(rhythmic chiming music) - [Announcer] NASA's Jet
Propulsion Laboratory presents the von Kármán Lecture, a series of talks by
scientists and engineers who are exploring our
planet, our solar system and all that lies beyond. - Hey, good evening
ladies and gentlemen. How is everyone tonight? - Good
- Alright. (sparse applause)
- Oh, good. Thank you so much for
coming out to join us on this relatively soggy
California evening. (chuckling) So, shall we? Planets orbiting other
stars, or exoplanets, have become an important
field of astronomical study over the past 25 years. Recent findings from
NASA's Kepler Mission suggest that nearly every
star you see in the night sky probably has
exoplanets orbiting it. The number of confirmed
exoplanets is now a few thousand and their discoveries
have yielded terms that would have sounded
alien to astronomers before the 1990s: hot Jupiters, pulsar planets,
super-Earths, mini-Neptunes and circumbinary planets. Now, Trends are emerging
among exoplanet populations which put our own solar
system in context, noting most exoplanetary
systems appear to be very unlike our own. Tonight's guest will
present a brief history of exoplanet
discoveries, the story of the transiting super-Saturn
extrasolar ring system and summarize NASA's
ongoing and future plans to discover and characterize
strange new worlds. Tonight's guest has been the
Deputy Program Chief Scientist of the NASA Exoplanet
Exploration Program since August of 2016. His research interests focus
on astronomical observations related to the
formation and evolution of planetary systems and stars, and in particular, their ages. He graduated with a BS in
Astronomy and Astrophysics and Physics from
Penn State in 1998, a Master's degree in Physics from the University
of New South Wales Australian Defense Force Academy while a Fulbright
Fellow in 1999, and he received his
PhD in Astronomy from the University
of Arizona in 2004. After his PhD, he was a
Clay Postdoctoral Fellow at the Harvard Smithsonian
Center for Astrophysics. More recently, he was
a Professor of Physics and Astronomy at the
University of Rochester and a staff astronomer at
the Cerro Tololo Observatory in Chile. He has also been part of
several astronomical discoveries over the years
including the discovery of the first transiting
extrasolar ring system, the nearest historical fly-by
of a star to the solar system and the discoveries of
low-mass stellar companions to the bright stars Alcor,
Fomalhaut and Canopus. He has discovered several
nearby star clusters within hundreds of light-years'
distance to the Sun, and recently he was
co-discoverer of a comet. He is an active member of the International
Astronomical Union and he is currently the Chair of the newly-formed IAU
Working Group on Star Names. Ladies and gentlemen,
please help me welcome tonight's guest:
Dr. Eric Mamajek. (audience applauding) - Thank you, it is absolutely
wonderful to be here. As he mentioned, I just
got to JPL in August, so I'm relatively
new to California. So, apparently, things are
wetter than where I came from. We now inhabit a water world
in Southern California. So I'm gonna tell you about Exoplanets: A Quest
for Strange New Worlds. This is a topic that's obviously
near and dear to my heart so the first part of the talk will be a little
bit personal to me because as the discovers
have sort of unfolded over the last few
decades, they sort of fed into my interest in astronomy. So I've been sort of
watching this field since elementary school. So, this is one of my
favorite places on Earth. This is actually Cerro
Tololo Observatory in Chile. And this is a few
of the domes there. If you go out at night
when the Moon is not up, if there's some low
cloud that's blocking out some of the lights from a
few of the small towns nearby and the mines, you get a
really, really, really dark sky. It's so dark as
you're walking around, you can see your
shadow on the domes. And that shadow is not from the
Sun, it's not from the Moon, it's from the stars. There's nothing else
illuminating the sky. You only have to go outside
dark-adapted for a few minutes and you start
seeing this effect. It is literally the light,
the integrated light from billions of
stars in the galaxy that's projecting the light
that's producing your shadow. This was a really
neat place to work. And so every once in a
while when you're observing, you could take a little
break and walk outside and see the stars. And on a typical, outside
of light-pollution, you should be able to
see hundreds or thousands of stars in the night sky. We've got something like a
few hundred billion stars in our galaxy. There's probably hundreds
of billions of galaxies in our universe. And so you wonder, are there
other planets out there, okay? So, this is, you're
seeing on the left what our galaxy looks
like from Earth. You see lots of stars, you
see these inky dark regions among the stars. Those are dark molecular clouds and as I'll tell you later, that's actually where stars
are forming, in those clouds. We now, astronomers over
the last several decades have been able to
measure the distances to stars more precisely. We can measure the distances
to these clouds more precisely. And we can sort of deproject
the edge on Milky Way into the Milky Way's
actual appearance. Now, this is an
artist's conception but a really good
artist's conception. Most of the stuff we
have mapped out is just in this little
quadrant down here within a couple thousand
light-years of the Sun. Our Sun would be a
completely imperceptible dot right here between
to spiral arms, okay? So the galactic bulge is here, it's about 30,000
light-years away. And our Sun is moving
around the galaxy at about 200
kilometers per second. You don't feel it. So, we'd like to know, are
there other planets out there? This is the preface
to a great book that came out a few
years ago by Sara Seager, who's a regular visitor to
JPL and a professor at MIT. She edited this book
called Exoplanets. And she wrote, "This is a
unique time in human history. "For the first time, we're
on the technological brink "of being able to answer
questions that have been around "for thousands of years: "Are there other
planets like Earth? "Are they common? "Do they have signs of life?" These are really big questions and we're sort of slowly
unveiling the curtain and then finding these answers. And we're sort of at
a lucky generation to be able to see this unfurl. So, this is me, about 1980. I grew up on a horse farm in
Southwestern Pennsylvania. Skies were moderately dark. Very quickly I was
