Sackler Astronomy Lecture: The Search for Planet Nine

Sackler Astronomy Lecture: The Search for Planet Nine


– My name is Eugene Chang and
as chair of the Department of Astronomy let me
welcome you to the 2016 Raymond and Beverly Sackler
Distinguished Lecture. The Sackler’s give to our
department so that we can host an annual public lecture
to further the sciences and arts at Berkeley. The Sacklers aren’t
able to be here tonight, but they will be sent a
video of this lecture, and so let me take the
opportunity on behalf of everyone here to thank the Sacklers,
thank you so much, from across time and space, thank you. (applause) The Sacklers have given to astronomy and, as an astronomer myself,
let me share an experience which I think maybe be
common to many astronomers, which is that when I’m
asked what is it that I do and I meet people off the
street, when I meet a person for the first time. They say, “What is it that you do?” I say, “Well, I’m astronomer.” And very often they would
react with great enthusiasm, very often. And they say, “That’s just so interesting. “I always wanted to study
astrology in school.” And it’s at that point that
I have to explain to them when you go to the library
there’s the non-fiction side and there’s the fiction
side and astronomers we want to write papers that’s for
the non-fiction side although we don’t always get it right
and so the things that we do sometimes have to be re-shelved. But generally we’re on
the non-fiction side. I used to be irritated at
having to make this distinction all the time, but in recent
years, I’ve learned to actually see that there
really isn’t much difference between astrology and astronomy. And, you know, what does astrology posit? Astrology posits that the
motions of the celestial bodies govern events on earth. Broadly speaking this is
true, it’s certainly true in detail for astronomers. My life, my research life,
which is basically my life, is dictated by what’s going on up There. Take the following horoscope,
for example, Pluto. Pluto currently, true
statement, currently in the constellation of of Sagittarius. What does this mean? According to astrologers,
it (mumbles) undo influence by Pluto on ideologies. According to Debra McBride,
an astrologer from Brooklyn, when Pluto is in the sign
of Sagittarius it signifies religious wars, or cultural warfare. Now, cultural warfare I think
accurately characterizes, characterized the astronomical
community back in 2006 when we, the astronomers,
were bitterly divided over the question of whether to
call Pluto a planet or not. On the one hand, you had
the weight of history, the weight of thousands
of school lunch boxes, the weight of astronomers
who’s grants in subtle ways depended on Pluto’s status
being preserved as the outer most planet. And on the other hand you
had the growing recognition, the new realization that
Pluto was just one of a vast collection of icy rocky
bodies strewn in the space beyond Neptune that is
collectively known as the Kuiper Belt. At the center of that controversy
was our speaker today, Mike Brown, who’s discovery
of a Kuiper Belt object who’s size was practically
identical to that of Pluto really brought this debate to a head. And his discovery of a Kuiper
Belt object that he later named Eris, very aptly. Eris is the goddess of strife and discord. Very appropriate. His discovery lead, ultimately
lead, the International Astronomical Union, the
United Nations of astronomers, the governing body for
issues of nomenclature, to rule that in fact we’ve
got it wrong all along. That there aren’t, sorry, nine
planets in our solar system, that there are, in fact, only eight. There are only eight, it
ends with Neptune and Pluto and Eris are members
of a new class of body, dwarf planets. And in recognition of
Mike’s, you know, role, decisive role in demoting
Pluto from it’s status, Time Magazine named him
one of the top 100 most influential people in the world. It’s true, it’s absolutely true. Los Angeles Magazine recognized
him as one of the most powerful Angelinos. And like all the great
crime bosses of history, Mike wielded his power brazenly. He wrote very cheerfully,
candidly, openly about his discoveries and all the
politics surrounding the status of Pluto in a
tell-it-all best seller that he entitled, “How I Killed Pluto
and Why It Had It Coming.” Which I have to say is one
of the most vindictive titles I’ve ever heard. It should come as no surprise
that Mike, as an astronomer, who has literally changed,
who’s discoveries have literally changed our
culture is a Berkeley alum. He was trained here in our
department of astronomy. He received his PhD in astronomy
working with professors Hyron Spinrad and Imka
Depoter who, Imka’s here as a distinguished guest today. It is here at Berkeley that
Mike was first introduced to the science of comets, which
hail from the Kuiper Belt. When you see a comet in
the sky, yes, it came from outer space, but more precisely,
many of them come from the Kuiper Belt. From the outer most reaches
of our planetary system, dislodged from those outer
most portions and corralled into the inner most
system where we can see it as a comet. It’s here at Berkeley where
he first started pursuing his interests in these frozen icy world. He’s pursued and maintained
that interest with spectacular success at Cal Tech where
he currently serves as the Rosenberg professor of
planetary astronomy. And it’s this subject,
Kuiper Belt science, that he’s going to tell us
about today as this year’s Sackler lecturer. So please join me in welcoming Mike. (applause) – Thanks Eugene. Thanks and thanks for coming,
thanks for inviting me to be here. It’s always fun to come
back to where I did my PhD. I want to finish up some of
the story that Eugene told ’cause he missed the
important part of the story, which is, as you remember,
Pluto in Sagittarius was (mumbles) all of these terrible things. Religious warfare, cultural
strife, terrible things. After it got demoted
all of that was fixed. (laughter) So this I think is even
better proof that astrology is working just fine. I’m going to tell you about,
I’m going to talk a little bit about some of the things
that Eugene talked about. About Pluto, about the
discoveries in this region of the Kuiper Belt that I’ll show to you. I’m going to show you how
those have lead us on to our new quest, which is to
find the real ninth planet in the outer part of the solar system. We call it planet nine because
we’re not very creative. But when we actually find
it, it’ll get a real name. And I think I’m going to
try to convince you today that it’s really out there and
that we really will find it. The story of another planet
in the solar system beyond the one that we know of
actually starts in something like 1790. 1790 Uranus had just been
discovered and astronomers were, actually, they were
interested in whether or not Uranus was a planet. Uranus was discovered by
chance, but by chance of a very careful astronomer who
was charting positions of things in the sky, saw something
that looked a little bit unusual. It looked a little bit fuzzy
and he went back and looked the next, realized it had
moved, and that is and remains the key signature of
something that’s part of our solar system. It’s moving compared to
all the background stars. And this was William Hershel
who made this discovery. And I sometimes try to
step back to that moment in history because this is, you
know, thinking about finding new planets is pretty exciting,
but imagine this first planet ever discovered in history. All the planets up to that
point, you know, we’re all the way out to Saturn, could
be seen with the naked eye. Everybody knew about these planets. Uranus was the first one
that was discovered by a telescope. I’ve never been able to
find anything written down about what a sort of psychic
shock that was to humanity to realize that the solar
system was bigger than they possibly thought. There’s a new planet out there. They didn’t know for sure
it was a planet at the time of discovery, they knew it
was something in the solar system moving and one of
the things they thought it might be is a comet. They knew about these
things called comets, they knew they were on
these very elliptical orbits that went out quite
far away, came back in. So the question that
everybody had at the time of discovery of Uranus is, what
kind of orbit does it have? Does it go in a circle
around the sun like all the planets do? An ellipse, really, but
we’ll call it a circle. Or is on a very elliptical orbit? The only way to figure out
what kind of orbit it has is to sit and watch it
year after year and see it as it goes around the sun. Uranus takes about 80
years to go around the sun. 80 years is a long time
to wait so in about 1820 an astronomer named Alexis
Bouvard in Paris decided that he would not, he
didn’t want to wait 80 years to figure out the orbit, he
