In the frozen depths of the outer solar
system, 500 astronomical units from the
sun, far beyond the orbit of Neptune,
something is very wrong.
The orbits of dozens of distant rocky
worlds out there seem to be tugged and
twisted by an unseen hand. And according
to our best models, the most likely
explanation is a hidden planet silently
circling the sun on a vast elongated
orbit. This world could be up to 10
times the mass of Earth. And yet, we
can't find it. Astronomers have searched
for this mysterious planet 9 for more
than a century. But every survey, every
telescope sweep has come up empty. In an
age where we can image planets orbiting
stars dozens of light years away and
glimpse the first galaxies born after
the Big Bang, the fact that something
this large could be hiding in our own
solar system is deeply unsettling.
But all this could be about to change.
Earlier this year, scientists found
something buried deep in the data from a
40-year-old space telescope. They've
combined it with information from a
newer data set. And now, for the very
first time, they may have an answer.
Have scientists finally found Planet 9?
I'm Alex Mccoan, and you're watching
Astramm. Join me today as we venture to
the edge of our solar system in search
of the missing planet 9. We'll delve
into the data these scientists are
studying and find out what it takes to
prove whether or not a planet exists.
With new telescopes coming online, is it
only a matter of time before our solar
system has nine planets once more?
The outer reaches of the solar system is
a mysterious place. Most unlike the
inner region we inhabit, it's so distant
that even if we set out at the speed of
light, it would take more than 8 hours
to get there. 9 billion km is a long
way.
Upon arrival, we'd find darkness
peppered with unusual icy rocks, many of
which we can barely detect, which we
call trans neptunian objects or TNOs.
The first TNO was discovered by Clyde
Tombbor in 1930. I suspect you've heard
of it. It's called Pluto. However, it
took another 60 years until we found the
next TNO. And an age of discovery began.
Today, we've charted nearly 5,000 of
these strange objects. But perhaps the
most important find came in 2003 when a
group of scientists led by Caltech's
professor Mike Brown decided to explore
this outer realm. It wasn't long until
they found Sedna, another dwarf planet
less than half the size of Pluto, but
with an inclined, highly elliptical
orbit. This led to an explosion of
interest in the outer solar system as
scientists rushed to explain why its
orbit was so unusual. If it were just
Ednner, it could be put down to chance.
But with the increased attention came
the discovery of many more Tennos with
equally strange orbits. Some cross the
orbital path of Neptune. Others moved in
the opposite or retrograde direction to
the eight planets. Many were just
greatly inclined. It raised the
question, how did these orbits come to
be? The only hypothesis that made sense
of all of them is a threebody
interaction known as the lid of coai
mechanism. It states that a near
circular but inclined prograde orbit can
trade its inclination for eccentricity.
But for that to happen requires three
things. The sun, the TNO, and a distant
perturber.
Mike Brown and his colleague Dr.
Constantine Batigan modeled the orbits
of 17 Tennos's and predicted that the
chance of their movements being random
was just 0.00006%.
Instead, their model suggested that
these objects were being perturbed by a
mass they couldn't see. A planet-sized
object to be exact. Enter planet 9.
Now, we can model all we like, but the
only thing that can prove this is actual
observation. As they say, seeing is
believing.
You'd think, given that planet 9 is
supposedly in our solar system, it
should be pretty simple to point our
telescope at where it should be and take
a picture. But this is in fact
exceptionally difficult to do. The
brightness of a planet in the optical
spectrum falls off at a rate inversely
proportional to the fourth power of
distance from the sun instead of the
usual square of the distance because for
us to see it, the already diffused light
has to reflect back.
Previous optical wide field surveys from
the Ziki transient facility, the dark
energy survey and Hanstars 1 have all
spent years hunting. But none of them
have found a single candidate for planet
9. However, there is something else we
can look for. All planets we know emit
their own radiation in the infrared.
A new team of planet hunters from
Taiwan, led by Professor Tommo Goto and
PhD student Terry Fan decided to take
advantage of this and look for planet 9
in two far infrared all sky surveys. The
first taken by the Iras or infrared
astronomical satellite in 1983 and the
second by the Accari infrared satellite
which is the Japanese word for light in
2006.
The IRA satellite conducted the first
ever all sky infrared survey above the
obscuring warm blanket of Earth's
atmosphere. Because of its vantage point
and its ultra cold sensor cooled with
superfluid helium to 2.5° above absolute
zero, it detected 350,000
new infrared sources, ranging from
galaxies to asteroids.
The Accari satellite was a similar
design, but it had better spatial
resolution and could record longer
infrared wavelengths. The combined data
set of IRS and Aari was truly huge with
2.4 million objects found across
multiple decades. Filtering this for
planet 9 candidates was a mammoth task.
Fan and Gooto had to track each object's
position individually.
Their strategy was to compare the
surveys across time, looking for objects
that had moved in a way the models
predicted Planet 9 would. They were
looking specifically for a planet
somewhere between 7 and 17 times the
mass of Earth with an orbital distance
of around 280 astronomical units at its
closest or perihelion and as far out as
1,120
astronomical units at its farthest or
ahelion. They also use that information
to estimate the diameter of the planet
and its black body temperature to narrow
down their search further. Objects
closer than around 500 astronomical
units had already been searched by other
groups. So Terry focused on the area
between 500 and 700 astronomical units
for his search. He then predicted what
angular distance planet 9 should cover
in 23 years. He was hopeful. An object
on a highly elliptical orbit moves much
slower near its abhelion. So, Planet 9
should spend more time out past 500
astronomical units and therefore be in
the survey area for longer.
Any data from these two satellites that
did not fit that prediction was
discounted. And incredibly, from over 2
million data points, Terry was left with
only 13 candidates.
From there, he painstakingly whittleled
those down by eye and was left with just
one.
It's hard to tell, but in the top left
corner of the Iris image, there are
seven pixels that are warmer than the
background. And in the Accari image
taken 23 years later, the candidate has
moved 47 and 12 arc minutes, the
equivalent of 1 and 1/2 full moons, to
the lower part of the image. Now, I
think we can all agree that if we saw
these images in isolation, we'd never
guess what it is, but context is
everything. We could be genuinely
looking at the first image of Planet 9.
Professor Goto says that if it is
confirmed, he may allow Terry to finish
his PhD early, which is probably fair
enough.
Much of the data surrounding this new
candidate fits that expected of the
proposed planet 9, but there is some
concern from Mike Brown and Constantine
Batigan about the inclination of the
orbit of this new object being too
steep. The team hasn't been able to
completely map out how it moves, but
Terry doesn't think we'll have to wait
long to find out. The telescope set to
follow up on these measurements is the
Vera Rubin telescope. Featuring the
largest camera sensor ever created at
3.2 GPI, it's able to capture objects
that are orders of magnitude dimmer than
previous optical sky surveys. And
scientists believe it could increase the
known objects in our solar system by up
to a factor of 100.
