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In 1977, two pioneers embarked on what might be
one of the most epic feats of exploration ever
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undertaken. Their goal? To unravel the cosmic
mysteries surrounding the solar system and our
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place in it. Not only did they provide us with
some of the first and best imagery of our solar
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system's outer planets, but they continue to
send us incredible new information about our
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universe from interstellar space - some
47 years and 24 billion kilometres later.
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The Voyager 1 and 2 probes are more than just
instruments and circuitry. They are a symbol
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of humanity at its best - curious, audacious,
ambitious, and resilient. Voyager didn't just
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capture dazzling photos of our gas giants
and their moons; it captured the hearts and
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minds of generations back home on Earth.
These are the probes that have gone the
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furthest that any human object has travelled.
They are trailblazers and ground-breakers. It
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is their unique opportunity – and their peril
– to travel beyond the reach of humanity,
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to capture images of things we have never seen
before so close up, nor have we seen since.
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"When I look back, I realise how little we
actually knew about the solar system before
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Voyager," says Voyager Mission Project Scientist
Edward Stone. "We discovered things we didn't know
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were there to be discovered, time after time."
So, are you curious to see what they learned?
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I’m Alex McColgan, and you’re watching Astrum.
And in today’s supercut we’ll cover everything you
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might ever want to know about the Voyager missions
– from the probes themselves, their Grand Tour,
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to their impending, tragic finale.
It’s one of life’s little ironies
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that it is not new, cutting-edge technology
that is advancing our understanding most at
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the edge of our solar system, but old machines.
They have an onboard computer with less memory
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than the one inside your car’s key fob. To this
day, they are still using 8-track magnetic tape
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from the 1970s – which makes them older than
many of you sitting here watching this. Such is
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the conundrum of deep space exploration, where
vast distances and extremely long travel times
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can mean that technology is antiquated by the
time it has reached the most ambitious targets.
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Of course, Voyager 1 & 2 were not initially meant
to travel all the way to interstellar space. They
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were instead built for a 5-year mission to
explore Jupiter and Saturn and their larger
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moons, which was only possible thanks to a rare,
once-every-176-years planetary alignment. However,
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after completing all of its initial objectives
on Jupiter and Saturn, the Voyager Mission
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team added flybys of Uranus and Neptune to
the probes’ objectives. Later, these, too,
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were completed, so NASA announced the start of the
even more ambitious Voyager Interstellar Mission,
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with the purpose of exploring the outer limits
of the sun’s sphere of influence and beyond.
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This final journey would take both probes off the
ecliptic to unexplored parts of the solar system,
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such as the termination shock and the denser
and hotter heliosheath, before finally crossing
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the heliopause into interstellar space.
But how did these incredible machines manage
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to accomplish so much beyond the scope of their
original mission? It all comes down to that old,
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but incredibly effective technology. NASA
scientists made a number of forward-thinking
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design choices that allowed the probes to far
exceed their initial objectives. To put it
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simply; they were built different. Here’s how:
Let’s start with one of the most consequential
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decisions: the fuel source. Each probe is equipped
with a long-lasting radioisotope thermoelectric
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generator, which converts heat from the decaying
plutonium 238 isotope into electric power. These
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generators were capable of producing 157 Watts
of electrical power upon takeoff – about enough
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to power a laptop and charge a mobile phone too.
This might not sound like much, but was more than
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Voyager needed. While a radioisotope generator
meant that power production was in constant
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decline (it would halve in strength every 87.7
years), it would still be enough power to keep
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the essentials on the probes running until at
least 2025. This long-term fuel capacity was no
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accident. You see, when the Voyagers launched
in 1977, NASA faced a unique opportunity:
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the planets would soon be in that one-in-176-year
alignment that had last occurred during Napoleon’s
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first reign! This rare alignment would not only
allow the Voyagers to visit Neptune and Uranus
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with minimal course adjustment but also give the
probes a gravity assist from each of the four
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outer giants they visited, thereby increasing
their effective velocity beyond what they
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could get from their own rocket propulsion.
This idea was relatively new at the time,
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having been only attempted previously on NASA’s
Pioneer missions to Jupiter and Saturn.
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However, this narrow window gave
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NASA a strict deadline. There wasn’t enough time
to plan follow-up missions, and the United States
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Congress wouldn’t earmark enough funding for a
longer expedition (like the Grand Tour NASA first
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proposed). So, what did Voyager’s team do? They
devised a series of engineering feats to optimize
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the probes for a potentially longer mission and
fervently hoped that the funding would follow.
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Each of the Voyager probes is equipped with
11 scientific instruments. Most of them have
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redundancies in case of machine failure, which
can be toggled on and off to conserve power. To
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adjust course and orientation, the probes are
equipped with gyroscopes for stabilization,
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referencing instruments and 16 hydrazine
thrusters, including 8 backups.
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Backups – and good backups at that – were key to
the voyager probes’ longevity. They proved to be
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vital as Voyager 2’s main thrusters stopped
working after 37 years. Its backup thrusters
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had to engage after 4 decades of idleness. And
guess what? They worked perfectly, highlighting
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the excellent engineering that went into them. The
Voyagers also have custom-built onboard computers,
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which are antiquated by today’s standards
but were cutting-edge in 1977. The probes’
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wide-angle and narrow-angle lens cameras are
controlled by a Computer Command Subsystem,
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which has fixed programs like fault
detection and correction routines.
