Without a doubt, Juno is one of the most
important missions that NASA has ever
launched. This is a probe that defied
the odds, surviving for years past its
original mission end date in a region of
space that is usually deadly to probes.
It is NASA's most distant planetary
orbiter. Investigating our solar
system's largest planet, and what it has
learned there has shaken our
understanding of everything we thought
we knew about Jupiter, its formation,
its composition, and the mechanisms that
give it such a powerful magnetic field.
But Juno didn't stop there. It has
investigated Io, Ganymede, and Europa.
It has studied auroras and the largest
volcanic eruptions we've ever seen in
our solar system. And as this incredible
probe has reached the conclusion of his
extended mission, it's time to ask the
question, what has Juno seen?
I'm Alex Mccoan and you're watching
Astramm. Join me today in this supercut
as we explore the discoveries Juno has
made around Jupiter over the years. And
like all good stories, this is a tale
that ends with a twist. So, let's start
from the beginning.
As far as NASA missions go, Juno is a
medium budget project with total expense
that was initially expected to be about
$1.1 billion over the course of its
mission time. Now, Juno is a massive
spacecraft, 20 m in diameter, and it
really has to be because unlike previous
probes we've sent out that are powered
by radioisotope thermmoelect electric
generators, Juno is a solar powered
spacecraft and it only gets 4% of the
sunlight it would do around Earth. This
means that even though these panels are
huge, it can only generate just above
400 W. It was launched on the 5th of
August 2011 using an Atlas 5 rocket.
Escaping Earth's atmosphere and entering
orbit is one of the most risky parts of
the whole mission. But everything went
smoothly and less than an hour after
liftoff, it was already on an escape
trajectory from the Earth.
Juno's journey to Jupiter was an
interesting one, as after it escaped
Earth's gravity, it headed into deep
space. At this point, it did a small
burn using its engines and headed
straight back to Earth, reaching it 2
years after it had first launched. You
may wonder to yourself, why would they
do that? Well, the answer is very
clever. When Juno reached Earth again,
the gravity of Earth started pulling
Juno towards it. This gravitational
influence increased the speed of Juno by
over 14,000 kmh,
slingshotting it at top speeds towards
Jupiter. This method is more fuel
efficient than burning the probe's
engines to get there.
After a monumental 5-year journey
spanning 2.8 billion km, Juno entered
orbit around Jupiter in 2016. Its
primary mission consisted of 33 polar
orbits of the gas giant and its closest
approach flying only 4,200 km above the
Jovian atmosphere. Being this close to
Jupiter is a big problem as far as
delicate scientific instruments go. You
see, Jupiter has an extremely powerful
radiation belt around the planet. Easily
powerful enough to fry most electronics.
Do you remember the previous Jupiter
probe, Galileo? Galileo faced a number
of setbacks due to the damage received
by Jupiter's radiation as its orbit went
right through the middle of the
radiation belt. So, mission planners
were keen to avoid a repeat of that as
much as possible. Being this close to
the planet means Juno would go straight
through that deadly radiation belt. This
is why the expected mission life of the
probe to begin with wasn't over 20
months in orbit with some instruments
not expected to last beyond the first 8
to 9 months. To try and prolong the
inevitable, Juno was surrounded by a 1
cm thick layer of titanium to protect
the internals from frying. It's kind of
like a tank going into space. But
whether this would be enough or not was
something that scientists were initially
uncertain of. So, what about Juno's
mission? Well, sadly, the initial plan
was for Juno to not turn its attention
to any of the moons, but instead focus
on Jupiter itself. It would measure the
amount of water in Jupiter's atmosphere
to determine which planet formation
theory is correct. It would look deep
into Jupiter's atmosphere to measure
composition, temperature, cloud motions,
and so on. It would also map Jupiter's
magnetic and gravity fields. We already
know the magnetic field of Jupiter is
hugely interesting due to its strength
and size. Did you know for example if
the magnetic field of Jupiter was
visible in our sky? This is how big it
would appear.
Juno would particularly explore and
study Jupiter's magnetosphere near the
planet's poles, especially the auroras,
Jupiter's northern and southern lights,
providing new insight into how the
planet's enormous magnetic field affects
its atmosphere. In this way, Juno would
follow closely after its namesake.
Juno's name comes from Greco Roman
mythology. The god Jupiter drew a veil
of clouds around himself to hide his
mischief. But his wife, the goddess
Juno, was able to peer through the
clouds and see Jupiter's true nature. An
apt name indeed.
On the 5th of July 2016, Juno
successfully arrived at Jupiter and
inserted itself into a polar orbit. It
adopted a perpendicular orbit which
brushed over the planet at its closest
approach, only 4,200 km above Jupiter's
atmosphere at its perove and 8.1 million
km at its ap.
The perove is the point of a
spacecraft's orbit when it is closest to
Jupiter. And an apoge is just the
opposite. It's the point in an orbit
when the spacecraft is furthest away
from Jupiter. Each orbit took 53 days to
complete, and NASA's original plan for
Juno was for it to complete its 33
orbits by the end of its mission in 2018
with a burn along the way to take Juno
into a close 14-day orbit towards the
end. However, this burn was later
cancelled as it was deemed safer. So,
Juno stayed in its longer orbital
position until 2021.
For all the worry over Juno's longevity,
however, it turned out that there was
nothing to worry about due in part to a
surprising discovery Juno made upon
entering Jupiter's magnetic field.
One of the reasons Juno approached so
close to the planet was to avoid
Jupiter's powerful radiation belt. But
there is a gap where the planet ends and
the radiation belt starts and Juno
threaded the needle to exploit that.
There was some concern that Juno would
still get a huge dose of radiation from
the parts of the radiation belt it did
hit, but the radiation was actually 10
times lower than expected in these
parts. Great for the health of the
probe. This was a stroke of luck for
NASA, for Juno, and for us. Of course,
another advantage of the tiny distance
from Juno to Jupiter at its closest
approach is that we have been able to
see Jupiter in unprecedented detail. The
first images of Jupiter's poles in
particular took people's breath away.