I recently made a video about the Vera
Rubin Observatory. So, if you want to
find out more about it, then click this
link. It's the best technology we have
for the task. As Mike Brown says, if you
were to hand me a big wad of cash and
say, "Go build a telescope to go either
find this planet 9 or find the best
evidence possible for planet 9," I would
probably go and build the Vera Rubin
Observatory. The telescope's 10-year
long legacy survey of space and time, or
LSST, is scanning the night sky to look
for solar system objects, generating 20
terab of data in a single night.
Give it a few years and we might know
for sure if this is planet 9. But in the
meantime, Terry, Professor Gooto, and
their colleagues are not resting on
their laurels. By filtering for the
predicted parallax of planet 9 in the
Accari data, they have in fact already
found two other possible candidates. One
way or another, they are pretty sure
that if Planet 9 is out there, they'll
find it. Of course, not everyone is as
confident. What if measurements show us
it's not there? What then?
Surprisingly to me, given the many
orbital behaviors a theory needs to
explain, there are several possible
hypotheses.
The first is of a new belt, a scaledown
version of what we see around a galactic
center. Twothirds of spiral galaxies,
including our own, are what's known as
barred spiral galaxies with a bar-like
central region composed of millions of
stars on aligned and highly elliptical
orbits known as X1 orbits around the
center of the galaxy and its super
massive black hole. These orbits emerge
out of group dynamics, lots of small
interactions rather than one big one.
Almost like a memoration of birds, many
tiny interactions between the
individuals leads to coherent beautiful
movement without the conductor. In our
solar system, we may find an equivalent
known as Zeric Madigan or ZM belt named
after the two scientists who proposed
it, Dr. Alexander Zerk and Dr. Anarie
Madigan. What we would expect to see
around our sun if it had a ZM belt is
what we see now clustered elliptical
orbits and it's proposed that Sednner
and other TNOs are actually part of that
belt. In this hypothesis a singular
massive body like planet 9 is not needed
if the combined mass of the ZM belt is
more than 10 to 20 Earths. Even better,
the LSST program at the Vera Rubin
Observatory will be able to detect if
this belt exists or not. But there is a
third explanation that will never be
directly seen by any telescope. The
cosmic equivalent of a hit and run that
happened a very long time ago. The
culprit here could have been another
star passing through. The gravity of the
object could have tugged on these outer
bodies, disturbing their orbit enough
and in such a way to cause the behavior
we see today. But what if it wasn't a
near miss? What if the object didn't
escape? What if instead of a passing
planet or star, our solar system
captured a primordial black hole? That
may sound implausible.
However, it has been proposed that this
is indeed not just possible, but around
as likely as capturing a planet of
equivalent mass. Primordial black holes
are believed to have formed in the dense
expansion phase of the Big Bang and do
not have a strict weight limit like
those that are formed by a collapsing
star. So one with the mass of a planet
can exist and would be about the size of
a football. Impossible to see from Earth
unless of course it's consuming
something. One final possibility is that
we need to rewrite the laws of gravity.
Proponents of modified Newtonian gravity
or Mand for short claim that their model
explains our current observations of the
cluster TNO orbits. The increased pull
from the galactic center under a Mond
model is calculated to align the orbits
towards it. And that's what we see. Now,
there are issues with Mand, which I
won't get into here, but it's curious
that it could provide a good fit for the
data for the Tnos in the solar system
without needing a Planet 9
planet, star, black hole, or a
gravitational rewrite. What do you hope
we'll find? Let me know in the comments.
Personally, I hope it's a planet. For
those of us who grew up and learned all
about Pluto before it got downgraded, it
would somehow be nice to go back up to 9
once more. And who doesn't want to
complete our understanding of the solar
system? Regardless of what it is, the
Vera Rubin Observatory is now searching,
and we're going to know for sure very
soon. I can't wait to see what's out
there.
For more than 70 years, we thought our
map of the solar system was complete. A
familiar and tidy collection of nine
worlds orbiting a single star. But far
out in the frozen darkness, billions of
kilometers from the furthest known
planet, a ghost was lurking. A tiny
point of light slowly, almost
imperceptibly
drifting across astronomers forgotten
photographs, unnoticed and unknown for
years.
Its discovery wouldn't just add a tenth
name to the roster of planets orbiting
our sun. It would trigger an identity
crisis for the solar system itself,
forcing astronomers into a bitter
conflict over the meaning of one of the
most fundamental words and in the
process redrawing our map of the solar
system forever. This is the story of the
world that true to its name sowed
discord in the scientific community.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we travel to
the chaotic outer edges of our solar
system to meet Eerys, the world that
started a war over the meaning of a
single word, planet.
The story of Aris begins not with a
lucky glance through a telescope, but
with a monumental effort to take an
inventory of the sun's most distant
subjects.
At the Palomar Observatory in
California, a team of astronomers Mike
Brown, Chad Truo, and David Rabinovitz
had embarked on a systematic survey of
the outer reaches of our solar system,
looking for signs of objects orbiting
beyond Neptune, dubbed Trans Neptunian
objects or TNOs.
The team were using the 1.2 2 m Samuel
Oshin telescope to capture images of a
wide field of the sky, putting them
through automated image searching
software that flagged objects moving at
a certain speed. And their search had
already proved fruitful with newly
discovered worlds like Quawa, Orcus, and
Sedna. They were gradually populating
this dark, distant realm. But the team
were hoping to find something bigger. As
Mike Brown later wrote, "There had to be
a tense planet. The possibility that
Pluto was a unique planetary oddball out
at the edge of the solar system seemed
absurd to me." He decided to manually
re-examine some old data sets that his
software had passed over. Then, after
months of rechecking, on the 5th of
January 2005, Brown began clicking
through a sequence of three images from
the 21st of October 2003. And there in
the images was a single faint dot of
light moving at a glacial pace against
the background of fixed stars. Brown
knew instantly that this was something
significant. It was bright, meaning it
was either large or highly reflective,
and it was moving far slower than
anything they had found before, meaning
it was incredibly far away. His first
thought was, "I found a planet."
The team began tracking the object
provisionally designated 2003 UB313
to determine its orbit and size. They
had planned to keep their discovery
under wraps until they had completed
further observations, but the
competitive world of planetary science
intervened. On the 27th of July 2005, a
different team controversially announced
the discovery of another large TNO home
after accessing Brown's team's public
observation logs. To avoid being scooped
again, Brown's team was forced to go
public. On the 29th of July, they
announced the discovery of not just one
but two major bodies in the outer solar
system. Humea and this new object that
would eventually become known as Aerys.
The secret was out and the solar system
would never be the same.
In Greek mythology, Eris is the goddess
of strife, a malevolent deity who, when
snubbed from a wedding, tossed a golden
apple inscribed for the fairest among
the goddesses, instigating a quarrel
that led directly to the Trojan War. In
2005, the discovery of the celestial
body that would bear her name was the
modern equivalent of that golden apple.
thrown into the halls of astronomy. It
ignited a scientific war over the very
definition of a planet. The problem was
simple yet profound. Initial estimates
suggested AIS was larger than Pluto, and
subsequent calculations based on its
moon's orbit showed it was 27% more
massive. If Pluto was a planet, then
Aerys, its more massive twin, certainly
had to be one as well. And if Aerys was
a planet, what about the other large
TNOs that had recently been discovered
such as Maka
and Sedna? Where would the line be
drawn? The discovery created an
unavoidable logical crisis. As Mike
Brown put it, we were either going to
have to add new planets or subtract one.