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Another key to its success lay in its computers.
Each probe had a computer called the Attitude and
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Articulation Control Subsystem, and no, it doesn’t
scold the Voyagers when they get sassy! “Attitude”
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refers to the probes’ orientations with respect to
the Earth, without which their high-gain antennae
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would be unable to send or receive signals from
NASA’s Deep Space Network. This is very important,
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as the probes’ transmitters only have
the Wattage of a refrigerator lightbulb,
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and at such immense distances, their radio
signals become barely detectable whispers. To
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communicate with the Voyager team and vice versa,
the probes’ antennae must be facing the Earth, and
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the Deep Space Network must in turn know exactly
where they are. Otherwise, they would be lost,
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like a needle in a 287 billion km haystack.
Each Voyager spacecraft has a 3.7 meter
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antenna for real-time transmission and an 8-track
digital tape recorder capable of buffering 536
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megabits for future transmission, enough to store
100 photographs. While this was a huge step up
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from the earlier Pioneer probes, which had no
onboard data storage, it’s still a fraction
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of what the smartphone in your pocket can store
today. Despite these limitations, the DTRs were
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built to last. Odetics, which manufactured
the them, claimed their DTRs could process
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over 4,000 kilometres of tape without taking
visible wear and tear. They had to withstand
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the harshest environments imaginable and undergo
rigours that had never before been tested. Yet,
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the Voyager DTRs performed without data loss
or machine failure until they were finally
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taken offline to conserve power. Not bad for
machines 12 years older than the world wide web!
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Durability was a chief concern during Voyager’s
planning. There are many unknowns in a mission
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of this magnitude. To get to Jupiter, both
Voyagers would have to pass through the asteroid
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belt. Scientists once believed that this region
would shred apart any spacecraft that tried to
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pass through it. However, Pioneers 10 and 11 had
previously been able to pass through the asteroid
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belt, which emboldened Voyager’s team to repeat
the stunt. However, failure would have meant
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disaster before the probes had even reached their
first target. Luckily, both probes made it through
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the asteroid belt unscathed (and we now know
that it is mostly empty space thanks to them)!
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Even with all these successes, and with the probes
performing far better than their engineers could
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possibly have hoped for, as the two spacecraft
travelled through the vastness between the planets
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there was still at least one more hurdle
to cross. What would happen to the probes
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in the extremely cold temperatures of interstellar
space? NASA installed multiple heaters to keep the
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machinery operational. Nonetheless, as the probes’
power waned, NASA had to turn off some of their
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heaters to conserve energy. When the cosmic-ray
detector’s heater was turned off two years ago,
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its temperature plummeted by 70 degrees Celsius.
Needless to say, sending a repair team 23 billion
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kilometers into space isn’t an option. So,
everyone thought the instrument would break,
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but… it continued to run smoothly! The fact that
the probes have operated so well for 45 years is a
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testament to their resilience and engineering.
But, with all this technology, what did they
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see? Let’s go back to the beginning, and follow
the path they blazed across our Solar System.
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On August 20th 1977, NASA launched the Voyager
2 space probe from Cape Canaveral, Florida. Its
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partner in crime, Voyager 1, was launched two
weeks later on September 5th, 1977. Even though
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both probes were Jupiter-bound, Voyager 1
was set on a shorter, faster trajectory,
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so taking off second made sense. It
overtook Voyager 2 on December 15th 1977,
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and exited the asteroid belt first.
Together, this dynamic duo was set to
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take a "dazzling parade of pictures" that
were absolutely revolutionary at the time.
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But don't take my word for it. Let's
jump in and you'll see for yourself.
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Thirteen days after launch, Voyager 1 sent
this photo back to Earth - the first of tens
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of thousands it would send back over the next 5
years. Taken 11.6 million kilometres from Earth,
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it's a sentimental place to start our journey.
It might remind you of the Earthrise photo taken
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by the Apollo 11 crew from the moon just
8 years prior. We can see our blue marble
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and its moon in the distance. I don't know
about you, but I find this photo so hauntingly
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beautiful - especially knowing how far this probe
has travelled, and how much it's seen since then.
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But we've got a long way to go, so let's move on
It would be almost two years before Voyager 1
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finally makes its approach to its first
target, Jupiter. Not bad, considering
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it's 714 million kilometres away. Voyager 1
arrived first on March 5th, 1979. You see,
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it travels at 17 kilometres per second, 2
kilometres per second faster than Voyager 2 - who,
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despite leaving Earth first, arrived four
months later on July 9th, 1979. This is
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because the trajectory Voyager 1 took allowed
it to gain more speed relative to the sun.
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Now, Voyager 1 was not the first spacecraft to
encounter Jupiter - that was Pioneer 10, seven
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years prior in 1972. And while the Pioneer mission
certainly provided great scientific insights, it
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didn't quite grab the imagination of the public.
But sending back stunning images like this,
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Voyager certainly did.
This is Jupiter in all its glory.