interested in things like geology and meteorology. I saw Mount St. Helens
the year after it blew up. I thought, this is crazy. How could the earth, you know,
how could a mountain explode? We didn't have those
in Pennsylvania, we had coal, limestone. It didn't explode. But it got you thinking
about the universe and physics and chemistry
and how the universe works. And it didn't take long
until I was interested in astronomy. But this also coincided
with pictures like this. I remember being
five or six years old and seeing the pictures
of this ringed planet and wondering what that was. And for a sort time, I thought
that must've been Earth. I thought I lived on
the ringed planet. And I was like, well, I
can't see the ring at night. But I saw these pictures
of Saturn so often that it made you wonder. And so I was sort of a
child of the Voyager era in the 1980s. You know, every few years, it
was all these great pictures coming from NASA from
these robotic space probes that were sent to the
outer solar system. The people in the
auditorium are sitting next to a model
of one right here. And the two probes
I'm talking about, of course, are Voyager
1 and Voyager 2. And they completed the
first reconnaissance of the outer solar system. Voyager 2 made it past all
four of the outer planets, Jupiter, Saturn,
Uranus and Neptune. And these are really interesting
worlds in themselves. Here's a picture of
Voyager 1 and Voyager 2. The Voyagers are now over
100 astronomical units away from the Sun, 100 times
the Earth-Sun distance. They're reaching the area where
the Sun's wispy atmosphere of ionized gas is sort
of melting into the gas from the rest of the galaxy. They've effectively
left the solar system. They haven't left
the Sun's gravity, but they've effectively
left the solar system. So Voyager was launched in 1977. And I knew, even in
elementary school, there was this interesting
place called JPL and there was these
interesting people at a place called,
you know, that worked for an entity called NASA
and they were explorers. And they wanted to study the
universe and study planets. And this sounded like a
really, really neat job. And it was an exciting time. The last few decades
have been very exciting, there's been a lot of very
interesting discoveries. And it's fun to be here at JPL and actually give
a talk on this. This is sort of our
classic, cartoon picture of the solar system with the
now-eight classic planets. And we were sort of
taught in the 1980s that we have these small
rocky planets on the interior. There's Earth, Mercury,
Venus, Earth, Mars, Jupiter, Saturn,
Uranus and Neptune. And the small, rocky planets
form on the inner part of the solar system. And then all of a sudden, out
past about two, three times the Earth-Sun distance, you
start getting these worlds that are dominated by the ices, things like water and
ammonia and methane. They're the so-called
astronomical ices, carbon, nitrogen and hydrogen
with hydrogens attached. And also, a lot of
hydrogen and helium. Jupiter and Saturn were
very much dominated by hydrogen and helium. And each of them have their
own little system of moons. All the moons were interesting, these small cratered worlds. Some of them had active geology. Couple of them have atmospheres. And so this was sort
our classic picture of the solar system
through about the 1980s. Shortly after, they
were finding the, there was discovery of the
Kuiper Belt out past Pluto. We now know there's
icy worlds out there. And there may even be another
planet, so-called Planet 9. It would not surprise me
if that was discovered in the next year or two. The dynamical evidence
looks pretty interesting. So one of the great, I would
say victories of physics and astronomical of
astronomy in the 20th century is this sort of
comprehensive picture of the formation, the
evolution and death of stars. We understand stellar
structure very well, the stellar atmospheres. If you could sort of
stand back and look at our galaxy over a time
scale of millions of years, billions of years, you would
see stars being formed, living their lives
and being snuffed out through various means. And this is just showing
the evolutionary pathways for small stars like the Sun. They're born in these
dark molecular clouds. I'll talk about this a
little bit more later. They collapse, basically
this is, why do stars form? Stars are forming
in the gas and dust floating around in the galaxy. It's where gravity wins out over gas-pressure and
magnetic-field pressure. It's a very inefficient
process, okay? Only a few percent of
mass in these clouds actually form stars. And then only a tiny
fraction of the mass that goes into forming
the, of the star, will end up forming the planets. So our Sun'll live
a nice happy life for about 10 billion years. We're about halfway through. At the end of its life,
it'll become a red giant. It'll exhaust its hydrogen
fuel and it'll furiously change its inner structure
to try to heat to higher temperatures to
burn other sources of fuel. It'll run out and eventually, it'll turn into a
planetary nebula. It'll blow off its outer layers. So this is is going on. This whole time scale here
is about 12 billion years. And for low-mass
stars in the galaxy, stars even down to
the mass of the Sun, some of them have had time
to go through this cycle. The massive stars, the
big, bright white-blue, blue-white stars you
see in the night sky, those live very short lives. These are stars that
are typically 10 or tens of times
the mass of the Sun. They correspondingly
live very short lives. Maybe tens of millions of years. And they go through a much
more destructive phase at the end, they
actually explode. And depending on their
mass, they'll turn into either a neutron
star or a black hole. But what doesn't go into the
neutron star and black hole contains a lot of metals
and a lot of stuff that turns into planets
and turns into life. And this process is
constantly enriching the gas in our galaxy. Our galaxy is slowly getting
full of so-called metals. So there's the periodic
table of elements you're used to seeing, that you learned
in your chemistry class. Most of the normal
gas in the galaxy is hydrogen and helium, up here, elements number
one and number two. They're about 98% of the
amount of normal matter in the galaxy. We're excluding so-called
dark matter and dark energy. That's for another talk. All the rest of the other
elements are less than 2%. Okay, if you averaged
out over the galaxy. But those are pretty
important because they end up turning into planets