The International Astronomical Union,
the global body responsible for
astronomical nomenclature, was forced to
act. At its 26th General Assembly in
Prague in August 2006, the question of
what is a planet was put to a formal
debate and vote for the first time in
history. The debate was vigorous and
exposed a deep rift within the
astronomical community, splitting it
into two main camps. On one side were
those who advocated for a geoysical
definition. They argued that a planet
should be defined by its intrinsic
properties. If an object is massive
enough for its own gravity to overcome
its material strength and pull it into a
nearly round shape, a state known as
hydrostatic equilibrium, it should be
called a planet.
Under this simple definition, Pluto,
Ays, the dwarf planet series, and
potentially dozens of other bodies would
have become planets.
On the other side were those who favored
a dynamical definition. They argued that
a planet's identity is tied not just to
its physical state, but to its
gravitational influence on its
surroundings. A true planet, they
contended, must be the dominant
gravitational player in its orbital
zone. In the words of the final
resolution, it must have cleared the
neighborhood around its orbit. The
voting process itself was fraught with
controversy. The final vote was held on
the last day of the 10-day conference,
by which time most of the 2,500
attendees had already gone home. Only
424 astronomers were present to cast
their ballots, a tiny fraction of the
global astronomical community. When the
votes were counted, the dynamical
definition had won. The IAU passed
resolution 5A, establishing a threepart
definition for a planet in the solar
system. It must a be in orbit around the
sun, b be in hydrostatic equilibrium,
and c have cleared its neighborhood.
Pluto sharing its orbital space with
Neptune and a host of other Kyber belt
objects failed on the third criterion.
A new category was created, the dwarf
planet, for objects that meet the first
two criteria, but not the third.
Crucially, a follow-up resolution was
defeated that would have made dwarf
planets a subcategory of planet.
Instead, the IAU declared that planets
and dwarf planets are two distinct
classes of objects. In an instant, the
solar system was officially reduced to
just eight planets. Critics immediately
pointed out flaws in this definition.
The phrase clear the neighborhood was
ambiguous and the first criterion in
orbit around the sun applied only to our
solar system and ignored the thousands
of exoplanets that we now know exist. It
was not a universal, elegant principle,
but a reactive, controversial, and local
fix. With the debate settled, at least
officially, the Discovery team had the
honor of naming their troublemaking
world. They chose EIS, a name Mike Brown
felt was perfect for the object that had
thrown astronomy into such strife. The
name was formally accepted in September
2006, cementing the legacy of this
distant world as the celestial apple of
discord.
Having established its role as a cosmic
disruptor, it's time to journey to Aerys
itself and understand the nature of this
renegade world. Eris does not reside in
the relatively stable disc-like Kyper
belt, the home of Pluto and many other
icy bodies. Instead, it belongs to a far
more chaotic and wild region known as
the Scattered Disc. The Scattered Disc
is a vast, sparssely populated halo of
icy objects with extreme orbits. These
are the solar systems outcasts. Bodies
that likely formed closer to the sun,
but were gravitationally scattered into
their current paths by Neptune as it
migrated into its current orbit billions
of years ago. Eris' orbit isn't a circle
like you might expect, but a huge
ellipse that takes it 557
Earth years to trace. At its closest
approach or perihelion, Aerys comes
within about 38 astronomical units of
the sun, roughly the same distance as
Pluto's average orbit. But at its
furthest point, or appelion, it swings
out nearly 98 astronomical units, almost
15 billion km away. That's nearly three
times Pluto's current distance from the
sun. Aris' orbit is also steeply
inclined at 44° to the ecliptic, the
plane on which the main planets travel.
This means Aerys spends its 557 Earthy
year-long year soaring high above and
plunging far below the rest of the solar
system.
For years, Aerys was thought to be
Pluto's larger twin. But in 2010,
astronomers had a chance to measure it
with incredible precision. Ays passed
directly in front of a distant star, an
event known as a stellar occultation. By
timing how long the stars light was
blocked from different locations on
Earth, they could calculate its size
with pinpoint accuracy. The result was a
surprise. With a diameter of 2,326
km, Eris was almost exactly the same
size as Pluto and in fact slightly
smaller. This revealed the most crucial
difference between the two worlds. With
a mass 27% greater than Pluto's packed
into a slightly smaller volume, AIS must
be significantly denser. Scientists
calculated its density at 2.43 g per cm,
substantially higher than Pluto's 1.85 g
per cm. This points to a very different
internal structure. While Pluto is
thought to be a roughly 7030% mix of
rock and ice, Eris must be composed
predominantly of rock with only a
comparatively thin mantle of ice on top,
a rocky heart in a frozen shell. That
shell is also one of the most brilliant
surfaces in the solar system. Eris has
an incredibly high albido of 0.99,
meaning it reflects 99% of the sunlight
that reaches it. This dazzling
brightness is potentially due to a
phenomenon called atmospheric collapse.
Like Pluto, Aerys has an atmosphere
primarily composed of nitrogen and
methane ice that is turned to gas. But
as its extreme orbit carries it into the
deep freeze of his appelon, this
atmosphere freezes solid and falls to
the surface as a fresh bright layer of
frost or snow. As Aris begins its
280year journey back towards the sun,
this frost will warm and sublimate,
turning back into a gas and renewing the
atmosphere, only to freeze and fall
again centuries later.
And more recently, observations from the
James Webb Space Telescope have added
another layer of complexity. Analysis of
different isotopes of methane on Eris's
surface suggests they may have been
produced by geothermal activity, hinting
at unexpected thermal processes deep
within its rocky core. This distant
frozen world may have, or at least once
had a warm heart.
The key to unlocking Eris's secrets and
the final piece of evidence that would
seal Pluto's fate came in September 2005
using the advanced adaptive optic system
on the WM KEK telescope, a telescope
that corrects for the blurring effects
of Earth's atmosphere to produce space
telescope quality images. Mike Brown and
his team spotted a faint companion
orbiting Aerys. it had a moon. This
changed everything. While an object's
size can be estimated from its
brightness, its mass can only be
determined with certainty by observing
its gravitational pull on another body,
for instance, a natural satellite. By
carefully tracking the moon's nearly
circular 16-day orbit, the team could
apply Kepler's law of planetary motion
to calculate the mass of AIS with great
precision. It was this calculation that
definitively proved AIS was more massive
than Pluto, making the planet debate not
just an academic exercise, but an urgent
necessity. The moon itself is a stark
contrast to its parent. While only 25%
the diameter of Aerys, this moon is one
of the largest of any dwarf planet,
second only to Pluto's own Kerin, and
larger than Saturn's Enceladus or Mimis.