was going to go back in time and see if he could find it. So what he did is he would
go back a couple of years and look at other astronomers
data where they had drawn where all the stars were and he realized, “Hey this person drew a star there, “but there’s not a star there anymore. “That could’ve been Uranus.” And he says, “Okay, if
that’s it I’m going to now go “back another couple of
years, there’s a star where “there’s not supposed to be one.” And he put it there and
went back a couple years, and he went back all the way
to, I’m going to show you this table just because you can’t read it. (laughter) he went all the way back
to that very first thing on the top of that plot there
is 1690 was the first time anyone had actually seen
Uranus was 100 years before it’s discovery. And he had data now from
1690 all the way up to 1819. He went through this math,
and I’m going to now go through line-by-line. I don’t even understand what all this is. Eugene probably does. Do you know what all that stuff is? He does, he’s nodding yes. But the important thing
here is that he has all the positions of Uranus from
1690 all the way up to 1819 and he proved in somewhere
up here he says in French that it’s on a circular orbit. He proves that it’s really
a planet, this is his big result. He also shows, it’s not quite
where it’s supposed to be all the time. All the pluses and minuses
that you see here in the second column are how far
away from where it’s supposed to be that it really is
and it’s kind of deviating here and there. And he does what any good
theoretical astronomer does when presented with data
that doesn’t make sense, he decided that the people who
were doing the observations probably were bad and
you shouldn’t trust them. He actually says this here,
it’s difficult, I don’t know. If you read in French you
can see where he says it up here. He does mention the possibility,
however, that there might be something else beyond
Uranus perturbing it’s orbit. He then actually gave his observations, gave his data to an
astronomer also in Paris, La Verrier, and he said, “You
should try to figure this out, “there might actually
be something out there.” La Verrier worked on it for
a while and realized that he could explain these data
very precisely with a planet beyond Uranus. La Verrier went to, basically,
the French Academy of Science and presented his
results and they were all very excited and they clapped
in their very excited ways. “Yay, nice job La Verrier.” And he was very excited and
he wanted them to go look for it because he could tell
you exactly where it was. And they, it did not
occur to them, I think, that you could use math
to discover a planet. They didn’t really think
that this was reality. They really thought that
this was a really beautiful mathematical demonstration
that you could make the numbers work out. Which is not the same as
thinking that you can use physics and math to predict things. And he’s like, “No, no,
there’s really a planet, “go look it’s right there.” And then, nah. So nobody in France would
look for this planet. He finally contacted the
Berlin Observatory and they opened up their telescope,
pointed to exactly where he said it was and they found
it the first night of his observations. There was Neptune was right there. And to me, these two moments,
Uranus as the discovery of the first, the first
discovery of a planet which just changes the way that
people must’ve thought about the solar system, but
Neptune the first really good demonstration that
math, this new-fangled math and physics stuff actually
is describing reality. It’s not just a cute trick
to make calculations. You can actually find things
you didn’t know that were there based on this math and physics. And I think those two things
were an incredibly powerful realization and this is in 1845. There’s an obvious thing to do. As soon as you have discovered
a planet using math and physics, the obvious thing
to do is to look for the next planet. So Uranus was discovered
by accident by careful observations. Neptune was discovered
by math and physics. A slew of astronomers
immediately started wondering, now it’s obvious, there must
be something else out there, too, that we haven’t
found, let’s go find it. So they started analyzing the orbit of, re-analyzing the orbit of
Uranus, looking at the orbit of Neptune as observations
were coming in and trying to see if there was
something else out there. The most famous of these
predictions of another planet beyond Neptune, there was
a series of people working on it, but the most famous one, by far, was from Percival Lowell. Percival Lowell predicted, he
had a series of predictions, but the one that really hit
home was the one that he called, I think he’s the one who
originally called it Planet X. This large planet beyond
the orbit of Neptune that’s perturbing the orbits
of Uranus and Neptune. And he predicted exactly
where it was supposed to be using the same methods
that La Verrier did to find Neptune and he sent some
astronomers up to Mount Wilson, which is in Southern California. Actually it’s literally
my back yard you can see the mountain where he is. And they took a picture
of the sky and it looked something like this. And, do you see the ninth planet there? No? Okay, he didn’t see it either. The astronomers didn’t see it. But they were looking for,
they were looking for something big, they were looking for
this sort of Jupiter-ish sized object that was tugging
on Uranus and Neptune. And a Jupiter-sized object,
it would be obvious, it would be like this big
in the frame here and you would take a picture
and you would just know. They didn’t see anything
here so they went back, he went back to the drawing
board, kept on doing calculations. He died before anything
was ever found out in that region of space. But not before he founded
the Lowell Observatory in Flagstaff and set them out
on the quest for Planet X. He and his quest for Planet X
and their quest for Planet X, they built a special
telescope to look for it, they hired Clyde Tombaugh
off the farm in Illinois. And Clyde Tombaugh took a few pictures, it looked kind of like this,
and realized that he was smart enough to know that
he didn’t know what a planet looked like. And he was smart enough to
remember all these things that we knew about planets,
which is the real way you identify a planet is you
don’t look for that big disc in the sky, you look for
something that moves. So he took a picture one
night and then he would take another picture the second
night and watch it move. Did you guys see it move? Sure you did. Okay, let’s try this again. Here’s the first night,
there’s the second night. How many people think they see it? Okay, we’ll see. We’ll try first night, second night. I don’t know why, but if you
repeat things four times, it’s a function of physiology,
the fourth time everybody sees it. So let’s try it the first
night and the second night. These are actually Clyde
Tombaugh’s discovery images of Pluto. And Pluto was very close to
the position that Percival Lowell had predicted Planet X should be. And so prediction was
made, discovery was made, New York Times headline on
the day of the announcement discovery, ninth planet discovered. First found in 84 years. Neptune was (mumbling)
lies far beyond Neptune, so far so good. Sighted January 21. Search begun by late
Percival Lowell, good. Special photo telescope, good. Makes thorough check, good. The sphere, possibly larger
than Jupiter meets predictions. Those are the big problems,
those are actually, that little phrase right
there contains the entire story of why Pluto was a
planet and is no longer a planet. Possibly larger than Jupiter,
I’ll show you in a minute how untrue that is. It’s wrong by about a factor of 50,000. And meets predictions, this
is an interesting story in science how science can go wrong. Science will usually correct
itself when it goes wrong, but one way that scientists
can fool themselves is to predict something, discover something, and assume that because they
had predicted this thing and they had discovered this thing, those two things must be the same thing. Turns out Pluto was not the
object that was predicted. Pluto has zero effect on the
orbits of Uranus and Neptune. And, in fact, we now know
many years later that Uranus and Neptune do not have any
measurable perturbations at all. There is no Planet X modifying
Uranus and Neptune’s orbit. What there really were, it
was actually like the original theoretical astronomers, it
was bad observational data. See, don’t trust the observers
is a good rule of thumb. It was both bad observational
data and we actually didn’t know the mass of
Uranus and Neptune very well. And that actually is
critical for seeing how they perturb each other. So, until the Voyager spacecraft
flew by Neptune in 1989, – [Woman] ’79. – Neptune.