and turning into life. Now the astronomers, this is
the astronomer's H-R diagram. Hydrogen, helium, metals. Okay, all the other 90 plus,
I think we're up to 118, but most of those
are short-lived. But the other 90 or
so stable elements, the astronomers just
call them metals. And they tend to
track each other in terms of their
relative abundance with respect to each other. So we talk about the
metallicity of stars and the metallicity
of the galaxy. And the amount of
metals in the galaxy is slowly getting
higher over time because stars are
living it and dying and they're returning this, the products of the
nucleosynthesis in the stellar cores, returning it to the galaxy. Now what happens to that stuff, there's all of our metals. Well, here's a
typical nearby nebula, this is the Orion nebula. This is a very beautiful nebula about 1,000 light-years away. There's a few thousand stars
that are forming in this gas. And so what we're
seeing is baby stars, less than about a
million years old that are condensing
out of this gas. And the very most massive
ones have already turned on. They're already
burning their hydrogen. They're giving off a ton
of ultraviolet radiation and they're blowing
away the gas. Those high-mass stars are
actually destroying the nest that the stars are
forming out of. Well, if you zoom
in on that nebula, here's some Hubble
Space Telescope images. And this is amazing. What you're seeing is
baby pictures of suns. These are all little
stars forming. And you'll notice,
if you zoom in, they look like little blobs. And we know the
distance to Orion. And we can measure the angle
that covers these little blobs. And the size of these
blobs is only on the order of a few hundred times the
Earth-Sun distance, okay? So we're talking about solar
system scales, here okay? So these are so-called proplyds, or protoplanetary disks. And they're fascinating. You can see some of
these look very dark. What you're seeing is this
illuminated nebula behind it. And the gas and dust
that's forming in planets around these little stars
is actually blocking out the light behind it. There's hundreds of these. This is one star-formation
region in our galaxy. This is the Orion nebula. There's thousands of 'em, okay? This is going on right now. So, star-formation is going on, there's super-novi, we
see planetary nebula, we see evidence
of stellar death. So there's this sort of birth
and death of stars going on. And we see during stellar birth, we see the ingredients
for forming planets. Okay, so that's great. We've seen some disks
around baby stars, we know that there's
metals there, there's material
for forming planets including things you'll
find in your vitamins and in your food
that life likes. So, how do we discover
and characterize planets? Why are they so hard to find? Why did it take until
only a couple decades ago to find planets? Well, a few of the first
hints were actually teased out here in the 1980s. This is a satellite called IRAS that was launched in
1983 from Vandenberg. This satellite did an
infrared all-sky survey and it found a few surprises. So one of the things it found was that a handful
of the nearby stars actually had big
infrared excesses. These stars were giving
off way more infrared light than they should be, okay? So we know what the
distribution of energies are for stars and how much
light they should give out in the infrared. There was a certain class
of stars that was giving off way more infrared light. And it was actually a
group, here at JPL, in 1984 and at University of Arizona, there was this great paper
by Smith and Richard Terrell, Brad Smith and Richard Terrell. And they actually went
to a telescope in Chile. And they decided to look
at one of these stars with a coronagraph. They blotted out the
light from the star. And they took a
deep image of it. And lo and behold,
they saw this stuff on both sides of
the stars, okay? This is actually, this
is what was responsible for the infrared light, but
this is ground-up dust grains orbiting this star,
Beta Pictoris, which we now know is
pretty young as a star. It's about 20 or 25
million years old. And this was sort of, this
was one of our first hints that there was planets there. Because if you see this dust, it should get blown
out by the star's light in a very short time,
maybe hundreds of thousands to millions of years. So there had to be some
population of things grinding up asteroids, comets, et
cetera that were creating, that were kicking up this dust. So this ended up being actually
nearby a baby solar system, so things were starting
to get interesting. I remember seeing this story
when I was in elementary school and that really sort
of made it clear that we were kinda
getting to the point where we're gonna start
finding these planets soon. So how do we find planets, okay? Well, you think you could
just take an image, right? You take your telescope,
you look at the star. If you squint hard enough
you may see a little dim dot next to the star. This is really tricky, okay? There's a few complications. One is the planets
themselves are only, a planet like Jupiter, is only about one-billionth
as bright as its star, okay? This is in the reflected light. So that planet is, the
star is giving off light, the light's hitting that planet and then that light's
being redirected to us. And the ratios about
one in a billion. It's even fainter for
a planet like Earth. Well, this is very challenging. The other problem is
that plants tend to be, if they're on the same
scale as our solar system, if they're several
astronomical units, the stars are so far away
that the angular separation is very, very tiny. So the star is right
up against the, sorry, the planet is
right up against the star and so you actually need to, you need to do something
to the star's light. Because the other problem is, we're on Earth, we're at
the bottom of an atmosphere and that atmosphere plays
with the light, right? The stars twinkle. The stars are twinkling 'cause there's these little
variations in the temperature and the humidity of the
air and the light waves that are going through
the atmosphere wiggle around a little bit. And so the blur out
the star's light and they will completely
swamp the poor planet. So you can't just
go to the telescope, look through it and
say, oh, I see a planet next to the star. You actually have to blot
out the star's light, or there's a few other tricks
I'll show you later, okay? So this is so-called
direct imaging. One of the ways to find planets that's been very
popular for decades and still has, unfortunately, it still shows promise but
