In 2015, there was a huge excitement in
the space community. That is because up
until then, the best image we had of the
Pluto system was
this. Hubble also squinted its lens at
Pluto, but it is so small and distant,
the best it could see was a few blobs of
color variation. But in 2015, this all
changed. That is because after a 9-year
journey, the New Horizon space probe
flew by the dwarf planet, giving us a
detail and fidelity of Pluto and its
moons like we had never seen
before. So, the question is, what did
the New Horizon's probe see and discover
during its flyby of the Pluto system?
And what has it been doing since the
flyby? I'm Alex Mccoan, and you're
watching Astramm. Stick with me in this
video and I will show you all the
highlights from the New Horizon's
mission to the Pluto system and
beyond. Let's first of all give you a
quick bit of context in case you are new
to Pluto or it's been a while since you
last heard about it. Pluto is a
remarkably pretty tiny world much
smaller than our moon. It's found in the
Kyper belt, a disperse belt of asteroid
or comet type objects beyond the orbit
of Neptune. Pluto was the last of the
traditional nine planets to be explored.
This was due to its distance from us,
but also because, can you believe this,
it wasn't considered a very interesting
celestial object. Thankfully, the team
behind the probe pushed hard for this
mission to be approved. And in 2006, New
Horizons was launched as part of NASA's
New Frontier program for medium-budget
space
missions. The goal of the mission was to
get to Pluto as soon as possible. And as
such, New Horizons was the fastest
launch ever. It being a light spacecraft
on the most powerful rocket available at
the time, a fully boosted Atlas 5. It
whizzed past the moon in only 9 hours.
The Apollo missions took 10 times as
long. On its way to Pluto, it used
Jupiter as a gravity assist, which
shaved 3 years off the arrival
time. It also used Jupiter as a trial
run for its systems, taking some
remarkable videos and images of the
planet and its moons. After this
successful trial, New Horizons went into
hibernation mode to prevent the wear and
tear of its instruments. Leading up to
its approach in 2015, the team turned
the systems back online, and every day
the spacecraft sent back images of the
Pluto system. This was an incredibly
exciting time for enthusiasts following
the story. We began to get hints of what
Pluto could possibly look like and saw
how different Pluto was from its biggest
moon,
Karen. Every day, the resolution got
higher and higher and more details could
be made out.
Yes, there were other scientific goals
for the mission, but the most
interesting thing to me was what it
looked like. Soon there could be seen
what looked to be a heart shape on the
dwarf
planet. On the 14th of July, the New
Horizon's probe made its closest
approach at only 12,500 km from the
surface of Pluto. However, mission
controllers didn't get a look straight
away. Firstly, the probe was too busy
taking a lot of photos during the flyby
to send anything back immediately. Once
data transfer commenced, they had to
deal with the slow uplink speed of only
1 kilobit per second. Further to that,
there was a 4.5 hour latency between the
spacecraft and the Earth. But what it
saw and sent back was
spectacular. Mountain ranges, ice
plains, glaciers, and an atmosphere. It
also had a good look at some of Pluto's
moons. Let's go into detail about what
it actually discovered during this
flyby. One of the first things observed
about Pluto is its unusual relationship
with its moons. For a start, Pluto's
biggest moon, Karen, orbits very closely
to Pluto and is also very big in
comparison. This means that the baris
center of the two objects or in other
words their center of mass is outside
the primary object. They actually both
orbit around a point in space. Not only
that, but both objects are tidily locked
to each other. This means that if you
stand on one, the other won't move from
that point in the sky. This is very
unusual because while some moons are
tidily locked to their parent planet,
the planet is not also tidily locked to
the moon. Karen is very different
visually from Pluto being much darker.
This implies they are not from the same
origin. The rest of Pluto's moons are
very small, only a few kilome across.
Their orbits are exceptionally circular
and are all co-planer with Pluto's
orbit.
The geology of Pluto is very
interesting. The biggest visible feature
on Pluto is this giant heart shape which
wowed the world when it first came into
view. It has since been named Sputnik
Plenicia. It is the size of Texas and it
has a strong color contrast to the
surrounding area. This is because it is
a giant ice plane. In fact, during the
flyby, it was confirmed that 98% of
Pluto's surface is composed of nitrogen
ice. On average, the temperature on the
surface of Pluto is
-229°, which means water ice would be
rigid and brittle. On the other hand,
nitrogen ices at this temperature act
like water ice on Earth, meaning it can
flow as glaciers.
This can especially be seen around the
edge of the heart. Glaciers flowing into
the gaps around the craters and mountain
ranges. The ice planes themselves have
giant polygon shapes across the entire
area. There are also no craters, which
means it must be a relatively new
feature or a feature that is being
continually renewed. It is perhaps only
10 million years old. The polygonal
cells show ridges on them which are
likely caused by sublimation.
the process of an ice turning directly
into a
gas. Ices sublimate and freeze here
regularly, creating troughs and pits,
meaning these polygons are likely to be
convection
cells. These cells are moving and can be
seen pouring into the mountain ranges
surrounding the region through
slowmoving glacias.