Some even say that scientists would not
have even recognized the planet from
these images. Just no one expected what
they saw. What you are looking at here
are many cyclones around the south pole.
What is remarkable is that the planet
looks so different from what we used to
seeing on Jupiter, namely its large
bands. However, in this image, the
contrast has been increased to see
details. The natural eye would see
something more like this. This image is
also a mosaic of several images in order
to show daytime on all sides of the
planet. The North Pole isn't quite so
clear as it's in winter and some parts
of the pole are in constant night. Juno
also has the capability to peer deep
into Jupiter's atmosphere using a
microwave radiometer, which was designed
specifically for this spacecraft. Using
it, scientists were able to see the
amount of ammonia in the atmosphere.
What they didn't expect to see was this
band of ammonia around the equator.
ammonia being orange in this image. The
pillar drops down from the cloud tops
over 350 km, the limit of what the MWR
can see. Scientists were puzzled by this
as they expected to see an even
distribution of ammonia throughout the
planet. They thought the gases in the
atmosphere would just mix up or at least
stick to the band pattern of the planet,
but these results were far from that.
This shows how variable the planet is
under the top layer of clouds.
But one of the biggest revelations about
Jupiter was not its cloud cover, but
something much deeper. For decades,
scientists argued what the core of our
biggest gas giant was like. Was it solid
or missing altogether? And in 2017,
NASA's Juno mission made that debate
irrelevant overnight. The data from Juno
suggested both sides were wrong and
revealed a third option no one expected.
Jupiter's core isn't solid, but it isn't
absent either. It's fuzzy. And that's a
problem because it upended everything we
thought we knew about Jupiter's
formation, its interior, and even its
bizarre magnetic field. Let me explain.
For decades, two competing theories
dominated the scientific conversation
around Jupiter's core. Many supported
the gravitational collapse theory, which
suggests that Jupiter formed directly
from the collapse of a gas cloud under
its own gravity. This would have
happened in the colder outer reaches of
the solar system before Jupiter migrated
to its current location. In this
scenario, the gas giant would have no
core at all. it would simply be a layer
cake of churning gas all the way
through. But this theory didn't have the
whole scientific community convinced.
Others were almost certain Jupiter's
core was solid, made up of heavy
elements like carbon, nitrogen, oxygen,
magnesium, silicon, and iron. As this
solid core grew larger and larger, its
gravity started capturing more hydrogen
and helium, swirling it together over
millions of years to form the planet we
all recognize today. Intuitively, this
seems to make sense. Our solar system
formation models suggest giant planets
could be created this way since ice and
rock would condense first in the outer
solar nebula, capturing gases in their
gravity as they migrated inward. This
theory known as the core accretion model
predicted a dense well-defined core with
a clear boundary separating the compact
center from the surrounding layers of
gas. To resolve the debate, early
missions to Jupiter all took their turn
trying to discern what lies beneath the
red giant's dramatic atmosphere. By the
1990s, scientists knew that Jupiter was
rich in heavy elements, implying the
planet was made of more than just
hydrogen and helium. The Galileo mission
also found evidence that Jupiter's
magnetic field must somehow be generated
by liquid metallic hydrogen in its
interior. But if the core is purely
liquid, how did Jupiter form in the
first place? The standard theory of
planetary formation requires a solid
nucleus to start gas capture. If Jupiter
once had such a core but somehow lost
it, how did that happen? Could
everything we know about how gas giants
form be completely misguided?
Despite the successful missions to
Jupiter, the planet structure remained a
mystery. The data gathered wasn't
precise enough to determine whether its
core was solid or diffuse, what it's
made of, or how exactly it generates
such a massive magnetic field. But that
all changed thanks to Juno's
discoveries.
Unlike Galileo that had gone on before
it, Juno was purpose-built to map the
planet's gravitational field in great
detail, about 100 times better than
previous maps. When it entered orbit on
the 4th of July, 2016, it began tracing
a highly elliptical orbit, swooping down
again and again from several angles. a
path that made this probe incredibly
sensitive to tiny changes in Jupiter's
gravity. But why are we interested in
gravity in the first place? What did
that have to do with figuring out what
Jupiter's core is made of? Well, we've
all seen gravity depicted like this, a
perfectly round cone, the same on all
sides. I'm sorry to tell you, this
diagram is a bit of an
oversimplification.
For a planet's gravity to be completely
uniform like this, the distribution of
mass inside it would also have to be
perfectly uniform. In reality, if you
zoom in really close, their
gravitational fields look a little more
like this. Planets are made up of many
different elements and materials, each
with their own masses, densities, and
distributions. These differences are
reflected as tiny, almost imperceptible
variations in a planet's gravitational
field. That's why Earth's gravitational
field is actually slightly different
over mountains than planes, and why
scientists are so fixated on mapping
Jupiter's gravitational field with
incredible precision.
As Jupiter's gravity fluctuated, it
caused Juno to speed up or slow down.
The spacecraft was so precise it could
detect changes in speed as subtle as
0.01
mm/s.
At the same time, Juno was continuously
beaming a steady radio signal back to
Earth, which scientists could decode
using the Doppler effect, where gravity
was stronger, Juno accelerated, and we
perceived a higher frequency wave. while
a deceleration due to weaker gravity
resulted in a lower frequency wave. By
repeating this over and over, scientists
built up a very precise map of Jupiter's
gravitational field, which directly
reflects how its mass is arranged
inside.
While the Galileo mission managed to
paint Jupiter's gravity in very broad
strokes, Juno brought it into razor
sharp focus. and what it revealed about
Jupiter's core caught researchers by
surprise. As I said, it turns out both
theories about Jupiter's core were
wrong. It seems to have a core, but it
isn't solid like we thought. It's fuzzy.
Instead of a dense, compact ball, it's
dilute, gradually blending with the
hydrogen-rich layers above it. It
doesn't appear to have any sharp
boundaries. It's also much wider than
expected, spanning about half the radius
of Jupiter itself.