– [Woman] Oh Neptune – ’89. ’89? 1989. That was when it was finally
determined for certain that there is no Planet X out
there perturbing the orbits. But it was too late for
the solar system because it accidentally got Pluto
as a planet because it is possibly larger than Jupiter
on the first day in the New York Times. So of course it’s a planet
if it’s possibly larger than Jupiter. Even Clyde Tombaugh, even
Clyde Tombaugh was a little bit dubious because he
knew that if it’s possibly larger than Jupiter, first
off, I should be able to find it easily and I can’t
figure out which one it is. Which one is it, now? When it moves, I’ll see it when it moves. There it is, I know it’s that one. So if we’re possibly larger than Jupiter– It’s not that? See, clearly it’s not a planet
because I can’t find it. So I don’t know which one it
is, but if it were possibly, if it were larger than Jupiter
it would be a big ball. So actually it must’ve been
fun to be an astronomer back in 1930 because I
read back in all the papers I could find about why people
thought it looked so small even though they knew it was
possibly larger than Jupiter. And my favorite explanation
that I saw in 1930 was that it’s actually, so it has to
be massive if its’ going to perturb Uranus and
Neptune, which it doesn’t, just to be clear, but they thought it did. So it’s massive, but it looks small. So what’s the explanation? The explanation that I
read was that it has a core made entirely of uranium, this is 1930, they don’t yet know
that’s a really bad idea. And then surrounding that
core is a liquid oxygen ocean. So liquid oxygen, so it’s
bigger than it really looks, and even better, the liquid
oxygen acts like a lens to make it look smaller. It’s the craziest idea that you
could possibly come up with. So in 1930 you could do
these crazy things and people wouldn’t laugh. I mean, they’d probably laugh back then. Turns out there’s actually
a real explanation for why Pluto looks so small in this image. Anybody know why it looks so small? – [Woman] It’s small. – Oh, that’s right, that’s the answer. I keep forgetting what the answer is. So in the whole debate
about Pluto being a planet, not being a planet, it’s
often lost just how small Pluto really is. Because of these lunch
boxes, like Eugene mentioned, where the planets are all
shown at more or less the same size because it makes a better lunch box. I’m just going to show you
the real sizes of the real planets just to remind
you how small things are. So this is, this is the solar
system if you actually put everything to the right scale. This big yellow thing in the
background is not the sun, this is Jupiter. Jupiter is huge. Saturn without it’s rings, huge. Uranus and Neptune. The four up there are
the terrestrial planets, Mercury, Venus, Earth, Mars. The little dots you can
barely see through there are the asteroids. The biggest one is the asteroid
Ceres that you might’ve been watching images from
as the Dawn spacecraft is in orbit around it taking
those cool pictures. The other ones are the largest asteroids, the criteria for inclusion
is that you have to be as big as one PowerPoint pixel
and, literally, that’s true. So, don’t blink, there is Pluto. It’s really kind of small. It really does not fit the
pattern of what you would think would be the next planet out there. And, I would also like to
point out, it’s actually not larger than Jupiter. It’s really not, really, at all. So, and of course, the other
weird thing about it is the orbit. If you look at the orbits
now, just the giant planets, Jupiter, Saturn, Uranus,
Neptune, if you put Pluto on there it has this really
bizarre orbit where it just kisses the orbit of
Neptune right here and then goes way far out and comes back in. And what’s more if you
take this and you turn it on it’s side and you look at them all, all the planets are in one
disc going around the sun and Pluto is tilted by about 20 degrees. Totally bizarre. Nobody really knew what
to make of it at the time, and even at the time in
1930, there was an argument about whether we should
call it a planet or not. But in 1930 if it’s the only
thing you know out there, it’s the only thing that’s
been discovered recently outside of the asteroid belt,
which is way inside here, might as well call it a planet. Pluto, the beginning of the
end for Pluto started in 1992 with the discovery of
the second object beyond the orbit of Neptune. That was made by someone
who was a post doc here at Berkeley at the time, Jane
Lou working with Dave Jude in Hawaii and I was in the
office next door and she came and told me all about it. I’m like, “Wow, that’s
weird, maybe there’s only one “of them.” And then answer is no,
there’s not only one of them, there are thousands and
thousands and thousands, this is even an old slide,
I should put more of them on there, of objects in
this region that we now call the Kuiper Belt. The little blue one is
Pluto, it’s just one of these and it’s actually, if you
look at it’s orbit it kind of shows you the whole range
of the main part of the Kuiper Belt. But every single one of these
objects in the Kuiper Belt has an orbit kind of like Pluto’s. It’s maybe elongated, it
might be tilted one way or the other. They’re kind of random
in all these directions. So even, even back before we
were smart enough to demote Pluto and not call it a planet anymore, by like 2002 it was pretty
clear that Pluto naturally belongs with this population
and not with this population. And if you look at the
sizes of the objects in the Kuiper Belt, there’s pluto,
there’s Eris the other big one the Eugene was telling about, which he says is about the same size. Which is a true statement,
but the correct statement is it is 25% more massive than Pluto. That’s the important point to remember, if anybody ever asks. Which one’s more massive? Eris. So there’s a whole belt
of bodies out there. It’s almost, it was a very natural, I like to think that all
you have to do to understand why Pluto is not a planet,
just look at this plot of the real sizes and you’re
like, “Oh yeah, okay, “it’s not a planet.” But what was interesting
was the demotion of Pluto was all fun and games, but
the real interesting stuff was the finding all these
other objects out there in the solar system. So I’m going to, I just
wanted to give you that quick introduction to remind you
about what was going on with Pluto and I’m going
to, now, move into more of these things in the Kuiper Belt. This next object I’m
going to talk about is, it’s about a third the size of Pluto. It’s size is actually
not that interesting, it’s orbit is what’s interesting. And at the time it was
discovered, it was pretty obvious that it was probably the
most important discovery that we had made in the Kuiper Belt, even if we didn’t know why. We knew it was important,
we couldn’t quite tell why. Let me show you why it’s so important, what’s so interesting about it. Here are these objects
I showed you, again, in the Kuiper Belt. This discovery was in 2003. So this is all the
objects we knew in 2003. I could fill in some more. We discovered this new object
and this new object was very different because
it was way out here. Yeah, “Wow” that’s the right reaction. Let’s try that again. We discovered an object
and it was way out here. – [Audience Members] Wow. – Thank you. So, when you find something way out there, you have your first reaction, besides wow, which is a great reaction,
is it might be a planet. It’s pretty far away. To see it at all at that
distance it has to be pretty big. And we don’t know how
big it is when we see it, but it has to be pretty big to see it. Might be a planet, but
one of the first questions we had is actually very much
like the Bouvard question. What kind of orbit does it have? Does it have a circular
orbit like the other planets, or does it have more of a cometary orbit? Does it come in to the
Kuiper Belt and go back out? Many objects that we know
come in to the Kuiper Belt and go back out. So it’s not entirely
surprising that we found some objects at that distance,
the question is whether it stays at that distance or
whether it comes in closer. So the answer, it turns out,
remember the question is circular orbit or does it
come into the Kuiper Belt? The answer is no. The answer is it’s almost
at it’s closest approach to the sun right now and then it
goes much much further away. It’s a 15,000 year orbit around the sun. And this is the object
that’s called Sedna. Sedna, we get to name all these, actually, so if anyone ever wants to
ask about crazy names you should ask me ’cause most
of these names I got to come up with. Sedna is the Innuit goddess of the sea, she lives in an ice cave
under the Arctic Ocean and so we were looking for
an appropriately cold name and that seemed like a pretty good one. She also had her fingers
cut up by her father, which is kind of creepy. Anyway, so Sedna was clearly
a really weird object. What’s weird about Sedna
