar System's outer planets that only occurs

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Speaker 1: once every one hundred and seventy six years. The alignment

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Speaker 1: allowed both probes to swing from one planet to the

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Speaker 1: next using a new technique called a gravity assist. Voyager

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Speaker 1: one's trajectory put it squarely in the path of Jupiter

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Speaker 1: and Saturn, while Voyager two's route would allow it to

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Speaker 1: pay a visit to all four outer planets, Jupiter and Saturn,

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Speaker 1: as well as Uranus and Neptune. It would take more

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Speaker 1: than a decade for Voyager two to complete its grand

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Speaker 1: tour of the outermost planets, but when it finally did,

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Speaker 1: it became the first and so far the only spacecraft

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Speaker 1: to have done so. As you've probably gathered, the primary

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Speaker 1: goal of the Voyager program was to explore the out

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Speaker 1: Solar System and gather information and photographs of its most

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Speaker 1: distant and least understood planets. The mission proved remarkably successful

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Speaker 1: on that front, providing NASA's scientists with detailed measurements and

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Speaker 1: close up views of each of the four outer planets.

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Speaker 1: The probes took hundreds of detailed snapshots of everything from

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Speaker 1: the icy moons of Jupiter to the famous rings of Saturn.

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Speaker 1: They also discovered evidence of active geysers and volcanoes on

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Speaker 1: some of the planet's moons, and because of the two

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Speaker 1: probe approach, they were able to capture planetary changes over time,

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Speaker 1: such as fluctuations, and the size and shape of Jupiter's

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Speaker 1: Great Red Spot. In addition, Voyager two made several key

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Speaker 1: observations in nineteen eighty six, when it became the first

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Speaker 1: spacecraft to visit the ice giant Uranus. It turned out

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Speaker 1: that the planet had rings of its own, as well

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Speaker 1: as ten more moons than was previously thought, and a

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Speaker 1: curiously tilted magnetic field that was of full fifty five

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Speaker 1: degrees off the planet's axis. Lastly, Voyager two provided our

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Speaker 1: closest look yet at the farthest planet in our Solar System.

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Speaker 1: The probe reached its closest point to Neptune in late

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Speaker 1: August of nineteen eighty nine, skimming about three thousand miles

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Speaker 1: above the planet's atmosphere. During that approach, Voyager two identified

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Speaker 1: five new moons as well as the presence of rings,

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Speaker 1: confirming that all four of the outer planets have them.

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Speaker 1: The probe's primary mission was exploration, but they also had

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Speaker 1: a secondary goal to serve as ambassadors of Earth should

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Speaker 1: they happen to cross paths with an extraterrestrial life form.

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Speaker 1: To that end, both Voyager one and Voyager two were

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Speaker 1: outfitted with a kind of introductory time capsule, a gold

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Speaker 1: plated copper disc containing a wealth of information about Earth

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Speaker 1: and its inhabitant. Those identical twelve inch phonograph records were

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Speaker 1: titled Sounds of Earth, and they featured a collection of

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Speaker 1: audio recordings that were meant to be representative of human

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Speaker 1: civilization and the planet as a whole. The selections were

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Speaker 1: carefully chosen by famous astronomers Carl Sagan and Frank Drake

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Speaker 1: in cooperation with a panel of historians, artists, folklorists, and musicologists.

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Speaker 1: The contents they settled on included spoken greetings in fifty

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Speaker 1: five languages, twelve minutes of nature sounds such as the

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Speaker 1: noise of wind waves, thunder birds, and other animals, recorded

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Speaker 1: messages from President Jimmy Carter and other world leaders, and

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Speaker 1: about ninety minutes of music from a variety of different

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Speaker 1: eras and cultures. Each record also included over one hundred

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Speaker 1: analog and coded images, as well as symbolic inscriptions detailing

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Speaker 1: the probes origins and how to play the disc. To

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Speaker 1: help with that last part, the record was accompanied by

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Speaker 1: a cartridge and needle, all of which were sealed up

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Speaker 1: together in a protective aluminum jacket, which was attached to

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Speaker 1: the hull of each craft. There's a lot that would

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Speaker 1: have to go right for an alien to actually find

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Speaker 1: and play Humanity's message, and of course the chances of

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Speaker 1: that happening between Earth and Neptune are slim to none.

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Speaker 1: So it's a good thing that the journey of the

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Speaker 1: Voyager probes didn't stop at the edge of our Solar System.

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Speaker 1: In August twenty twelve, Voyager one became the first man

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Speaker 1: made object to cross the boundary into interstellar space. Then

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Speaker 1: in November twenty eighteen, Voyager two became the second. Both

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Speaker 1: probes are now traveling well outside our Solar System, cruising

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Speaker 1: through empty space in the Milky Way. As of twenty

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Speaker 1: twenty four, Voyager one is fifteen point two billion miles

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Speaker 1: from and Voyager two is twelve point seven billion miles away.

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Speaker 1: Because the probe's power sources are plutonium based, they're actually

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Speaker 1: still transmitting data back to Earth at the time of recording,

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Speaker 1: but that won't always be the case. NASA estimates that

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Speaker 1: both craft have enough fuel and power to keep their

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Speaker 1: instruments running through at least twenty twenty six, but at

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Speaker 1: some point after that their transmissions will cease. However, that

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Speaker 1: still won't be the end of the road for the

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Speaker 1: Voyager twins. Thanks to their inertia and momentum, they'll keep

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Speaker 1: right on sailing through the galaxy long after they've run

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Speaker 1: out of juice. In fact, unless the probes collide with something,

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Speaker 1: they'll pretty much keep going forever, and in about forty

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Speaker 1: thousand years they'll make a close approach to another planetary system.

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Speaker 1: When that happens, there's an off chance that something or

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Speaker 1: someone will interrupt their journey, and if they do, hopefully

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Speaker 1: they'll work out out how to play the Golden record

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Speaker 1: and not think we're too silly for sending it. I'm gay,

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Speaker 1: Blues Gay, and hopefully you now know a little more

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Speaker 1: about history today than you did yesterday. If you'd like

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Speaker 1: to keep up with the show, you can follow us

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Speaker 1: on Twitter, Facebook, and Instagram at TDI HC Show, and

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Speaker 1: if you have any comments or suggestions, feel free to

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Speaker 1: send them my way by writing to this Day at

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Speaker 1: iHeartMedia dot com. Thanks to kazb Bias for producing the show,

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Speaker 1: and thanks to you for listening. I'll see you back

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Speaker 1: here again tomorrow for another day in History Class