The findings quickly sparked a flurry of
questions, including whether our
understanding of how Jupiter formed
needed a refresh in light of this
exciting new data from Juno.
A popular theory soon emerged to explain
this unexpected discovery that Jupiter
once had a solid core to begin with, but
a catastrophic collision in its early
history shattered and scrambled it in
with the surrounding lighter gases to
give us the fuzzy core we see today. The
only problem is our standard model for
how giant planets like Jupiter form
doesn't work without a solid core. So
either Jupiter's fuzziness somehow
developed later on or our models are
wrong. Anyway, for such a dramatic
shattering to occur, the collision must
have been massive, possibly with another
young planet. Scientists speculate that
up to half of Jupiter's core could have
originated from the remains of this
planet. It was a neat enough theory,
except for one unexpected hiccup.
A curious team of researchers tried to
model this giant collision using a
supercomput. They wanted to emulate the
exact event that would lead to the
results Juno showed us. So they designed
several possible scenarios of a massive
object colliding with a Jupiterized
planet and ran multiple simulations
varying the size of the Jupiter
protolanet and the angle and speed of
collision. But try as they might, they
couldn't find an event that led to the
fuzzy core Juno showed us. Every time
they tried, the models did the same
thing. The impact would initially rock
the planet to its core, but after a
while, the dense rocky material would
settle back down again, like sediment at
the bottom of a glass. It didn't
dissolve into the rest of the planet. a
sharp boundary would reappear, clearly
separating the core from the outer
hydrogen layers. It didn't fit the Juno
data. So, it was back to the drawing
board.
Funnily enough, the next clue in this
puzzle didn't come from Jupiter at all.
It came from its next door neighbor.
Well, that is if you consider 648
million km away next door. We've known
since 2014 that the waves in Saturn's
rings are caused by vibrations inside
the planet. This gives us an insight
into what the planet's core might look
like, similar to how earthquakes let us
study Earth's interior. When researchers
paired Cassini's gravitational field
data with these wave measurements, it
painted a staggering picture. These
observations show that at least some of
Saturn's deep interior doesn't convect.
This is a big deal. Inside a giant
planet like Saturn, heat is constantly
trying to escape. Normally, that happens
through convection. It's what is
constantly happening in Earth's mantle
or when you heat up a soup. Hot fluids
rise to the surface, cool, and then fall
back down, only to be heated up and rise
again. On and on it goes. If Saturn were
fully convective, it would mix heavy
elements throughout its interior. There
wouldn't be a dense central region at
all. The whole thing would be a fully
mixed homogeneous soup. But if it were
partly stable against convection, we'd
expect to see a gradient of material
with heavier elements concentrated
towards the center and tapering outward.
And that's exactly what the data shows.
Researchers published their findings in
2021, arguing that the only way to
explain Saturn's ring wave data,
gravitational field data, and partial
lack of convection is that it too has a
fuzzy core. As it happens, Juno data
also suggests large regions of Jupiter
may not be convective. We seem to be
slowly connecting the dots.
If Saturn and Jupiter have fuzzy cores,
they likely stem from a common
denominator rather than a random
collision event. Now, scientists are
working on a new emerging theory of how
the gas giants came to be, one in which
fuzzy cores are a natural part of
planetary formation. We haven't arrived
at a neat explanation yet, but it is
clear that the old assumptions we had
about the largest planets in our solar
system are incorrect.
Jupiter and Saturn are not made up of
solid core and gas envelope, nor do they
have a completely mixed interior. Their
fuzzy cores are made up of a
compositional gradient with more heavy
elements concentrated in the center
which dissolve out into the gas envelope
without a clear boundary.
This complexity and uneven mixing
challenges our current models for
planetary evolution. Where our old
simplistic model predicted the giants
would cool predictably over time, these
new models don't follow the same
patterns. And the same is true for all
the gas giant exoplanets we've
discovered and studied so far. So Juno
was already throwing out everything we
thought we knew about Jupiter, including
the very way these massive gas giants
formed. Incredible.
One of the biggest surprises to
scientists came from Juno's magnetic
field data. For years, scientists have
known that Jupiter's magnetic field is
generated through a dynamo process in
its metallic hydrogen layer. This layer
spans 20 to 60,000 km deep, where
temperatures can exceed 30,000 Kelvin,
and pressures are millions of degrees
greater than on Earth's surface. Under
these extreme conditions, hydrogen is in
a liquid state. But even more incredibly
here, hydrogen's electrons become
deoized or free flowing. This creates an
electrically conductive metallic state.
Coupled with Jupiter's fast rotation,
this metallic liquid hydrogen creates a
dynamo effect. Though the exact process
of how it's powered remains a mystery.
Whatever it's doing, it's working.
Jupiter has the largest, strongest
magnetic field of any planet in the
whole solar system. Its magneettosphere
spread 7 to 21 times the diameter of
Jupiter, tapering into a tadpole shape
behind it that extends into Saturn's
orbit about 1 billion km away. However,
Jupiter's magnetic field also has some
quirky characteristics. It's much
stronger in the northern hemisphere than
the southern hemisphere. has intense
localized magnetic spots and two
magnetic south poles.
Scientists hoped Jupiter's fuzzy core
might actually explain some of these
strange behaviors. Frustratingly for
them, the opposite turned out to be
true. Jupiter's fuzzy core actually
complicates rather than explains its
magnetic field. Magnetic fields in
planets are usually created by swirling
motions of electrically conducting
material like the metallic liquid
hydrogen in Jupiter's core. However,
Juno data showed that large regions of
Jupiter like Saturn seem to be at least
partially non-convective.
Researchers modeled the fluid dynamics
of Jupiter's interior in two potentially
non-convective regions to see how they
would affect the magnetic field. one in
the upper part of the planet's interior
and the other lower down corresponding
to the dilute core. They concluded that
the upper stable layer helps explain
Jupiter's magnetic field even better
than previous solid core models.