has not borne much fruit, I'll put it that way, is so-called astrometry. And that is looking for
the wobbles of a star due to a planet
tugging on it, okay? So the planet itself is pulling
gravitationally on the star. We think of the planets
orbiting the Sun and the Sun is at the
center of the solar system. That's not quite true. There's something
called the Barycenter. Jupiter is the big
source of gravity that's tugging on the
Sun and the Sun actually moves around the inner
solar system a little bit on the time scale similar
to Jupiter's orbit. It's pretty gradual. It's on the order of hundreds
of thousands of kilometers but it's something and if
you're far enough away, you can measure the position
of the star accurately enough, you should be able to
tease out that signal. But it's very tough,
so this is just showing how you could use
multiple stars. If you could accurately
measure the angle between the star with the
planet and these other stars, over time, you might be
able to see the little bumps and wiggles of the
star's position and tease out
the planet. This is the, one of
the first techniques that ended up being
very fruitful. This is so-called
Doppler Spectroscopy or the Radial velocity method. So what are we doing? So, you've got your
planet orbiting the star, it's tugging on the star,
the star is moving around. And as it's moving around,
its velocity is changing. It's moving towards you, it's
moving away from you, okay? So the light is being
Doppler-shifted. It'll be blue-shifted if
its moving away from you. It's red-shifted if its
moving away from us. Now the planet is not that
massive compared to the star. It's a very, very
subtle signal, okay? If we're talking about
Jupiter pulling on the Sun, we're talking about a a
12-meter-per-second signal over 12 years, okay. 12 meters per
second's about as fast as Usain Bolt goes
in ten seconds, okay? Very slow. If we're talking an
Earth-like planet, we're talking about ten
centimeters per second, which is how I would run
next to Usain Bolt, okay? Very, very slow signal, okay? So this is just sort
of generalizing. We don't see the colors
changing red and blue. When the things are moving
near the speed of light, you actually see a color shift. We see that with quasars. But this is a very
subtle signal. You're looking at the
spectrum of the star and the lines are
moving back and forth, very, very tiny amounts. So this is the so-called
Doppler spectrocity technique and there's been many
hundreds of planets found through this technique. The technique that's
been very fruitful for the last decade and a half is the so-called
transit method, okay? This is what happens
when a planet passes in front of its star. Now the trick is,
you need to measure how bright the star is
very accurately, okay? So here's time, here's
how bright the star is. If we got a star like the Sun, over time it only varies
at about the one part in a thousand level
over a long time, you might see some star-spots
appear here and there that make some little dips. But if you have a
Jupiter-sized planet pass in front of the Sun, you'd
get a dip of about 1%. Okay, now we're talkin'. We can measure 1% dip for a
lot of the brightest stars. If you get a planet like Earth, which is another factor
of 10 smaller than Jupiter and its area is another
factor of 100 smaller, we're looking for a signal
that's one part in 10,000. Hm, okay, that's getting tough. It's very difficult
to do from the ground. It's difficult to measure
the brightnesses of the stars that accurately from the ground but if you go to space, voila. Now we're talking about
discovering Earth-like planets. So I'll talk about the
Kepler Mission here in a bit. The Kepler Mission
has been responsible for finding most of the planets that have been discovered now. We're talking
thousands of planets. So this is a great technique. This is just another
movie showing differences in the sizes. So if you had large planet, let's say a
Jupiter-sized planet, and an Earth-sized planet,
you'll get different depths in the light curve, okay? So get roughly 1% signals
for a Jupiter-like planet and about a one part
in 10,000 signal for an Earth-like planet. Now, the other thing,
Kepler has been finding is multiple
planet-systems, okay? There's actually been
systems seen now, we have a great vantage point, we happened to see
multiple planets passing in front of the star. And if you're really
lucky, you start to see gravitational
perturbations. The planets are
pulling on each other. And we can actually
measure those masses. I'll show a plot later
in this talk exploiting that technique to
measure some masses. So Kepler has found
some very interesting multi-planet systems. And there's, these have
been very interesting because it's easier to get
the masses of those planets. This is another technique
called microlensing. This has been put to good use over about the last
decade and it's now gonna be a primary means
of finding planets for, one of the means
of finding planets for the upcoming WFIRST mission. So, you have your
telescope down here and let's say you have
a background star, but something passes
in front of it, let's say some mass, let's
say a star or a planet. As it passes in front, the
space-time is curved, okay? Light is not following
straight lines. You think a light beam is
gonna follow a straight line. The light is following
a straight line in four dimensions, oh, God, here we go,
we're going into Einstein. What, from our perspective
are three-dimensional beams passing through time,
from our perspective, that straight line looks curved. And the mass actually
acts like a lens. You'll actually get
the light from the star bend around around
that mass and focus. And what you get is
an enhancement in the amount
of light. So this is time and then this
is the brightness of the star. So you'll get these
characteristic curves and if this thing
that's passing in front has a planet, you get
an extra little curve on top of it, okay? So may get this curve and then
you get another little one. And this technique so
far has been sensitive to very small planets. We're talking things down
well below the size of Earth. Now, the trick is, this
doesn't happen all the time. You need these two
stars to line up. So you need to look at
many, many, many thousands of stars or millions of stars. And so WFIRST is
gonna be surveying the center of our galaxy. I showed you that
picture at the beginning, of our, the center
of our galaxy. Some of the richest star
fields in the galaxy, and then if you start
looking at a lot of these, statistically, you'll start
