[Music]
Io is one of the most curious objects in
our solar system.
The innermost of Jupiter's big moons. It
has plenty of features that set it apart
from anything else that we have ever
seen, including volcanoes,
aurora, and a sulfur atmosphere.
I'm Alex Mccoan, and you're watching
Astramm. And together we will go through
everything you could want to know about
the hellish world of Io.
Let's get to know the context of Io a
little better. Jupiter has 79 moons that
we know of so far. There's a few that
orbit close to the planet in and around
the planet's rings. Beyond that are four
large moons known as the Galilean moons
named after Galileo who discovered them
in 1610. From innermost to outermost,
these moons are Io, Europa, Ganymede,
and Kalisto.
Beyond them are the irregular moons of
Jupiter, all of which are much further
out than the previous moons.
Io orbits very close to Jupiter, only
350,000
km above Jupiter's cloud tops. This
means from Io's surface, Jupiter would
appear 39 times bigger in the sky than
our moon. Io orbits Jupiter in only 42.5
hours compared to our moon's monthly
orbit.
Its orbit is actually in sync with two
of the other Galilean moons. It orbits
twice for every orbit of Europa and four
times for every orbit of Ganymede. This
is what we call an orbital resonance.
Orbital resonances greatly enhance the
mutual gravitational influence of the
moons, which means the gravitational
forces from the other moons cause the
orbit of Io to have a little more
eccentricity than it otherwise would
have.
This is likely the primary heat source
for most of its geological activity. As
Jupiter's gravity pulls and tugs on Io,
causing tidal heating. At some points in
its orbit, the tidal bulge on Io is
thought to be up to 100 m. This effect
is similar to what we see on Earth with
the ocean's tides being caused by the
moon. Although on Earth, the effect is
much more minimal. The tides only
usually shifting about 2 meters from
high to low.
Io is getting 300% more tidal force
exerted on it in comparison to our moon
on us because of its close proximity to
the biggest planet in the solar system,
Jupiter. And the other big moons in the
system don't allow the moon's orbit to
be any less eccentric, meaning Io isn't
going to be getting any restbite anytime
soon. A day on Io is the same as its
orbital rotation, which means that Io is
tidily locked to Jupiter. Just like we
can only see one face of our moon from
Earth, only one face of Io can ever be
seen from Jupiter.
Io is a pretty big moon, although it is
the second smallest out of the Galilean
moons.
It is comparable in size to Earth's moon
and shares a similar density, meaning it
has a similar amount of gravity. But
interestingly, it does have the highest
density of any other moon in the solar
system. One of its many unique features.
Another is that it is composed of mainly
silicut rock and iron.
Similar to the terrestrial planets and
our moon in comparison to most other big
moons in the solar system, which are
made of water, ice, and silicates,
Io in fact has the least amount of water
of any known body in the solar system.
Its core is likely to be made of iron or
iron sulfides surrounded by a silicutri
mantle and crust. The core is not
thought to be convecting though as no
magneettosphere has been detected around
the moon. The mantle is thought to be
liquid near the crust and is at least 50
km thick. This is where all the
volcanism originates.
Which brings us to perhaps the most
interesting part about Io, the hundreds
of huge volcanoes all over its surface.
Before the 1970s, we didn't know much
about Io at all, although telescopes
were starting to pick up hints that the
moon was devoid of water and that it may
have a surface of sulfur.
The first mission to see Io in any kind
of detail was Pioneer 11, although the
quality was still not great.
What it did detect, however, is that Io
was made of silicut rock and not water
ice and that it has a thin atmosphere.
Pioneer 10 was also meant to take some
close-up shots of Io, but this was lost
due to Jupiter's radiation interfering
with the onboard command system. The
radiation Pioneer 10 went through was
10,000 times stronger than the maximum
radiation around the Earth.
The next missions to Jupiter were the
Voyager 1 and 2 missions in 1979.
Voyager 1 flew by at a distance of only
20,000 km and was able to take some
impressive close-ups of Io's surface.