However, the lower region representing
the non-convective dilute core did not
explain Jupiter's magnetic field on its
own. In other words, a completely stable
fuzzy core produces a magnetic field
that's very different from the one we
actually observe. Now, researchers
believe Jupiter's dynamo is more
complicated than originally thought.
It's possible that below the uppermost
molecular hydrogen layer, Jupiter has a
layer of helium which rains down through
the liquid hydrogen like oil passing
through water. Some think this could
have an effect on the magnetic field.
Another theory claims Jupiter's dynamo
doesn't operate in a homogeneous way
like it does on Earth and that instead
the planet's lopsided magnetosphere is
the result of variations in density,
electroconductivity,
or both. But on the whole, no one knows
exactly how this magnetic field is
produced or what role the fuzzy core
plays in its creation.
One thing we do know for certain though
is Jupiter's magnetic field is
responsible for the biggest, brightest
auroras in the solar system.
On Earth, aurora is only visible for a 4
to 6mon window. On Jupiter, they never
stop, covering the poles with a dazzling
display of color, hundreds of times more
powerful and energetic than the auroras
we're familiar with. By stringing
together far UV images from Hubble's
imaging spectrograph, scientists were
able to create these videos of the
auroras in action. Aren't they
spectacular?
Like Earth, aurora appear as bands
around the north and south poles. But
unlike Earth, these auroras are mainly
visible in the ultraviolet and are
mainly produced from alternating
currents, not direct currents. When Juno
measured the power generated from the
direct currents in Jupiter's
magnetosphere, it was nowhere near
enough to account for the brightness of
the aurora, leading scientists to
speculate that the remainder of the
power is coming from alternating
currents. At this time, it is believed
that these alternating currents are
produced because of the turbulence in
the magnetic field. Especially at the
north pole, the magnetic field lines are
much more complex, which interferes with
a direct flow of currents. This is
evident when comparing the north and
south pole aurora. At the north, the
aurora is much more dispersed, looking
more like filaments and flares. Whereas
at the south pole, where the magnetic
field lines are smoother, the aurora
seems to be more structured and round.
Let's look at these auroras in another
way. Juno has an infrared aurora mapper,
giving us a view of Jupiter's auroras
like we've never seen before. The whites
and greens from this image are ions
striking Jupiter's ionosphere from
space, and the reds could be ions coming
from the planet itself. If this is the
case, it has never been observed before.
What you will notice is this bright spot
and tail in the aurora. This is visibly
where Io's electromagnetic influence
meets the planet. What is slightly less
apparent, though, are these other spots.
These are from other large moons in the
Jovian system, Europa and Ganymede. So
while not as powerful as Io's influence,
these other moons have their own
fingerprints connecting them to the
planet too. Most of this data collecting
took place for only a few hours per
orbit as Juno whizzed by the planet. All
the instruments collected as much as
possible during this time, including the
camera.
This remarkable video is a time-lapse of
Juno approaching the northern hemisphere
and leaving again as it looked towards
the southern hemisphere. And this image
is a collection of all the frames that
were used in the video. As Juno
approached the planet, you can see the
storms around the north pole and
gradually the view shifts to the mid-
latatitudes. Zooming in on some of these
shots, we can see the classic swirls and
patterns we expect on Jupiter. But
having a really close look, we can see
these white specks. These specks are
actually water or ammonia ice clouds as
can be seen by the shadows they create.
They are higher in the atmosphere than
the rest of the cloud layer. And
although they look small, they are
actually over 50 km wide. Jupiter is
just really big. So it looks small. Now
you've noticed them once, you'll start
to see them everywhere.
Many of these discoveries were made
early on in Juno's mission. And
fortunately, as the halfway mark for its
planned number of orbits approached,
there proved to be more and more to
uncover about Jupiter. While we knew
about Jupiter's radiation belt, Juno
completely surprised scientists by also
discovering a small and less powerful
radiation belt right above the equator,
which hugs the planet tightly. So far,
the mechanisms behind this radiation
belt are unknown. But there were also
more discoveries about Jupiter's large
ring of radiation. Jupiter is surrounded
by a large donut of charged particles.
The particles in this plasma tausurus as
it is called come particularly from the
volcanic activity of Jupiter's closest
large moon Io which blast particles into
orbit around Jupiter. Just to give you
an idea of how volcanically active Io
is. This was New Horizon's view of Io as
it passed by Jupiter on the way to Pluto
the Tashtar volcano in a full eruption.
Juno has also had a look at Io in the
infrared, the hot spots indicating where
volcanic activity is occurring. Io
ejects one ton of particles into orbit
around Jupiter per second.
As Io travels through the plasma taurus
and interacts with Jupiter's
magnetosphere, this causes a flux tube
to exist between the planet and the
moon. A flux tube being an electrical
current that travels along a cylindrical
tube of magnetic field lines. It is very
powerful. It can develop up to 400,000
volts and 1 million to 5 million amps of
current. Juno was able to get very
accurate readings of the flux tube
during its 12th orbit as it passed
directly through it. No, this didn't fry
the spacecraft as the flux tube has a
large diameter and so it isn't
concentrated enough to do damage to the
craft. Also, Juno was in and out in a
matter of seconds.
Juno was well equipped to study
Jupiter's magneettosphere. You'll notice
that this design paired with the fact
that Juno rotates makes it a little like
a fidget spinner. This isn't just to
make a pretty spinning spacecraft. Juno
was specifically designed to detect
various fields and particles around
Jupiter. And having a spacecraft with a
large spinning radius helps with that.
This is particularly evident with this
instrument here, the magneettometer
found at the end of one of the solar
panels tasked with mapping out Jupiter's
magnetic field. Through Juno's data, we
now have a highly detailed map of
Jupiter's magnetic field, which became
more accurate with every passing orbit.