Sputnik Planenicia could be compared to
Greenland and Antarctica in that it
controls the climate of Pluto
heavily. Although it is not known for
certain, Sputnik Plenicia could have
formed from an impact and ices filled
the crater in from a potential
subsurface liquid ocean. This filledin
basin actually causes a positive
gravitational anomaly. A gravitational
anomaly is where the gravity at one
point is different from elsewhere on the
object. The ice plane is directly facing
away from Karen, which would align it up
with the object's tidal axis. Due to the
short distance between Pluto and Karen,
tidal effects are very strong on both
objects. This could be the reason why
Pluto is tidily locked to Karen and the
two objects can't look away from each
other. Surrounding the ice plains are
vast mountain ranges made of water ice
which when viewed from the side on look
spectacular. Water ice is the only type
of ice detected on Pluto that would be
strong enough to support heights of
several kilometers at this temperature.
Among the mountains found on Pluto,
there might also be some which are cryo
volcanoes. Some of the most likely
candidates being right Mons. It is 4 km
tall, one of the highest peaks on Pluto,
and a big depression is found in the
center. Cryo volcanoes could be a
contributing factor for Pluto's young
surface. Here is an extremely
interesting region called Tartarus
Dorsa. It is an extensive, highly
distinct set of 500 m high mountains
that resemble snakes skin or treebark.
They are thought to be penitentes.
If that is true, Pluto is the only place
in the solar system other than Earth
where they have been observed. Even on
Earth, they are very rare, but some can
be found in the Atakama Desert and other
dry, high altitude
regions. The ones on Pluto are much
taller and cover a much vaster area than
on
Earth. We can only imagine what they
look like up close.
Another obvious feature of Pluto is the
dark material that seems to be sprinkled
on the surface in some areas. The
biggest such area is called Cthulhu
macula. It is weirdly reminiscent of a
whale in shape as can be seen in this
image. The region on Pluto is much more
heavily created than the heart which
implies the surface there is much older.
Mountain ranges can be seen in the
middle of Cthulhu macula, topped with
what is thought to be methane ices.
Methane apparently condenses as frost at
higher altitudes on Pluto. The dark
color is thought to be a deposit of
tholins, a kind of tar made up of
hydrocarbons that have interacted with
sunlight. Similar deposits can be seen
on one of Saturn's moons, Apotus. So,
the process has been seen elsewhere in
the solar system.
Scientists suspected this substance was
stolen as soon as New Horizon started
sending images back. But its
distribution over Pluto's surface was
baffling. Why are only some areas
covered? Also, how dynamic are the
processes surrounding the distribution
of
tholins? Has Pluto looked like this for
a while or is this a changing
environment? It turns out that these
tholins may well be connected to
cryovcanism found on Pluto. Pluto is one
of the few objects in our solar system
where cryov volcanoes are actively
shaping its surface. Water from either
the mantle or from pockets of water
trapped in the crust erupt over the
surface of Pluto, creating a varied
landscape. But it turns out that it's
not just water found in these eruptions,
but tholins are clearly mixed in too.
Data from Hubble suggested that Pluto
was getting redder and new horizons may
have passed by during Pluto's reddest
time of its year and new horizons may
have found out why. Here in a region
called Viking Terror, we see a cryo
volcano that has fountained this
watertholin slurry across the immediate
surroundings. Just next to this region,
we see a crater and trough filled by
this slurry during another eruption. By
the trough, you can see where this
slurry flowed down and pulled. This can
also be seen in another region by Veral
Fossai, another trough where this slurry
has traveled down. However, the most
interesting thing about tholins is not
found on Pluto itself, but rather on its
twin dwarf planet,
Karen. In this enhanced color image of
Karen, what do you immediately notice?
the red cap over its north pole.
Incredibly, because Pluto's gravity is
so weak when it erupts this slurry
mixture, some of it escapes Pluto
altogether and makes the 19,000 km
journey to Karen. The tholins are
localized here because Pluto and Karen
are tidily locked to each other. They
only ever show each other one
face. Poetically speaking, Pluto is
always hiding its heart from Karen in
this eternal waltz.
This means that more tholins fall on a
specific spot on Karin rather than all
over. And speaking of Karen, some
interesting discoveries have been made
about it, too. It is a water ice world,
unlike Pluto, whose surface is
predominantly nitrogen ice. As such, it
doesn't really have an atmosphere like
Pluto does, as the water ice is locked
to the surface. On Pluto, the nitrogen
ice sublimates depending on Pluto's
seasons, meaning Pluto's atmospheric
density can vary by many orders of
magnitude over the course of its year.
With this sublimating and refreezing of
the atmosphere, Pluto's appearance may
change dramatically over the course of
its 248 year long seasonal cycle.
For me, the most impressive discovery
that New Horizons was able to confirm
was that Pluto has an atmosphere. And
not only that, but the images are
incredible. Due to Pluto's small size
and weak gravity, the atmosphere appears
to extend high above the surface of
Pluto. Earth's atmosphere, while being
much more massive and dense compared to
Pluto, hugs the planet comparatively
tightly. as the gravity is a lot
stronger. The atmospheric pressure on
Pluto on the other hand is exceptionally
low, roughly 10 microbars or 100,000 to
1 million times weaker than the surface
pressure on Earth. It is theorized that
the pressure could increase to as much
as 18 to 280 mibars, three times the
surface pressure on Mars and a quarter
of the surface pressure on Earth.
This may happen throughout Pluto's year.
At some points in its orbit, it is
closer to the sun than Neptune. This
would make the temperature rise, causing
the surface ices to sublimate into
gases, the process of which there is
evidence of in the ice
plains. But the last time Pluto was
thought to have an atmospheric density
similar to Mars was 900,000 years ago.
At this pressure and temperature, the
conditions could be right for liquid
nitrogen to form on Pluto's surface.