is not that it takes 15,000 years to go around the sun, that’s okay. What’s mainly weird about
Sedna is that it never comes close to a planet. The planets, the distance
from Neptune to Sedna is further than Neptune to the sun. So to be on this crazy
elongated orbit like this, we don’t think anything
forms on elongated orbits. To be on elongated orbit
something has to kick you into that orbit or pull
you into that orbit. So at the time we discovered
Sedna we had a couple, we didn’t know, we had a couple
of interesting speculations. We said maybe it was a
passing star that’s now not around anymore. Maybe it was a lot of stars
early on in the history of the solar system. Maybe it was a planet,
that seems kind of stupid. But we had all these crazy
ideas, but we didn’t know. So I’m going to now quick
fast forward through some history and I’m going to do
it in the way that we did it. I’m going to show you,
now, this other depiction. There’s Sedna again. And I want you to think
about two things when I’m going to show you these other objects. One is, think about Sedna,
the direction that Sedna points from the sun is
like the hand on a clock. And so that has some angle. Sedna’s currently pointing
down this direction and that is in our coordinate system, which must be a weird coordinate system, that is 90 degrees. So it must be zero as this
direction, sorry to say. So, Sedna’s at 90 degrees
and the other thing that I’m plotting on here is the closest
it ever gets to the sun. Closest it ever gets to the
sun is nearly 80 of these things that we call astronomical units. Astronomical units is the
distance from the earth to the sun. So it’s basically 80 times
the earth to the sun distance. You don’t care about any of
that, what you should care about is the distance of Neptune. Neptune is this bottom
line right here in blue. That’s how far Neptune is. And this is about as far
away as normal object in the Kuiper Belt get up here. This is weird. So to find something way way
way up there really looks like it’s been pulled away
from the sun in some way. Very strange. Turns out, actually, just a
year earlier another object had been found that
wasn’t quite as extreme, but still had some of the same properties. It was pulled away from
the sun a little bit. And, interestingly, about
in the same direction as you can see up there. And at the time that the
astronomers who discovered it said, “I don’t know maybe a planet, “maybe it’s just Neptune doing
weird things, who knows.” Nobody really had any
good ideas how it could’ve gotten there. Couple years later,
actually, one astronomer from Brazil looked at these
two objects and said, “You know, a big planet
way out there could pull “both of those out and
cause these things.” I think he was roundly
ignored, mostly because everybody knows there’s
no more planets out there and that’s a ridiculous suggestion. So everybody went on. And a couple years later
there was another object and it was a little bit pushed out. The other reason that
he was ignored, I think, is because these are
pushed out a little bit, but maybe not that significantly. And this one, if there’s only one of them, there are many many explanations, you don’t need a planet for it. So there was another couple,
look there’s another one. This was an important one
when it was found a couple years ago, the other one
that’s pushed out the most. And again, very interesting
that they’re all off here in this same direction. At this point when these
five that were distant and pushed off in one
direction had been discovered is when I first sat up and took notice. I had discovered the
one back there and said, “Maybe a planet, maybe something else.” But when this next one, when
this last one was discovered like it and it was clear that
all five of these distant things were all pointing
one way, I was like, “Something funny is going on here.” And I don’t know what’s going
on, but there’s something funny. So whenever there’s something
funny going on that I don’t understand, I stand up from
my desk and I walk four doors down to my colleague,
Konstantin Batygin, who’s also a professor in
planetary science down at Cal Tech. He is a pure theorist who
understand all these things in gory detail, but you
really would not want to get him at a telescope, its a bad idea. And I’m sort of the opposite. You know, I can go through
the physics but I really don’t think in the same way that he does. So he and I are really an
interesting combination. If you ever are outside
of our office you’ll hear the two of us arguing in
different languages and it’ll be really unclear
what’s going on to any of us. But he said, “That’s really interesting.” He said, “Are there other
objects that are doing “that, too?” And I was
like, “You know what? “It turns out that there
are two more objects that “aren’t pulled away, but
they’re actually the two “other most distant objects
that are in the solar “system.” So if you take the seven
objects with the most distant orbits in the solar system
are all pulling off in one direction. The first thing we thought was, you know, it’s not a planet because that’s dumb. So, we tried really hard for
about six months to come up with all sorts of other
crazy ideas for why it’s not a planet because planets,
everybody knows there’s not a planet out there. That’s a crazy idea. And we could not figure
out how to make it work. So we looked at these objects again. Let me show you, okay so
what’s also interesting about these objects, they’re
not just all pointing off in one direction, I just
showed you the top down view, if you look carefully,
they’re all actually tilted compared to the solar system. You can see the solar system in there. And they’re all tilted in
about the same direction compared to the solar system. So it was pretty suspicious
that something was holding all of these things together. You should not find seven
objects all pointing in one direction, all tilted in
one direction and we were trying to figure out what was going on. And so, with much
reluctance, I have to say, we decided, you know,
he sat down and actually could write it down on the
board and show that a planet, a planet could do it,
it could be a planet. And what we thought is, it
must be a planet that goes, you know I’ve actually, I
asked my daughter early on about this. She’s 11, she was 10 at the time. Like, if you saw these, where
would you put the planet if it’s going to keep them in place? And the answer is obvious,
you put a planet that comes all the way around all of
these things and sort of herds them in place and keeps
them from moving around. And that’s the obvious
answer where the planet was. And we decided to try to
simulate this on a computer so what we did is we
started the beginning of the solar system, we put a big
massive planet on an elliptical orbit, we put a bunch of objects
on these other elliptical orbits and we waited to see what happened. And we knew what’s going to happen here. I’m going to show you this movie. You know what’s going to happen. So here’s the planet, it’s
a little washed out now, but the planet is in this pink. Everyone of these blue
things is an object that we put into the Kuiper Belt
just to see what would happen to it, and we knew what’s
going to happen, right? All of these things are
going to disappear and it’s going to be left with
just these that are here. So let’s watch, this is going
to be four billion years. Hope you brought dinner. Here we go, they’re starting to go. When it turns green, the
green ones are so close that we don’t care, we only care
about the distant ones. You can’t really see the green. But here they go, they’re
starting to, here we go. Here we go. Alright. They start, they try to come
in here, but they keep moving. Every time they come over here
they move around and go back. Here we go, notice that
there are many many times fewer objects than there
were to begin with. Things have been cleared out, but they’re not clearing
out the right way. In fact, they’re doing
exactly the opposite of what any reasonable person would
expect is that they are generally being cleared out
of this region and they are being trapped into this
region, this very broad region, exactly the opposite
direction of the planet. Now, to me and to Konstantin,
this was bizarre because, we’re talking a massive planet here. The planet that we tried out
was about the size of Neptune. And these objects, every
object here crosses the orbit of that planet at some point. And crossing the orbit of
planet, eventually you’re going to get close to it
and it’s going to give you a kick out of the solar
system, and that’s bad. So we were, we did not,
after four billion years, no. We were totally opposite. But look at that, totally
makes something that looks no dissimilar to what we see
in the solar system today. We didn’t believe it, we thought
we’d done something wrong. We good and double checked
and it took us another six months to really figure
out what was going on. And it’s actually an
interesting, it’s an interesting thing that happens. It actually turns out to