picking these events up. So, I showed you that
there was the detection of that dust around
Beta Pictorus in 1983. With the IRAS satellite,
things started to get interesting around 1989. This is the star HD 114762. These are our lovely
stellar designations, okay? Stellar designations are
the phone-number names. This was a giant planet,
orbiting in about 80 days, roughly at about the
same distance Mercury is from its star, but this planet's about 11 times
bigger than Jupiter. We don't know the
inclination of this system, we don't know how tilted it is because it didn't pass
in front of its star. But around 1989, this
star was being used as a standard. When they were measuring the
velocities of other stars they kept coming back to
this one as a useful ruler of how fast a star was moving. And they noticed that this,
this standard star itself was moving at the hundreds-of-meters-a-second
level. So there was this
nice paper Dave Latham from Harvard Smithsonian
Center for Astrophysics. And they said, "Well, this
could be a failed star, "it could be a planet." And back in these days,
it was a little voodoo to start saying you
detected a planet. But as we look back now, this
could be the first planet that was actually
detected, this one is real. Things got really
interesting around 1992. This was 25 years
ago, this week. Hard to believe. January, 1992, there
was the discovery of three planets
around a pulsar. So what's a pulsar? This is the remnant
of a massive star that's undergone a supernova and all that's left
is this huge mass about the mass of
our Sun, but packed into about 10 kilometers, okay? So, roughly the
size of Pasadena, but with as much mass
as our Sun, okay? It would not be a very
nice place to live, okay? The whole thing is
made of neutrons, okay? There's so much pressure there the protons and
electrons themselves have actually fused
into neutrons. So it's essentially
a gigantic nucleus. Well, it has a
huge magnetic field and it spins rapidly and it
gives off these radio waves. And those radio waves
can be picked up by astronomers on Earth. And lo and behold, this
new pulsar called B1257+12, also known as Lich, now,
it has a new IU name. This object was
moving back and forth. The timing of the radio
signals was changing and it was fairly complex
because lo and behold, was three bodies pulling on it. So, these two outer ones,
and I can't remember the original letter. There's letter designations
B, C, D for these. I like the, there's
the new IU names, these are easier
to remember now. Poltergeist and
Draugr, these two are about three times the
mass of the Earth. Phobetor is very small. It's on the order of the
size of Mercury or such. And these were
very tiny planets. There was no other effect
they could think of that could
replicate this variation in
the pulsar's signals. So this was really the
first rock-solid evidence I would say of
extrasolar planets. And again, that was 25
years ago this week. Around 1995, things
got interesting again. This was the
discovery of 51 Peg b. This was a Hot Jupiter. This was a very
unexpected signal. 51 Peg is very sun-like star. It's a yellow, main-sequence
star like the Sun. Sort of middle-aged
and lo and behold, the star was moving
back and forth at about the
100-meter-per-second level in its orbit. And what you need to do,
what you need to explain that is a half-Jupiter-mass planet
on a four-day period, okay? Nobody was expecting
this before 1995 because as you saw
from our solar system, we had an example
of one solar system. We don't have any giant
planets within a few astronomical units of the Sun. They're, you need
ices to form those. So, why would you have
a giant plant so close? But it was there and it
was quickly confirmed by another group in California. So, right away we
were starting to see some very strange objects, okay? The first one I showed
you was 10 Jupiter masses. This was really
pushing the boundaries of what you might
consider a planet. The second example was
planets around a dead star, pulsar planets. And then the next
example was a Jupiter orbiting its star in a few days. Okay, we're nowhere
near finding anything like our solar
system yet, by 1995. I'm gonna skip a lot of history, which is gonna make a lot of
exoplanet astronomers mad. I'll apologize if I've
left out your planets. There's a few
thousand of them now and all your missions
and all your telescopes. So, we're gonna skip
through to what I think is a few interesting
cases, here. And just to show you some
interesting examples. So, the Kepler Mission
launched in 2009. I'll show you a few
plots from that mission. And one of the surprises was
a circumbinary planet, okay? Could a planet
actually form out here, outside the orbits of its stars? And the answer seems to be yes. And they're finding
many examples of these. And they're roughly, they
tend to be on the order of a factor of five further away that the separations
between the two stars. As we look at young stars,
we do see examples of pairs of young stars that actually
have a disk of material orbiting both. We see circumbinary
disks of gas and dust that probably formed
these planets. So, I'll be the first
astronomer whose given one of these talks that
does not mention a certain movie about
a certain person that was bulls-eyeing womp
rats on their desert planet that had two stars. I'm not gonna mention it. Kepler also found,
has found so far, small, rocky planets
in the habitable zones of their stars. So what do we mean
by habitable zone? You can start many an
argument defining exactly what the habitable zone means. It's the range of
orbital separations orbiting a star where you could
plausibly have liquid water on the surface of the planet. Liquid water seems to be the
main environmental constraint for life, at least
on our planet. You need water. And so, if you move
a planet too close, if you took Earth and
you moved it a bit closer to the Sun, you initiate a
runaway greenhouse effect. You'd actually boil
off the oceans. If you moved the
Earth too far away, the Earth starts
to get very cold, you actually start
freezing out carbon dioxide up in the atmosphere and
you start forming clouds that act like a big mirror
and you get a runaway which actually makes
the planet colder. So there's sort
of a narrow range of orbital separations
where a planet can have liquid water. And so this is just
a little gallery of the planets so far,
out of the 2,000 plus that Kepler has found
that happen to be in the habitable
zones of their stars. These are the different
types of stars. M stars, these are the