Some evidence of this might be found
here in what appears to be a frozen
lake. At any rate, within just one year,
Pluto's atmospheric density can vary by
a factor of four due to seasonal
variations. That is a massive contrast
compared to other solar system objects
with atmospheres, which generally stay
pretty consistent. The atmosphere
consists of the same ices found
condensed on the surface, namely
nitrogen, methane, and carbon
dioxide. The other fascinating discovery
New Horizons made about the atmosphere
is that it has up to 20 haze layers.
Haze layers themselves were not
unexpected, but the amount of them was.
They can clearly be seen in some of
these images, acting like layers of a
thin kind of fog. Sunlight can be seen
streaming through one such layer in this
photo. The shadows from the mountains
clearly seen in contrast to the sunlight
shining through the haze. The layers do
not appear to be level across the
planet. Here you can see this haze layer
high above the surface, but on this side
of the image it touches the surface. On
a side note, to me these are the most
breathtaking photos of Pluto, and I
purposefully saved them until last. You
can truly appreciate depth and the scale
of the mountain ranges. Pluto almost
seeming like a toy replica due to the
extreme topographical relief. But these
mountains appear so high because Pluto
is so small and its gravity is not
strong enough to pull them
down. In June 2020, scientists released
a paper stating that under Pluto's
surface is believed to be an ocean of
liquid water, very much like the icy
moons of the gas planets.
It was originally thought that Pluto
formed cold being so far away from the
sun. However, evidence from New Horizons
suggests that this is not the case, but
rather it started off hot. This means
it's always had an ocean. And if that is
true, then there is a case that
habitability on Pluto may be just as
good as habitability on the closer icy
moons. In fact, if Pluto is the standard
for dwarf planets found in the Kyper
belt generally, there may be many more
habitable worlds out there. How do we
know it had a hot start? There is
evidence of expansion, not contraction
on its surface. These cracks show the
crust is moving apart, not folding over
itself. If this is true and Pluto had a
hot start, perhaps with bombardments
from other planet decesses heating it up
during the early stages of the solar
system, it could be that shortly after
it was formed, it would have had enough
thermal energy that it was once an ocean
world. This really puts a new
perspective on how the solar system
formed.
While the absence of craters is limited
to Sputnik Planenicia, it is amazing how
few craters there are on Pluto and Karen
generally. This might not just be
because their surfaces are young, but
perhaps the Kyper belt is more devoid of
smaller objects than we may have first
thought. The flyby was over in a matter
of days, and New Horizons started
heading deep into the Kyper belt. New
Horizons had traveled so far from Earth
at this point that when it looked at our
closest star system, Alpha Centuri, it
was clearly in a different place from
New Horizon's perspective than from
ours. This is due to the parallax
effect, something I've done a video
about here if you want to see some more
astronomical examples. It's just
mind-boggling to me to think about how
far New Horizons has traveled relative
to us. So much so that Alpha Centuri has
moved from New Horizon's perspective.
Conversely, however, New Horizons has
traveled all that way, and that's the
only difference it's made to the view of
our closest neighbor. Space is just so
big. When New Horizons made its flyby of
Pluto back in 2015, it barely slowed
down at all. Its trajectory after the
encounter actually took it further into
the Kyper belt. Given that this region
is so far from Earth, it is largely
uncharted territory, a place where no
man has gone
before. So, did the New Horizon's team
know of an object that they could visit
next? Yes, they did, and its name is
Aracoth. But incredibly, they didn't
even know of its existence before New
Horizons was launched. So, what is
Araoth? What does it look like? And what
makes it unlike anything we've ever seen
before? You see, the year previous to
the Pluto flyby, time had been given to
the New Horizon's team with the Hubble
Space Telescope so that they could
locate an object for New Horizons to
visit after Pluto. Hubble actually
discovered three new objects reasonably
close to where New Horizons would be
going. And after studying the data, the
35 km long object now known as Aricoth
was chosen. As a result, Aracoth would
be the first object visited that was
discovered after the spacecraft visiting
it was
launched. New Horizons was healthy and
well after the Pluto flyby with
propellant left in its tank and years
left in its RTG. And so commands were
quickly sent to New Horizons by the
mission team to adjust its course so
that it could rendevous with a promising
new target.
Being so small and far away, we didn't
know much about the object. All Hubble
could detect was its color and the dips
and peaks in its brightness as it
rotated. However, scientists also
observed Araoth's occultation of a star.
Incredibly, from this occultation, they
were able to predict the shape of
Aracoth. And as you will see later, this
prediction was almost exactly right. At
the very least, they knew it would be an
elongated object, so potentially a
contact binary or simply a long asteroid
type object. It was up to New Horizons
to confirm their
predictions. 3 years after leaving Pluto
in August of 2018, New Horizons began
its approach phase at a distance of 172
million km.
At this distance, Araoth was barely
visible to New Horizons against the
backdrop of distant
stars. But by December 2018, it was
bright in New Horizon's
[Music]
view. Traveling at 51,000 km an hour,
New Horizons was rapidly gaining on
Araoth, and science data at this point
was already beginning to be
collected. As New Horizons got closer
and closer, Arath's shape could start to
be
resolved. It was bizarre looking, what
appeared to be a contact binary, and was
relatively craterfree with a lumpy
surface. It was unlike any of the
asteroids or comets we had ever seen up
close before.