What it saw was a remarkable landscape
full of vibrant colors and a total
absence of impact craters. It found
mountains taller than Everest
as well as volcanic pits hundreds of
kilome wide.
and what looked to be lava flows.
Most notably, however, was the presence
of plumes coming from the surface. This
proved that Io is volcanically active,
and it is still the first and only place
this has been visibly seen beyond Earth,
not including cryo volcanoes. Voyager 1
also confirmed that the surface of Io is
covered in different sulfur frosts. This
is what gives Io its many spectacular
colors.
It found that it is these sulfur
compounds that dominate the atmosphere.
Voyager 2 also saw Io in July of 1979,
but was much further away at 1 million
km, although it still saw seven of the
nine plumes Voyager 1 saw in March,
which meant those volcanoes had likely
remained active throughout those four
months.
The really interesting images came about
with the Galileo spacecraft that arrived
at Jupiter in 1995.
The spacecraft wasn't especially
designed to study Io, but it was able to
acquire some of the highest resolution
images we now have of its surface.
[Music]
Sadly though, Galileo never worked at
full capacity as it had quite a few
mechanical malfunctions, which means we
could have had even better images had it
been fully operational. What it was able
to see though were plumes from many
volcanoes
as well as confirming the volcanoes were
erupting sulfur and silicut magmas
similar to what we have on Earth except
the magma on Io is also rich in
magnesium.
The surface of Io is spectacularly
colorful. The yellow planes are composed
of mainly sulfur. The white areas are
mainly fresh sulfur dioxide frosts.
Towards the poles, the sulfur is damaged
by radiation, which can be seen as the
poles appear redder than the rest of the
planet. In other places, the colors of
red are the deposits left by volcanic
plumes that reached hundreds of kilome
above Io.
The most obvious deposit is from the
volcano Pelle. Sadly, an inactive
volcano when Galileo was around, but
Voyager 1 was able to see a massive
plume when it passed by. In this image,
this plume is 300 km tall and 1,200 km
wide. In other words, roughly the size
of Alaska.
Interestingly though, the source of lava
flows on Earth are typically the
depression you would normally see at the
top of volcanoes. But these depressions
are not found on high peaks on Io.
Instead, you have these lava lakes with
high walls along the outside. Here is
Loki, the largest volcano depression on
Io, 200 km in diameter.
These lakes are directly connected to
the lava reservoir below, but usually
have a thin layer of solidify crust on
top. On average, Loki produces 25% of
the average heat output of Io. But
sometimes the crust on the lava lake
sinks back into the lake, causing Loki
to produce 10 times more heat than
normal.
This can especially be seen in one of
Io's other big volcanoes, Tashtar.
Normally, this area looks like this.
But here, the crust is seen falling into
the lava lake. In this image where there
is just white, the radiant energy from
the lava curtain was so intense that the
camera only registered white.
In 2007, New Horizons used Jupiter as a
gravity assist on its way to Pluto. It
also used the opportunity to test its
equipment. It focused its lens on Io
during its flyby, and what it saw was
amazing. Tvashtar, the volcano I just
mentioned, was in full eruption, and the
plume could be seen hundreds of
kilometers above Io's surface. You can
also see smaller eruptions around the
moon.
I must admit, this is one of the most
impressive things I've ever seen of
space.
Even though the volcanoes tend to be
flat, it also has some extremely tall
mountains. The highest one reaching 18
km tall. These mountains tend to be
completely by themselves, not as part of
a ridge or a range. Although most are
not volcanoes, lava lakes are found near
them, indicating there are faults in the
crust near these mountains.
Another of the unique aspects of Io is
its interaction with the magnetic field
of Jupiter.
Jupiter has an extremely large and
strong magnetic field and Io orbits
within some of the strongest sections.
The unusual thing about this interaction
is that when particles from some of Io's
thin atmosphere and its eruptions are
lost to space, these particles float in
orbit around Jupiter in what is known as
a neutral cloud. This cloud can extend
far beyond and behind the orbit of Io.
