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Language: en
so you think planet 9 exists with 99.8%
probability
something like that yeah maybe 19 I'll
push too high
99% probability this just wishful
thinking I mean if you're that sure find
it in the farthest reaches of our solar
system way past Neptune and Pluto a
ninth planet may be lurking it's
predicted to have a mass five times that
of Earth and to orbit once every 10,000
years on a highly elliptical inclined
orbit so why do some scientists suspect
that such a strange object exists that's
what I've come to Caltech to find out
we're going to do your work you know my
I usually do it wherever okay wherever I
have a couple minutes of free time which
isn't really so this is where a lot of
it is nothing
my name is konstantin batygin I am a
professor of planetary science at
Caltech and I do all kinds of
astrophysics seeing planetary studies
including stuff about planet 9 these are
variable transformations I'll tell you
where the planet 9 boundary lies it's
like that so everything to the left of
that is all fun at night so I'm here to
find out about hidden planets and how to
find hidden planets with math okay so
how do we do that I mean do you want to
start at the beginning of this sort of
endeavor or do you want to jump into
planet 9 where do you want to start well
let's actually let's start at the
beginning because the beginning it has a
long and beautiful history to it in its
origins dates back to 1781
I believe when Uranus was first
discovered by Herschel and when Herschel
discovered Uranus he immediately
realized that the star that was slowly
moving across the sky
had actually been imaged many many times
before and there was a matter of going
back to old observations and kind of
retracing the orbit that Uranus was
falling on on the sky and astronomers
and mathematicians of the time
immediately noticed that there was a
problem with
orbit of this newly discovered planet it
was deviating from where was supposed to
be but I'm a French mathematician by the
name of or bomb the very a eventually
did this beautiful and very complicated
set of calculations that said okay if
there is a planet is there right and
that part of the sky then we can explain
the anomalous motion of uranus and when
once there was a mathematical prediction
of where to look astronomers were then
able to discover neptune with basically
pinpoint accuracy how quickly did they
find neptune so this is a remarkable
story they found neptune in one night
because they knew exactly where to look
there could be a ninth planet there's
there's a lot of space for a ninth
planet in the outer solar system but
there's no good evidence for a ninth
planet at the present time and a
particularly scary thing about the ninth
planet is that a lot of people want to
believe that there's a nice planet and
we all know this is huge psychological
bias to the effect that if you want to
believe something is true you will find
evidence real or not that it's true
everyone and their brother in the last
170 years have predicted planets beyond
neptune but all of these theories have
failed today I think that we meaning
myself and my collaborator slash
partner-in-crime Mike Brown are right
our understanding of the solar system
has evolved dramatically in the last 20
years we've discovered that there exists
this one additional belt of icy debris
called the Kuiper belt runs these are
kind of big icy asteroids that are maybe
the size of LA floating around beyond
Neptune who's responsible for finding
the Kuiper belt
I found the Kuiper belt with mine with
blue we were looking for anything
actually
beyond the orbit of Saturn so the puzzle
in 1985 the puzzle was why is it that
the inner part of the solar system is
full of asteroids and comets and also
kind of things planets all this stuff
but then when you go beyond Saturn
there's Uranus
there's Neptune and there's Pluto and
then that's it why would the outer solar
system be so empty it's a very simple
question of the kind that I can
understand and the answer was well let's
have a look you know maybe it's not
really empty maybe it is in which case
that would be interesting but maybe it's
not so we started a survey to find stuff
beyond Saturn and we did the survey for
a long time five years or something six
years and found actually nothing for
that whole time including nothing just
beyond Saturn will be expected to find
stuff until finally in 1992 we got this
thing way out and we could tell
immediately it's way out
45 or 50 au from the slow motion across
the sky we found this thing out there
what we call now the first identified
Kuiper belt object it's actually the
second because Pluto was misidentified
back in 1930 for all sorts of reasons
connected with sociology and propaganda
and things like that
people wanted to find a planet and so no
matter what Pluto must be a planet so
that process is continued we have more
than 2,000 of these objects now so in 25
years 2,000 of these things have been
found we think the population is vast
there's a billion things bigger than a
kilometer across maybe more maybe a
couple billion it's some of the more
distant objects that appear to some
people to show this orbital alignment
and they have in particular very large
perihelion distance so he never come
close to the Sun they never come close
to even Neptune if you look at the most
distant objects in this belt of debris
called the Kuiper belt all of their
orbits kind of point into the same
direction is it possible that there are
some going in the other direction we
just haven't found them they're there
yeah of course that's a great question
generically when you search for objects
in the night sky there there always
called observational biases you are
always limited to finding objects only
where you look so this is a key question
that you have to ask right is it that we
only found objects that are all pointing
that way right their orbits pointing
that way because we only look there the
answer is that there is a chance that
this is a this is all a false alarm okay
and that chance is one in 500 there are
bodies that occasionally will swing out
into other directions it's more that
overall if you look at it there is an
overall tendency so here what we see is
a pretty typical kind of simulation of
the type that we do we start the solar
system in an initial kind of totally
random state where all the objects are
pointing everywhere for scale these pink
circles here are Uranus and Neptune and
this long ellipse this long pink ellipse
is planet nine these blue guys these
blue orbits are long period Kuiper belt
objects the ones that in the real solar
system we see the clustering among and
these gold or greenish ellipses are the
more short period more proximate members
of the Kuiper belt which are not
clustered at all so it takes a long time
but about two billion years into the
evolution of the solar system you begin
to see the fact that objects that are