be more or less the same thing that happens with Neptune and Pluto. Remember how I told you
that Pluto kisses the orbit of Neptune? Just goes just inside of it. The only reason that Neptune
doesn’t eject Pluto is because they’re locked into this very
special orbit where Pluto goes around two times,
precisely, for every three times that Neptune goes around. And so whenever Pluto is
inside the orbit of Neptune, Neptune is on the other side. These guys all do exactly
the same thing with this massive planet and that’s
the only reason that they stick around for all this time. It really was not what we
expected, but it fits what we saw in an incredible way. Let me show you, again, what this planet, where we think this planet is. Not only does it, is it
the opposite direction, but again, as we sort of
guessed, these things are in this tilted by it a little bit. The planet needs to be tilted
by about the same amount to do the things that we think it did. So, this was our first
year of this project. And we were at that stage
which I like to think of as the French academy stage. We were very pleased with ourselves, we were willing to clap for ourselves. Yeah, a very nice cute
mathematical demonstration. Neither one of us really
believed there was a planet out there. One, it’s ridiculous, right? Everybody knows there
are only eight planets. But it just, this was,
there’s only seven objects, it just didn’t seem like
a good enough explanation, and besides, people had
been saying there’s a planet for 170 years and they have
always been shown to be wrong or have had bad data
or have had bad theory. And, generally, if you say
there’s a planet out there your colleagues will laugh at you. So we didn’t really want that to happen. And everything, we couldn’t
explain everything. There were actually some
interesting things going on from our simulations that
didn’t make sense to us. And one of them is we found
that if we were going to make these objects stick around
the way that they’re sticking around, we made another
set of objects, too, that is very different. I don’t have a good picture
of the prediction so I’m going to try to picture this for you. Okay, imagine the sun is here,
the planet goes like this, all of our objects go like this. The other thing that happens
is that, through a complicated set of gravity, the
objects that go like this occasionally turn, the
orbits turn sideways and they move this way. Or their orbits turn sideways
and they move this way. So they turn, if you look
at it from the top down it almost looks like wings
coming off of this pattern that you see here. This is inevitable. You cannot get rid of those
wings, and we don’t have wings, our solar system, sadly, I
guarantee just to Konstantin, our solar system doesn’t have wings. And if you predict that
there have to be wings and there are no wings,
you know you’re wrong. One of the nice things
about these theories, it makes these very big predictions. And we were sitting there
scratching our heads, pounding our faces on the
table trying to figure out why there were these wings
when there weren’t wings. Maybe it’s this, maybe it’s this. And at one moment I just
had this inkling in the back of my mind that, you know, actually, maybe they’re not wings, but
I knew there was at least one object who’s orbit
is perpendicular to the planets of the solar system. So I looked up it’s
parameters and it didn’t, it wasn’t a wing, it was more
like a wart or something. But it lead me to look at a
whole collection of objects I hadn’t thought about, which
are things that go in closer than Neptune. Which is you remember that
plot of the Kuiper Belt, there are a lot of them. I had actually ignored those
because I thought Neptune would ruin everything. But it turns out if you
look at the objects, and Neptune, there are
some objects that come in perpendicular and then go
out really long distances. There are five, in fact. And we tracked these five
objects down and had their parameters, I was like,
Konstantin was in my office, I’m like, “Okay, I am going
to plot these on the screen “and we’re going to see where they are. “If they’re wings it’s
’cause there’s a planet. “If they’re not wings, we’re wrong.” And we put them on the
screen and I’m going to give you the illustrated version
of what they look like here. They are the green ones,
which are, you can’t really– This was not quite working
out, but these are, they look like lines
almost because from above they’re perpendicular
and they’re the wings. They are exactly where
they were predicted to be. This is a moment, as a
scientist, you don’t just want to do cute math that
explains something that you already knew, you want to
make a prediction about something you didn’t know. Usually this takes a while
to verify your predictions. This, because we were dumb
enough not to have looked at this to begin with,
this was one a prediction verification in about
a couple week period. When we finally found these wings we were, I would say this was the
moment that was our eureka moment. This was the moment that
our jaws hit the floor. And it went from in our heads
cute math that we should all clap at, to, “Okay
let’s call up Berlin and see “if they’ll go try to
find our planet for us.” This is when we knew there was
something really out there. So, we’re now firmly convinced. It’s been even a year since
that moment now and many many other things we’ve now realized. A planet in the outer part
of the solar system explains many other unknown things
about the solar system that I’m not going to get
into the gory details today. Gory details, if you want
the gory details I’m talking at four o’clock tomorrow in a
much more technical seminar. But it’s the gory details. But let me tell you some
of the fun things about this planet. First off, we of course
call it planet nine because, a couple reasons, one,
it’s the ninth planet, two, it really irritates
people who love Pluto. And it just cracks me up. So that’s the main reason
we call it planet nine. This is how big it is. To have the effects that it
has, it has to be at least 10 times the mass of the earth. Actually, these days
we think 15 to 20 times fits a little bit better. So that puts it at Neptune,
Uranus/Neptune mass. If it’s 10 it’s a little bit smaller. But Uranus or Neptune. This is a substantial planet
in the outer solar system. This is 5,000 times
more massive than Pluto. This is not one of these things
that we’re going to argue about whether it’s a planet or not. When we find this thing,
it’s the ninth planet of the solar system and it will be
a pretty amazing thing to do. So, the question, of course,
is where is it and how are we going to find it? Well, one of the interesting
things I showed you is that it’s, I showed
you how it’s tilted. It’s orbit is tilted with
respect to the solar system. And we can figure out what that tilt is. We know what that tilt is
because it’s tilted the same way that those very
distance objects are. If it’s tilted with respect
to the solar system, that tells us something
really good, which is, it tells us where to look for it. We don’t need to look
over the whole sky because we know, at least we know the swath of sky that it’s in. So think of it this way,
here’s the solar system, there’s Planet Nine, and it’s orbit. What I want you to look
at is not just the orbit, but the constellations behind it. This basically tells us
the path through the sky that Planet Nine takes. We have to go, and then it
disappears, nobody knows why. Oh, and then comes back. We have to go find it. There’s, actually, Taurus
right there, Aldebaran. Orion would be right down in here. We need to go search this
swath of sky and we’ll find it. It’s actually a little bit
better than that because we also know, the other
thing that we know is that it’s on this very eccentric orbit. And we know which part of it’s
orbit it is where it’s close and which part is where it’s far. We know how big it is. So we know how bright
it is when it’s close and how bright it is when it’s far. When it’s close, it’s
actually pretty bright. Pretty bright, you know, for astronomers. In the sense that it is
an object that people with really top end backyard
telescopes could see it. When it’s close. Which will be about 7,000 years. Hold onto your telescope. So we know it’s not close
because it would’ve been discovered easily by then. And we can go systematically
through all the times when astronomers have looked
around the sky to rule out various places in the sky
where it is and isn’t. And in the end, we can figure
out that it most likely has to be at it’s most
distant from the sun. Which is also not surprising,
that’s where they spend their most time. Interestingly, when it’s
at it’s most distant from the sun it can only be spotted
by the biggest telescopes we have on earth. Here are some of the
biggest ones and some of my favorite ones. The two in the middle here
are a favorite around here. These are the Keck
