Many people remember exactly where they were
when humans first set foot on the Moon. But for those of us born after 1969, we’ve
got to hang on to other epic moments in spaceflight history. I vividly remember watching the first launch
of the space shuttle in 1981 when I was 9 years old, and I remember when NASA’s Voyager
spacecraft swept past each of the outer giant planets in the Solar System: Jupiter, Saturn,
Uranus and Neptune. It’s been nearly 40 years since the Voyagers
blasted away from Earth, on their voyage into interstellar space, and here’s the most
amazing part. They’re still operational. Still working hard to deliver us science,
from the outer Solar System. As I record this video, Voyager 1 is the most
distant object ever created by human beings, more than 20 billion kilometers away from
Earth, more than 4 times the distance to Pluto. Here’s the really mind bending part. Voyager 1 is the farthest object we know of
in the entire Solar System. But I’m getting ahead of myself, it’s
time to look back, nearly 40 years and remember the Voyager missions and their amazing accomplishments
over the decades. The Voyager missions were developed in the
early 1970s to take advantage of a rare alignment of the giant planets in the Solar System. With the right launch speed, trajectories
and planetary slingshots it could be possible to send a spacecraft past each of the large
planets in the Solar System: Jupiter, Saturn, Uranus and Neptune. Over the course of their primary mission,
the spacecraft were to visit Jupiter and Saturn, but the mission controllers couldn’t help
but add Uranus and Neptune to the list, reprogramming the spacecraft as they explored the Solar
System to continue onward. Between them, the twin spacecraft observed
4 planets, 48 moons, as well as their rings, and magnetospheres. Their original mission should have been only
5 years, but they were extended to 12, and now, almost 40 years later, they’re still
going and going. Voyager 2 lifted off first, on August 20,
1977 with a trajectory that gave it the option to add Uranus and Neptune later on in its
trip. Voyager 1 went second on September 5, 1977
but followed a faster, shorter trajectory. Their first destination was Jupiter, the largest
planet in the Solar System. Voyager 1 arrived at the giant planet on March
5th, 1979, passing within a few hundred thousand kilometers of Jupiter’s cloud tops. It observed the incredible storm systems in
Jupiter’s upper atmosphere, and helped to discover that Jupiter, like Saturn, has a
ring system. Perhaps the biggest discovery at Jupiter was
with its moons. The Voyagers discovered that Jupiter’s innermost
large moon Io has active volcanoes, spewing lava high into space - the first time volcanism
had been seen anywhere else in the Solar System. They observed cracks on the surface of Europa
and Ganymede, indicating that both worlds have some kind of subsurface ocean beneath
an icy crust. Between them, the two spacecraft took more
than 33,000 pictures of Jupiter and its moons. Next up was Saturn, and in my opinion, the
highlight of the whole Voyager program. Although the Ringed Planet had already been
visited by Pioneer 11 in 1979, the Voyagers took things to the next level. Voyager 1 arrived in November, 1980 and sent
back high resolution images of Saturn, as well as its moons and rings. Voyager 1 was selected to make a closer flyby
of Titan, Saturn’s largest moon and the second largest moon in the Solar System. It discovered that Titan’s atmosphere is
mostly made of nitrogen, like Earth. Unfortunately it was too dense to see down
to the surface. We’d need to wait for Cassini to show us
what’s down there. Voyager 1 discovered that Saturn’s upper
atmosphere seems to contain less helium than scientists were expecting, which indicates
that the helium is slowly sinking down into the center of the planet. Voyager 2 arrived 9 months later in August,
1981. It passed within 41,000 kilometers of Saturn
and made even more observations of the planet and its environment. Together, the Voyagers provided the first
tantalizing hint of geysers emanating from Enceladus - which Cassini confirmed decades
later. And together they discovered the huge hexagonal
vortex at the planet’s north pole. At this point, the Voyagers parted company. Voyager 1 continued on from Saturn with no
more destinations, while Voyager 2 performed a slingshot maneuver that put it on course
to visit the outer ice giants. Voyager 2 still had two more destinations
to go. Its next destination was Uranus in January,
1986, when it passed within 81,500 kilometers of the planet. This was the first time (and so far last)
time that any spacecraft ever reached Uranus. These are the only close up pictures we have
of Uranus and its moons, thanks to Voyager 2. The spacecraft made several new discoveries
about Uranus. The planet was flipped over onto its side
by some collision in the ancient past. Voyager discovered that not only does Uranus
have a magnetosphere, but the it’s twisted into a corkscrew shape that trails behind
the planet as it orbits the Sun. Voyager 2 observed the planet’s rings, and
collection of moons. But perhaps the strangest discovery was its
moon Miranda. Voyager 2 observed huge cracks and canyons
