(mysterious music)
Out in the darkest,
coldest part of our Solar System,
a hidden force appears to be disrupting
the rhythm of space.
(mysterious music)
Totally dominates all of that region of space.
Each thing that's come near the guy,
flings them into the Sun.
It's evidence, some say,
of a massive hidden world orbiting our Sun.
So we think this thing is as five
to 10 Earth masses in size.
It is so, so, so, so dim.
If you were to compare it with, say,
like Jupiter, it's probably the difference
between staring pointblank at a stadium light
versus looking at a firefly miles away.
(tense music)
Now, astronomers across the world
are racing to be the first to lay their eyes
on the Sun's lost planet, if it even exists.
(mysterious music)
It's never been seen, but there are astronomers
who are convinced it's there.
Some call it Planet X.
Others call it Planet Nine.
(mysterious music)
A few years ago, no one could have even imagined
that there might be another large planet
silently orbiting the Sun billions of miles past Neptune.
(mysterious music)
But now, a new generation of telescopes
is allowing astronomers to see far beyond
what they could have ever observed before.
(mysterious music)
Just a generation ago,
even the most powerful telescopes in the world
struggled to sense anything past the known planets.
When people first started looking for planets,
asteroids, anything that moves in the Solar System,
they didn't buy taking pictures of the sky
with giant glass photographic plates.
Photographic plate is a piece of glass
to paint photographic emotion on it.
You put on the back of telescope,
you take the picture of a huge slab of the sky.
Astronomers worked in complete darkness,
painstakingly preparing image after image.
(somber music)
You put it on the light table,
and you see it's full of thousands
and thousands and thousands of stars, galaxies,
and anything else that happen to be there.
In this view, I probably see a hundred stars.
Countless hours were spent comparing images
taken from the same spot in the sky.
Night-to-night, galaxies and stars held their positions.
Planets moved, and other objects circling the Sun,
however, would appear to shift.
This is how the great discoveries of the 20th century,
like Pluto, were made.
(energetic music)
Could there be evidence of one more planet
hiding in a slide like this one?
The photographic plates, although they have
this great historic data and historic value,
it's not sensitive enough
to have seen Planet Nine, probably.
The story of the lost planet
could only begin after more precise digital cameras
were bolted onto the world's most powerful telescopes
beginning in the 1990s.
One of the first major discoveries
that came out of this upgrade
was the discovery of the Kuiper Belt.
With the 1992 discovery of the Kuiper Belt,
a massive ring of icy debris near Pluto's orbit,
astronomers finally had proof
that there was something beyond the planet.
The moment those first few objects were discovered,
it was clear that this is just the tip of the iceberg.
By the end of the 1990s,
we knew of hundreds of objects
that were similar to Pluto in terms of their orbits.
(mellow music)
Astronomers were now observing
some three billion miles from Earth,
but they weren't satisfied.
And so as soon as the Kuiper Belt was discovered,
people started saying,
"Oui, maybe there's something else
"even farther out there."
After years of scanning the night sky,
Mike Brown would answer that suspicion
with the discovery of Sedna in 2003.
(mellow music)
The first hint that something was wrong,
that the Solar System had some
additional tricks left up its sleeve,
came with the discovery of the object, Sedna.
Sedna, as a physical body, is not too remarkable.
It's just another icy ball,
little bit smaller than Pluto.
But its orbit is completely wild.
To go one time around the Sun,
it requires 10,000 years.
And at its outermost reach of its orbit,
it goes out to a thousand times
the distance between the Earth and the Sun.
No one had ever seen
anything like Sedna before.
But what really puzzled scientists
wasn't just the size of Sedna's orbit.
It was the shape of Sedna's orbit.
And the weird part about Sedna's orbit
is it never comes close to the Sun.
This was weird, because we thought
to go on an elongated orbit,
it need to have gotten close to something,
and go on on a slingshot and come back around.
But Sedna never comes close to anything.
It was clear that there was something else
in the Solar System that we hadn't seen before.
Objects in our Solar System
aren't only impacted by the Sun's gravitational force.
They're pushed around by each other's
gravitational force as well.
(suspenseful music)
It turns out that is the first clue
to the existence of Planet Nine,
even though we tried really hard
not to jump up and down and say it at the time,
because we needed a lot more evidence
before we were convinced
that there was something out there.
Everyone realized that Sedna cannot be alone.
There has to be an additional population of such bodies.
But for the next 10 years,
search after search came up empty.
(mellow music)
Enters Scott Sheppard,
at the Carnegie Institution for Science
in Washington, D.C.
Using the four-meter Blanco telescope in Chile,
he and his team began the deepest, widest survey
of the outer Solar System ever attempted.
In a matter of days, they make their first discovery.
And we started observing, and this is what we see.
We take three images of the sky,
each image separated by about two hours.
And we make a movie of those three different images.