telescopes that are run by a partnership that includes
the University of California and also Cal Tech where I am. So many of us astronomers
are on these two telescopes a lot. They’re great telescopes,
but they’re terrible for one thing, which is looking
for faint things in the sky where you don’t quite know where to look. They’re terrible because they
don’t specialize in that. They specialize in studying
things in gory detail when you know where they are. But not in finding things
where you don’t know where they are. So all the big telescopes
on the planet specialize in different things. One of the telescopes there,
next door it turns out, is the Subaru telescope. The Subaru is the Japanese
National telescope. It’s not named after the car,
the Subaru is the (mumbles) in Japanese, which is why the Subaru logo, the Subaru car logo is
the little (mumbles). I drive a Subaru, which is why I get to– No, it’s not. I do drive a Subaru. So the Subaru telescope
has specialized in a couple different things, but one
of the things they’ve done particularly well is taking
images of vast swaths of the sky at once. And I’ll show you how in a
minute, but that’s what we want. We don’t know exactly where
it is so we need to cover a lot of sky to find it. Once we find it, we will
then use things like the Keck telescopes, but we’ll also
use Hubble Space Telescope, the James Webb telescope
once it’s up there, everything else you can
think of, we’ll be using once we find it. Let me show you how they
specialized in taking pictures of vast areas of the sky. They built themselves the
largest astronomical camera in the world. They used to have a camera
that was pretty big called Supreme Cam. Or Suprime Cam, it’s a bad
pun in many different ways. Suprime Cam, but then
they built a bigger one so it’s called Hyper Suprime
Cam and it is the camera, this is not the telescope,
this is the camera. The camera is bigger
than an Anime character. (laughter) It includes the largest lens ever built. This is a lens that’s on the camera. The lens was actually
literally built by Canon. It’s the largest lens they ever built. It’s the largest, it was,
now it’s not quite anymore, but it’s still, it’s almost
the largest electronic detector on a telescope
anywhere in the world. And it covers this huge swath of sky. They amount of sky that it
covers, it’s impressive to me, it won’t be impressive
to anyone other than me. It covers about this much sky in one shot. Which is, yeah, it’s pretty
huge because it’s bigger than the moon. The full moon is there. You can get the whole full
moon in one shot and those Keck telescopes that
are great, that I love, that I use a lot, the
biggest that they can cover in one shot is right there. That’s about 80 times smaller. So the Subaru is, without a
doubt, the premier instrument in the world to cover this. We’ve calculated that
we need about 20 nights on the Subaru telescope to
cover all the area of the sky that we need to find Planet Nine. 20 nights actually sounds
like a pretty small number. It’s an interesting number
that’s somewhere between trivial and impossible. Which is actually a good place to be. If it were two nights, trivial. If it were 200 nights, kind of impossible. 20 is bigger than an
astronomer typically gets on a big telescope like this. But it’s not crazy over a
two or three year time period with a large collaboration
from Japan we think that we’ll be able to cover
this region in 20 nights. So I think within the
two to three year period at the Subaru telescope, I
think we will find Planet Nine. We’re not the only ones
looking, by the way, so we’ve been very good about
publishing very detailed maps for anyone who wants to to look for where we think it is. So there are many groups around looking. I would like to find it
myself because it’d be more fun for me, but if somebody
else finds it that’s great for them. We’ve actually been out
there to Subaru once. I want to show you now the
one picture that you might never see again. This is me right there. This is Konstantin Batygin,
theorist, at a telescope, danger. He actually hit his head,
it was good he was wearing a hard hat. That’s the camera way up
at the top there that is, even in this view it looks huge. It’s bigger than a person
way up there at the top. That’s why this telescope can
see this vast areas of sky. So I just want to give you
a tiny picture of how much of the sky we’re going
to look at this fall. And we make these calculations
of where we think it’s going to be, you can’t
quite see it, in green. And how big the field of
the telescope is and that’s, that’s of swath that we’re
going to do in the fall. And this means nothing
to anybody except for the occasional astronomer in the room. But let me show you
what I want you to leave thinking about. So I want you to leave
thinking about a couple things. One is that there is a
new planet out there. We were, we were pretty
convinced six months ago when we first published our paper. In the ensuing six months
we’ve learned so much more. I am willing to say that
if there is not a massive planet out there that the
solar system has got some really weird stuff going on. There are so many little
details that this explains perfectly that I am as certain
as you can be about anything in astronomy. I am certain it’s out there. And I want you to think
about this as actually real. This is not a French academy
clap your hands abstraction, this is a real thing in the sky. Here’s what I want you to
do, I want you to wake up early tomorrow morning and before sunrise, everybody promise, and I want
you to go out and look east. In the pre-dawn sky
you’re going to see Orion, you’re going to see, there’s
Orion, you’re going to see, there’s the Plates, think
about Subaru when you see the Plates. There’s Aldebaran and Taurus. And when you look at these,
when you look at Taurus right next to Orion, I want you to think, “This is Planet Nine, Planet
Nine is probably right “there in Taurus.” The area that we think
that we need to search to find it is right there. It’s probably right there. If you could pick an area of
the sky to put it that you could describe to people
where it was, you know, if I said it was in
Sagittarius like Pluto, some of you would know but
other of you would be like, “I don’t know where that is.” If I say it’s like right next to Orion, everybody can go find Orion. Go find Orion. Okay, you don’t have to get
up early if you don’t want to. Wait for a few months it’ll
be up a little bit later. But when you see Orion,
I want you to think, “That’s Planet Nine.” Planet Nine is out there to
be found somewhere in this swath of sky. And we might not find it this
year, we still have a couple more years that I think
we need to do to find it. We may not find it this year,
someone else may find it this year, but I really do
think that within the next two or three years that
you will be picking up the newspaper or opening up
Twitter or there will be an embed in your head and
it’ll blink up and down that Planet Nine is spotted. I think we know it’s out there. I would almost say we have
discovered it’s existence and now we just need to
spot it to know precisely where it is. I’m going to leave you with
an interesting thought that this is all quite prescient
of, this of course is the, our modified version of the
Planet Nine from Outer Space poster, I don’t have to
tell that to an audience in Berkeley. But Ed Wood, when he probably
approved this poster, was quite prescient in a way
that I didn’t even realize until I looked really carefully at this. So Planet Nine from Outer
Space, God now I can’t remember the plot. There’s, you know– Maybe there’s no plot. But it involves Vampirina
and (mumbling) and all. And it’s the aliens are making,
I actually can’t remember. But there’s an important
scene that takes place here in the graveyard. And if you blow the poster
up really carefully, nobody knew this back in 1969 or so, but it actually says
RIP Pluto right there. (laughter) Who knew? Who knew? Thank you very much. (applause) – [Audience Member] How
many days separation between two photos do we need to be to see it? – So that’s a great question. It’s so far away the question
is, if we take a picture, I showed you those pictures of Pluto. Those were a day apart,
but you don’t even need. To see Pluto you can do it an hour apart. We need one night of
separation between our images to see it. Which is actually great. It’s moving fast enough
that if we take a picture of the sky and we come back to
the same spot the next day, it moves by just this perfect amount. Just a little bit more than
the size of the star itself and it doesn’t move by a
huge amount so it’s easy to find these things. It’ll be, when we point to
the right spot in the sky, we’ll take three pictures
in a row over three nights and it’ll go tick tick
tick and that’ll be it. I’ll drop my laptop
instead of dropping the mic or something. But we will know where it
is, it’s going to be very exciting when it happens. – So, presumably a planet