As expected, Juno confirmed that Jupiter
has a dipolelike magnetic field,
although it is not very aligned with the
rotational axis. What was very
interesting though is that scientists
discovered something called the Great
Blue Spot, a region on Jupiter where the
magnetic field is very concentrated.
Comparing Juno's magnetic field data
with previous Jupiter missions like
Pioneer, Voyager, and Galileo has also
revealed a first for the solar system.
Jupiter's magnetic field structure has
been found to change very gradually over
time, which is called secular variation.
Interestingly, this was most apparent
around Jupiter's Great Blue Spot. This
variation is thought to be driven by a
region right at the base of Jupiter's
atmosphere, which we'll get to in a bit.
One factor for the strength of the
magnetic field is due to the rapid
rotation of Jupiter. One day on Jupiter
only lasts about 10 hours. Various
forces from this stir the liquid up
which generates Jupiter's internal
dynamo. Interestingly, it is the
rotation of the magnetic field from
which we can measure a day on Jupiter as
simply viewing Jupiter's visible bands
couldn't give you a definitive result.
And this is why you'll notice that these
bands look very peculiar, moving in
opposite directions from each other at
different speeds. But this isn't so
unusual if you also consider the
invisible jet streams on Earth. What is
striking though is the colors and
turbulence found in these bands. So
let's try and understand what's going on
from examining these Juno images.
The cloud layer you are seeing here is
the ammonia cloud layer. Some are white.
These represent fresh clouds likely only
recently pulled up from the deeper parts
of the atmosphere. On the other hand,
while the red colors you see are also
ammonia clouds, these clouds have
interacted with UV light from the sun.
Think of it like a photochemical smog.
The reddish smog you see in summer over
large cities. The coloring substance
isn't exactly known, but simply put, the
longer it is exposed to the sun, the
redder it gets. Interestingly though,
comparing these bands to what you see at
the poles, you'll notice it is a lot
bluer here. This could be because UV
light doesn't reach here as easily
compared to the equator.
Looking closely at Jupiter, you'd be
hardressed not to notice the stunning
vortexes and storms across the planet.
And Juno had the opportunity to orbit
directly over the Great Red Spot where
it discovered something very
interesting. It was known that the Great
Red Spot rises high above the cloud
deck. But what scientists didn't expect
is how deeply it penetrates Jupiter's
atmosphere. The instrument on board Juno
designed to peer into the atmosphere had
a range of 350 km. And it seems that the
Great Red Spot extends down even further
than that. Also interesting is that the
spot is cooler than the surrounding area
up until a depth of 80 km. And beyond
that, it actually gets warmer than the
surrounding area. This heat perhaps
driving the storm. It has been theorized
that the Great Red Spot is a permanent
feature on Jupiter, but we've only had
about 400 years to observe it so far. A
mere blink in astronomical time scales.
Looking over the poles, other possible
permanent features have been observed.
In contrast to Saturn, which has a
hexagon on one pole and a single vortex
on the other, Jupiter has five vortexes
around the south pole and eight around
the north. It's hard to say exactly how
permanent these storms are, as Juno has
only been there for 3 years at this
point of the video. And Juno was the
first time we have really been able to
have a look at Jupiter's poles, but they
have been reasonably constant throughout
that time. Under the ammonia cloud layer
is thought to be a water ice cloud
layer. Although this has not been
confirmed as this layer hasn't actually
been seen yet even by the end of Juno's
mission. This had been one of the
science goals of Juno though and it had
several microwave detectors to try and
find this elusive substance. Jupiter
generates heat from within which can be
seen through an infrared camera. the
densest parts of the cloud layer
blocking some of this heat from being
visible. Similarly, Jupiter also emits
microwaves which hypothesized water
clouds would absorb. So, in theory, Juno
should have been able to detect where
the water is present in Jupiter's
atmosphere by searching for where
Jupiter's microwaves aren't visible.
Although, this data has either not been
released or nothing has been found yet.
By 2021, Juno was reaching the end of
its original plan 33 orbits of Jupiter.
However, scientists were delighted to
discover that the probe was still going
strong. The radiation Juno encountered
had done minimal damage to Juno's
hardware, and even its camera was still
functioning, which was one of the first
pieces of equipment expected to fail.
Waste not whatnot, as the old saying
goes. So, when scientists realized that
their probe was still in excellent
condition, rather than send it to its
pre-planned demise, crashing into
Jupiter's atmosphere, they extended
Juno's mission for an additional 42
orbits. Excitingly, Juno would now
extend its view to not just the planet,
but Jupiter's moons, too. So, what did
Juno see there?
On the 7th of June 2021, Juno performed
its close flybys of Ganymede using a
gravity assist to bring its orbital
period from 53 days down to 43 days.
Juno had already performed a distant
flyby of Ganymede in 2019 when it
reached a proximity of 97,000 km. But
this one brought the probe within just
1,000 km of the moon's surface.
In this photograph captured by Juno Cam,
you can see nearly half of Ganymede's
total surface in breathtaking detail.
For reference, the resolution is about 1
km per pixel. I love the crisp rendering
of Ganymede's unique structural
features. You can practically feel its
texture with your fingertips.
Notice how the icy surface is littered
with craters, light and dark patches,
and long striations.
The darker areas show older terrain
which is heavily crated whereas the
lighter areas are comparatively younger
and less cratered. But what about those
long striations?
We know based on previous data that
Ganymede contains at least one vast
salty subsurface ocean beneath its icy
outer layer which some speculate could
be suitable for life. Scientists think
that these long structural features
might reveal faults produced by tectonic
movements generated by heat from the
moon's iron nickel core, but this is a
subject of ongoing research.
This image taken from the same flyby on
the 7th of June shows Ganymede's Tros
crater in greater detail. The reason it
appears so bright is that it's covered
in ice. Here is another image from the
7th of June, which I find remarkable.
It's a photograph of Ganymede's dark
side and it was taken by Juno's stellar
reference unit navigation camera. The
stellar reference unit was designed to
keep Juno on course using starlight
which makes it ideal for photographing
low light conditions. For scale, the
resolution is between 600 and 900 m per
pixel. Again, notice the moon's long
striations and craters, some of which
are stacked on top of each other.