It's also tidily locked to Aerys, but
estimates of its mass from how much it
causes Aerys to wobble in its position
are far below what would usually allow
tidal locking. This suggests that Aerys
itself dissipates energy far more easily
than we first thought. While Aerys is
brilliant white, its moon is incredibly
dark. Described as being darker than
coal, this suggests a very different
surface composition, devoid of the
bright frosts that coat Ays, the leading
hypothesis for the moon's origin is a
giant impact, much like the one that
formed Earth's moon. Early in the solar
systems history, a massive object likely
slammed into the young Aerys, blasting a
cloud of debris into orbit that
eventually coalesed to form a single
satellite. This violent birth would have
stripped away volatile ices, leaving
behind a darker, rockier body. Just as
Aris was named for the goddess of
discord, her moon was given the name of
her mythological daughter, this Nomia,
the demon spirit of lawlessness.
The name is fitting for a moon born from
chaos, orbiting a world that overturned
the established laws of the solar
system.
In the years since the 2006 vote, Mike
Brown has earned the name the Pluto
Killer. But this misses the true legacy
of his discovery. Finding Aerys didn't
kill Pluto. It revealed Pluto's true
family, making our solar system larger,
more complex, and more interesting. For
decades, we had a flawed model. Eight
planets of a certain character, and then
one strange outlier. By forcing this
reclassification, Eris gave us a more
accurate and coherent picture of our
cosmic home. There are four inner rocky
terrestrial planets. There are four gas
and ice giants. And beyond them lies a
vast third realm, a swarm of thousands
of icy dwarf planets, a population of
worlds whose existence we were only just
beginning to grasp. Eris and Pluto are
kings of this third zone, the largest
and most prominent members of the Trans
Neptunian population discovered so far.
And Aerys itself remains the ultimate
mystery. It is the most massive known
object in our solar system that has not
been yet visited by a spacecraft. While
NASA's New Horizon's mission gave us a
breathtaking, intimate portrait of
Pluto, Aerys remains a distant point of
light. its secrets held across billions
of kilometers of empty space. A proposed
flyby mission would take an estimated 25
years just to reach its destination, a
journey that would span generations.
For the foreseeable future, the goddess
of discord will keep her secrets.
Her discovery resolved one great debate,
but it opened up a new chapter in our
exploration of the solar system,
reminding us that the most exciting
discoveries are not those that provide
the final answers, but those that reveal
just how much more there is left to
explore.
In the summer of 1977,
NASA's Jet Propulsion Laboratory
launched a pair of Titan Centaur rockets
containing nearly identical spacecraft
known as Voyager 1 and Voyager 2. These
twin probes were built to last for 5
years with the intention of studying
Jupiter and Saturn and their larger
moons. Incredibly, nearly 45 years
later, NASA is still in constant
communication with both probes, which
take routine commands and transmit data
back to Earth's deep space network,
making Voyager the longest running
mission in the history of space
exploration.
After completing all of its initial
objectives within four years, NASA
extended Voyager's mission to include
the two outer giants, Neptune and
Uranus, before embarking on the even
more ambitious Voyager Interstellar
mission with the purpose of exploring
the outer limits of the sun's sphere of
influence and beyond. Voyager 1 and 2
have now traveled 22 billion km and 18
billion km from Earth respectively. So
far they have left the heliosphere and
entered interstellar space. But time
even for the longived Voyager probes is
running out. Perhaps as soon as 2025 the
probes will lose their remaining power
supply and go dark forever.
In preparation for this, NASA has begun
taking the prob's instruments offline in
the hope of extending the life of the
mission for a few more years. But when
the Voyager probes inevitably go dark,
they will leave behind a wealth of data
that is unprecedented in its size and
scope. So now that we are entering the
Voyager mission's final days, we can
ask, what did Voyagers 1 and two
discover out there? Did the probes and
their instruments hold up under the
rigors of interstellar travel? And why
are scientists so surprised by what they
learned?
I'm Alex Mccoan and you're watching
Astramm. Join me today as we look at the
most stunning discoveries of the nearly
45 year Voyager mission and relive the
remarkable journey the probes took after
they left Neptune's orbit, traveling
from the solar systems icy outer giants
to the brink of interstellar space.
While Voyagers 1 and 2 were supposed to
be on a 5-year mission, their team of
forwardthinking scientists and engineers
made a number of design choices that
enabled the probes to hold up over a
much longer journey. Each probe is
equipped with a longlasting radioisotope
thermmoelectric generator, which
converts heat from the decaying
plutonium 238 isotope into electric
power. These probes also have
redundancies of most of their 11
scientific instruments in case of
machine failure as well as 16 hydroine
thrusters including eight backups.
Most importantly, the launch happened at
the perfect time. When the Voyager
planetary mission launched in 1977, NASA
took advantage of a once in 176-year
alignment of the planets, which not only
allowed for flybys of Neptune and Uranus
with minimal course adjustment, but gave
the probes a gravity assist from each of
the giants they visited, thereby
increasing their effective velocity
beyond what they could get from their
own rocket propulsion.
This idea was relatively new at the
time, having been only attempted
previously on NASA's Pioneer missions to
Jupiter and Saturn.
In 1981, Voyager 1 escaped the ecliptic,
which is the Earth's plane of orbit
around the Sun, heading 35° to the
north. Voyager 2 later went under the
ecliptic, heading 48° to the south.
After the Voyager planetary mission was
extended to become the Voyager
Interstellar mission, the cameras on
both probes were deactivated in order to
conserve power. The last image taken by
Voyager 1 is the famous pale blue dot
photograph of Earth taken from a
distance of around 6 billion km. The
most remote image of Earth ever taken.
However, this was barely the start of
the Voyager's journeys. To reach
interstellar space, the probes would
have to traverse the termination shock,
a region in which hypersonic solar winds
ran into fierce resistance from the
interstellar wind. Beyond the
termination shock, the voyagers would
encounter the helio sheath, where
slowing solar winds pile up, becoming
denser and hotter, followed by the
helopor, the final boundary between the
heliosphere and interstellar space. But
in spite of what you may think, the
start of the interstellar medium doesn't
actually mark the end of our solar
system. Indeed, it will be another 300
years until Voyager 1 reaches the Ort
cloud, the vast region of billions of
icy planetessimals that surround our
solar system like a bubble and another
30,000 years until it exits the cloud,
leaving our solar system forever.
When the Voyagers traveled through the
helio sheath, they made an incredible
discovery. Because the sun's magnetic
field spins in opposite directions on
its north and south poles, the spin
creates a ripple where they meet called
the heliospheric current sheet. Sort of
like the rings created by dropping a
stone in water. However, when the sheet
reaches the termination shock, it
compresses as though the ripples were
hitting the edge of a pool.
The Voyager probes discovered that after
the termination shock, these stacked up
ripples form magnetic bubbles. This
means the boundary of the helio sheath
is not as smooth and clearcut as
scientists thought. Instead, it is a
fluctuating and magnetically bubbly
environment.