But also surrounding Jupiter is
something known as a plasma taurus, a
donut of ionized particles that follows
the rotation of Jupiter's magnetic
field. The plasma taurus rotates a lot
faster than Io's orbit at 70 km a second
compared to Io's 17 km a second orbital
velocity. Io orbits right through the
middle of it with the particles from the
Taurus bombarding the particles in the
neutral cloud, exciting them to higher
energies. These newly ionized particles
feed into the Taurus, attracted by the
magnetic field lines of the
magnetosphere. These particles are lost
from the neutral cloud into the plasma
taurus at a rate of about 1 ton of
matter per second, which greatly
increases the size of Jupiter's magnetic
field.
In fact, if it was visible, Jupiter's
magneettosphere would be about the same
size as the moon in our sky.
Io's interaction with Jupiter doesn't
end there. Jupiter's magnetic field
lines, which Io crosses, couple Io's
atmosphere and neutral cloud, to
Jupiter's polar upper atmosphere by
generating an electric current known as
the IO flux tube.
A flux tube is basically a concentration
of magnetic field lines. The sun has
these between sunspots and is very
visible on the sun because of the
charged plasma that flows between them.
Io's flux tube causes an aurora trail
around Jupiter's poles. This point here
is the flux tube from Io striking the
upper atmosphere of Jupiter.
Aurora are also visible on Io, although
they are not just limited to the poles.
The different colors represent the
different particles being ionized. Green
is sodium, red is oxygen, and blue from
sulfur.
Since late December, the Hunga Tonga
Hunga Hipe volcano has seen a lot of
activity in a series of pretty big
eruptions.
On the 14th of January, it was spotted
erupting again by local scientists.
This seemingly huge eruption shot ash 20
km into the atmosphere, creating a
pillar which stretched high above their
view.
But this is all about perspective. The
impressive sight from a ground view only
appeared like a tiny little pillar from
space.
The next day, this happened.
This eruption seen by both the GO West
and Himawari 8 geostationary satellites
show the biggest explosion captured on
camera perhaps ever.
Initial reports state this could dwarf
even the biggest man-made nuclear
explosion. And it's not hard to see why.
Just look at how big the ash cloud is.
If we overlay it over Europe, we can see
that it covers an impressive surface
area. Sorry, Luxembourg.
Not visible in the satellite images, but
detected with radio wave listening
instruments. More than 200,000 lightning
flashes were counted in the plume.
Volcanic lightning is still an ongoing
topic of study and we don't exactly know
the processes that cause it due to the
difficulty in studying it. But
scientists are starting to suspect that
positively charged particles come from
the eruption itself as well as
interactions with ash and the
atmosphere.
While the island itself was uninhabited,
the islands nearby are damage from
volcanoes comes in many different forms.
The most obvious is the ash cloud.
The nearby islands around Tonga have
been blanketed with some news reports
saying it looks like a gray moonscape on
these islands now covered by a thin
blanket of ash.
These before and after satellite images
are revealing.
Residents here were all told to stay
indoors while the ash was falling as
breathing it in can be damaging to the
lungs.
Ash has settled on fresh water supplies,
contaminating them. And what was once a
green and colorful place now looks like
what would happen if you turn the
saturation on an image all the way down.
This isn't great for plants initially as
it will block the sun's rays from
hitting their leaves. Although
eventually it will be good for the soil
of the islands as volcanic ash is a
natural fertilizer containing many
important minerals.
However, the lightest ash particles
didn't just go horizontally across the
atmosphere, but they have also certainly
penetrated the stratosphere. Typically,
the Earth's troposphere and stratosphere
don't mix that well. So, if ash gets
into the stratosphere, it will stay
there and circulate around the globe for
months to years. The tiniest ash
aerosols contain sulfuric acid, hydrogen
sulfide, and hydrochloric acid.
