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 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.
get 20% off their entire first year annual plan.
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 Irasa 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 IRAs and Accari 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 used 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 IRA 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 a half arc minutes, the
equivalent of 1 and a half 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 GP. 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 murmmoration 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 Zaderic Madigan or
ZM belt named after the two scientists
who proposed it, Dr. Alexander Zaderk
and Dr. Anmarie Madigan. What we would
expect to see around our sun if it had a
Zvel 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.
watching from the sidelines, now is the
perfect time to join the community.