On the 1st of January 2019, New Horizons
made its closest approach at a distance
of only 3,500 km from its surface. And
it was on this day that it captured most
of its science data. This flyby made
Aricoth the most distant object ever
visited by a spacecraft being 6.5
billion km from the sun at the time or
roughly 45 times further away than the
Earth is from the Sun. Being this far
away, the data speed was abysmally slow
between Earth and New Horizons at only 1
kilobit per second. Although, I will
mention that it's incredible to me that
the technology was there for them to
communicate with New Horizons at all.
This slow data transfer speed has meant
that it's taken around 2 years to send
all of the data it collected around
Aricoth back to Earth. The highest
priority data was sent back first,
namely the images. Although I do
remember at the time that the highest
resolution images took a while to arrive
back. Only low resolution images were
available when all the media outlets
were publishing stories of the flyby,
meaning I would guess that most of the
general public never saw Aricoth in all
of its glory. So, here it is, the
highest resolutions we have of this
fascinating object in true color.
What you'll immediately notice about
Aricoth is that it is reddish in color.
Unlike most asteroids nearer to home,
which are grayer and darker, it's red
because of a similarity it shares with
Pluto. It has an abundance of tholins on
its surface. Theolins are organic
compounds that have been broken down by
solar and cosmic rays. Organic compounds
on the surface probably included methane
and ammonia at one point. However,
Aracoth does not have any of these
substances left, probably due to its low
mass. What Arath spectra does reveal is
that it has methanol, hydrogen cyanide,
and water ice on the surface. This
abundance of methanol on Arath's surface
is the main factor behind its red color,
as irradiated methanol is likely the
cause of the tholins.
However, there is a bit of a mystery in
Aracoth spectra as interestingly there
is also an absorption band at 1.8
micrometers in Arath spectra and
scientists do not know what this
compound is. It is yet to be identified.
It's nothing we've seen before. It's a
shame we weren't able to get a sample of
its surface to be able to say for sure.
The next thing you'll notice about
Araoth compared to asteroids closer to
home is the absence of small impact
craters. It is believed that this is due
to the nature of the Kyper belt itself.
It could have 20 to 200 times the mass
of our asteroid belt, but a lot of this
mass is also contained within large
Pluto-like bodies which dot the belt.
While we can't say for sure what the
population of the Kyper belt is, it is
definitely more spread out than our
asteroid belt simply because it's 20
times as wide and has a much bigger
circumference. Being this far from the
sun means orbital speeds are much
slower. So even if an impact does occur,
it will be at a low velocity. Meteorites
you see creating shooting stars in the
Earth's atmosphere may hit us at around
75 km a second. Whereas impacts in the
Kyper belt, may only be at speeds of 300
m/s.
This depression here, which looks like a
crater, may not actually have been
formed from a collision, but it could be
a sinkhole caused by the escape of
volatile substances just under the
surface. The lack of collisions means
that what we see of Aricoth now is like
a time capsule from the early solar
system, an object that has been
preserved for billions of years.
Although a slow collision is one of the
ways this object may have come into
being. When asteroids in the asteroid
belt impact each other at high speeds,
they either cause craters or cause the
body to completely fragment. But a slow
collision like those in the Kyper belt
may cause both objects to simply merge.
It may also be that the two loes of
Aricoth formed side by side in a
swirling cloud of ice fragments that
coalesed into two orbiting bodies.
Eventually, these bodies got closer and
closer until they joined together. In
any case, the merging would have
happened very slowly because there
weren't many fractures or stress lines
to speak of. So, the maximum speed of
the collision would be no more than 2 m
a second. Plus, the two objects would
have also had to have been tidily locked
to each other before merging, too. The
fact that both lobes of Arath look very
similar gives weight to the theory that
they formed in the same
region. Before Arakoth got its formal
designation, you may have known it by a
different name. It was originally
nicknamed Ultima Thuli. Now, the
individual lobes are known as Ultima and
Thuli. You'll also notice some very
bright regions on the surface. The ones
in the crater are probably from
avalanches as material fell inward after
the sinkhole appeared. The other major
bright patch is found around the
connecting point between the two loes.
It's not known with certainty why this
region is brighter, but theories suggest
that this region sees the least amount
of sunlight. So perhaps volatile
substances can build up here, like
ammonia ice. It could also be that
because this region would be the center
of gravity of the object, loose material
rolls down the loes to collect in the
center. With a density of only 0.5 g per
cime cubed, Aricothth is not going to be
densely packed, but it is probably
porous. Volatile materials would have
escaped the interior of the object over
time due to an internal heat source, but
then these materials would freeze on the
surface, leaving behind only rocky
remains inside. This heat source can
still be detected to some degree, as
models suggest that Aricoth should only
be 12 to 14 Kelvin. However, New
Horizons found that it was in fact 29
Kelvin. That is still extremely cold,
just not quite as cold as we were
expecting. There's one last mysterious
characteristic of Aracoth that isn't
immediately apparent from these images
that only got discovered after trolling
through the New Horizon's data, and that
is that Araoth is in fact much flatter
than we would have expected. We didn't
notice it at first because Aricoth
rotates like this, meaning we didn't see
too much of it lit up from a side angle.
We don't really know why it's flat.
Maybe it was due to centrifugal forces
when the individual loes formed,
implying it was spinning a lot faster
than it is today. Or maybe it's due to
the way Aricoth orbits and rotates,
meaning one side of the object is
constantly exposed to the sun for
decades at a time. This would cause
volatile substances to escape only on
one side until later in the year when
the other side is exposed to the sun.