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It's kind of hard to accept that these are actual
photos and not paintings, or some AI-generated
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image. If you look closely, you can spot two of
its moons - Io, on the left, and Europa, the beige
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one on the right - but more about them later.
Lucky for us, Voyager 1 even recorded its
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approach to the great gas giant.
It took photos at regular intervals
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every 10 hours - or one Jupiter day. This means
the planet is in the same point of its rotation
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in all the photos. The 66 photos were spliced
together to create this time-lapse movie,
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spanning Voyager 1's approach to Jupiter from
January 6th to February 3rd, 1979 - covering a
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distance of 27 million kilometres. I personally
can't decide if it is incredible or terrifying.
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But let's get a closer look, and see
what surprises this planet is hiding.
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Something that immediately stunned scientists
was Jupiter's atmosphere. They expected to
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see east-west and west-east winds in
Jupiter's different atmospheric zones.
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But what caught them by surprise was the amount
of turbulence, plumes, and rotational movement,
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which are super clear in this image.
You can immediately see how dynamic
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the atmosphere over Jupiter is.
Scientists had already suspected
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Jupiter's most notable characteristic - its Great
Red Spot - might be a counterclockwise rotating
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formation. Not only did Voyager data confirm this,
it also showed a surprising amount of similar
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phenomena in other parts of the atmosphere.
The white spot you see below the Great
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Red Spot is one example of these surprise
storms. Turns out Jupiter's atmosphere is
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littered with them - and we had no idea.
When we think rings, we think Saturn,
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but thanks to Pioneer data, scientists have long
suspected that the same is true for Jupiter.
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Voyager data not only confirmed the existence
of four Jovian rings, it was also the first to
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image them. This picture taken as Voyager leaves
Jupiter highlights the rings beautifully, as that
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glowing orange line protruding from the planet.
Before we leave Jupiter and continue our journey,
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I did promise we would come back to its moons
- Io and Europa. Possibly the biggest shock
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from the Voyager expedition is the discovery
of volcanic activity on Jupiter's moon - Io.
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Prior to Voyager, geologists thought Io
would be covered with large impact craters,
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like our own moon. While they did find circular
markings on Io's surface, they didn't appear to
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be from craters. The dark spots you see indicate
the presence of volcanic hot spots and lava lakes.
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This photo shows lava flow from less than 1
million years ago - which is incredibly recent
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and totally unexpected. We now know Io as the
most geologically active site in the solar system.
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At the time of these images being
taken, it would've been incredible
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to capture Io mid-eruption. Imagine
expecting to see a moon similar to ours
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and then stumbling upon a sight like this.
These blue explosions on the surface of Io
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shot material and gas 100 kilometres into
space. The volcanoes are incredibly active,
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going off relentlessly every few hours,
treating Voyager to several jaw-dropping photos.
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The next moon out from Io is Europa and it
could not be more different. An icy world,
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Voyager 1 was the first to show us that Europa is
covered by curious scratch markings. Scientists
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supposed them to be some type of ice fracture
patterns on Europa’s surface. It was also
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Voyager data that first suggested there might
be a swirling ocean lurking under the ice.
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Today, we know of 95 moons orbiting
Jupiter. However, prior to 1979,
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that number was 13. Voyager discovered three new
satellites - Thebe, Metis, and Adrastea - bringing
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the total to 16 moons by the early 80s. Sadly,
we don't have any pictures of them from 1979,
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though they have been imaged since.
The next stop on Voyager's Grand
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Tour was Saturn. After 21 months of travel,
Voyager 1 arrived on approach to the Ringed
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Planet in November 1980, closely followed by
its companion 9 months later in August 1981.
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Like I said before - you think rings,
you think Saturn. So let's start there.
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Prior to Voyager's mission, Saturn was
believed to have just 5 major rings. However,
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Voyager 1 showed us that these rings are actually
made up of hundreds of thin ringlets. This was
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the closest flyby any probe had undertaken back
then - hence the greater detail and learnings.
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Voyager discovered a ring too, the G-ring,
and also provided key details about the
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F-ring discovered by Pioneer 2 one year prior
in 1979. Voyager 1 showed us that the F-ring
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is kinked and multi-stranded in nature. It
also identified two shepherd moons within
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the F-ring - Prometheus and Pandora. This was big
news because this discovery confirmed scientists'
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theories that shepherding moons exist around
narrow rings to keep ring material in line.
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Voyager also introduced us to some ghostly
features on Saturn's B-rings. They appear
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scattered around the rings in this photo, and
are said to resemble broad spokes in a wheel.
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They seem innocent, but they actually caused quite
the stir in the scientific community for a while.
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You see, up until 1980, we thought that Saturn's
rings were caused exclusively by gravitational
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forces. That's all well and good, except
these spokes completely fly in the face
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of that theory. Their existence is
not consistent with gravitational
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orbital mechanics. We still don't know what
causes them, but the leading theory involves
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electrostatic repulsion separating very small
dust particles from the main surface of the ring.
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Sadly, as much as data from Voyager
taught us about Saturn's rings,
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it also taught us that Saturn is losing its rings.
Gravity is pulling the rings into the planet,
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turning them into a kind of dusty rain of ice
particles. According to NASA, this could cause
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Saturn's rings to disappear in 300 million years.