of this size had to come from somewhere, like
maybe the (mumbles) disc? – Yeah, so where did it come from? This is actually one of
the more exciting things because it’s not just,
the goal is not just to go spot it and say, “Haha,
we found a planet.” Actually, that’s the goal. The goal is to find a planet,
study it, learn about it, figure out what it’s telling
us about the solar system. So where did it come from? We don’t know, so let me
start by saying we don’t know. We can tell you that there’s
a mass out there doing something, we can’t tell
you anything about it’s history yet. But we can speculate. Might be in the fiction
section of the books. But let me tell you our
favorite speculation on where it came from because it
actually makes sense. Maybe 10 years before all
this happened Konstantin Batygin, who’s my partner
in crime in all this, and I were working on an
entirely different problem that we were interested in. Which is, what would happen
if there were a fifth giant planet early on in the
history of the solar system? How would it effect the
planets that we know and the Kuiper Belt? And so we did computer
simulations, putting five giant planets. And what always happens
when you put in five giant planets, almost always,
one of them gets ejected. And we didn’t care, it gets ejected, who cares what happens
when it gets ejected. We only paid attention
to what signature it left as it was being ejected. It now seems pretty obvious
that once you’re ejected one thing that might happen
is that you don’t get ejected all the way and you
eventually find yourself in a Planet Nine like orbit. I think the most likely
explanation is that it is something that formed
in the region of Uranus, in the region of Neptune. That’s why it’s about the
same size mass as those guys and it got ejected. So, interestingly, in many
different ways, Planet Nine makes us seem more like
other planetary systems that we see around the galaxy. We see other stars that
have planets that kind of look like they might have
a similar history to them. So it’s not, it’s not a
bizarre idea that we might’ve had something like that ourselves. – [Audience Member] Is there
a relationship for (mumbling) maximum possible distance
from any given star that you could have a planet– – Yeah, so the question is,
is there some way to figure out what’s the most distance
you could have a planet out there? And the answer is yes, it’s
not a simple formula that you could do, but it’s really,
so there are a couple things. First off, gravity goes forever. So the only thing that makes
the sun, the sun influence not go forever is that there
are more stars in the galaxy. So, parts of our solar
system, this thing called the Oort Cloud, the other sorts of comets. Eugene talked about the
Kuipeer Belt having comets, the Oort Cloud also has
them, it’s half way to the nearest star. So that is tremendously
further away than anything we’re talking about here. There might actually be large
objects out there in the Oort cloud, but they’re on
kind of not very stable orbits. If you really wanted to
be on an orbit that’s been kind of stable for the
age of the solar system, you wouldn’t want to go more
than a couple times further than we think Planet Nine is. At that point you start
to get influenced by stuff on the outside. So right now we think
Planet Nine might be, it’s furthest extent it
might be 10,000 times the earth sun distance. I said 10,000, 1,000 times. If you went out to 5,000
things get iffy out there. (mumbling) The distance to the next star and, also, the overall effect of all
the starts in the galaxy are what really make the difference. – [Man] Right here in the corner. (mumbling) Proto-Sednas, I like that. (quiet talking) No, not scale this at all. I didn’t go into the
details, but we had to pick, we actually did thousands
of simulations to figure out what mass we needed. If you have too little
mass, nothing happens. If you have too much mass,
everything gets ejected. (indistinct talking) Yeah and we actually, before
we found one that worked we actually had calculated
from just analytically what we thought would work
and it turns out to be about right. And that’s where we come
up with something like 10 times the mass of the earth. – [Man] In the far back. (indistinct talking) – So, no. The only thing we know, do
we know it’s composition? No, we know it’s mass. That’s it. All we know is that it’s a point mass. It might be made out of hamburgers. People ask me, “What
if it’s a black hole?” The answer is, it’s not a black hole, but if it were a black hole, I don’t care. If it’s 10 times the mass
of the earth it can be a black hole. But it’s not a black hole. What if it’s two objects
orbiting each other? It’s not two objects orbiting each other, but if it were, I don’t care. As long as it’s 10 earth masses. However, I can tell you
something about things that are 10 times the mass of the earth. Because that’s about the
most common mass of a planet that we find in our galaxy. If you’d asked me this question
10 years ago I couldn’t tell you anything about it. But now we know many many
stars have planets that are about 10 times the mass of the earth. And by and large, we think
that all, that most of them that are 10 times the mass
of the earth are gas giant planets rather than
rocky earth like things. So it’s rather than scaling earth up, you scale Neptune down. So we think that’s most
likely it’s composition. Also, that’s what you would
get if you formed in that Jupiter, Saturn, Uranus, Neptune region. So that’s, this is the speculative part, but I think it’s a pretty
good speculation of what it’s going to be like. However, when we spot it we
will then get to use things like, the first thing
we’ll do is use the Keck telescopes to look at light
reflected off of it to learn about it’s composition. When the James Webb telescope
gets into space it will be a fabulous telescope for studying it. So we have many other things
to learn when we actually finally spot it. It’s probably not a core of uranium, and probably not surrounded
by a liquid oxygen ocean. That is fair to say. (mumbling) So the question is, do we
expect Planet Nine to have Trojans? So let me first explain what that means. That if you looked at, if
you look at the orbit of Jupiter and on those scales
that I showed you here I wouldn’t have shown you anything. But if you look at Jupiter,
Jupiter in particular in our solar system goes around the sun, but just in front of it in
the same orbit by 60 degrees and just behind it in the
same orbit by 60 degrees there are thousands and
thousands of objects, little asteroids,
circulating with Jupiter. They’re these very special
stable spots where you can put things that are
stable for the age of the solar system. And Jupiter has them. As far as we know Saturn and Uranus don’t. Neptune does. The Earth, Earth occasionally
kind of gets things there that don’t really stay. Would planet nine have
Trojans and the answer is no. Planet Nine would not
have Trojans because that crazy elliptical orbit doesn’t
allow those same stable spots to be stable. So let me make sure I
believe that when I said it. I’ve never actually thought
of it exactly that way. You would, you occasionally
get things that share it’s orbital period. It’s– – [Man] It’s possible. – Yeah, you get things,
so they’re not Trojans, but you get things in the
one to one resonance, yeah. They’re actually not,
they’re not co-orbital. They have the same semi-major axis. Which is, in the case of a mass– – [Man] One to one. – But they’re not in the same orbit. So I’m not going to call them Trojans, but yeah you can get– – [Audience Member] Would
the trajectories of Uranus and Neptune be affected? I mean, we know them pretty well. – Yeah, the answer is yes,
but at the scales of 10s of kilometers. And we don’t know them that well. So, actually, the thing that we know best, it’s an interesting
exercise to ask yourself. What’s the best measured
large scale distance that we know of int eh
solar system over a moderate time period? Anybody want to guess? I can’t hear, so I’ll tell you the answer. The best measured distance
over a decade old time period is the distance from the earth
to the Cassini spacecraft around Saturn. So, that is a precisely measured distance. Cassini’s been in orbit
around Saturn for more than 10 years now and it’s been
precisely ranged and so people know exactly where
it is and have built these models of everything in the
solar system based on this. And people have tried to
use perturbations to that, to see if you can see
Planet Nine pulling Saturn a little bit. And it turns out that there
are enough other things that are close that have
more of an effect on that distance, so it’s not
the position of Saturn, it’s the distance from
the earth to Saturn, and you can move around the
earth by just a little bit by making the passing
asteroids a little bit more massive or a little bit less massive. And that’s more of an