collinear with planet nine have all been
scattered away removed from the solar
system dynamically and the only kind of
remaining members of the distant solar
system the objects that point the
opposite way
again it's a remarkable gravitational
signature gravitational one-way sign if
you will that something is confining
these orbits keeping them clustered and
pulling them all into the same plane you
know the experts
I think of Scott Shepard and Chad Raheel
who first noticed this alignment they
call it a two point six sigma or result
which means that you know it doesn't
really meet the threshold for acceptance
the scientific would you be looking at
five Sigma is that I mean this the
standard thing is three Sigma right but
half of all 3 Sigma results are wrong
that's what I always say as an observer
so the more significance the better but
two point six is not enough so even
though these clusters of asteroid orbits
in the Kuiper belt provide the best
evidence for Planet 9 there's a chance
that further Kuiper belt observations
will find different uncluttered orbits
but regardless there are two other solar
system mysteries that could be explained
by the existence of Planet nine these
properties of Planet nine they seem like
kind of nuts like a period of ten
thousand years that's not like any of
the planets that we have found so why
would we have such a strange planet
hanging out out there yeah great
question indeed none of this is
reminiscent of anything solar system
right if you for a second ignore the
period right and ask yourself about the
mass mass of five Earth masses we don't
have anything in the solar system that's
five earth masses we go from one to 17
when we go from Earth to Neptune is it
wild actually turns out this is the most
common type of planet in the galaxy that
we have discovered around other stars
it may be reversed that the fact that
the solar system doesn't host a object
which is five earth masses kind of
closer to the Sun is actually kind of
weird indeed five earth masses as it
turns out it's kind of standard outcome
of plant information there are more wild
things out there oh and this is really
my favorite aspect of the Planet nine
hypothesis it's the fact that
Planet 9 actively flips orbits on their
side you should not expect to find
objects in the solar system that are
flipped on their side and are orbiting
the Sun perpendicular to the planets and
you should definitely not expect objects
that are orbiting the solar system the
wrong way yet we find them right they
exist in the Kuiper belt and this has
actually been a problem since before
Planet 9 was even a thought find at nine
has this intriguing mode of dynamical
evolution that it instills upon distant
orbits where it takes them and at the
expense of kind of circular izing these
distant objects by making their orbits
less elliptical flips them upside down
and then makes them more elliptical
again it's a complicated dynamical
evolution and really at a detailed level
you have to go to the computer
simulations to understand how it works
but the key kind of product of Planet of
the existence of Planet 9 is the
expectation that such objects would
exist and we see them and I really there
isn't another kind of natural mechanism
to generate these highly inclined bodies
you know you have the plane of most of
the the bodies and then some of the
bodies are there apparently have their
orbits almost tilted up to 90 degrees is
that just hmm weird or is that stronger
evidence for that's one of the things
that they claim to explain with the
planet 9 hypothesis and that's a good
thing
in favor of the hypothesis but again you
know you need to find the planet to be
sure what's going on in the region that
we have not yet been able to probe
because we can't see faint enough we
don't know yeah we don't know so when do
you think we're gonna find by 9 that's a
great question so observing the sky has
proven to be an extreme challenge the
search for planet 9 is is extremely
extremely difficult it's just kind of
dim enough at the outer parts of its
orbit where he can be discovered with
telescopes but you but everything has to
go right and by everything has to go
right mean no moon the atmosphere has to
be calm so that the light is not messed
up by the turbulence such nights do come
around every year but they don't come
around very often
so since 2017 we've had exactly good two
successful runs right successful
observational runs where we had sort of
the string of nights where we could take
pictures of the same part of the sky
over and over again so we are about 20%
maybe a little bit more now 25% done
with the survey that we are carrying out
to search for planet 9 if things go at
this rate it might take about a decade
I think the commencement of the LSST
telescope which is coming online 2022 23
that's gonna help a lot because that's
going to first of all discover many more
of these objects and we'll be able to
refine the theoretical model better and
also just by direct observation
it'll rule out or it'll either find
planet 9 or rule out a big chunk of its
horbet so we could kind of zero in that
way a lot more so it's a it's an
iterative process
I would guesstimate decade or less so
volumetrically we've discovered most of
the solar system in the last 25 years
something like that
what do you mean volumetrically I mean
that the volume of the region occupied
by the planets is very small it's 10,000
cubic astronomical units but as you go
further out you know the volume of that
sphere that encapsulates all the objects
that we've been able to observe it's
just going up dramatically so if you go
ten times further out which were now
just about able to do you increase the
volume that you're looking at by a
factor of a thousand a whole bunch of
stuff going on you know solar system is
to me an unknown place you know we fool
ourselves to thinking that we know
everything about it just because we've
only been looking
we have a lot of data from spacecraft
and so on but the further away you go
the less known it is and the more
mysterious it is and this ninth planet
thing is part of that because
essentially when you go far enough away
from the Sun there's enough room to hide
almost anything you want it will be so
faint you can put almost anything big
planets small planets whatever you want
we would not have seen it yet
if frienda when you do find it who gets
to name it oh that's something we don't
think about you don't have a name in the
back
the only David Bowie yeah there was a
there's a online petition on change.org
to name Playa nine David Bowie and I
thought it was kind of silly initially
but then there's this whole David Bowie
like mythology that you could create
past moons you could have Ziggy Stardust
and you know star mint and all of these
things so so you know kind of like I'm
not saying that seriously but also it
would be kind of remarkable if we had
Jupiter Saturn Uranus Neptune and David
Bowie
you