so-called red dwarfs. These are the most common
types of stars in the galaxy. About 3/4 of the stars in
the galaxy are M dwarfs, including the next star after
the Sun, Proxima Centauri. K stars are a
little bit smaller, typically about half
the mass of the Sun. And then these are the G
stars like our Sun, okay? So we have been finding a lot
of these habitable planets around the M stars and K stars. It's been a little bit
tougher for the G stars because you have to trace
the planets further out, to periods closer to a year and Kepler had a
limited lifetime for detecting planets
passing in front of a star. So this is not indicating
that there's fewer planets around the G stars, simply
that our current techniques are more sensitive to
the very close-in planets around these lower-mass stars. This was one of my favorites. This was in one of the first
directly-imaged planets called Fomalhaut b. This is a bright
nearby southern star. It's Alpha Piscis Austrini
in the southern fish. This is the brightest star
in that constellation. It has a big disk of
material around it. I was telling you
about the IRAS Mission in the early '80s. This is one of the first big
infrared excesses detected with that satellite. There's a lot of
dust in that system. And back in 2009, Paul
Kalas and colleagues were looking at
images of Fomalhaut with a coronagraph in place. So they're blotting out
the bright star, here. Fomalhaut's, you know, probably in the top 10 or 20
brightest stars in the sky. They had to blot out
the light with Hubble and see all the faint structure. And lo and behold, there
was a little dot moving. And this appears to be a
planet orbiting the star. What's weird about this thing is that the colors of it
look like reflected light from the star. So what we may be seeing
here is not a Jupiter, or maybe even not
even a Neptune, we may be seeing reflected light from icy particles,
something like Saturn's rings or a cloud of material
orbiting the star. So the nature of this object's
a little bit nebulous, but it's been very interesting. But we could be
seeing a tiny planet with a ring system around it. So speaking of rings,
I wanted to tell you about one of projects
I've worked on recently. This is a object, I won't give
you the full phone number, 'cause it's horrible. This one has one of those
horrible astronomical names with about 15 digits in it. We shortened it to J-1407. This was a nearby young star, a few hundred light-years away. It's similar to the
Sun, but it's only about 15 million years
old, very young star. And we were looking through data from a robotic telescope
that was monitoring the brightnesses of thousands
of stars looking for planets. And when we were looking
through the data, one of the young stars
that we were studying, back on 2007, so this is time, this is April and May of 2007, and this is the brightness
of the star, okay? One is its average brightness
over a few-year period. And the star rotates really
rapidly every three days and it has star-spots and
so in the course of a day it'll go do-do-do-do-do-do,
you know, it'll vary by about
two or three percent. And then all of a
sudden in April and May, over about 2007, the star started behaving
very badly, okay? We started seeing dimming at the tens of
percent level, okay? That should scream
that there's something very interesting going on. You just don't see
stars turn off, okay? At its dimmest point, the
star had dimmed 95%, okay? This really got our attention. The shape of the variations
was even more interesting because it looked like
you had to be passing some structure in
front of the star that it might be symmetric. So we first saw this
in December 2010 at University of Rochester. My graduate student,
Mark Picho and I, I remember in December
2010, looking at this plot, trying to figure out what
the heck to make of it. And the first thing
that came to mind was how the rings of
Uranus were discovered. So Uranus has these very
faint rings around it. The Kuiper Airborne
Observatory was used in 1977 to observe Uranus and Uranus
passed in front of a star and the star blinked off. And they detected
the rings of Uranus. And I thought, could
this be like that? But these rings would have
to be absolutely huge, very massive. The bottom is just a zoom-in
of some of the structure. Each little clump of points
here is one night of data, okay? This is a real telescope,
a real robotic telescope from the ground, so you
have to worry about things like clouds and power-outages
and things that. And so there's lots of
gaps in the data, okay? We only have data covering
about 20% of the time here. But even during after the
gaps, you'll see the star has still dimmed tens
of percent, okay? So we tried to piece together
the story of this star. And you'll notice by the
way, if you look at it, there's sort of this big
inner dip over a couple weeks and then you see these
little dips on the side. And even in the course of
a night, the variation, it can vary by tens of percent. This is a really bizarre object. It took us about a
year to analyze this and come out with a
paper that even had a plausible first attempt at
what we thought this thing was. This is not that first attempt, this is about our
third attempt, okay? This is a movie from about 2015. This is the time, this is
the brightness of the star. The orange line
is a model trying to fit those yellow data points. The yellow data are
the actual measurements of the star's brightness. It's not perfect, okay? It does a reasonable job. It probably fits
about 90% of the data. And at top, this is our
model of a huge ring system around a companion we call
J-1407 little b, okay? We're not sure
exactly what this is. It's probably a giant planet. It could be a failed star
called a brown dwarf. I'll talk a little
bit about those later. Right now, we
think it's probably less than tens of times
the mass of Jupiter. The whole system, this
whole system of rings you could fit well inside
the orbit of Mercury, okay? But it's much bigger than
Saturn's rings, okay? The whole system is
about 200 times bigger than Saturn's rings. This is a totally
different beast. This is not like
Saturn's systems. Saturn has a ring system, covers a few hundred
thousand kilometers, very icy particles and
they exist in a region where the tidal forces of Saturn would shred the material
apart in case it tried to form a moon. It'll say, no big
moons here, okay? Gravity will tear
these objects apart. This system's about
200 times larger. And so what we think
we might be seeing is the material that would go into forming a system of