Voyager's trip to Saturn raised so many questions,
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that a dedicated mission was mounted in
the 90s to exclusively study the Ringed
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planet. Cassini probe launched in 1997, and
orbited Saturn for 13 years. You can check
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out a video of mine on what it found here.
But, we aren't leaving Saturn territory yet.
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Voyager provided some decisive breakthroughs
regarding the planet's moons. We already
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knew of 14 moons, but Voyager showed us
three more bringing the total number at
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the time up to 17 moons.
Let's see what we can
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learn from Titan and Enceladus.
Pioneer 11 was the first probe to
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image Titan, Saturn's largest moon, and the
data it gathered captured the interest of
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researchers. So, Voyager was sent to follow up.
It found that Titan had a thick, nitrogen-rich
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atmosphere - the first and only encounter of
such an atmosphere beyond our home planet.
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Enceladus also turned out to be exceptionally
quirky. Take a look at this photo. Enceladus
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is visible out in the distance, with
Saturn in the foreground. Now, I know
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it's tricky to see, but that moon is erupting.
Enceladus spews out 300 kilos of water vapour
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up to 10,000 kilometres above its surface - 20
times its own diameter. As it orbits Saturn, the
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frequent plumes of water vapour that erupt leave
behind a doughnut-shaped cloud that feeds one of
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Saturn’s icy rings. This data was suggested by
Voyager data, but it wasn't until we flew Cassini
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out there that we could confirm it to be true.
Further geological data and imaging shows that
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Enceladus' terrains are an unexpected mixture
of old and new. The left side which appears
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smooth is the newer side, and the right side
with the densely packed impact craters is the
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older side. This suggests Enceladus
is a very geologically active moon,
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which it wasn't previously thought to be.
Before we make our way to the wonky world
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of Uranus - we have to say goodbye to Voyager
1. After its flyby of Titan and Saturn's rings,
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its path was bent upward out of the ecliptic
plane. From here, the probe headed straight
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for interstellar space. Of course, it would be
another 32 years before it would reach that.
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But not to worry, Voyager 2 took a slingshot
around Saturn instead, to propel it on to
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Uranus and Neptune. These would be the first
and only flybys of the planets in human history.
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Five years after arriving at Saturn, NASA's
Voyager 2 arrived on approach to Uranus in January
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1986. At its closest, the probe came within 81,500
kilometres of Uranus's cloud tops. Voyager 2
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revealed an absence of visible cloud features in
Uranus's atmosphere. Unlike Jupiter and Saturn,
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Uranus displayed a serene, featureless cloud
deck, challenging scientists' preconceptions
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about the atmospheric dynamics of gas giants.
The false-colour image on the right brings out the
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subtle differences in the atmosphere of the polar
regions - which are tilted on a 98-degree axis.
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But it was another tilt that
stunned Voyager scientists.
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It was previously unknown whether Uranus had a
magnetic field, but Voyager data showed us that
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not only does Uranus indeed have a magnetic field,
it is also tilted at an astonishing 59 degrees.
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That means its magnetic and rotational
poles are not at all in the same place.
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Until then, it was thought that these poles
were always aligned. It certainly is here
00:24:34
on Earth - our magnetic and rotational poles are
only shifted by 12 degrees. This stark deviation
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found on Uranus defied conventional
planetary magnetic field models and
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forced scientists to rethink their assumptions.
One side-effect of this misalignment of poles is
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that as the planet spins, its magnetosphere
— the space carved out by its magnetic
00:24:57
field — wobbles like a poorly thrown football.
Scientists still don’t know how to model it,
00:25:04
but it might look a little something like this ↓.
Voyager 2's observations unveiled more details
00:25:11
about the known rings of Uranus, and
discovered two more. It is the first
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to capture images of these dark rings, like
its outermost ring visible in this photo. The
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rings are composed of fine dust particles.
Voyager 2 also discovered two shepherd moons
00:25:27
orbiting one of the newly discovered rings,
similar to its findings with Saturn's to the
00:25:32
F-ring. Here, they can be seen from 4 million
kilometres, in a photo from January 21st, 1986.
00:25:41
This mission significantly increased the known
count of Uranian moons. Prior to Voyager 2,
00:25:47
we only knew about five moons orbiting Uranus.
Voyager 2 sent us the first ever images of these
00:25:53
moons, which you'll see in a second, but it also
discovered 11 more moons, bringing the total to
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16 moons. Voyager's discovery provided
valuable data on their new moons sizes,
00:26:06
compositions, and orbital characteristics.
Today, the number of known moons stands at 27.
00:26:13
OK - back to Uranus's five OG moons. They
all appear to be ice-rock conglomerates,
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similar to the moons of Saturn. Oberon and
Umbriel, pictured here on January 24th, 1986
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are riddled with impact craters. They
seem to have little geologic activity,
00:26:33
judging by their old and dark surfaces.
Titania, which sits between those two,
00:26:39
4th furthest from Uranus, is marked by huge
fault systems and canyons indicating some
00:26:45
degree of geologic - and probably
tectonic - activity in its history.
00:26:51
Ariel has the brightest and possibly youngest
surface of all the Uranian moons. This photo
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taken from just 129,000 kilometres suggests
Ariel underwent geologic activity that led
00:27:02
to many fault valleys and extensive flows of
icy material at some point in its history.