And you see background stars,
are these circular-type objects,
and they do not move over a few hours time span.
We also see very distant galaxies,
so they are the oval-looking things here and here.
What we find is this object here is actually moving
relative to the background stars and galaxies.
And so, the reason that we found
this object so interesting
was because it was so distant.
And it actually took another year of observations.
We had to re-observe this object a few months later,
and then again, a year later,
to actually get the orbit for the object.
Sheppard and his partner on the project,
Chad Trujillo, nicknamed the object Biden,
and continue to study its orbit.
What they find only deepens the mystery.
Like Sedna, Biden orbits the Sun
but never comes close to the known planets.
(suspenseful music)
They then analyze the orbits
of about a dozen other objects
found beyond the Kuiper Belt.
They, too, had unusual elongated orbits.
Stranger still, when they compare
all these objects' orbits in three dimensions,
they realize that they all share a common alignment
along what astronomers call their argument of perihelion.
An unknown gravitational force
appeared to be stretching, clustering,
and tilting the orbits of these distant objects.
For Sheppard and Trujillo,
the data pointed to an uncomfortable conclusion.
It's kind of almost a crock pot-type thing
to say that there's a planet in the outer Solar System.
So, we didn't really want to go that direction,
but the evidence was there.
Caltech's Konstantin Batygin
and Michael Brown were intrigued
by what Sheppard and Trujillo were suggesting.
That discovery was the inspiration for me
and for Mike to go and look at this closer.
But before they could get on board
with the idea of a new planet,
Batygin and Brown needed to better understand
the impact of the proposed planet's gravitational force
on the outer Solar System.
We looked at the data for a long time
and we realized that our theory of a planet
made a projection that, in addition to these objects,
all elongated in one direction,
there should be another set of objects
elongated at 90 degrees to these,
and also twisted by 90 degrees.
Those are weird orbits that nothing
that we knew of in the Solar System has.
So I found these ones, they were twisted
the way we thought they were twisted.
They were really distant.
I didn't know how they were pointed though,
and so, Konstantin was in my office,
I'm like, "Konstantin, I found these objects.
"I'm gonna plot their positions on my screen."
Press the button, and they were, boom,
exactly where our theory said they should be.
I remember this moment.
This is where I went in my head,
a switch flip from, this is a kind of cute idea
that explains the data to,
"Oh, there is a giant planet out there
"and we know where it is."
The race was on to find it.
(tense music)
Typically, when you think of proof of something,
you wanna see a picture of something
before you believe that it's really there.
In the case of Planet Nine,
we don't have a picture of it yet.
All we have for it for now
is the gravitational evidence.
But the gravitational evidence for it
is really solid.
(mysterious music)
Batygin and Brown had found the evidence
they were looking for, and this wouldn't be the first time
a planet was predicted before it was ever observed.
(tense music)
Because of the shape of Uranus' orbit,
astronomers understood decades before they saw it
that another planet, Neptune, must be orbiting nearby.
A similar phenomenon could be observed near Jupiter.
Jupiter is a very massive planet
that is just outside the asteroid belt.
So we see clustering of asteroids.
And so even if we never even saw Jupiter,
we would know Jupiter exists because we see
clusterings of various main belt asteroid together.
(tense music)
Probability that we would see these elongated orbits,
and they will be clustered the way they are,
and they will be tilted the way they are,
the probability is .2%.
There is a .2% chance, say, two chances of a thousand
that what we see has just stood a chance.
(tense music)
No matter how convinced these teams are
that another planet is out there,
until someone observes it,
it remains only a theory.
In a way, astronomers are back to where they were
when telescopes were fitted with glass plates,
their technology struggling to keep up
with their biggest ideas.
(mellow piano music)
To fully grasp the challenge
of finding the lost planet,
you need to understand the scale
of the known Solar System.
(mellow piano music)
So imagine these are the orbits
of the eight major planets that we know of.
And here's Neptune, it's the most distant orbit known.
So if we're gonna plot Planet X's orbit on this graph,
its minimum distance where we think the planet exists,
is out this distance.
It's estimated that the planet's orbit
takes it some 30 billion miles from the Sun.
This distant out,
he Sun would just be another star in the sky.
Their challenge now
is to narrow down where on this predicted orbit
to direct their telescopes.
It's a daunting task, to say the least.
(upbeat techno music)
So what we're gonna do now
is do a little scaled demonstration
of looking for Planet Nine
with a terrestrial telescope.
And we're gonna go and walk
about a hundred meters that way
to get you a sense of scale
of how big the field of view is.
(upbeat music)
The biggest camera we use is called
Hyper Suprime-Cam on Subaru telescope
and it covers about 1.5 square degrees of the sky,
which is about this as viewed from 100 meters away.
(upbeat techno music)
So, even though this is a big field of view
compared to other telescopes on Earth,
or even in space, this is still
just a tiny percentage of the full night sky.