moons around a giant planet or little planets
around a brown dwarf. I don't even know what,
there's no word yet for, I guess satellite. You would say a satellite
around a brown dwarf. The other interesting
thing is we see these gaps. We've seen disks before. We see disks around young stars. They can be huge, tens of
times the Earth-Sun distance. We don't see too much
structure in them. There's a lot of
structure in this. To explain these dips,
these big variations at the tens-of-percent level, there has to be
gaps in the disk. Well, if there's gaps,
why is there dust preferentially in some lanes
and not in other lanes, okay? So, especially this one,
this one really stood out. We put ring-gap. We could be seeing
moon formation. This could be the
first indirect evidence of exo-moons
orbiting exoplanets, orbiting other stars. We haven't seen any moons, yet. All we've got is this disk. But something has
gotta be clearing out these lanes in this disk. We've gone looking for
more objects like this. We keep finding, we've
found a few disks. We have a system that'll
be coming out next year that is somewhat analogous,
but we haven't found one whose structure is as
rich as this system. By the way, so my
co-author, Matt Kenworthy at University of Leiden had this cheeky graphic
he came up with. If you replaced
Saturn in our system with this set of rings, this
is what it would look like during the day. It would be picking off
about 1% of the stars' light. It would be like a huge mirror. There is the moon. So how'd you like to
come out during the day and see that thing? It was a slow news
day in January 2015. 2015 was such a nice
year, compared to 2016. And so for a few hours on CNN, this was not fake news,
this was real news. This beautiful graphic
was done by Ron Miller at Black Cat Studios. He's done a lot of space art. And I wanted to mention that. But he had this beautiful
artwork that went with it. I'm doing an experiment
with a student at University of Rochester to
build a robotic observatory. He's building it, I'm here. Hi, Sam. (audience chuckling) We're hoping to
build this experiment to put in Australia in 2017, and we wanna watch
a nearby exoplanet called Beta Pictoris b. I showed you that disk system. There's a little planet
they discovered in 2009. And this is a movie of
the images of that planet over the last, over
about 2013 to 2015. And as you see, it's
gonna come very close to its star in 2017. It's not gonna pass
exactly in front of it, but it's gonna
come pretty close. So we wanna probe the
region near the planet to see if there's any evidence
of a moon-forming disk like J-1407. This system's only a little
bit older than J-1407. We're talkin' about
20 million years. So we could be, if we're lucky, we may catch a
snapshot of a disk passing in front of
a star and maybe see if we can catch
moon-formation in action. So I now work at
JPL, I'm now working with the NASA Exoplanet
Exploration Program. Its purpose is described in
the 2014 NASA Science Plan. We are here to discover
planets around other stars, characterize their properties,
identify candidates that could harbor life. So we're supporting
various space missions and some ground-based
efforts too, at achieving discovering
planets and characterizing them. This is just a little snapshot
of some of the activities that the Exoplanet
Exploration Program does. A few of the missions
here that're managed are the Kepler and
now K2 Mission. Kepler is the the
mission that's finding all these transiting planets. It has transitioned now, a
couple of the gyros are dead. They're in a phase now
where they can only observe certain parts of the sky
and they now call this the K2 Mission, but
it's still finding many dozens of planets. This is the WFIRST Mission
I'll talk a little bit about here in a few minutes. There's development
of a starshade. I'll show you the
animation of the starshade. And then there's lots
of other activities, including some efforts
to characterize disks around nearby stars and measure their radial velocities in
support of these missions. Let me click on this. And fortunately,
the sound is off. I wanna thank Dan Fabrycky
at University of Chicago. This is the classic
Kepler Orrery. These are the multi-planet
systems that Kepler found. Every one of these
is a solar system. And this is only showing
the planets that we can see, that happen to be along
the line-of-sight, okay? They're sorted by size,
so you get some things that are probably
Jupiter-sized, here, all the way down to
very tiny things, approaching maybe half
the size of the Earth. Some of these are three-,
four-, five-planet systems and there's a lot of these. And we can now start
to measure masses because these planets are
tugging on each other. I think it was
supposed to zoom in. There we go. And they're sorted by the
size of the orbits, okay? But it's amazing. And these are very
close-in systems, so pretty much none of these
are like our solar system. These are the systems
that have planets very, very close to their star. Most of these planets
are closer to the star than Mercury and Venus. Okay, so that's dizzying, turn away if it's
hurting your eyes. (audience chuckling) So the Kepler Mission
was launched in 2009. This has been a
phenomenally-successful mission. And again, it's in this
so-called K2 phase now, where it's using a
limited amount of fuel to look at different
fields along the ecliptic, along the path where the Earth, in the Earth's orbital plane. And also, very soon,
the TESS Mission being developed at Goddard
Space Flight Center. It's gonna be similar to
Kepler, but it's gonna look, it's going to image
the whole sky. Kepler basically looked
at one region of the sky and stared at 100,000 stars and discovered about
5,000 candidates and we have about 2,000 of those
that are confirmed planets. So from the Kepler
and K2 Mission, this is showing the
sizes of the planets that have been discovered
along with the temperature of the host star. Our Sun is around
5800 Kelvin, here. So these are the yellow stars,
these are the orange stars, these are the red stars. We're starting to find
a lot of planets now that are similar in
size to the Earth, okay? So the Earth's size
is a one on here, Uranus and Neptune are
around a four on here. And you'll notice a lot of
these things are intermediate in size between the Earth
and Uranus and Neptune. This is one of the interesting
results from Kepler, is most of the
planets we're finding, there's no counterpart
in our solar system. There's planets
intermediate in size between Earth and Venus