This messy finding has prompted a
complete revision of our model of the
helio sheath.
On the 25th of July 2012, the Voyager 1
space probe became the first man-made
object to leave the sun's heliosphere
and enter interstellar space. It was
traveling at an incredible speed of 540
million km per year or 3.6 astronomical
units. An astronomical unit being the
distance between Earth and the Sun. The
distance at which Voyager 1 crossed the
helop was about 120 astronomical units
from the sun which itself was a
revelation. It was unknown where exactly
the helop occurred.
Funnily enough, some early models put it
as close as Jupiter and others much
further. Remember, the helop is the
boundary where the sun's solar wind is
stopped by its collision with the
interstellar medium. kind of like the
crashing of two powerful bodies of water
against each other. Solar wind is the
steady stream of charged particles such
as electrons, protons, and alpha
particles that come from the sun's outer
layer. The interstellar medium, by
contrast, consists of charged particles,
gases, and cosmic dust left over from
the Big Bang and other ancient
supernova. When these charged streams
hit each other, they change course and
form a region of equilibrium called the
helopor boundary.
At first, NASA wasn't sure if Voyager 1
had truly crossed the helop and entered
interstellar space. As models predicted,
the prob's plasma wave detector found a
massive increase in plasma density, 80
times what it had registered in the
outer helio sheath, and a spike in
galactic cosmic rays. But something
strange didn't happen that left
scientists baffled. After crossing the
helopor, Voyager 1 detected no change in
the ambient magnetic field. Why was that
so surprising? Well, theoretical models
assumed that the ambient magnetic
orientation would change in a region
dominated by the magnetic fields of
other stars. But remarkably, Voyager 1
detected no discernable change in the
ambient magnetism.
NASA was so confused that they waited
nearly a year before announcing that
Voyager 1 had in fact entered
interstellar space.
On the 5th of November 2018, Voyager 2,
traveling at the slightly slower speed
of 490 million km or 3.3 astronomical
units per year, joined Voyager 1 in
becoming the second man-made object to
enter interstellar space. The crossing
also occurred 120 astronomical units
from the sun. And like the Voyager 1 6
years earlier, the probe detected no
change in the ambient magnetic field.
But something else surprised scientists.
You see, the sun goes through 11-year
solar cycles during which its activity
waxes and wanes. Voyager 2's crossing
occurred at a time when solar winds were
peaking. models predicted that the size
of the heliosphere would fluctuate with
the solar cycle, meaning it would have
been expanding when Voyager 2 made its
crossing. Yet, Voyager 2 crossed the
helop at exactly the same distance
Voyager 1 had 6 years prior, meaning our
models were wrong. Like the
magneettometer finding, this
demonstrated the value of testing
theoretical models with field data. We
now suspect the boundary between the
heliosphere and interstellar medium is
much more twisted and filled with
fluctuations than prior models proposed.
One leading idea is that our sun emerged
billions of years ago from a hot and
heavily ionized region following the
explosion of one or more supernovi and
that magnetic turbulence persists to
this day near the helopor. If so, the
probes will likely encounter a different
magnetic orientation as they travel
further away, but their instruments will
probably be long dark by that time.
Although the historic Voyager mission
will soon be ending, the twin probes are
just beginning their cosmic journeys. In
40,000 years, Voyager 1 will likely
drift towards a star in the Camellopilus
constellation, while Voyager 2 will pass
1.7 lighty years from the star Ross 248.
In 296,000
years, it will pass 4.3 lighty years
from Sirius. These small, intrepid
probes will likely outlast the Earth
itself as they continue their solitary
wanderings across the Milky Way. And if
by chance they encounter intelligent
life in one of the far reaches of our
galaxy, they will be a testament to
mankind's ingenuity and resilience. On
each of the probes is a golden
audiovisisual disc called the golden
record. These records carry photographs
of Earth and its many life forms, the
sounds of whales and of babies crying,
music by Mozart and Chuck Berry, and
dozens of indigenous peoples, and
greetings in 55 languages.
They would offer a distant stranger a
glimpse of who we are and what life on
Earth is like. As for us, we must say
goodbye to these old familiar friends
and continue our own lives here on
Earth. Hopefully, the Voyager mission
will not be our last brush with the
stars, but only the beginning.
In the dark, frigid void beyond Neptune
lies a vast and mysterious region where
the ancient remnants of our solar
systems birth drift silently through the
darkness, perfectly preserved by the
deep freeze of space.
To reach this shadowy expanse from
Earth, we must travel past the rocky
planets, flying by Mars, and then beyond
the swirling storms of Jupiter and
Saturn. Farther still, out beyond the
blue giants, Uranus and Neptune, we
finally reach our destination.
Welcome to the Kyper Belt. A vast ring
of icy debris encircling our solar
system like a frozen halo.
This isn't just a collection of distant
rocks. Is a time capsule from 4.6
billion years ago, holding the untouched
building blocks of our cosmic
neighborhood. It is home to several
dwarf planets and mysterious objects
that have left many astronomers
scratching their heads.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we explore the
worlds lurking in the shadows of our
solar system and piece together clues
about its history, about planetary
formation, comet activity, and even the
origins of life.
Before we knew for sure that the Kyper
belt was real, astronomers suspected
that something existed beyond Neptune.
For decades, everyone's favorite dwarf
planet, Pluto, was thought to be an
isolated object in the outer solar
system. But something didn't add up. Its
small size and unusual orbit suggested
that Pluto wasn't alone and that maybe
it was merely one of a number of yet to
be discovered distant objects.
In 1951, astronomer Kerard Kyper
predicted the existence of a belt of icy
objects just beyond the orbit of
Neptune. But without telescopes powerful
enough to detect these objects, the idea
remained theoretical for decades. That
changed in 1992 when astronomers David
Jarrett and Jane Louu discovered the
first confirmed Kyper belt object known
as 1992 QB1.
Pluto and its moon Karen were both
discovered before 1992 QB1, Pluto in
1930 and Karen in 1978, but these
objects were only confirmed as KBOs
after the 1992 KBO. Since then,
thousands more Kyper belt objects have
been identified, populating this distant
region beyond Neptune.
To grasp the true scale and position of
the Kyper belt, let's imagine we're
traveling in a spaceship, starting from
the sun and moving out towards the outer
edge of our solar system.
As we move along our journey, let's
compare the Kyper belt to both the more
well-known asteroid belt and the less
well-known odd cloud.
Starting near the sun, we zip past the
rocky planets, Mercury, Venus, Earth,
and Mars. Between Mars and Jupiter, we
see the asteroid belt made up of the
leftover materials from when our planets
formed. a thin spread out ring of rocky
debris. The asteroid belt is about 2.2
to 3.2 astronomical units away from the
sun and about one astronomical unit
wide. As a reminder, one astronomical
unit is equivalent to the distance from
the sun to the earth.