effect than Planet Nine has because Planet Nine is so far away. So, so far, nobody has come
up with a way to use any current knowledge to find a perturbation. God, but I wish they
could because that would, that would not just
tell us that it’s there, but that would point
in the exact direction. That would be fantastic. Early work suggested it might be possible. I think we’ve now proved it’s not true. Anybody who has good ideas,
go figure them out, tell me, I’ll go look. – [Audience Member] Have you
and the team been through the data on the object
enough to set a lower limit as to what another planet 10 might be? – So that’s a great question
which is, basically I’m going to say, if there’s a planet nine, why not a planet 10? Why not a planet 11? And I actually love this
question because this is, you know, if there’s a
Uranus why not a Neptune? If there’s a Neptune why
not a something else? We get to ask these questions now. The last decade has been
so boring, you know? There are eight planets. (snores) If there’s nine there might be 10. How are we going to find them? So right now the answer is
we cannot tell you anything about planet 10. If there is, if there
isn’t, if there’s evidence. And the reason is is because
the evidence for Planet Nine is these objects who have
orbits that are sort of similar to Planet Nine’s distance away. Planet 10 has to be even further. We don’t know of any objects out there. They’re going to be fainter,
they’re going to be hard to find. Planet 10 is going to be
fainter than Planet Nine, Planet Nine requires the
biggest telescopes we have in the world. So, I tell this, I give
this talk often for groups of kids and I explain, you
know, Planet Nine is the perfect planet for our generation. It’s things that we can
find now, it’s telescopes we have now. But if there’s a planet 10 it’s not me, it’s not people I know, it’s kids. It’s the next generation
of astronomers are going to go off and have to find this Planet 10. Which is so much better than
saying, “No, eight planets, “suck it up.” – [Audience Member] Are there
any probes that are currently flying to the outer solar
system now that if in a couple years from now
you knew where to go, you could actually change their– – The interesting question
about whether any probes are on their way that
are maybe going the right direction, that you could maybe redirect. And so there’s two answers. One is that, no, turns
out none of them are going the right direction. And two is, none of them have fuel. You cannot redirect any of
these spacecraft even more than like– So unless you’ve gotten really lucky. But it’s cool to think about
how do you get a spacecraft out there? Could you get a spacecraft out there? I’ve actually been, for the
last three or four years, I’ve been working with teams at JPL on, when I say working with
team at JPL it makes me sound like I actually know something. They’re working and I’m
like clapping my hands, on how to get things to
the outer solar system really quickly. This was not anything
to do with Planet Nine, this was before we
thought about Planet Nine, this was because many people
are interested in different things in the outer solar system. And the answer is actually
there’s current technology that could get you out
there pretty quickly. You know, whenever we send
a spacecraft to the outer solar system, we do a
gravitational slingshot around Jupiter to get things sped up. Turns out there’s even a
better gravitational slingshot in the solar system and it’s the sun. So you go straight in,
slingshot like mad off the sun and you’re going really fast. So the actual technical hurdle
turns out to be shielding. How close can you get to
the sun without burning yourself up? So we’re working on that. But at that point, it still
will take you 50 or 60 years to get there. But I actually think that when we find it, it will provide the incentive
to really start to think about these fast missions pretty quickly. So I’m actually kind
of excited about this. In the sense that you can
be excited about things that happen after you die. (laughter) – [Audience Member] So if
you find this Planet Nine, what are you going to call it? – If I find it what am I going to call it? That is a jinx and I’m not
going to answer that question. Nah, nah, nah, nah, nah. And I have not even thought about that. I mean, people ask that
question all the time. I literally refuse to
think about it and have not thought about it, really, honestly. Although– (laughter) I will say that my daughter
has a name that she has picked out. She has two names. Her first suggestion was
call it Pluto so that Pluto can be a planet again. And her second suggestion,
her name is Lila, her suggestion was, “Call
it the Lila Planet.” That’s good, okay. (indistinct talking) Yes. (indistinct talking) Okay, so let me get
the, the two questions, did I talk about this 10 years ago? The answer is yes because
10 years ago is right when we had discovered Sedna. And so that talk in New
York, I remember this talk because we had just discovered
Sedna, I talked all about Sedna and how maybe a planet it doing it. I didn’t actually think it was a planet, we actually thought there was a– (mumbling) It was just one at the time. Trust me on this one, I remember this. But we talked about that. But the other question,
what was the other question? Mass! Oh, why can’t we tell
you right where it is? So, the question is, how
come we’re so bad when La Verrier was so good? I think is really the
question you’re asking. La Verrier said, “It’s
right there, go look.” And it was right there. One night, they found it. We say, “It might be here,
we might need 20 nights “and our telescopes are bigger.” The reason is is La Verrier
had it a little bit easier. He had a full orbit of Uranus
to watch the perturbation. So, if Neptune’s here,
as Uranus goes around, it’s a little slower here
because Neptune’s tugging, slow, normal, fast
because Neptune’s tugging. Basically, it’s a big sign that says, “I’m a planet and I’m over here.” None of the objects that
we have have made any appreciable movement in the 10
years since we’ve known them. Sedna we know for 10 years
Sedna has a 10,000 year period. So it’s moved that much. If you could wait for
10,000 years and you told me it’s position for 10,000
years I would point to Planet Nine. So we don’t have that one
extra piece of information. It is amazing to me how much
we’ve been able to tease out from what we do have. I still am holding out hope
that there’s some clever way that we can figure out
exactly where it is. And we have a few tricks we’re working on. So far they’ve all been total failures. But we have hope. – [Man] One last question here. You’ll be the last one. (indistinct talking) – Are you going to ask me about a name? ‘Cause I’m not going to answer. If you ask me about a
name, I’m going to stick my fingers in my ears. (mumbling) Percival Lowell. So, just to be, although this
is speculating about a name, I will say that when it is
found, even if I’m the one who actually spots it with the telescope, this is me and Konstantin,
who I talked about the whole time. If it were just me, we
would not be saying, we would not know anything
about this planet. If it were just Konstantin,
we wouldn’t know anything. It was this really, it
took the two of us who are very different people finally
learning to speak each others language through a
low of screaming and yelling and arguing, in a good
natured way, to really finally make sense of both what we’re
seeing in the sky and how to interpret it. It’s been, it’s been a
tremendously enjoyable two and a half years
for me working on this because I’ve learned so much
and I’ve enjoyed working with him so much. So, he’s got to be in there too. That’s all I’m going to say. And then I’m going to stick
my fingers in my ears. Can we have a question
that’s not about a name? ‘Cause I’m not going to
answer questions about names. – [Audience Member] So, do
you have any idea of when Planet Nine would’ve been ejected? Was it caused by migrating
inwards or just– – Yeah, when it was Planet Nine ejected? I said it got too close, it was ejected. It most likely happened very early. Very early, you know, so the solar system, that simulation I showed
you was four billion years. The solar system in the first
even just 100 million years, even shorter than that, was
really going through all kinds of perturbations
and rearranging itself. And in the very earliest
perturbations it would’ve done it. It needed to have been
early for other reasons, which is that just ejecting
it isn’t good enough, you have to eject it and
then have it not escape completely. It’s actually a little bit
like the problem of Sedna early on of being ejected
by then sticking around. That makes, it’s easier to
do if there still are some stars around, which (mumbles). So we actually think it was really early. 10 million years, maybe,
maximum when all that rearrangement took place. (applause) (upbeat music)

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