I've seen a lot of photos of Ganymede,
many of which I've covered previously,
but I'm flawed by the level of detail
Juno was able to capture in such low
light conditions.
Interestingly, one of the most
surprising discoveries from the mission
came not from the orbiter itself, but
from Hubble. Yes, that Hubble. Allow me
to explain. You see, to support Juno's
exploration of the Jovian moons, NASA
asked Hubble to monitor Ganymede's
ultraviolet signals.
Ganymede has an atmosphere, albeit a
very thin one. And one of NASA's goals
was to find traces of oxygen they long
suspected was hiding there. Nearly
everyone expected to find plenty of
oxygen based on previous analysis of the
moon's ultraviolet emissions. But much
to our surprise, Ganymede's atmosphere
had very little oxygen in it. What they
found instead was a whole lot of water
vapor. This discovery led to a
significant revision of our model of
Ganymede's atmosphere and could suggest
that water vapor might even be present
in the atmospheres of icy bodies
throughout the solar system.
After visiting Ganymede, Juno made its
flyby of Europa on the 29th of
September, 2022, which gave the probe a
gravity assist that shortened its orbit
to 38 days. Here is a dramatic image
from the flyby taken at a distance of
351 km. It shows a portion of Europa
just north of the equator. What I find
extraordinary here is the dayight
boundary known as the terminator. The
deep shadows really accentuate the
ridges, troughs, and craters that riddle
the moon's surface, showing it in almost
three-dimensional relief. Scientists
think that Europa, like Ganymede,
harbors a vast ocean beneath its icy
exterior. But new findings suggest there
could be a lot more going on than the
simple ocean crust model would have you
believe. What do I mean by this? Well,
hold that thought as we study the next
image.
This photograph was taken by Juno's
stellar reference unit camera and shows
a zoomedin portion of Europa's surface.
It was taken during the moon's night
from a distance of 412 km with a
resolution of 256 m per pixel. This is
the highest resolution image that Juno
took of Europa. At a glance, your first
thought might be, "What am I looking
at?" Well, what you're seeing is a
heavily fractured region of Europa's
surface crisscrossed with grooves and
ice ridges. And that oddly shaped dark
patch just to the right of center could
yield important clues as to what's
behind this geological complexity.
Scientists believe this darkened area
shows an eruption occurring below the
surface ice. The thing is, Europa's icy
shell is over 10 km thick. Imagine the
pressure needed to penetrate so much
ice.
However, a new paper published by
American Astronomical Society proposes a
groundbreaking new theory, pardon the
pun, with a different explanation.
According to the paper's authors,
Europa's cryovcanic activity shows
evidence of brine reservoirs trapped
within the icy outer crust. This would
mean that far above the moon's
subsurface ocean, there could be legs of
high salinity brine that slushes about,
expanding the surrounding ice like a
balloon and bursting through on
occasion. It's a compelling theory, but
to prove it, we may have to wait for the
European Space Ay's Clipper mission,
which will reach Europa sometime in
2030. I know that's 4 years away, but
it's not too early to mark your
calendars.
Let's head back to Jupiter. You see,
while Juno was paying visits to Ganymede
and Europa, it also solved a big
mystery, one that goes back more than 40
years. When the Voyager mission first
visited Jupiter in 1979, the probes
detected mysterious flashes in Jupiter's
atmosphere. Scientists assumed that
these were lightning flashes similar to
those we see on Earth, meaning water
would have to be present in all its
states. solid, liquid, and gas. Given
what we know of Jupiter's atmosphere,
this would put the storms at least 45 km
below the visible cloud tops. However,
Juno disproved this theory. And the
truth is stranger than we imagined.
Juno's stellar reference unit camera saw
something weird. Nighttime flashes at a
far higher altitude than we thought
possible. Given the incredibly cold
temperatures at this altitude, reaching
below minus 888° C, scientists deduced
that the storms were made of ammonia
water-based clouds, a phenomenon that
doesn't exist here on Earth. In these
strange and violent thunderstorms, the
ammonia acts like an antifreeze, forming
a solution of two parts water, one part
ammonia that remains liquid despite
unimaginably cold conditions. And
apparently as these thunderstorms
produce powerful lightning strikes, they
are raining down massive hail made of
water ammonia slush and unusual
precipitation that scientists are
calling mushballs.
Jupiter is a strange planet and the more
we learn, the stranger it gets.
Juno completed orbit after orbit and
over time it shifted its attention away
from Ganymede and towards Io. Io is
Jupiter's third largest moon and the
most volcanically active world in the
solar system. In 2023 and 2024, Juno
bravely made several close flybys of Io,
coming within about 1,500 km of the
surface of this hellish Jovian moon.
During these encounters, Juno snapped
its first ever images of Io's northern
latitudes, mapped Io's surface, and
captured photos of ghostly plumes rising
above the horizon. Io is dotted with
hundreds of volcanoes across its
surface.
Massive fountains of molten lava, some
towering dozens of kilometers into the
sky, paint a violent portrait of Io's
volcanic prowess. The moon's relentless
volcanic fury is driven by tidal
heating, as immense gravitational forces
stretch and squeeze Io. An easy way to
conceptualize tidal heating is to think
of Io like the rope in a game of
tugofwar caught between the pole of
Jupiter's powerful gravity and the pole
of neighboring moons Europa and Ganymede
that orbit farther away from Jupiter. As
Io orbits the giant planet and
experiences the tug and pull from other
nearby moons, it stretches and flexes,
generating friction and immense heat in
the moon's interior. This heat is what
sparks the volcanic activity across Io's
surface. Juno's microwave radiometer
instrument pierced through the
atmosphere, gathering critical data to
craft detailed maps of Io's landscape,
revealing that it has a relatively
smooth surface compared to Jupiter's
other Galilean moons. It's theorized
that this smooth surface is the result
of a constantly renewing surface.