Research is still underway to model the
cause. As New Horizons left Araoth, it
looked back and caught one last glimpse
of its silhouette against the backdrop
of stars. Who knows if Arath will ever
be visited again, so it may well be that
this is the last close-up view that we
will ever have.
What's next for New Horizons? Well, it
still has life in its battery and 11 kg
of fuel still on board. So, the hunt is
now underway to search for any
additional
targets. Beyond that, it will follow the
path of the Voyagers, passing through
the heliosphere of the solar system in
the 2030s. Even if no other Kyper belt
object can be discovered close enough to
its current trajectory that it can do a
third flyby, the New Horizon's team is
already submitting proposals for an
extended mission that will have a
completely different focus. They want to
convert New Horizons into a highly
productive observatory conducting
planetary science, astrophysics, and
heliospheric observations that no other
spacecraft can simply because New
Horizons is the only spacecraft in the
Kyper belt and the sun's outer
heliosphere and far enough away to
perform some unique kinds of
astrophysics. Those studies would range
from unique new astronomical
observations of Uranus, Neptune, and
dwarf planets to searches for free
floating black holes and the local
interstellar medium along with new
observations of the faint optical and
ultraviolet light of extragalactic
space. Beyond that, New Horizons has
already given us a wealth of data on
Kyper belt objects that we would not
have known about otherwise. Who knew
that this is what Pluto would look like?
that Karen has a red cap, that Arakoth
would be flat. And considering these are
the only Kyper belt objects we've ever
seen up close is bound to be a lot more
out there that's still waiting to
surprise
us. Pluto is a captivating member of the
solar system, but whenever I make an
astr video about it, for all that I
cover, I can never cover everything.
Sometimes my videos leave you in the
comments with questions unanswered,
like, "Why is Pluto so hard to see from
Earth when telescopes like Hubble can
see distant galaxies? How is it that New
Horizon's photos of Pluto were so
illuminated when it's supposed to be so
dark out there, so far from the sun?" I
love these sorts of questions as the
answers to them give us a fascinating
insight into the way the universe works.
So, if you've ever had questions about
Pluto, this might just be your moment.
It's time for you to get some
answers. I'm Alex Mccoan and you're
watching Astramm. And I'm going to
answer four of your top questions about
Pluto. The answers to these questions
will be intriguing, unique, and even
emotive. But let's jump right into it.
How can Hubble see distant galaxies
clearly but not
Pluto? Hubble has taken some of the most
breathtaking images of space that we
know of, giving us clear views of
galaxies millions of light years away.
And yet, it struggles to take clear
images of celestial bodies much closer
to us, like Pluto and other trans
Neptunian objects. Surely that doesn't
make sense. How can it see something so
clearly so far away and yet the most
detailed view of Pluto is
this? The answer is a lot simpler than
you may think. It's all about the
angular diameter of the object in
question. This fantastic image is the
Andromeda galaxy, a galaxy found roughly
2 million lighty years away from us. You
might think that this distance would
make it relatively small from our
perspective.
But even though it is so far away, use a
high exposure camera and you'll find
that it is actually six times bigger
than the sun or a full moon in our sky.
This is because it is big. 220,000
lightyears across. And at that size, 2
million lighty years away from us is not
enough to make it seem tiny. Its size
and distance from us means that it
covers 3° across the night
sky. It is so big, in fact, that when
Hubble looked at it, it couldn't see the
whole thing in one go. It simply
couldn't zoom out enough. So, this image
is actually a mosaic of hundreds of
Hubble exposures. And even then, they
couldn't fit the whole galaxy in at
once. This is true of other galaxies as
well. Now, most galaxies aren't as close
or as big as Andromeda, but they are
still big enough for Hubble to image
them and see interesting details while
it's at it. Here's the pin wheelel
galaxy, 21 million lighty years away.
Notice how it covers the gap between
some foreground stars found in our
galaxy. That's to give you some idea of
how big it is in the sky.
If you could see it clearly with your
naked eye, it would appear just smaller
than the moon. I hope this is giving you
some
perspective. Even though it is so far
away, it is huge and so still has a
large apparent size in our sky. As you
can imagine, this makes it much easier
to image.
Just as a side note, I can only imagine
how beautiful it would be if all
galaxies local to us were bright enough
to be visible to the naked
eye. But what about Pluto? We might need
to clarify our measurements. To describe
the size of something in the sky,
astronomers use degrees, ark minutes,
and arc seconds. 60 ark minutes in a
degree and 60 ark seconds in an arc
minute.
So Andromeda was 3° across and the moon
is about 30 ark minutes across. The
pinwheel galaxy is about 28 ark minutes
across. Pluto is a minute 0.11 arcsec
across at its closest approach to us.
That makes it ridiculously small in our
night sky. A wonder that Hubble can
resolve any details on it at all. But
again, closer and larger planets, which
have bigger apparent sizes, can be
resolved more easily by Hubble. That's
why sending New Horizons to Pluto back
in 2015 was so exciting. We really
didn't know what to expect before we got
there, as we don't have a telescope
powerful enough to resolve any details
on Pluto. And so, everything New Horizon
sent back was a revelation. Here's one
last example from right here on Earth to
really hit the idea home. In this
picture, you can see objects at various
distances and sizes. I want you to think
of this flower as Pluto. It's small and
blurry at this distance. And yet,
there's some buildings in the background
much further away than the flower which
are clear in this image. Imagine these
are the galaxy's Hubble
images. So that should clear up the
mystery of our first question. On to
number
two. Why does Pluto and his big moon
Karen orbit around a point in empty
space? Not all of you would know that
Pluto was doing this, but those who had
heard of it might have caused to wonder.