00:27:08
Miranda is the closest of the five to the
planet, second only in proximity to Puck,
00:27:14
the little rocky satellite discovered by Voyager
in 1985, and had the most surprising findings.
00:27:23
Voyager flew by Miranda on January 4th, 1986, at
a distance of just 30,000 kilometres. This small
00:27:31
moon turned out to be a captivating puzzle
of geological dynamism, shaped by a volatile
00:27:37
history. Voyager 2 identified traces of internal
melting and sporadic "upwelling" of icy material,
00:27:45
manifesting in extensive, canyon-like faults
plunging to depths of up to 20 kilometres.
00:27:52
The lunar canvas is further adorned with oval,
racetrack-shaped features etched like cosmic
00:27:59
scratches. Voyager also saw "terraced" regions,
where a mosaic of old and young, bright and dark,
00:28:06
and heavily and lightly cratered terrains coexist.
The chevron-like characteristic seen here suggests
00:28:13
Miranda's original surface
was pulled apart and the
00:28:17
fragments forcibly re-aggregated back together.
Three weeks later, on January 25th 1986, Voyager
00:28:24
2 departed Uranus, and snapped this wonderful
goodbye shot from 1 million kilometres as it
00:28:30
set off to its final planetary target, Neptune.
After three years of travel at a speed of 54,000
00:28:38
kilometres per hour, Neptune finally came into
view. Voyager 2 approached the furthest planet
00:28:44
in our solar system on August 25th, 1989, just
over 12 years since it took off from Earth.
00:28:52
It produced the first up-close images we
ever received of the giant blue planet,
00:28:58
passing only 5,000 kilometres above its
north pole - the closest of any flybys.
00:29:04
Hydrogen was found to be the most
common element in Neptune's atmosphere,
00:29:09
although the high abundance of methane is
what gives the planet its blue appearance.
00:29:14
Voyager 2 measured extraordinary wind speeds in
Neptune's atmosphere, with the equatorial winds
00:29:19
blowing at speeds reaching almost 1,100 kilometres
per hour. These remarkable speeds were yet another
00:29:27
surprise and highlighted just how dynamic
and ferocious Neptune's weather systems are.
00:29:33
Scientists also discovered a massive storm
on Neptune, aptly named the Great Dark Spot.
00:29:40
This turbulent storm was seen to be rotating
counterclockwise, just like the Great Red Spot
00:29:45
on Jupiter, and exhibited winds reaching up
to 2,400 kilometres per hour - the strongest
00:29:52
recorded in the solar system!
One NASA analyst, Ken Bollinger,
00:29:57
commented on the findings in 1989 saying,
"Everyday what you see is brand new,
00:30:03
nobody's ever seen it, it's just an incredible
feeling. There's changes going on constantly
00:30:08
on Neptune that happen very, very fast."
Voyager 2 also imaged Neptune's rings for the
00:30:15
first time. Up until 1986, scientists suspected
the planet might have rings, but couldn't be
00:30:22
certain. Intriguingly, the spacecraft identified
several partial ring structures — or ring
00:30:28
arcs — within Neptune's ring system. These arcs
raised questions about the mechanisms responsible
00:30:35
for their formation and stability, since they
mainly consisted of incomplete and dusty rings.
00:30:42
A trip to Neptune wouldn't be complete without a
quick stop-over at its largest moon - Triton. The
00:30:48
coldest known planetary body in the solar system,
Triton turned out to have a fractured surface,
00:30:55
complete with erupting geysers, and a pinkish
nitrogen ice cap over its southern pole.
00:31:02
Scientists also identified dark plumes, which
could indicate the possibility of ice volcanoes.
00:31:09
Voyager 2 also discovered 6 new moons
orbiting Neptune, including these:
00:31:16
As Voyager 2 turned around to snap
one last look at Neptune and Triton,
00:31:21
it had officially completed its "Grand
Tour." Neptune's gravity bent its path
00:31:26
downward out of the ecliptic plane. From here,
it continued its voyage into interstellar space,
00:31:33
just like its counterpart Voyager
1 had done 9 years before.
00:31:38
Speaking of Voyager 1, let's see where it's
ended up since we last checked in in 1980.
00:31:45
One year after Voyager 2 finished up with
Neptune, Voyager 1 was already about 6 billion
00:31:51
kilometres away. In order to conserve power
for the long journey into interstellar space,
00:31:57
scientists were going to switch off its cameras
forever. However, on the advice of Carl Sagan,
00:32:03
the team decided to turn the camera around for one
final picture - a look back at home and how far we
00:32:10
had come. And so, on February 14th 1990, Voyager
1 took the most remote selfie in history from 6
00:32:20
billion kilometres away. The result?
The infamous Pale Blue Dot photo.