(mellow techno music)
With each observation,
astronomers have a near-infinite number
of targets to choose from,
each loaded with celestial objects.
The second challenge is that
Planet Nine is so far away
that it appears really, really, really small,
really tiny on the field of view.
So, to give you a bit of a sense of scale,
I have my surgical tweezers here.
I'm gonna try and create a little model
of how big Planet Nine would appear on the telescope.
We have this little white piece of tape.
This is actually a little big,
maybe by a factor of a thousand,
compared to how Planet Nine would actually look,
but the real issue, the biggest of the challenges,
is the third one, which is that Planet Nine
is exceptionally dim, because when you take an object
and move it really, really, really far away from the Sun,
it just does not reflect that much light.
So, a much better analogy
than this white piece of tape here
would be a black piece of tape.
(tense music)
So, there it is.
I'm sure it's completely invisible to you,
but I promise you it's there.
And that's a pretty good representation
of what it's like to look for Planet Nine.
You are looking from 100 meters away
at a patch of sky this big,
and you are looking for something
that is just painfully, just exceptionally dim.
How Planet Nine got
so far removed from the other planets
is one mystery, however, astronomers think they've solved.
Main theory is probably got it formed
in the giant planet region,
probably formed near Jupiter and Saturn.
And I like the thought
of a bunch of giant planets out there.
The early evolution of the Solar System
is actually a very violent and chaotic place.
Probably what happened was, Planet Nine came
a little too close to Jupiter or Saturn
and got scattered out into this,
probably this long period orbit.
Pushed far beyond
the gravitational reach of its siblings,
the ejected Planet soon establishes itself
in its new 20,000-year orbit,
(tense techno music)
a relic from a different time and place.
(tense techno music)
Most likely, if it formed in the giant planet region,
it formed a 50% rock and 50% ice.
(suspenseful music)
Out here, the gravitational pull
of this rocky, icy mass would be too much
for other objects to handle.
Playing the role Jupiter played among the known planets,
Planet Nine starts clearing a path
through the outer regions of the Solar System.
Any of these smaller objects there,
if they ever got close to the planet,
they would basically be ejected
from the source of gravitation,
that the planet would swat it like a fly.
It dominates more of the Solar System
than all the other planets put together.
Nothing in the outer part of the Solar System
is safe for long from Planet Nine.
Not even Sedna and Biden
and the other extreme objects,
which first revealed the possibility
that this planet could be hiding in our own backyard.
Those are the only ones that haven't yet
been destroyed by Planet Nine,
'cause it just hasn't had time to eat everything yet.
I think about this sometimes,
if we existed four billion years from now
instead of right now, we wouldn't be able to know
that Planet Nine was there, probably because
nothing would be left in its region of the sky.
(suspenseful music)
Astronomers understand Planet Nine's past.
They can predict its future.
But where it is right now remains a mystery,
(suspenseful music)
a mystery that the teams from Caltech
and the Carnegie Institution for Science
are racing to solve.
Our survey is trying to cover
as much sky as possible to very faint depths.
But we're limited by a technology in our telescopes.
Sheppard and Trujillo's strategy
is to keep scanning the sky,
looking for other objects like Sedna and Biden
to help point the way to the lost planet.
We've covered about 30% of sky,
but we're still not scratching the surface.
If we wanna find the planet,
and we're looking for the planet,
the main goal of our survey
is to find more of these smaller objects
that can better narrow down the orbit of the planet.
Over the past four years, I have spent
nearly all of my personal research time
looking for Planet Nine.
There's nothing else
that is nearly as important to me
personally, emotionally, scientifically,
as finding this planet.
And for Mike Brown, history shows
that there may be one more surprise twist in this story.
Planet Nine may already have been observed.
Somebody has taken a picture of it already.
The reason I'm convinced about this, actually,
is because every major body
that's been discovered in the Solar System
for the past 200 years, literally,
has been seen many, many years before its discovery.
Uranus was observed for 91 years before.
People went back and found previous observations
up to 91 earlier, 21 different times.
Neptune was predicted by Le Verrier, found by Galle.
It was observed by Galileo.
Galileo drew in his notebook a little star
that turned out to have been Neptune.
Pluto was seen 16 years before its discovery.
The trick is not to take the picture of it.
The trick is to figure out
which one of those little spots
that just looks like a star
is actually not a star, but actually your object.
No one's life is going to change because
there's additional planet in the Solar System
really, really far away.
But it would completely redefine the scale
of what we think of as our cosmic home.
And human beings have always been explorers.
And understanding our cosmic home
is something that everyone wants to do.
It's weirdly wired into our DNA.
If, or when, the Sun's lost planet
is finally discovered, it'll be a triumph of science,
mathematics, and collaboration,
but for now, it remains invisible, a theoretical planet
on our lonely epic journey around the Sun,
waiting, it seems, to be discovered
and to upend our view of the Solar System forever.
(mysterious music)