Is there something invisible and hugely
dense there? Perhaps some kind of tiny
lurking black
hole. As the New Horizon's probe
approached Pluto and Karen in 2015, it
saw this orbiting phenomenon up close
and in detail. But in reality, no black
hole explanation is necessary.
Scientists were expecting this before
New Horizons even arrived, even though
they had never detected anything present
at that point. This is because
everything in space, not just Pluto,
orbits around a bar center. A barisenter
is the center of mass between two
objects. To help visualize this, if I
get a nice butternut squash on one end
of a stick and a kiwi on the other, we
can see that the center of mass is more
towards the butternut. For most of the
planets with their much greater mass
than the moon's orbiting them, the
center of mass in these situations
resides within the planet itself,
meaning it wobbles as the moon's gravity
tugs on it. With Pluto and Karen,
though, they are much more similar in
mass, which means the point in which
they orbit is outside of Pluto, making
it appear like they are swinging around
an invisible object in space.
The only other place that this happens
with all the other big celestial objects
in the solar system is surprisingly the
sun and
Jupiter. So another enigma about Pluto
solved. Now what about number
three? A lot of you have asked how are
the New Horizon's images of Pluto so
bright seeing as Pluto is so far away
from the sun. Surely Pluto would be
pitch black in reality, right? Well, the
answer is with your naked eye, if you
were to look at Pluto, it would indeed
be darker than in these images. But
interestingly, not as dark as you may
suspect. Thankfully, we don't have to
try and imagine it because twice a day
on Earth at dawn and dusk, the
illumination of our sky matches how
bright Pluto can get at its high noon.
NASA calls this Pluto time and you can
check this website out to find out when
it will happen next where you are. As
you can see, it's Pluto time here and my
mobile phone camera can still easily
take a
video. Pluto is an average of 40 times
further away from the sun than the Earth
and only has a 1600th of the sunlight.
Direct sunlight on Earth is 100,000
lumens per square meter. So on Pluto, it
would be around 60, the equivalent to an
indoor stairway or corridor lighting.
Even if that level was a problem for our
cameras, we can still see darker objects
by utilizing longer exposure times.
Here's nighttime where I am, and with a
15-second exposure, my camera can pick
up a lot of details. And if it still
appears dark, I can always up the
brightness afterwards in some editing
software.
So, there you go. Why Pluto appears so
bright in New Horizon's
photos. We've got one last question to
go. And I think this perhaps is the
biggest question the general public ask
about Pluto. It is part a search for
answer, part a cry at the injustice of
it all, but its answer actually comes
with some fascinating nuance. It is, of
course, this. Why is Pluto not a planet
anymore? Before I explain, did you know
that we once were considered to have 100
planets in our solar system? It's true.
Throughout the ages, the number of
planets in our solar system has gone up
and down quite a lot. And no, before you
ask, this is not because planets
suddenly appeared and disappeared, but
rather due to how they were discovered.
Since antiquity, there were five planets
beyond Earth, which are the ones visible
to the naked eye. Mercury, Venus, Mars,
Jupiter, and Saturn. The ancient Greeks
added the sun and the moon to their list
of planets, but that idea never really
caught on. In the late 1700s, Uranus was
discovered, which was revolutionary at
the time, as no one considered there
could be more planets beyond the visible
five. After this discovery, more and
more planet candidates were being found
like Siri, Vesta, Palace, and Juno,
which are all found in what we now know
as the asteroid belt or the large belt
of asteroids between the orbit of Mars
and Jupiter. But these were not
initially listed as
asteroids. In science textbooks in the
early 1800s, they were all listed as
planets. In the middle of the 1800s,
Neptune was discovered, and within a few
decades, we had quite a list of planets
on our hands. There just wasn't a clear
distinction between the eight planets we
know today and the large asteroids that
were being
discovered. By the
1860s, over 100 asteroids had been
found, and they were finally given their
own distinct classification as
asteroids.
Asteroids were described as objects that
couldn't be distinguished from stars by
the fact that they move across the sky.
So, you might as well ask why Palace
isn't considered a planet or demand
justice for
Juno. A lot of people in the world feel
like Pluto has been hard done by, but
Pluto was just another victim of this
ruthless refinement of categorization.
In 1930, Pluto was discovered and with
the excitement of finding something so
large and distant, it was classified as
a
planet. However, within a few decades,
it was discovered that it didn't follow
the conventions of traditional
planets. The planets we know have
circular orbits that align roughly with
the plane of the solar system. Pluto, on
the other hand, orbits at an angle to
the solar system. And his orbit is so
elliptical that at some points during
its year, it's closer to the sun than
Neptune. But it was also unique, so no
one minded it being called a planet. But
then in the 1970s, Pluto was discovered
to be a lot tinier than expected. It
turned out that its mass is only 16th of
our moon.