Most of the known asteroids reside in
this part of our solar system, ranging
in size from the largest asteroid,
Vesta, at 525 km wide, almost the
distance from London to Belfast, to the
smallest objects, some of which are just
tens of kilome across. However, despite
residing in such a large space, the
total mass of all of the asteroids in
the whole asteroid belt combined is only
about 3% of the mass of the moon.
Beyond the asteroid belt, we encounter
the gas and ice giants, Jupiter, Saturn,
Uranus, and Neptune, colossal worlds
that dominate the outer solar system.
Finally, as we pass Neptune's orbit at
30 astronomical units, we reach our
destination, an even more remote icy
frontier, the Kyper belt.
This vast expanse stretches from 30 to
50 astronomical units and is home to a
range of intriguing objects from frozen
relics of the early solar system to
dwarf planets including Pluto, Omea,
Eis, Makumake, and countless other
smaller objects.
Like the asteroid belt, the Kyper belt
contains ancient debris from our early
solar system. In fact, Kyper belt
objects are considered some of the
oldest surviving pieces of our solar
nebula that originally formed the
planets of our solar system. And so, at
one point in the very distant past,
these stray pieces might have been able
to come together to form yet another
planetary body. However, Neptune's
gravity prevented the icy objects from
coalescing and never allowed them to
form something new.
Unlike the asteroid belt, which is
primarily made of rocky material, the
Kyper belt consists of mostly frozen
methane, ammonia, and water ice, forming
a frozen, thick, doughut-shaped ring of
debris. The Kyper belt contains hundreds
of thousands of large icy bodies bigger
than 100 km across and more than a
trillion comets, not to mention smaller
debris and dust. And the average
distance between objects is so large it
can be hard to imagine. Each of those
objects is on average between 0.02
to 0.1 astronomical unit apart. Imagine
10 million km between objects.
Here in the dim outer reaches of our
solar system, these icy bodies drift in
near silence, preserving vital clues
about the origins of planets and comets.
But it doesn't end there. That was just
the main region of the Kyper belt.
Overlapping the outer edge of the main
region is another area of Kyper belt
called the scattered disc, which
continues out to nearly 1,000
astronomical units with some Kyper belt
objects on orbits that reach even
farther beyond that. So, while the
asteroid belt and Kyper belt share some
similarities, as you can see, one is
vastly more expansive than the other.
And while we may have reached the end of
the Kyper belt, there's still another
massive structure that surrounds every
other object and belt I've mentioned so
far. In a recent video, I talked about
the Orort cloud, the colossal structure
of orbiting icy debris that encircles
our entire solar system. It's so
jaw-droppingly far away that even our
most powerful telescopes can't catch a
glimpse. So, how do those two
structures, the or cloud and the Kyper
belt, differ from each other? For one,
the Kyper belt is thousands of times
closer to the sun than the center of the
or cloud, which is theorized to stretch
from 2,000 to 100,000 astronomical
units. Another major difference is that
the Kyper Belt is donut-shaped, while
the or cloud is spherical, like a
gigantic bubble of swarming debris.
But something these structures do have
in common is that they are both sources
of the celestial phenomenon that we know
as comets.
The or cloud is the source of many long
period comets while the Kyper belt is
where some short period comets are born.
While the Kyper belt today is one of the
most massive structures in the solar
system, it's just a small fraction of
what it once was. Originally,
altogether, it probably contained 7 to
10 times the mass of Earth, but the
shifting orbits of the four giant gas
and ice planets cause most of that to be
lost to space. What remains is no more
than about 10% of Earth's mass. Not only
that, but the Kyper belt today continues
to slowly erode away. As objects
occasionally collide and break apart,
smaller fragments are left in their
wake, and some of the resulting dust is
blown out of the solar system by the
solar wind. Sometimes these collisions
or Neptune's gravity will cause Kyper
belt objects to head on a new path
towards the sun, creating short period
comets, which have orbits of less than
200 years.
Over time, the sun's radiation causes
comets to shed material, producing the
spectacular tails we see from Earth.
Several famous comets originate from the
Kyper belt, or it scattered disc,
including Hal's comet with an average
orbital period of 76 Earth years, or
comet Shoemaker Levy 9, which broke
apart and smashed into Jupiter in 1994
in the first ever observed collision of
two solar system bodies. As we all know,
Jupiter survived, but the impact was
visible from Earth and was quite a
spectacular sight to behold. You can see
it out for yourself if you check out my
video on the aftermath of this
collision.
You may also have heard in the news
recently about a near-Earth asteroid
named 2024 Y4.
While there is a very very small chance
of this asteroid colliding with our moon
or even a smaller chance of it impacting
Earth, the short period comets
originating from the Kyper belt pose no
immediate threat to us in the next 100
or more years. In other words, you don't
need to worry about that.
Despite the Kyper belt being just a
small remnant of what it once was, it
still offers a nearly endless frontier
of objects for us to explore. And unlike
the or cloud, which we have not been
able to visit yet, we have been to the
Kyper Belt.
While most of what we know about the
Kyper Belt comes from groundbased
telescopes and the Hubble Space
Telescope, NASA's New Horizons is the
only spacecraft to have actually been
there. It performed a flyby of the dwarf
planet Pluto and Kyper belt object 2014
MU69
which was later officially named Araoth
meaning sky in the Native American
Powatan or Algonquian language.
This flyby of Arath in 2019 was the most
distant flyby in the history of space
exploration, taking place 1.5 billion km
beyond Pluto, with the New Horizon
spacecraft getting as close as about
3,500 km above the surface of the
object. And even among the swarm of
mysterious objects that make up the
Kyper Belt, Aricoth still managed to
surprise the New Horizon's team. Its
strange shape was unlike anything we had
ever seen in our solar system.
Aricoth is a small icy KBO known as a
contact binary. Composed of two distinct
loes that at some point merged into one
body, its shape resembles a flattened
snowman.
At just 35 km long, 20 km wide, and 10
km thick, you might not think there's
much to learn from this relatively tiny
object. But what Arakoth lacked in
atmosphere and diverse geology, it made
up for in its unique structure. The
bizarre pancake snowman shape of this
Kyper belt object provides crucial
insights into how planetary building
blocks came together in the early solar
system and how planets may have formed.
Arath's shape seemed to give it a
counterintuitive gravity field and
rotation. And several papers published
since the flyby have led to an almost
undeniable truth about how planet
decimals form. Something the New
Horizon's team didn't expect. Planet
decimals form when smaller objects come
together to make larger bodies which may
eventually combine to create a planet.
Until now, there have been two competing
theories. hierarchical accretion, which
proposed that small objects would crash
into each other at high speeds until
they created something bigger, and local
cloud collapse, where nearby objects
would slowly come together because of
their gravitational attraction, thereby
forming larger and larger bodies. And
now, thanks to the Araoth flyby and
important research into the object's
geology, geoysics, composition, and
formation, we can be fairly certain that
the theory of local cloud collapse is
correct.
The object's smooth surface, and the
lack of fractures from stress confirm
that the cosmic snowman formed at low
speed. Alan Stern, a planetary scientist
and the lead for the New Horizon's
mission, said that the evidence was so
strong, we've decisively solved a
multi-deade debate about how planet
decimals form.