Interestingly, this may have a very
slight cooling effect on the Earth as a
whole, as sulfuric acid, for instance,
is known to reflect sunlight back into
space. However, the negative
consequences are that eventually these
particles will come back down into the
troposphere where they will return to
the surface in rain droplets, or in
other words, acid rain.
The next thing you'll notice is this
incredible shock wave blasting away from
the volcano. The fascinating view is
best seen in the infrared as infrared is
better at detecting the slight change in
atmospheric temperature caused by the
pressure wave. The pressure wave
traveled faster than the speed of sound
and it was loud. This video may give you
some idea of the scale of this shock
wave as it passed by an island 65 km
away.
Holy
>> To be honest, we can be grateful that
everyone's eardrums didn't rupture.
However, there have been reports that
windows from residences were blasted out
by the shock wave. This pressure wave is
believed to have traveled around the
world at least four times as detected by
weather stations in various countries
across the US. The shock wave wasn't
audible, but the effects could be seen
in the slight fluctuations in air
pressure as it passed over the country.
However, the shock wave was heard in
places as far away as New Zealand and
Australia, even in Alaska.
Generally speaking, underwater volcanic
eruptions don't cause tsunamis. But
simply due to the scale and sudden
nature of this one explosion, it did in
fact cause a tsunami, although not a
very big one. In the end, it was still
enough to do some damage across the
Pacific, however, to coastal regions
facing the eruption. When news that a
tsunami was possible, boats and ships
were put out to sea to face the wave
head on. As tsunamis reach shore, the
amplitude of the wave increases, causing
it to look much more visible compared to
a tsunami far out at sea, which is why
the wave looks so big here. These boats
are not too far from shore.
The last damage I want to examine is to
the volcanic island itself. This island
is very new. It's only been in existence
since 2014. This is because it lies
right on the Pacific and Indo-Australian
convergent plate boundary, a
tectonically active area. Before 2014,
it consisted of two mostly submerged
islands with the cauldra around 150 m
below sea level in between them. It had
since erupted, filling the gap, merging
the two islands. As a result, it is
actually being studied by NASA
themselves to better understand how
water impacts volcanoes. As there are
plenty of old volcanoes on Mars that
would have also been surrounded by
water.
Scientists wanted to track the erosion
of this newly formed island formed in
the ocean to see if there are
similarities to the erosion patterns on
the literal fields of Martian volcanoes,
potentially providing additional
evidence that certain Martian volcanoes
were once also surrounded by oceans of
water.
It's also interesting for scientists to
be able to tell exactly how analogous
planets like Earth and Mars really are,
despite their differences.
As for Hunga Tonga Hunga Haipe, the ash
building the island initially was easily
washed away by the lapping seaater like
a sand castle disappearing to the tide.
However, after about 6 months, the
erosion stopped as the ash and seawater
actually combined to produce a harder,
more resistant type of rock. And had
volcanic activity stopped for good,
Hunga Tonga Hunga Haipe would probably
have remained a small island for many
years to come.
However, the force of the January 15th
eruption has absolutely decimated the
island. What was one stretch of land
only last year is now two separate
islands again with the cauldra
disappearing back below the sea level.
However, just imagine if one day Earth
was to meet a similar fate to Mars and
its sea was completely drained. What now
looks like a tiny little island to us
would still look like a towering 2,000 m
high mountain from the seafloor.
While volcanoes on our own planet are
pretty intimidating, you can take solace
in the fact that an explosion of this
size could have been a lot worse for us
humans. Moreover, this particular island
will continue to be examined by NASA for
years yet, helping us understand our own
planet, but also our neighbors in the
solar system. And why should we care?
Well, volcanic activity at this scale
can have global impacts. And by studying
their interactions with the atmosphere
and oceans, we not only can help predict
our futures, but understand the past on
planets like Mars.
Enceladus,
perhaps one of the most intriguing
objects in the entire solar system.
And yet it is only the sixth largest
moon of Saturn and in natural light it
looks very unassuming.
However, there's a lot more to Enceladus
than meets the eye. It's an active icy
world with jets of water vapor pouring
out from its southern hemisphere.