00:32:28
In the immortal words of Carl Sagan himself,
“Look again at that dot. That's here. That's
00:32:35
home. That's us. On it everyone you love,
everyone you know, everyone you ever heard of,
00:32:44
every human being who ever was, lived out their
lives. The aggregate of our joy and suffering,
00:32:51
thousands of confident religions, ideologies,
and economic doctrines, every hunter and forager,
00:32:59
every hero and coward, every creator and destroyer
of civilization, every king and peasant, every
00:33:06
young couple in love, every mother and father,
hopeful child, inventor and explorer, every
00:33:13
teacher of morals, every corrupt politician, every
"superstar," every "supreme leader," every saint
00:33:21
and sinner in the history of our species lived
there--on a mote of dust suspended in a sunbeam.”
00:33:29
"There is perhaps no better demonstration of
the folly of human conceits than this distant
00:33:34
image of our tiny world. To me, it underscores
our responsibility to deal more kindly with one
00:33:41
another and to preserve and cherish the pale
blue dot, the only home we've ever known."
00:33:48
This sentiment rings with as much
power today as it did 33 years ago.
00:33:54
But what came next? What did the Voyager
probes see and do in interstellar space?
00:34:01
In 1981, Voyager 1 escaped the ecliptic, which
is the Earth’s plane of orbit around the Sun,
00:34:08
heading 35 degrees to the north.
Voyager 2 later went under the ecliptic,
00:34:14
heading 48 degrees to the south.
However, this was barely the start of
00:34:19
the Voyagers’ journeys. To reach interstellar
space, the probes would have to traverse the
00:34:24
termination shock, a region in which hypersonic
solar winds run into fierce resistance from the
00:34:31
interstellar wind. Beyond the termination shock,
the Voyagers would encounter the heliosheath,
00:34:37
where slowing solar winds pile up,
becoming denser and hotter, followed
00:34:43
by the heliopause – the final boundary between
the heliosphere and interstellar space. But,
00:34:50
in spite of what you may think, the start of the
interstellar medium doesn’t actually mark the end
00:34:55
of our solar system. Indeed, it will be another
300 years until Voyager 1 reaches the Oort Cloud,
00:35:02
the vast region of billions of icy planetesimals
that surrounds our solar system like a bubble,
00:35:08
and another 30,000 years until it exits the
cloud, leaving our solar system forever.
00:35:15
When the Voyagers travelled through the
heliosheath, they made an incredible discovery.
00:35:20
Because the Sun’s magnetic field spins in opposite
directions on its north and south poles, the
00:35:26
spin creates a ripple where they meet called the
heliospheric current sheet, sort of like the rings
00:35:32
created by dropping a stone in water. However,
when this sheet reaches the termination shock,
00:35:38
it compresses, as though the ripples were hitting
the edge of a pool. The Voyager probes discovered
00:35:45
that after the termination shock, these stacked-up
ripples form magnetic bubbles. This means the
00:35:52
boundary of the heliosheath is not as smooth
and clear-cut as scientists thought. Instead,
00:35:57
it is a fluctuating and magnetically bubbly
environment. This messy finding has prompted a
00:36:04
complete revision of our model of the heliosheath!
On July 25, 2012, the Voyager 1 space probe became
00:36:13
the first manmade object to leave the Sun’s
heliosphere and enter interstellar space. It was
00:36:19
travelling at an incredible speed of 540 million
kilometres per year, or 3.6 Astronomical Units,
00:36:27
an astronomical unit being the distance between
Earth and the Sun. The distance at which Voyager 1
00:36:33
crossed the heliopause was about 120 Astronomical
Units from the Sun, which itself was a revelation:
00:36:40
it was unknown where, exactly, the heliopause
occurred. Funnily enough, some early models put
00:36:47
it as close as Jupiter, and others much farther.
Remember: the heliopause is the boundary where
00:36:54
the Sun’s solar wind is stopped by its collision
with the interstellar medium, kind of like the
00:36:59
crashing of two powerful bodies of water against
each other. Solar wind is the steady stream of
00:37:05
charged particles, such as electrons, protons
and alpha particles, that come from the Sun’s
00:37:11
outer layer. The interstellar medium, by contrast,
consists of charged particles, gases and cosmic
00:37:18
dust left over from the Big Bang and other ancient
supernovae. When these charged streams hit each
00:37:24
other, they change course and form a region of
equilibrium, called the heliopause boundary.
00:37:31
At first, NASA wasn’t sure if Voyager 1 had truly
crossed the heliopause and entered interstellar
00:37:37
space. As models predicted, the probe’s plasma
wave detector found a massive increase in plasma
00:37:42
density, 80 times what it had registered in
the outer heliosheath, and a spike in galactic
00:37:49
cosmic rays. But something strange didn’t happen
that left scientists baffled. After crossing the
00:37:56
heliopause, Voyager 1 detected no change in
the ambient magnetic field. Why was that so
00:38:03
surprising? Well, theoretical models assumed
that the ambient magnetic orientation would
00:38:09
change in a region dominated by the magnetic
fields of other stars. But remarkably, Voyager
00:38:15
1 detected no discernible change in the ambient
magnetism. NASA was so confused that they waited
00:38:22
nearly a year before announcing that Voyager
1 had, in fact, entered interstellar space.
00:38:29
On November 5, 2018, Voyager 2, travelling at the
slightly slower speed of 490 million kilometres
00:38:37
(or 3.3 Astronomical Units) per year, joined
Voyager 1 in becoming the second man-made object
00:38:44
to enter interstellar space. The crossing also
occurred 120 Astronomical Units from the Sun, and
00:38:50
like the Voyager 1 six years earlier, the probe
detected no change in the ambient magnetic field.