And thanks to New Horizons, we get to
see the most famous Kyber belt object,
Pluto.
The spacecraft performed a flyby in
2015, allowing us to get up close and
personal like never before. and take
those stunning images. The mission
collected observations of Pluto and
Karen, the dwarf planet's largest moon,
and was able to collect data on Pluto's
other satellites, Nyx, Hydra, Kerberus,
and Stixs. Of course, we've all seen the
stunning photographs of Pluto's
heart-shaped surface region, also known
as Tomba Rigio. But did you know that
the heart-shaped feature is actually a
glacia? The western lobe of the heart
named Sputnik Plenicia after Earth's
first artificial satellite Sputnik 1 is
a vast nitrogen glacia that stretches
1,000 km wide and 4 km deep and is
undoubtedly the largest known glacia in
the solar system. The eastern lobe of
the heart gets its light color from
nitrogen that is carried from Sputnik
Penicia and deposited as ice.
Not only did we get stunning images of
Pluto, but the data from New Horizons
forever changed how we understand our
favorite dwarf planet. It revealed that
Pluto is far more complex than we
previously thought and offer clues to
the origin of its heart-shaped feature.
The data led some to believe that
Pluto's heart-shaped region could be
explained by an internal water ice
ocean. However, a recent study led by
astrophysicist Harry Valentine from the
University of Ben has revealed another
more likely culprit. The heart shape may
have been caused by a low velocity
impact that left a gigantic splatter
across the surface of Pluto, creating
the western half of the heart shape.
This impact would have come in at an
oblique angle, as in not straight on.
Imagine throwing a water balloon across
dry pavement in the same way you might
skip a stone across a pond. When the
balloon scrapes the pavement, it pops,
leaving an elongated splat of water
across the pavement. This kind of
angled, low velocity impact is similar
to how the western lobe of Pluto's heart
feature may have been created. But it's
not just Pluto that we get to see up
close. The images of Pluto's moon Karen
were also incredible. Can you make out
the enormous equatorial tectonic belt?
His existence suggests a longgone water
ice ocean on Karen.
So what comes next in our quest to
understand the Kyper belt and
consequently to understand our solar
system? New Horizons is expected to exit
the Kyper belt sometime between 2028 and
2029. And while there is no current
target for a further flyby, it is
possible that NASA identifies another
suitable target. New tools like the
James Web Space Telescope could help us
to further analyze the composition of
Kyper Belt objects. And perhaps in the
distant future, a robotic mission might
allow us to land on one of these
mysterious objects or even collect a
sample for a return mission back to
Earth. Who knows what else we'll
discover out there in this vast frozen
frontier. As technology advances, future
missions will hopefully push deeper into
the Kyper belt, revealing more of its
long-held secrets, one icy world at a
time.
What if I told you that there is a
colossal structure that begins at the
edge of our solar system?
One that encircles our sun and all of
the planets. But we've never seen it. A
shell made up of billions or even
trillions of ancient icy chunks the size
of mountains marks the outermost
boundary of our solar system. Or so we
think.
Jaw-droppingly far away, beyond the
reach of even our most powerful
telescopes, the or cloud is a region
shrouded in mystery and speculation
where the sun's influence grows faint as
it brushes up against the void of
interstellar space. What exactly is this
odd cloud? If we've never directly
observed it, how do we know it's out
there? And why do some people question
its existence? Let's find out. I'm Alex
Mcccoan and you're watching Astramm.
Join me today as we venture to the
farthest reaches of our solar system and
beyond to construct an image of this
unseen astronomical wonder.
You've probably heard of the asteroid
belt and maybe even the Kyper belt. At
two different locations in our solar
system, these roughly donut-shaped bands
of debris each move in the same
direction and more or less on the same
orbital plane as the planets around our
sun. The asteroid belt is the closest to
the sun of these two debris rings,
located between Mars and Jupiter, and
consists of millions of orbiting
asteroids.
The Kyper belt on the other hand was
first proposed by astronomer Gerard
Kyper as the origin of short period
comets in the midentth century. It is a
massive field of icy debris out past
Neptune. Occasionally a piece of Kyper
belt debris will get pushed by gravity
sending it on a new orbit closer to the
sun. In some cases this creates a new
short period comet. These comets have
orbits of less than 200 years and are
often predictable as they continue to
make subsequent orbits around the sun.
At the same time that Kyper was
investigating short period comets, a
Dutch astronomer named Yanort was
contemplating the origin of long period
comets. Few scientists of the 20th
century made more contributions to
astronomy than u. In 1927, he calculated
our place in the Milky Way galaxy. And
in 1932, he was the first to find
evidence of dark matter, to name a few
examples of his discoveries. In 1950,
Ort was the first to theorize the
existence of a thick bubble of swarming
icy debris that surrounded our entire
solar system, now known as the Ort
cloud. But unlike the asteroid belt and
Kyper belt, it's still yet to be
directly observed.
To understand this theory, let me
explain what led or to this proposition.
Unlike comets with short orbits, such as
Hal's comet with an average period of
75.3 years or comet Enka with a period
of just 3.3 years, long period comets
were unpredictable.
For one thing, their orbital periods
were so long that in some cases they
could take as many as 30 million years
to complete one orbit. And curiously,
these comets came from all different
directions and had various orbital
inclinations.
It was a mystery on the grandest of
scales, but noticed a few things that
all of these long period comets had in
common. Their
orbits indicated that these comets
weren't coming from far out in
interstellar space, but that their
origin had to be closer to home.
However, as I'll explain in a moment,
not too close to home. So, if these long
period comets weren't coming from the
Kyper belt and weren't coming from far
out in interstellar space, where were
they coming from?
ought found a peculiar similarity among
the orbits of these comets, one that
might provide the answer to that
question.
The point in a comet's orbit where it is
most distant from the sun is called the
appelon or noticed that all observed
long period comets seem to have an
appelion that all grouped around a
certain distance around 7.5 trillion km
from the sun. That's right, trillion
with a T.
As you can see, when it comes to the
distances I'll be talking about in this
video, our typical units of measurement
fall a bit short. So, instead of using
kilometers, I will switch to
astronomical units. One astronomical
unit or AU is defined as the distance
between Earth and the Sun or about 150
million km. So, Earth is 1 AU from the
sun. The appelia grouping that or
noticed where the long period comets
reached their farthest orbital distance
from the sun was about 50,000
astronomical units. To help picture the
orbits of these long period comets, keep
in mind that the outermost planet in our
solar system, Neptune, is around 30 AU
from the sun or about 4.5 billion km.