Thanks to the remarkable Cassini
mission, we have studied and observed
Enceladus in exquisite detail and
perhaps know more about it than some of
the closer and bigger Jovian moons.
However, although we've seen a lot from
the outside, it's the inside of the moon
that still holds so many mysteries.
I'm Alex Mccoan and you're watching
Astramm. And together we will explore
some of the most fascinating details of
Enceladus, piecing together photos and
data from a variety of missions to find
out almost everything you could want to
know about this special moon. So stick
with me on this journey of discovery.
Let's first of all discuss where
Enceladus fits into our solar system.
Enceladus is currently Saturn's 14th
closest moon. I say currently as Saturn
has some tiny moonlets hidden in its
rings that may or may not be classified
as moons in the future. It is the second
closest major moon though, second only
to Mimis. That means that its orbit
takes it just outside of Saturn's major
rings. Its orbit follows the planes of
the rings very precisely, and it only
takes 33 hours to orbit Saturn once.
Interestingly, it is in a 21-1 orbital
resonance with Dioni, Saturn's fourth
closest major moon. In other words, it
orbits twice around Saturn in the time
Dioni orbits once. This orbital
resonance is believed to prevent
Enceladus' orbit from ever becoming
perfectly circular, which causes
Enceladus to undergo tidal deformation.
This is significant as these tidal
forces heat up Enceladus' core.
You see, as far as we can tell,
Enceladus's surface is predominantly
made of clean water, certainly with
little to no rocks or much else there.
Because Saturn is situated so far away
from the sun, it means the outer layer
of water on Enceladus has frozen over.
Enceladus is essentially a frozen ocean
world, a giant ball of water ice.
Because it is free from other materials
on the surface, the moon is one of the
whitest objects in the solar system with
a bond albido of 0.81,
which is pretty much as high as snow. As
such, it is one of the coldest
satellites of Saturn with a noon
temperature of -200°
as the white color of its surface
reflects a large percentage of the
sunlight reaching it back into space.
However, about 30 to 40 km down under
the surface of Enceladus, pressures
start building and heat energy generated
from the tidal defamation of its orbit
has increased the temperature of the
water ice to the point where the water
at this depth can exist in a liquid
form. It could well be that there is an
entire mantle or a global ocean of water
that the ice crust is resting upon. Very
much like the magma mantle that our
rocky crust on Earth rests upon. At the
very least, scientists expect there to
be a huge pocket of water under the
moon's south pole. How do we know this?
Well, the most obvious indication are
the huge plumes of water being ejected
from the cracks in the crust, something
referred to as water or cryo volcanism.
These jets are really active,
consistently blasting around 250 kg of
water into space every second at speeds
exceeding 2,000 kmh.
This is powerful enough that most of the
water vapor particles escape Enceladus'
weak gravity, and they end up in orbit
around Saturn, forming Saturn's E-ring.
This ring around Saturn is very diffuse
and so isn't really visible unless it is
backlit by the sun.
From this angle, the light shining
through the water particles make the
ring appear exceptionally blue. In fact,
this ring is considered the bluest
object in the solar system, even more so
than Neptune due to the ring's
uniformity.
The E-ring is Saturn's second outermost
ring, and it is 2,000 km wide. Its shape
is also heavily influenced by the orbit
of Enceladus. Enceladus' plumes create
tendril shapes in the rings as more
material erupts out of it. However,
these sections of the ring tend to
smooth off as Enceladus moves further
away along its orbit.
During the course of Cassini's mission,
Cassini was able to pass through these
plumes to detect the substances being
ejected from them.
Cassini wasn't designed with this in
mind. Scientists didn't know about the
plumes until Cassini got there. However,
Cassini was equipped with an instrument
called the cosmic dust analyzer designed
to detect what the tiny dust grains in
orbit around Saturn are made of. And it
was able to use it for Enceladus'
plumes, too.
as it wasn't specifically designed with
this in mind, it might not have given us
the full picture of what's in these
particles. But while water was the
predominant substance detected, amino
acids, carbon dioxide, nitrogen, and
methane were also found. Amino acids are
significant as they are the building
blocks of life and can be found around
the thermal vents at the bottom of
Earth's oceans. Does this mean Enceladus
has thermal vents of its own? and if so,
do they have ecosystems of life around
them?