Tremendous heat and pressure within Io
keeps much of its subsurface in liquid
form. And that magma is constantly
escaping to the surface to relieve the
pressure. Whether by filling in craters
or bursting through cracks, these
frequent lava flows could erase impact
craters and cover flood planes with
smooth lakes of lava and glassy
obsidian-like rock that reflect
sunlight.
One striking image from Juno's 60th
flyby on the 9th of April 2024 captured
Io's south polear region. While this
image was taken from 16,500 km away from
the surface, you can still pick out
several dark spots across the moon, many
of which are lavafilled cauldrons and
volcanic depressions.
Several of Io's volcanic eruptions were
also captured by Juno Cam. the mission's
visible light camera. On the 15th of
October 2023, Juno Cam spotted a plume
over the Prometheus volcano just below
the terminator line. The Prometheus
volcano is one of the most prominent
volcanic features on Io, having been
seen repeatedly in images of the region
taken by Voyager, Galileo, and the
Hubble Space Telescope, and now by Juno
as well. Voyager 1 was the first to
observe Prometheus in 1979. A volcano
made up of an enormous cauldra and lava
flow with a tall plume of 50 to 100 km
that rises above the end of the lava
flow. On the 3rd of February 2024, Juno
caught another two plumes in one photo
from just 3,800 km above the surface.
These might have been two plumes from
one gigantic volcano or two volcanoes
that were just close to each other.
Juno Cam also gave us a better look at
two landmark features on the Jovian
moon. One of these was Io's largest
volcanic depression, Loki Patera. This
200 km wide area has a lake filled with
cooling magma just reaching the surface
rimmed with hot lava and dotted with
unnamed islands. The flyover imaging of
Loki Peterraa provided spectacular
reflections of the lake suggesting that
it along with other areas on Io is
smooth as glass. In addition to visible
images, the spacecraft used its Jovian
infrared auroral mapper or GIRM to study
heat sources on Io, an instrument that
was originally designed by the Italian
Space Agency to monitor auroras on
Jupiter. This instrument was able to
pinpoint significant heat sources across
the moon and provide measurements of
thermal emissions radiated in infrared
wavelengths.
Because of this, NASA scientists with
the Juno mission were able to identify
another lava lake on Io. This one is
called Coors Patera.
Visible and infrared images were
combined from two of Juno's flybys, one
in 2022 and the other in 2023 to create
a map of Io's volcanic activity. Here,
data from the space probe's infrared
mapper was overlaid onto Junoam's images
of Io, which you see as spots of red,
yellow, and bright white color. The data
on the left was collected from 80,000
km, and the data on the right was
captured at 58,000 km. To put that into
perspective, the infrared data in these
images has a spatial resolution of about
20 km per pixel and 15 km per pixel,
respectively. Meaning these hot spots
represent absolutely massive areas of
volcanic activity.
And for the first time ever, 30 years
worth of data was combined to create a
map of volcanic activity on Io. This map
shows the varying power output of
hotspots where magma has erupted out
from the moon's interior. Notably, the
map shows the presence of polar
volcanoes.
While it does not confirm the presence
of a magma ocean beneath Io's crust,
this information certainly does support
that possibility.
During the flyby on the 15th of October
2023, Juno also captured the first of
its kind close-up images of Io's
northern polar region taken from 11,700
km above the surface. Because NASA's
Voyager and Galileo missions did not
gather complete images of this area, Io
discovered three neverbeforeseen
mountains in the northern latitudes.
Those mountains are circled in red in
the upper part of this image from Juno
Cam near the line dividing day and night
known as the Terminator. These close
flybys also gave us a look at another
stunning feature on Io. Steeple
Mountain. A striking peak shaped like a
cathedral spire. Steeple Mountain is a
unique landform that rises between 5 and
7 km above Io's surface. Can you imagine
what it might be like to watch the sun
rise behind this jagged summit or the
views if you could climb to the top?
But perhaps one of the most awesome
moments in Juno's evaluation of Io came
on the day we saw its biggest ever
eruption.
On the 27th of December 2024, as Juno
was doing a flyby of Io, lights lit up
all across the moon's scarred surface.
Numerous volcanoes out of Io's 400
erupted simultaneously
across a 65,000
km region, releasing the most energetic
volcanic event we have ever seen in our
solar system to date. Their synchronized
fury seemed to confirm that they were
all connected to the same lava channel.
And yet, even more curiously, not all
the volcanoes within this region
erupted, indicating that some may have
been connected to a different lava
channel network. Io may or may not have
a magma lake beneath its surface, but it
certainly seems to be quite spongy down
there, and it is dealing with a
planet-sized version of heartburn.
But Juno did not just look at the Jovian
moons during its mission extension. It
looked again at Jupiter, too. Getting up
close and personal to Jupiter's
turbulent atmosphere, peering into its
swirling storms and mesmerizing stripes.
Remember, as the largest planet in our
solar system, Jupiter is a colossal
Titan stretching nearly 70,000 km across
and 11 times wider than Earth. It could
fit 1,000 of our Earths inside. In fact,
some individual storms on the surface of
Jupiter are so big they would swallow up
our entire home planet.
As part of his mission, Juno ventured
ever closer to Jupiter's north pole with
each passing orbit, allowing its MWR
instrument to capture a series of images
from different orientations.
This combination of images allows for
improved resolution and analysis of the
polar storms at different wavelengths.
And this data revealed that not all
polar cyclones are created equal. For
example, this series of images depicts
Jupiter's northern polar cyclones in
three different wavelengths. From the
left, these images show microwave,
visible, and infrared light. The
infrared image, which tells us about the
heat in the atmosphere, and the
composite visible light image both
depict Jupiter's northern polar storms
as well defined and of similar size.
However, the microwave image tells a
different story. Take a look at this
storm, for example. It shows a notably
reduced emissions intensity compared to
other storms despite appearing distinct
in the other two wavelengths of light.