The main region of the Kyper belt
extends from Neptune's orbit at 30 AU
out to around 50 AU. But recent evidence
from NASA's New Horizon spacecraft
suggests a second region of the Kyper
belt called the scattered disc, which
continues to around 1,000 AU. It's with
these key findings from observed comets
that they didn't come from far out in
interstellar space. The orbital
distances clustered around 50,000 AU and
the fact that they arrived from any
direction and orbital inclination that
theorized a special spherical swarm of
icy debris that he believed to be the
origin of long period comets. In the
years since then, mathematical models
have shown agreement with the odd cloud
theory, and astronomers have further
theorized various mechanics by which the
odd cloud came to be in its current
state. The leading idea is that the odd
cloud formed from ancient debris,
leftovers from when our planet formed
4.6 billion years ago. After the planets
formed, the surrounding area was still
rich with these smaller leftover chunks
of material called planetessimals.
The gravity from these early planets
then scattered the leftover material in
every direction. Some material was flung
out of the solar system entirely. But a
significant portion was sent into
seemingly random eccentric orbits around
the sun. These scattered planet decimals
had eccentric enough orbits that they
were influenced by gravitational forces
outside of our solar system while still
remaining captured in our sun's orbit.
And it's believed that this is how these
billions or trillions of icy chunks came
to be part of the or cloud.
Gravitational pertubations can force
kyper belt objects out of place creating
short period comets.
We think that similar forces are what
send cloud objects into elliptical
orbits with the sun thereby creating
long period comets. These pertubations
could be caused by passing stars or
molecular clouds or tidal forces from
the Milky Way itself. In fact, about
70,000 years ago, Schultz's star gained
the title of the star that came closest
to our solar system, actually grazing
the outer region of the Orc cloud. But
luckily for us, it didn't cause any
catastrophic disruptions to the Orc
cloud or our solar system at large.
Schultz's star is a low mass binary
system made up of a red dwarf and a
brown dwarf companion. So 10 millennia
ago, even at a much closer distance to
the or cloud, the gravitational
influence of this binary star was
significantly weaker than that of our
much more massive sun.
However, while most objects experienced
little to no impact during the low mass
stars brief encounter with the edge of
the or cloud, numerical simulations from
2018 concluded that Schultz's star is
believed to have nudged at least some
objects out of place, creating and
influencing the trajectory of some long
period comets.
But the sun has been around for over 4
billion years, and that's a lot of time
for other close encounters with stars in
the distant past. Could these
interactions have prevented the or cloud
from forming? Our models suggest no.
However, odd cloud material may get
exchanged with passing stars over eons.
You see, other more recent numerical
simulations have suggested that odd
clouds could exist around other stars,
too. Our odd cloud may also have both an
inner and an outer region, each with its
own distinct shape. Some scientists
suggest that the inner region may be
more like a disc similar to the donut
shape of the Kyper belt while the outer
region is suggested to form the
spherical shell more widely associated
with the or cloud. Altogether, the inner
edge of this two region or cloud may be
2,000 astronomical units from the sun at
its closest, with the far edge
stretching all the way out into
interstellar space, potentially reaching
as far as 100,000 astronomical units
from the center of our solar system.
This means the or cloud could extend
more than 1.5 light years across. To put
that into perspective, since we're
talking about very, very large
distances, consider Voyager 2 spacecraft
for a moment. As of the publication of
this video, Voyager 2 has traveled to a
distance of about
139 astronomical units from the sun
since its launch from Earth at 1 AU in
August of 1977.
That's about 3.3 AU per year, or about
56,000 kmh.
It's the second farthest humanmade
object in space just after Voyager 1. In
August 2007, Voyager 2 passed beyond the
boundary of the heliosphere, the
outermost layer of the sun's atmosphere.
It extends out beyond the planets and
three times further than the distance to
Pluto. Outside of the heliosphere, the
sun's constant flow of charged particles
called the solar wind is finally impeded
by the interstellar medium. And in
November 2018, Voyager 2 finally crossed
the final layer of solar turbulence
called the helio sheath and continued on
into interstellar space.
Despite passing beyond the heliosphere
and well past the main Kyper belt,
Voyager 2 would still need to travel for
another 300 or so years just to reach
the innermost edge of the or cloud.
That's how far away it is. And to fly
through the or cloud, that could take
another 30,000 years. Even when
traveling at 56,000 kmh,
it still takes all that time just to
travel around 1 12 light years. If
you've ever wondered why interstellar or
intergalactic space travel is difficult,
keep in mind that our nearest stellar
neighbor is Proxima Centuri at around
4.25 lighty years away.
However, some still question the
existence of the or cloud mainly because
we're unable to directly observe it.
Another argument has been made that long
period comets may come from other places
such as interstellar space. And in fact,
the first observation of an interstellar
comet, one that had origins from outside
our sun's influence, was made in 2019 by
amateur astronomer Gennady Borisov.
Professional astronomers joined in to
collect data on comet Borisovv named
after its first observer. They found an
unusual composition, a higher
concentration of carbon monoxide than
the average comet originating from our
own solar system, suggesting that this
comet may have formed in the presence of
a red dwarf, a different type of star
than our sun.
And yet the vast majority of astronomers
agree that the or cloud is really out
there despite the fact that we've never
laid eyes on it.
Plenty of indirect observations and
mathematical models show great support
for the theory and the evidence
continues to add up. But why is it
exactly that we've never been able to
see the old cloud? After all, with
telescopes, we can see stars far beyond
our own solar system and even the shapes
of distant galaxies.
The difference is size and light. Think
about it. A piece of or cloud debris is
roughly the size of one mountain on
Earth. Let's consider Mount Everest at
around 9 km tall. Now consider the or
clouds innermost boundary begins
somewhere around 3,000 AU or roughly 450
million km from the sun. The distance
from the sun to the nearest piece of or
cloud debris is 50 million times the
size of the debris. Talk about looking
for a needle in a hay stack. But more
crucially even is that stars and
galaxies give off light but debris does
not. The planets are relatively close to
the sun. So, they are able to reflect
the sun's light and therefore are
visible. Likewise, the asteroid belt and
even the Kyper belt are close enough to
the sun that we can use telescopes to
directly observe their debris. But
outside of the heliosphere, the or cloud
is just too far and too dark for our
telescopes to catch a glimpse. Despite
the or cloud's gargantuan footprint and
pivotal role in shaping our
understanding of the origin of many long
period comets, for now we can still only
infer its existence through mathematical
models and indirect observation. But
don't let our inability to make direct
observations discourage you from
following the evidence. I can think of a
few other times in history when
scientists put forth monumental theories
despite a lack of direct observation.
For example, in the 16th and 17th
centuries, respectively, Capernacus and
Galileo put forth the theory that the
planets orbited around the sun,
contradicting a widely held belief at
the time that the Earth was the center
of the solar universe. Their theory of a
heliocentric solar system was not based
on direct observation, but rather on
indirect observation of the orbit of the
planets. As we know, that theory turned
out to be spoton. That's the thing I
love about science and the pursuit of
knowledge. There's always more to learn.
The farther we travel through time, the
better our understanding of the solar
system will get. Who knows? Maybe in 100
years, future astronomers will have
found a way to prove the existence of
the or cloud once and for all. Or maybe
they'll have found a whole new
explanation for long period comets.
Until then, the or cloud remains one of
astronomy's most compelling enigmas.
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