While evidence for an underground ocean
is abundant, scientists still aren't
completely sure about Enceladus'
internal structure. At some points in
the past, scientists believe that
Enceladus was water all the way through.
However, data from Cassini suggests that
Enceladus' mass is in fact greater than
previously thought, meaning it must have
some amounts of iron or silicut material
in its core.
Scientists are starting to lean towards
the theory that the internal structure
is differentiated, meaning it's a
celestial body with defined layers
within it. An object of this size really
doesn't have to be differentiated. In
fact, it's so small at only about 500 km
across that it is right on the
borderline of being in hydrostatic
equilibrium or in other words being
rounded by its own gravity. There are a
number of objects out there of similar
or smaller sizes that are not in
hydrostatic equilibrium like Neptune's
Proteus. In any case, assuming it does
have a differentiated interior, this
core is likely to be predominantly
rocky. This is important as thermal
vents in Enceladus's water ocean would
have to come from a rocky core. A rocky
ocean floor would also provide nutrients
and minerals essential for what we
believe life would need to form and
evolve. Thermal activity clearly does
exist due to the way Enceladus has
plumes in the first place. And the amino
acids detected in the plumes suggest a
rocky core.
As Cassini passed over Enceladus, it
also mapped out the thermal emissions
from the moon. It turned out that the
jets line up with what has come to be
known as Enceladus' tiger stripes. These
are large depressions roughly 130 km
long, 2 km wide, and 500 m deep. It is
believed that these are tectonic
fractures in the moon's icy crust.
What is really interesting about the
surface features of Enceladus is that
there are virtually no impact craters at
all over the southern hemisphere and not
many anywhere else.
This implies that Enceladus' surface is
very young. As while it does have a thin
atmosphere made up from the ejected
water from the plumes, this isn't nearly
enough to burn up asteroids before they
hit the surface. Some water from the
plumes obviously settles again on the
surface which smooths it off over time.
This is another reason why Enceladus is
so round for such a small celestial
body.
In fact, apart from the tectonic
fractures and few craters, Enceladus'
topographical variation is really quite
minimal. There are no mountain ranges to
speak of, although there is what you
might call a rough terrain around the
South Pole if you zoom in far enough.
This is perhaps the highest resolution
image we have of its surface. And as you
can see, it really does appear like a
giant glacier. It's interesting to note
that even in this small view, there are
some smooth sections of ice, but also
jagged regions.
Over the north pole, the clear
difference is the number of craters
present there. While there are tectonic
fractures here, too, there are no plumes
on this side of the moon. So the surface
here is clearly a lot older than around
the South Pole, which is why it has more
of a cratered surface. As Cassini flew
through the plumes around the South
Pole, it also took the opportunity to
image the surface closely around the
tiger stripes.
The surface here is pretty incredible,
unlike anything you would have seen on
Earth. It's like the surface has been
folded, squashed, and shifted around,
leaving these remarkable fracture lines
and formations in the surface ice. The
fact that Cassini was able to get so
close to Enceladus is a feat in and of
itself. It's fantastic that we can have
such a close-up view of something so far
away. Unfortunately though, since the
Cassini mission has ended, we no longer
have anything in orbit around Saturn
that can study Enceladus further.
There have been plenty of mission
proposals in the past, but all of them
were cancelled before they came to
fruition. What would be incredible is a
probe that could either make its way
into Enceladus' ocean somehow or at the
very least search the plumes for signs
of life. There is already a mission
called Dragonfly going to the nearby
moon of Titan. However, this won't have
anything to do with Enceladus.