00:38:57
But something else surprised scientists. You
see, the Sun goes through 11-year solar cycles,
00:39:03
during which its activity waxes and wanes. Voyager
2’s crossing occurred at a time when solar winds
00:39:09
were peaking. Models predicted that the size of
the heliosphere would fluctuate with the solar
00:39:15
cycle, meaning it would have been expanding when
Voyager 2 made its crossing. Yet Voyager 2 crossed
00:39:22
the heliopause at exactly the same distance
Voyager 1 had six years prior, meaning our
00:39:28
models were wrong. Like the magnetometer finding,
this demonstrated the value of testing theoretical
00:39:35
models with field data. We now suspect that the
boundary between the heliosphere and interstellar
00:39:41
medium is much more twisted and filled with
fluctuations than prior models proposed. One
00:39:47
leading idea is that our Sun emerged billions of
years ago from a hot and heavily ionized region
00:39:54
following the explosion of one or more supernovae,
and that magnetic turbulence persists to this day
00:40:00
near the heliopause. If so, the probes will likely
encounter a different magnetic orientation as they
00:40:07
travel farther away, but their instruments
will probably be long dark by that time.
00:40:12
After all, the probes are
already starting to fail.
00:40:18
In early May 2022, Voyager
1’s signal went… strange.
00:40:24
Imagine you are a NASA scientist. You arrive
at your computer for the day, and begin looking
00:40:29
through the Voyager 1 telemetry data. Voyager
1 sends back status updates about its systems,
00:40:36
letting you know whether everything is
functioning normally. It takes 22 hours
00:40:41
now for a signal to reach Earth from Voyager 1,
so communication is a little slow between you
00:40:46
and the craft you’re overseeing. Currently,
it is more like sending letters than texts.
00:40:53
However, today, something is wrong.
The information it has sent you is
00:40:57
gobbledegook. Instead of precise data explaining
exactly what Voyager 1’s thrusters are doing,
00:41:04
and what orientation it believes itself to be at,
00:41:07
you get long strings of 0’s, or 377’s.
The information does not make sense.
00:41:14
It suggests that Voyager is doing things
and pointing directions that cannot be.
00:41:20
You quickly check your computer again – yes,
00:41:23
you did just receive a signal from Voyager 1.
So, its antenna must be pointing towards you,
00:41:29
the same as it always has. It cannot be pointing
in the strange directions it is claiming,
00:41:34
or you would not be getting a signal at all.
And not only are you receiving the signal,
00:41:40
but it’s at the exact same strength too, so
it has definitely not changed its direction.
00:41:46
And, ping, onto your computer comes Voyager
1’s latest science data. Strangely enough,
00:41:53
this is all normal. While over the years
Voyager 1 has had to turn off 5 of its
00:41:58
11 pieces of scientific equipment - and
a further 2 have stopped working due to
00:42:03
general degradation - the remaining 4 continue
to take readings about the interstellar medium,
00:42:08
magnetic fields and cosmic rays.
Nothing here is garbled in any way.
00:42:14
You check its other systems. Voyager
1’s power supplies are a little low,
00:42:19
but that’s to be expected. The plutonium
oxide that fills its 3 generators have a
00:42:24
half-life of 87 years, but Voyager 1 has been
travelling for 45 now. It is no wonder the
00:42:30
efficiency has started to decline. In fact,
the experts believe that Voyager 1 will not
00:42:36
last past 2025. But that is some time away.
It does not explain what is happening now.
00:42:43
After checking its other systems, it
is just one that is behaving strangely.
00:42:48
The AACS – the Attitude Articulation and
Control System. This computer is one of 3
00:42:57
on Voyager 1, and remember, its job is
to make sure the spacecraft’s large,
00:43:02
3m antennae continues to point towards Earth.
This AACS has stopped sending coherent data.
00:43:10
You lean back, puzzled. The situation
is not as bad as you might have thought,
00:43:15
but it is troubling. It’s kind of like
receiving post from a postman who says
00:43:19
hello to you every morning, only for
some reason he starts speaking another
00:43:23
language one day. The packages he delivers
are still the same, and they’ve arrived at
00:43:29
the same address. It’s just the words the
man speaks make no sense to you anymore.
00:43:35
To further compound the strangeness, Voyager
1 doesn’t think that anything is wrong with it
00:43:39
at all. The spacecraft comes equipped with
emergency “safe mode” settings that it can
00:43:44
go into if it detects that anything is not
working the way it ought to be. Essentially,
00:43:49
these involve powering down until scientists can
figure out what’s wrong with it. And these have
00:43:54
not activated. So Voyager 1 believes that all
its systems are working the way they should be.
00:44:01
The data is given, the scene is set. This was the
question that NASA engineers faced in mid-2022. A
00:44:08
single fault like this might not seem like a big
deal, but it hints at something potentially wrong
00:44:13
with further systems. And if that is true,
it might spell an end to the whole mission.
00:44:21
Voyager 1 is by now 23.8 billion km away from you.
Your solution will have to be made via deduction,
00:44:30
alongside careful, 22-hour-each-way questions
and answers with the faulty spacecraft.