The MWR instrument records the glow of
Jupiter's atmosphere in microwave light
with six different radio channels that
each peer deeper and deeper below the
cloud tops. The highest frequency sees
the top of the cloud cover while the
lowest can see up to 320 km below. This
microwave imaging enables Juno to pierce
deep into Jupiter's atmosphere beneath
what we can see with the naked eye. Take
another look at the polar cyclones in
microwave light.
These two storms at the 4 and 6:00
positions were about the same size as
the other nearby cyclones in visible
light, but they show more intense
microwave signatures than the other
storms, which indicates that these
extend at least 100 km beneath the top
of the clouds that we see. Also
intriguing is that the central cyclone
is clear in both the visible and
infrared images, but in the microwave
light, the cyclone all but disappears.
This indicates that the central cyclone
subsurface structure may be very
different from the surrounding storms.
On its 61st to 66 flybys, in my opinion,
Juno captured some of the most
spectacular images of Jupiter's folded
filamentary regions in the northern
hemisphere, offering a detailed view of
the chaotic clouds and cyclonic storms.
In this region, the same zonal jets that
are known for creating Jupiter's famous
banded cloud patterns break down. And
without these jets, the planet's clouds
swirl into turbulent patterns that
rapidly evolve over the course of just a
few days, like a choreographed dance
that's always changing and never ends.
This unforgettable swirling canvas of
blues, whites, and browns is something I
could stare at for hours. And for
planetary scientists, these beautiful
and sometimes terrifying images hold
clues about Jupiter's weather patterns
and atmospheric dynamics.
On the 7th of March, 2024, Juno's 59th
per gave us a rather special set of
images of Jupiter. Here we see the
planet's famous atmospheric belts and
swirling storms, including the Great Red
Spot. But if you look a little closer, a
charming detail is revealed. Jupiter's
tiny moon Amla is visible in these two
images. At just 84 km wide, Amthea is
shaped like a potato as it lacks the
mass to pull itself into a sphere. This
tiny moon circles Jupiter inside Io's
orbit and takes roughly half of one
Earth day to complete an orbit.
Curiously, Amthea holds the title of the
reddest object in our solar system. Its
crimson surface radiating more heat than
it absorbs from the distant sun. Perhaps
this is caused by electric currents that
are induced within the moon as it orbits
within Jupiter's magnetic field. Or
maybe it's caused by tidal heating from
Jupiter's gravity. And of course, Juno
captured some lovely images of Jupiter's
classic bands on its later orbits,
including this one from the 54th Perove
on the 7th of September, 2023,
and this one taken during the 62nd orbit
on the 13th of June, 2024.
Another objective of the Juno mission is
to quantify the amount of oxygen and
hydrogen molecules, which make up water,
that are present in Jupiter's
atmosphere, to help us understand more
about the planet's water abundance.
Jupiter was likely the first planet in
our solar system to form, and it
contains the majority of gas and dust
that didn't become part of the sun,
which means it is also a critical piece
of the puzzle of our solar systems
formation. Additionally, the planet's
water abundance has implications for its
meteorology, like how wind currents flow
and what the planet's internal structure
is like. Luckily, Juno is helping us
answer these important questions. MWR
data from these later orbits has helped
to gauge Jupiter's water abundance,
showing roughly three to four times the
elemental abundance of hydrogen at the
equator as compared to the average
concentration of that element found in
the sun. This supports the idea that
water ice material may have been the
source of heavy element enrichment
during our solar systems formation. If
this is the case, it would mean that as
Jupiter formed, it accumulated not only
hydrogen and helium, but also heavier
elements contained in water ice
material, which was not abundant in the
early solar system. However, further
measurements from Juno showed a
surprisingly low water abundance in
Jupiter's core, raising new questions as
scientists expected to see more water in
the core if water ice were indeed the
primary source of Jupiter's heavier
elements. So for now, the formation of
Jupiter remains a mystery that
scientists are still trying to sort out.
Now all good things must come to an end.
Juno was originally intended to be shut
down in 2018. Even Juno's extended
mission was supposed to finish by
September 2025. And yet there is a
little twist at the end of the tale of
this inddehaticable probe. because
against all odds it is out there still.
There are many question marks over this.
You see, due to political events, the US
government was shut down at the time
that Juno's mission was supposed to end.
This left the fate of Juno in a strange
state of limbo. News pundits at the time
speculated that the probe had possibly
been shut off, and we just hadn't been
told, as this had always been the plan.
Juno was supposed to be de-orbited at
the end of its mission into Jupiter's
atmosphere as a way of making sure that
it never accidentally impacted Jupiter's
moons. We hope to one day investigate
those moons for signs of life and NASA
was keen not to muddy the waters. So, by
all reason, with the deadline passed,
Juno should now be shut off. And yet,
Juno lives still. NASA has been cy about
the fate of Juno, but just a few days
prior to me writing the script for this
video, they posted an article about Juno
data and how it was helping to narrow
down the exact thickness of Europa's ice
shell. Much of the article refers to
prior data. And yet, at the end comes
the captivating words, "Juno will carry
out its 81st flyby of Jupiter on the
25th of February.
So for a probe that was intended to
solve the mysteries of Jupiter, it
seemed that Juno has become one instead.
Its fate is somewhat unknown. NASA had
faced the threat of sweeping budget cuts
last year, and Juno was one of the
missions at risk of being cancelled,
shut down to avoid its running costs.
But Congress seems to have rejected this
idea, passing a bill that roughly
maintains NASA's budget at previous
levels. So perhaps missions like Juno
will get a new lease of life. Perhaps it
will simply be allowed to drift slowly
into Jupiter's warm embrace, allowing it
to capture a closer look than ever into
those ammonia clouds and eventually that
fuzzy core. Who knows how long that
process will be, but for now it is out
there still doing science, still going
strong. Waste not want that after all.
for this resilient probe. As long as it
is still functioning, perhaps not even
the end of its mission will be enough to
stop Juno from discovering Jupiter's
secrets.
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