So although a couple of mission
proposals are currently under review to
go there, that means we are
unfortunately still a couple of decades
away at least, which is a shame because
who knows what secrets lie in wait under
that crust.
So there we have it, a look at the
intriguing little moon of Enceladus.
[Music]
Triton is an exceptionally unusual,
although often forgotten moon.
It has so many unique characteristics,
it makes it one of the most interesting
objects in the solar system.
But because it is the largest moon of
Neptune, the planet furthest away from
us, it also means that we have only
visited it once
very briefly as Voyager 2 flew by all
the way back in 1989, 30 years ago.
But what did the visit reveal? and what
have we found out about it since?
I'm Alex Mccoan and you're watching
Astramm and together we will find out
everything there is to know about the
fascinating world of Triton.
First of all, let's discuss where Triton
fits into our solar system and its local
system.
Triton is one of 14 known moons of
Neptune. Seven of these moons are
regular moons,
or in other words, moons that orbit
along Neptune's ecliptic with very
circular orbits or orbits with very low
eccentricity.
After these inner regular moons, we get
to the irregular moons, the first of
which is Triton.
An irregular moon is a moon that follows
an inclined, eccentric, and often
retrograde orbit.
This by itself is already where Triton
is set apart from any other spherical
moon in the solar system. It has an
irregular orbit.
Triton orbits clockwise around Neptune
as Neptune rotates counterclockwise
and Triton orbits at a 130° angle to the
ecliptic of the planet.
Although it should be noted that its
orbital eccentricity is close to zero,
its orbit is almost perfectly circular.
All other large moons in the solar
system are regular moons, orbiting the
same direction as the rotation of their
parent planet.
What this heavily implies is that Triton
did not form alongside Neptune, but it
is in fact a captured object,
specifically a captured dwarf planet.
No wonder then, that it is by far the
biggest of Neptune's 14 moons,
comprising 99.5% of the mass found in
Neptune's orbit.
But how big is that in scales we can
relate to?
Well, it is the second largest moon in
relation to its parent planet,
second only to Earth and its moon.
While it is smaller than our moon, it
orbits closer to Neptune than our moon
orbits Earth, which means it appears
about the same size in the sky.
It is the seventh largest moon in the
entire solar system. And most
interestingly, it is bigger than Pluto.
Pluto is often considered the king of
the Kyper belt, the biggest object that
we know of that formed there until we
consider that Triton once ruled that
area before Neptune captured it.
So although Triton is a moon of Neptune,
it could be said that it is the biggest
and most massive Kyper belt object.
Further evidence for this was found as
New Horizons passed Pluto in 2015,
suggesting Triton and Pluto share a near
identical composition, which supports
the theory that they share a common
origin.
Beyond Triton are six other irregular
moons found much further out. They are
almost certainly captured objects, too,
with unusually eccentric orbits that
take years to complete. They were
probably perturbed into these weird
orbits by the gravity of Triton.
So if Triton was a captured object, how
did that happen? Objects need to lose
momentum to be captured, otherwise they
would have enough momentum to escape.
Well, we can't know for sure, but the
leading theory right now is that Triton
was once part of a binary system,
perhaps like Pluto and Cheron.
As Neptune approached Triton and its
moon, the gravity from the encounter
would have caused the binary system to
fall apart with Triton's moon being
slingshot away and Triton losing enough
momentum to be captured in orbit around
Neptune.
I mentioned that Triton shares similar
characteristics with Pluto. What exactly
does that entail?
Well, they both have a predominantly
nitrogen ice surface with other ices
mixed in like water and carbon dioxide.
It has quite a flat terrain. Its
topography never varies by more than a
kilometer.
Although Voyager 2 did see ridges and
troughs, plateaus and ice plains.
What you may find unusual though is that
it has very little in the way of
craters. This implies its surface is
very young and is constantly being
renewed.
Like Pluto, it also has some reddish
patches, which is thought to be methane
having reacted to UV light from the sun,
producing what is known as tholins, an
organic compound that has a supposedly
tarlike consistency.
