For most people over the age of 20, our understanding of the solar system has changed quite a bit
over recent years.
We grew up knowing exactly what the solar system looked like, from our central Sun all
the way out to Pluto.
However, that all changed in 2006 when the international astronomical Union made a highly
controversial decision to place Pluto into a new category.
This, as many of you watching, will agree did not go down well, and still to this day,
many people consider Pluto as the ninth main planet in the solar system.
But now there may be a new ninth planet lurking out there, because, in 2016, a theory was
presented to the world that suggested a massive undiscovered planet is lurking far beyond
Pluto.
So is there a giant undiscovered new 9th planet that we have missed in the outer solar system?
And if there is, why haven't we found it yet?
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The idea of an undiscovered large planet, now known as planet nine, but originally called
Planet X originated in the early 1900s.
Astronomers suggested that the wobbles observed in the orbits of Uranus and Neptune could
be explained by another planet further out in the solar system.
When Pluto was discovered in 1930, astronomers thought this was the mysterious object affecting
the orbits of Neptune and Uranus, but it was later revealed that Pluto was far too small
to cause such an effect.
So what was going on?
Well In 1989, the answer to this mystery was finally revealed, because NASA’s Voyager
2 flyby collected data that showed there was no wobble in these outer planets’ after
all.
Leaving astronomers to seemingly be searching for something that did not exist.
Decades of searching for Planet X had been in vain.
Nothing it seemed was out there.
But as it turns out, there is actually lots out there.
At around the same time that astronomers were giving up the hunt for a giant Planet X, smaller
objects beyond Neptune, in some cases Pluto sized, were being discovered, and as these
discoveries mounted, it became clear that a massive population of strange worlds existed
in a region that we now call the Kuiper belt.
With the discovery of the Kuiper belt, came many other mysteries, including once again
the possibility of an undiscovered giant planet.
In January 2016 researchers Konstantin Batygin and Mike Brown from Caltech presented mathematical
evidence that suggested that the elusive Planet X, which they called Planet nine, due to the
reclassification of Pluto, did exist after all.
This hypothetical planet could be 10 times as massive as the Earth, more than 20 times
farther from the Sun than Neptune, and could have a year that is anything from 7,400 to
20,000 Earth years long.
And so just like the many astronomers before them, the hunt for an undiscovered giant Planet
lurking at the edge of the solar system was back on.
The reason many astronomers think that Planet 9 could exist, is because of some interesting
movements amongst certain objects in the Kuiper Belt and the scattered disc.
Which are regions beyond Neptune filled with hundreds of thousands of icy bodies.
These mysterious objects include a dwarf planet named Sedna, and five other Kuiper Belt objects
that are being tilted at the same angle and in the same direction, causing them to have
orbits that are clustered together.
It is predicted that this may be due to the gravitational pull of a massive unknown object,
and incredibly, since 2016, 11 other objects have been identified as also having strange
orbits that are not due to the influence of Neptune.
So Could this be the result of an undiscovered ninth Planet?
Based on the apparent gravitational pull, scientists have estimated that the hypothetical
Planet 9 would have a mass around 10 times that of the Earth.
Using this information and what we already know about our solar system, it has been theorized
what this planet may look like if it does indeed exist.
The first possibility is a Rocky planet Nine, but not like the terrestrial planets, Mercury,
Venus, Earth or Mars, instead, a bizarre, possibly volcanic world.
A common type of planet that can be discovered around other stars in our galaxy is a "rocky
Super Earth", these are worlds that are larger than Earth, but smaller than Neptune.
However, no such planet has been discovered in our solar system, so could Planet Nine
be our missing "super earth"?
The second possibility is that Planet Nine is a giant version of the thousands of icy
objects that populate the Kuiper belt.
If Planet Nine is made of ice then it would be the largest object ever to form in this
region, possibly 5 thousand times the mass of Pluto.