This made things a little awkward. Why
call Pluto a planet but not our moon
when it was so much bigger than
Pluto? Trouble continued for Pluto in
the '90s when telescopic technology had
greatly increased and other worlds were
being discovered in and around the orbit
of Pluto. Just like the discovery of the
asteroid belt, it quickly became
apparent that there was another belt
beyond the orbit of Neptune, now known
as the Kyper
belt. These objects are still being
discovered. The most famous ones being
Eris, Sedna, Homea, and
Mak, but seriously, they have found a
lot. Just look at this
list. In 2006, the International
Astronomical Union knew that something
had to be done. It was time to come up
with a new definition for the word
planet. They finally classified a planet
as a celestial body that A is in orbit
around the sun, B has sufficient mass
for itself gravity to overcome rigid
body forces so that it assumes a
hydrostatic equilibrium or a nearly
round shape and C has cleared the
neighborhood around its orbit. So
although Pluto fits the bill for the
first two categories because it lies in
the Kyper belt, it has not cleared its
orbit and thus is not a
planet. I have heard argument that lots
of the planets actually have many
asteroids in their orbits too. But it is
a bit different to have some asteroids
around you compared to being in an
actual belt. Pluto is instead known as a
dwarf planet, which is almost the same
except it's not massive enough to have
cleared its orbit. We shouldn't see this
as a slight against Pluto, but rather
because of these new discoveries, we
have a whole new category of celestial
objects to learn about. Also, because of
the classification change, there is a
silver lining for the once planet
series. It got promoted from being an
asteroid to becoming a dwarf planet.
Better than
nothing. So, there you have it. Four
questions about Pluto solved. But how
many more questions have now arisen?
Perhaps as you've watched the icy beauty
of Pluto and learned of its mysteries,
all that's happened is it's got your
mind turning in even more directions.
like the mythical hydra. Maybe this is a
beast that can never truly be slain with
just chopping off its heads. But that's
part of the beauty of the universe. We
can learn so much and there is still so
much more to learn. It's the journey
that is the most
satisfying. If watching this video has
sparked in your mind any more questions
about Pluto, its motions and
characteristics, or about our solar
system in general, let me know in the
comments below. I might do more videos
like this one going forward and would
love to know what you think. But for
now, whatever you were wondering about
Pluto, hopefully you now know a little
bit
more. This is Pluto, a strange and
beautiful world so remote that the sun
looks merely like a bright star in its
firmament.
The icy dwarf planet, which sits at the
edge of the Kyper belt, a discshaped
region of dispersed bodies beyond the
orbit of Neptune, looks like a fever
dream of towering peaks, nitrogen ice
glaciers, and winding
canyons. It's extremely tiny, much
smaller than our own moon, and far more
colorful. Its surface hue varies from
white to red to burnt orange and
charcoal black. As a contrastive body,
it is second in the solar system only to
Saturn's moon,
Apotus. Yet, until recently, even high
powered telescopes like Hubble could
only make out just a few blobs of color
on it. Pluto is so small and distant,
being nearly 5 billion km from Earth at
its closest approach, that we only had a
vague sense of what it looked like.
However, that all changed in 2015 when
NASA's New Horizon's probe transmitted
the first uplose images of Pluto ever
taken, and they were
astonishing. Veterans of this channel
may remember previous videos I released
on the New Horizon's mission, but those
were just the tip of the Plutonian
glacia, so to speak. When it comes to
Pluto, there's a lot to talk about, and
we still have many more questions than
answers. So, what else can we learn
about Pluto? What surprised scientists
and how are recent studies changing our
understanding of the dwarf planets past
and
present? I'm Alex Mccoan and you're
watching Astramm. Join me today as we
return to Pluto and highlight some of
the most incredible features New Horizon
saw on its
flyby. New Horizons launched in January
2006 from Cape Canaveral Air Force
Station. Its primary mission was to
photograph and collect information on
Pluto and its moons, Sharon, Stixs, and
Nyx, not to mention Keraros and Hydra,
which hadn't been discovered yet. On the
14th of July 2015, 9 years into its
mission, New Horizons made its closest
approach to Pluto, capturing a
breathtaking glimpse of its surface that
exceeded our wildest imaginings. ice
mountains, nitrogen glaciers, cryo
volcanoes, and
canyons. But given the immense distances
involved, transmission was limited to
just 1 to 2 kilobytes pers. It took 15
months to downlink the full data set,
which caused a sensation every time NASA
released a new image. As I look at these
images today, my sense of wonder hasn't
dimmed. There's so much information to
unpack. It feels a bit like working on a
puzzle. And like any good puzzle, the
fuller picture only reveals itself after
you've taken the time to piece it
together. Let's start with a unique
feature called the brass knuckles.
Located near Pluto's equator, it is
comprised of six lowland regions called
maculelet with an average width of 480
km each roughly the size of Iceland. If
we take a closer look, we can see that
they are interlaced with a network of
canyons. From west to east, they are
Kran, Allah, Balrog, Muhammab, Kame,
Aname, and
Mango. Each of these names come from a
different netherworld spirit from world
mythology. So, for those Lord of the
Rings fans watching, you'll be excited
to know that Balrom Macula is a
reference to that wizard battling demon
of Middle Earth.
We think the brass knuckles get their
dark color from a tar made of tholins
which are hydrocarbons formed from the
interaction of methane and nitrogen with
cosmic rays. Tholins are in abundance
throughout Pluto such as here in the
neighboring well-shaped region known as
Cthulhu
macula. The reason the brass knuckles
appear separate is that each macula is
divided by towering uplands covered in
ice. These uplands stand several kilome
tall and are likely made of frozen
nitrogen, methane, and carbon monoxide
on top of a bedrock of water ice. On
Pluto, water ice is strong enough to
form mountains because of its low
gravity. Nitrogen ice, however, is much
softer, which is why it tends to flood
the lowlands on Pluto. One can only
imagine what these colossal ice
mountains must look like from the
canyon's perspective.