While organic compounds do not mean life
is present there, organic compounds are
the basic chemicals from which life
forms.
Life likely couldn't exist on the
surface of Triton anyway, as it's far
too cold and the sun far too dim to
support any life form that we can
imagine.
But what's interesting is what could be
found under Triton's crust.
Under Triton's surface is thought to be
a rocky and metallic interior, which
gives Triton a reasonably high density
for a moon at 2 g per cm cubed.
Because of this and also due to the big
step up in size from the next biggest
moon in the solar system, Titania, it
has more mass than all the moons smaller
than it in the whole solar system
combined.
The radioactive decay from the rocky
core could be enough to heat and power
convection in a subsurface ocean of
water, much like what is thought to be
under the surfaces of Europa, Enceladus,
and some other large moons in the solar
system.
And just like Europa and Enceladus,
cryovalkcanism is an active process
today on Triton,
liquid water in the mantle erupts onto
the surface like lava on Earth. This is
the main reason why the surface is so
young. It is being actively renewed by
liquid water erupting and then freezing
on Triton's surface.
Some very young lava planes have been
identified. Sparse and flat regions yet
interestingly with a wall that surrounds
the plane. This is called a plenicia or
in other words a solidified lava lake.
We also can see cauldra which is the
collapse found at the center of a cryo
volcano where lava planes form from.
It is thought that the water from these
eruptions would have also brought
minerals from the underground oceans
onto the surface. Perhaps even being the
source of the tholins and organic matter
I mentioned earlier.
If this is the case and organic
compounds are found in the subsurface
ocean, it means that there's a
possibility that conditions are right
for life to have been able to form
there.
We also see long lines permeating over
the surface. These are likely faults
caused either by tectonic activity or
freeze thor weathering processes.
If we look at some more of the Voyager 2
images of Triton, we can see the results
of some recent eruptions. You'll notice
what looks to be dark deposits on the
surface in cone or funnel-like shapes up
to 150 km long. However, these smaller
eruptions may not originate from the
mantle itself.
Voyager 2 spotted some plumes reaching 8
km high, but these are thought to be
because of a solid greenhouse effect
within the moon's icy crust.
Imagine the surface of Triton consisting
of a clear ice which is settled on dark
deposits like tholins. The sun shines
through the ice warming the darker, more
absorbent tholins beneath which sublimes
a pocket of ice under the surface. As
the ice is sublime, the pressure builds
in the air pocket until the surface
above the pocket gives way, causing an
eruption.
This eruption also takes the dark
deposits with it, spreading them out
over the surface again.
If this is the case, a very similar
process has been seen on Mars's poles
with carbon dioxide ices and darker
deposits under the ice layer.
This process can only exist because of
one thing. Triton has an atmosphere,
although not as thick as scientists were
initially expecting.
Triton's atmosphere is thin, only 0.014
mibars, about the equivalent of 80 km up
on Earth. Although, like Pluto, this
density varies through seasonal changes.
Since Voyager 2's observations, Triton's
atmosphere has become denser as the
surface has warmed, evaporating a little
of the nitrogen ices on the surface.
However, when Voyager 2 passed, Triton's
atmosphere was still dense enough to
support weather up to 8 km above its
surface. In this image, you can actually
see clouds on Triton.
And going back to the image of the
plumes, you can see the deposits from
the eruptions all end up facing the same
direction due to a prevailing wind in
that region of the moon.
Like Pluto, Triton's atmosphere is hazy.
The cause of which is thought to be
hydrocarbons in the atmosphere not yet
broken down into tholins by UV light
from the sun.
The constant depositing of organic
compounds through cryovalkcanism.
Ice is evaporating and freezing again
through seasonal variations and a
weatherrich active atmosphere makes
Triton a very dynamic world. Unlike most
other moons in the solar system,
it is more a dwarf planet than a moon,
likely a sibling of the more famous
Pluto in the Kyper belt.
All of these factors combined make it
one exceptionally unusual moon.
And there we have it. Everything you
could want to know about Triton.
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