It would also likely resemble Pluto in many ways and due to its colossal size, possibly
even be hiding a deep sub-surface slushy water ocean.
Perhaps the largest single body of water in the solar system.
The third possibility, which is also the most plausible, is that Planet Nine is a gas planet,
perhaps a smaller version of Neptune or Uranus.
Scientists have long theorised that the middle of the early solar system was a gas-rich zone
that eventually coalesced into the four gas planets that can be observed today.
Over time, collisions and ejections shaped them and moved them out to their present locations.
But it could also be possible, that a 5th gas planet began to form within this region,
a world that perhaps passed too close to Jupiter or Saturn, resulting in it being ejected into
a distant, eccentric orbit.
If Planet Nine is a gas planet, it would have no solid surface, just a small dense possibly
rocky core that is covered in thick layers of stormy clouds.
Its atmosphere would likely be similar to Neptune's, however, Planet 9 may well be a
gas planet like no other within our solar system, possibly a strange, partly translucent
world that is glowing in the darkness of space.
Considering there is quite a lot of evidence pointing to a ninth Planet, you may be wondering,
why haven't we found it yet?
Surely a giant planet would have been discovered by now?
While the Sun is very bright here on Earth the further away you get, the darker it is.
This makes objects deep in our solar system faint and hard to detect.
If you could stand on Pluto for example, then the Sun would only be about 300 times as bright
as the moon.
At midday, it would be similar to the amount of light we receive near a sunset here on
Earth.
It is often said finding Pluto was like finding a piece of coal in the dark, and planet 9
is predicted to be even further out than Pluto.
Konstantin Batgygin, one of the researchers hunting for planet 9, suggests that part of
Its elusiveness may be due to it being at the far edge of its own orbit, and likely
reflecting little to if any sunlight.
Basically, living in a shadow.
However, while it will be hard to find, astronomers calculate that if it is there, today’s telescopes
should be able to spot it eventually.
So how are we trying to find it?
Well, the 8.2-meter Subaru telescope in Hawaii is aiding the search.
While this is one of the best options currently available, the team only has access to Subaru
approximately three nights a year to search for the mystery planet.
There is a chance that NASA’s Transiting Exoplanet Survey Satellite, known as TESS,
may also catch sight of planet 9 while it is searching for exoplanets around distant
stars.
But the best hope to find this elusive world lies with a new telescope currently under
construction in the mountains of Chile.
In 2023, the 8.4-meter Vera Rubin Observatory will begin taking photographs of the entire
night sky very rapidly.
It will uniformly capture our visible sky and take repeated observations every few nights,
using its 3.2 gigapixel camera capability.
This will allow astronomers to track the movements of objects in our solar system and beyond.
Many researchers are confident that a giant ninth planet does exist out there, based on
their "tracking" of its gravitational impact through the Kuiper belt and the scattered
disc, but it could still take years to discover.
And so Planet 9 still only exists as a theory.
Of course, there are some sceptics who do not believe there is a ninth planet out there.
They say that the evidence is just a natural bias in sky surveys.
They suggest that we do not know enough about the Kuiper Belt objects to truly say if they
are acting strangely or not, let alone what could be causing this so‐called strange
activity.
There are even some that believe it is actually a primordial black hole, one of the densest
regions in space formed during the first seconds of the Universe’s existence.
As searches for Planet 9 keep coming back empty-handed, critics continue to say it is
just a ghost in the data.
However, despite these critics, many Planet 9 enthusiasts and researchers continue to
hunt for this mysterious world.
So is Planet 9 really out there?
It's always wise to be sceptical, but, something must be responsible for all those unusual
orbits that can be found in the outer solar system.
Hopefully, with continued efforts and advancements in technology, we will soon be able to confirm
whether there is an undiscovered ninth planet out there or not and if there is, better understand
its role in the solar system.
I really hope you enjoyed this video, if you did, then why not watch one of my others,
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