on the surface of Miranda as deep as 20 km. Is it possible that the moon was smashed up
in the ancient past, and then reformed from the shattered pieces? The final stop on the Grand Tour was Neptune,
visited by Voyager 2 in the summer of 1989. I remember this image vividly, on television
and in the newspapers, it was the summer I graduated from high school. Voyager 2 passed just 4,950 kilometers above
Neptune’s north pole, closer than any other object during its voyage. Since this was Voyager 2’s last stop, NASA
was willing to throw caution to the wind. The spacecraft discovered that the winds on
Neptune blow faster than anywhere else in the Solar System, triple the speed of Jupiter. It discovered that the planet has storms swirling
across its surface like the other giant planets. It fine tuned estimates of Neptune’s mass,
discovered six new moons and observed its ring system up close for the first time. Perhaps the most tantalizing was the close
up images of Neptune’s moon Triton. A bizarre moon that dominates the Neptunian
system, and orbits backwards from all the other large moons in the Solar System. Scientists think it was a captured Kuiper
Belt Object, stolen in the ancient past. With Triton in its rearview mirror, Voyager
2 carried on, out into deep space. Once the Grand Tour was over, but the Voyagers
still had more science to do. We’ll talk about that in a moment, but first
I’d like to thank: Anton Velmozhniy
John Clark Alex Boisselle And the rest of our 765 patrons for their
generous support. If you love what we’re doing and want to
get in on the action, head over to patreon.com/universetoday. In August, 2012, the spacecraft officially
made the leap to interstellar space, escaping the Sun’s heliosphere. In case you weren’t familiar, the heliosphere
is a region of ionized plasma that surrounds the Sun, blown out into space by its solar
wind, like an inflated balloon. This bubble is what separates the Sun’s
solar wind from the collective solar winds of all the other stars in the Milky Way. The Voyagers crossed the region dominated
by the Sun into interstellar space. Even though they’re now more than 20 billion
kilometers away, they still emit signals of about 23 watts; as much power as a refrigerator
light bulb. Although, by the time these reach Earth, they’re
a billion-billionth of a watt. And yet, they continue onwards. Now, let’s look into the future. What happens next for these spacecraft? At their current pace, they’ll reach the
Oort Cloud in about 300 years. That’s the huge cloud of icy objects thought
to surround the Solar System, and the source of the long period comets we see from time
to time. Unfortunately, they’ll be dead much sooner
than that. Sometime in the next couple of years, the
the radioisotope thermoelectric generator that powers the spacecraft isn’t going to
be able to give it enough electricity to keep its equipment going. The gyroscopes that allow NASA to re-orient
the spacecraft will cease operations. The data recorder will shut down. And in 2020 or so, NASA will start to shut
down their scientific instruments one by one as the power levels continue to decline. Finally, by 2025 to 2030, the Voyagers won’t
have enough electricity to do anything else. We got 40 years from them, but we’ll be
lucky to get to 50. And then, they’ll continue to drift off
into the darkness. Their journey through the Oort Cloud will
last 30,000 years, and in 40,000 years or so, they’ll get within a couple of light-years
of the star Gliese 445. But the Voyagers were built to last. Each was equipped with a Golden Record, containing
sounds and images selected by Carl Sagan. Aliens who encounter the Voyagers will enjoy
the sounds of Earth, like whales, surf and the wind, as well as musical selections. Oh, and a handy map to Earth using a map of
pulsars. The records were made of gold and etched with
a sample of Uranium-238, which has a half life in the billions of years. Future alien civilizations could use this
to determine when the Voyagers were constructed. Ann Druyan, the co-creator of Cosmos, says
that the records themselves will be playable for a billion years. The Voyager spacecraft were some of the most
ambitious robotic spacecraft humans ever built. They carried our senses out to Jupiter and
Saturn, and then Voyager 2 helped us see Uranus and Neptune for the first time ever. We still depend on and reference the images
and observations from these hardworking spacecraft for so much of our understanding of the outer
Solar System. I’ll miss them when they’re gone. What about you? Do you have nostalgic memories about the Voyager
spacecraft? Let me know your thoughts in the comments. In our next episode, we look at the Van Allen
Belts. The radiation that surrounds the Earth; another
dangerous hazard that astronauts face - as if they need any more ways that the Universe
is trying to kill them. That’s next time. Of course, I’ve got a playlist of videos
about the Voyager missions. First up, a video from NASA a few years ago
when Voyager 1 reached interstellar space, Tom Scott visits the Voyager control room
at NASA, Vsauce has message for the future, including Voyager’s golden record, and then
a pair of longer lectures from NASA scientists working with Voyager.