Nitrogen is the most common material on
Pluto's surface. 98% of it. In fact,
nitrogen ice also accounts for a large
part of Pluto's most iconic feature, its
heart-shaped region known as Tomba
Regio, named after Pluto's discoverer
Clyde
Tomba. The western lobe of the heart is
a smooth basin filled with nitrogen ice
called Sputnik Planenicia, while the
eastern lobe is much rougher. In this
image, you can see the relief in
remarkable
detail. Scanning from west to east, you
can almost feel the difference with your
fingertips. The eastern side looks
pitted like an orangish skin. Scientists
think Pluto's winds are carrying
nitrogen from Sputnik Penicia up into
the atmosphere and depositing it back
into these eastern uplands, which is why
their albido is so high. Albido being
the measurement of how much light a
surface reflects.
Notice how the uplands have a bright icy
sheen due to all the nitrogen ice
deposited there. We think that some of
that nitrogen in turn slides back into
the lowlands via glacial flow, meaning
the western and eastern halves of the
heart have a transactional relationship.
It's an unusual arrangement, but who are
we to
judge? Over on the western side of
Sputnik Planenicia is a towering
mountain range called Alidrici
Monz. Here the winds blow tiny particles
of methane ice towards the mountains and
deposit them back onto the surface like
grains of sand. This is remarkable in
itself since Pluto's atmosphere is very
thin. We didn't expect its winds to be
capable of this kind of transport. Most
likely these methane particles are
uplifted by sublimating nitrogen ice.
The process which a substance changes
phase from solid to gas. We think the
sublimating nitrogen rips tiny
grain-ized particles of methane ice
which carry up into the atmosphere and
settle closer to the mountains. These
methane deposits form a vast 2,000 km
field made of transverse dunes somewhat
resembling those in China's Taklamakan
Desert or California's Death Valley. But
unlike those deserts here on Earth,
these dunes form in frigid temperatures
of
-230° C. The tiny grains of methane that
form the dunes are much lighter than
sand, and in Pluto's low gravity would
likely feel like dust spilling through
your fingertips. However, given the
minus 230° temperatures, I wouldn't
recommend
trying. The dunes aren't the only item
of interest in this corner of Sputnik
Plenicia. On the western side of the
mountains is a deep trench which you can
see as the dark blue band on this
colorized elevation map. Based on our
measurements, the peaks adjacent to the
trench vary from 200 m to 1 km in
height. While the furthest peaks are
much higher, reaching 3 km in height,
nearly as tall as the Rocky Mountains.
This means the mountains get taller as
you move further from the trench. Why is
this significant? Well, we think it
might be connected to what's going on
underneath Pluto's surface. You see, one
of the most fascinating revelations
we've recently made about Pluto is that
it may have had and might still have a
vast subsurface ocean. This is a
characteristic it would share with
several moons in our solar system, such
as Ganymede, Europa, and Enceladus. The
fact that Pluto could host liquid water
at all is remarkable when you consider
how far away it is from the sun. It
would have to generate significant heat
from nuclear decay in its core. Yet
Pluto is smaller than our own moon.
Given the dimminitive size of its core,
you wouldn't expect it to generate a lot
of heat. So, the evidence for a
subsurface ocean took a lot of people by
surprise.
This is very interesting, but I'm sure
you're wondering what it has to do with
the mountains we just looked at. Well, a
2019 study published at the Luna and
Planetary Science Conference argues that
the Aladrrisy Mountains have very likely
moved east through solid state
convection. This movement could have
produced both the deep trench on the
mountains western side as well as the
uplift we see in the rising peak
elevations moving from west to east. If
this theory is true, these dynamic
processes happening on Pluto's surface
would seemingly support the idea that
there is a layer of liquid water beneath
its icy crust. We see other evidence as
well in the form of cryo
volcanoes. Right mons is one potential
cryov volcano we've looked at previously
on this channel, but here it is in the
highest resolution color view that the
New Horizon's team assembled. What
you're seeing is a composite of images
taken by the probes lurorry camera and
its Ralph multisspectral visible imaging
camera. Rightmons is a massive structure
made mostly of water ice standing 4 km
tall with a gaping depression in the
middle and it may have been active
fairly recently as evidenced by the lack
of impact craters in the surrounding
area.
Scientists spotted another potential
cryov volcano to its southwest called
Picardmons. And it's even more massive,
rising 7 km tall. Sadly, it was already
in darkness by the time New Horizons was
able to capture it. So, the images
aren't quite as clear as those of Wright
Mons, but you can see it here in this
colorized topographic map. It too has a
huge depression in its center. The
depressions of both structures are
reminiscent of cauldras we see here on
Earth, but they are much larger relative
to the size of the
volcanoes. Looking closely, they appear
to be concentric rings surrounding the
depressions, indicating perhaps a series
of eruptions followed by a retreat of
magma and subsequent collapse of the
vents. Just to be clear, we haven't yet
confirmed that these are definitely
cryov volcanoes, but the literal
mountain of evidence is hard to
deny. So, there we have it. Another
group of incredible features New
Horizons found on Pluto. And given the
surprising revelations about its
possible subsurface ocean, you can be
sure that there will be a lot more
research on the subject. What more
discoveries do you think we'll make?
Could we one day find life in Pluto's
ocean? Will we send a probe to another
of the dwarf planets in the Kyper belt,
such as Aerys? It's been proposed, but
the space flight alone will take over 20
years. All the more reason to appreciate
the wonderful images New Horizons
captured. Thanks for watching and thanks
to our crew of astronauts over at
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knowledge freely available to everyone.
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