00:44:36
By evaluating the rest of the systems and finding
them normal, you can rule out some of the more
00:44:41
unusual explanations. No, this probably is not the
work of aliens trying to mess with you. Although
00:44:49
NASA scientists were open to the idea of the
Voyager probes maybe one day being picked up
00:44:54
by alien life, as evidenced by the golden disks
installed on the probes filled with messages about
00:44:59
us for aliens to read if ever they stumbled across
it, this was more a symbolic gesture. Besides,
00:45:06
it seems that this would be a strange
way for aliens to communicate with us.
00:45:10
And no, the laws of physics have probably
not broken down. Voyager 1 has not entered
00:45:15
a wormhole that is skewing where it thinks
it is while still somehow getting the signal
00:45:19
back to you. Given that the scientific data
all appears to be providing normal readouts,
00:45:25
it’s much more likely that the
problem lies with the AACS itself.
00:45:30
For four months, scientists and engineers
gently prod and examine Voyager 1,
00:45:35
testing theory after theory and trying to
come up with a solution that fixes things
00:45:40
without causing any further damage in the
process. They could switch over to a backup
00:45:46
system. It would not be the first time they’d
started using a new computer on Voyager 1 after
00:45:51
the old one stopped working. Voyager 1
is built with redundancies; this isn’t
00:45:57
even the first AACS computer that’s been used
– a previous one became defective a while ago.
00:46:04
They also contemplate just leaving
things be. After all – the science
00:46:09
data is still coming in. Would it
be the end of the world if Voyager
00:46:12
1 simply carried on speaking garbled
messages? Perhaps this could simply be
00:46:17
the new normal… except it implies that
a deeper problem is being overlooked.
00:46:22
Can you figure out what was going wrong? If you
can, perhaps NASA should look to hiring you.
00:46:30
It turns out that in the intense, radiation-filled
environment of interstellar space, something had
00:46:36
made Voyager decide to start using that
older, broken AACS computer to send data
00:46:42
back to Earth. Because of the faults in this
computer, the data had become corrupted,
00:46:47
resulting in the strange numbers. So actually, in
this case the fix was easy. All NASA had to do to
00:46:54
fix it was to ask Voyager to start using
the right computer again. Once Voyager 1
00:46:59
did that, the problem was resolved.
Well, I say easy. And I say resolved.
00:47:07
It still took a couple of months for Voyager 1
to start behaving normally again. And even then,
00:47:13
in November 2023 another of
Voyager’s onboard computers – this
00:47:18
time the Flight Data Subsystem – underwent a
similar problem and became unable to send
00:47:23
home usable science and engineering
data. It took until June 2024 until
00:47:28
that particular problem was fully resolved.
Voyager 1 is an old ship, now. As it continues
00:47:35
to travel through interstellar space, it may
encounter more and more faults. In July 2023,
00:47:42
a routine series of commands sent to Voyager
2 caused the probe to orient its antennae
00:47:47
2 degrees away from Earth. This seemingly
small divergence was enough that over the
00:47:53
massive distances involved, NASA completely
lost the ability to talk to Voyager 2,
00:47:58
or hear back from the probe. It was only through
sending out an interstellar “shout” from the Deep
00:48:03
Space Network facility in Canberra, Australia that
a signal was able to be sent to Voyager 2 telling
00:48:09
it to reorient itself back towards Earth. The 37
hours of waiting for the shout to arrive and for
00:48:16
the probe to signal back that it had followed the
command must have been tense for NASA personnel.
00:48:22
The probe could have been lost forever.
One way or another, it’s inevitable that
00:48:28
the Voyager probes’ will stop transmitting back
to Earth. Whether through error or malfunction,
00:48:34
or simply running out of power, the end is
unavoidable, and the curtain will fall on
00:48:40
this incredible mission. But even then the twin
probes are just beginning their cosmic journeys.
00:48:47
In 40,000 years, Voyager 1 will likely drift
toward a star in the Camelopardalis constellation,
00:48:54
while Voyager 2 will pass 1.7 lightyears
from the star Ross 248. In 296,000 years,
00:49:04
it will pass 4.3 lightyears from Sirius. These
small, intrepid probes will likely outlast
00:49:11
the Earth itself as they continue their solitary
wanderings across the Milky Way. And if by chance
00:49:16
they encounter intelligent life in one of the far
reaches of our galaxy, they will be a testament
00:49:22
to mankind’s ingenuity and resilience. [Remember I
mentioned that on each of the probes was a message
00:49:28
to the stars? These golden audio-visual discs are
called the Golden Record, and carry photographs
00:49:35
of Earth and its many lifeforms: the sounds of
whales and of babies crying; music by Mozart
00:49:42
and Chuck Berry and dozens of indigenous peoples;
and greetings in 55 languages. They would offer a
00:49:49
distant stranger a glimpse of who we are, and
what life on Earth is like. As for us, we must
00:49:56
say goodbye to these old familiar friends and
continue our own lives here on Earth. Hopefully,
00:50:02
the Voyager Mission will not be our last
brush with the stars, but only the beginning.
00:50:11
Thanks for watching I was honestly Blown
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00:50:16
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