and Uranus and Neptune and they seem to be
very, very common. This was a plot form 2015
showing the distribution of planets. These are the big
Jupiter-like planets. Here's the Neptune-sized
planets, two to six Earth radii. These are so-called
super-Earths, 1.25 to two Earth radii. These definitions you'll see
vary a little bit over time. And these are Earth-size
and smaller, okay? Now this could be
a little bit biased because these smaller planets
are harder to pick out. They cover a smaller area. If you de-bias this plot,
if you take into account that it's harder to find
the smaller planets, you start to get a
distribution like this. And we still have this excess. There's lots of little
so-called mini-Neptunes and super-Earths, for
lack of better terms here. And we're seeing a
lot of Earths, also, compared to the number
of these gas giants and things intermediate
between the size of Neptune and Jupiter. Coincidentally, the
hypothesized Planet 9 you may have heard about
that they're looking for, the dynamical
estimates, if it's real are something on the order
of five to 10 Earth-masses. And so that would actually
be intermediate in size between Earth and Neptune. So if there is a Planet
9, it could be part of this class of planets
that so far we have not seen up close in our solar system. But they're very, very
common around nearby stars. This was a recent plot
that was put together on showing the masses and
the radii of these exoplanets and I've plotted Earth on here. One Earth-mass,
one Earth-radius. Here's Neptune, 17
Earth-masses, four Earth-radii. And here's a lot of these
things that are intermediate between the Earth and Neptune. We're seeing a lot of the
so-called super-Earths and mini-Neptunes. These are gas giants
up here, okay? So Jupiter, if you
could plot on here, Jupiter is about
300 Earth-masses and about 10 or 11 Earth-radii. So Jupiter's up
here, Neptune, Earth. So we're finding a lot of these
things that're intermediate. These lines are showing, what if you made a
planet out of pure iron? Okay, astrophysically, we
don't think that's gonna exist, at least far out. Maybe close in we might
get things similar to that. Things that are
dominated by rock. Things that are
dominated by ice. And when we mean ice, we
mean the astrophysical ices, things like water,
ammonia and methane. And if you get bigger
than this line, you have to start adding
hydrogen and helium, okay? So Uranus and Neptune are
good examples of that. Uranus and Neptune have
sort of a sprinkling of hydrogen and helium,
but they're probably mostly dominated
by ice and rock. Earth has a big iron-nickel core and a big silicate
mantle and crust and just a little
thin veneer of water that covers most of the planet. But we're finding a
lot of these things intermediate in size. And you'll notice,
you start running out of the rocky planets
once you get up to about 10 Earth-radii. They all start
getting big, okay? And for the big fluffy planets, you start losing these
big, large-radii planets right around two Earth-radii. These things could be
considered gas dwarfs. There're things not that
much bigger than Earth that are dominated by gas. But you may also get things
about 10 times the mass of the Earth that are
mostly rock, okay? So this intermediate
region's very interesting. We're seeing a huge
variety of the densities of these planets and
that's gonna translate into a huge variety
in their compositions. This is the WFIRST Mission. This is a project
being formulated now. There's work on
developing a coronagraph for this instrument, here. The coronagraph is the
instrument for blotting out the lights of stars. This was a very
interesting mission concept that the so-called 2010
Astronomical Decadal Survey came up with. The astronomical
community comes together about every decade and comes up with recommendations
on missions. And this was a very
interesting case because it can study
extrasolar planets, dark energy and dark matter. So it satisfies the
people that study galaxies and cosmology and it studies
the people that study planets. And it's actually formulated
to work on planets in two different regimes. It's gonna have a coronagraph
for blotting out the light of nearby stars and
it's also gonna image near the galactic
center and look at many thousands and
thousands of stars to look for
microlensing candidates. In case a star with a
planet passes in front, it'll see an enhancement
in brightness. So what that
project is gonna do, this is showing the
orbital separation, semimajor axis in
astronomical units, so the Earth is one,
here's the Earth. And this is the planet
mass and Earth-masses. Now Kepler, Kepler in
this shaded region, these are the planets that
pass in front of the stars. So you're very
sensitive to the planets that are very close to the star but you tend not
to find the ones that are further away,
just 'cause geometrically, it's much more rare to see
the distant planets line up. So WFIRST is gonna help us
sample the outer region. This is the realm of the
Jupiter-, Saturn-, Uranus- and Neptune-type planets. And even things down to
Earth-size and smaller. So we're gonna get a statistical
survey of this region, this sort of
one-to-10 astronomical-unit region using WFIRST. This is an interesting
plot and I apologize, 'cause I, this one's
gonna get a little messy but this is showing
the distribution of masses of objects. We've got stars over here. And this is their density,
how many per cubic parsec. Parsecs are astronomer's ruler, it's about three and
a quarter light-years. So it's basically the number
of stars per density, okay? So, this is one solar mass. There's the Sun. And this is not fitting
all the data we have but the distribution of stars, it increases as you
get to lower masses and then it decreases. And recently, we've
been finding things floating around in space
that are very low-mass. This is 10 to the
minus three Sun-masses. That is roughly a Jupiter, okay? So things the size
of our Sun are here. Things the size of
Jupiter are here. Okay, so here's the stars. Okay, we've been studying
stars for a long time. This is the mass
function of the stars. It peaks around a couple
tenths of a solar-mass. We tons of these
little dim red dwarfs in the solar neighborhood. The mechanism for forming stars, for collapsing gas in
the inner-stellar medium seems to prefer
forming red dwarfs. Our Sun is actually
kind of a massive star, it's at one solar-mass. And you tend not to
see things bigger than about 150 times
the mass of the Sun. Those are very, very
massive short-lived stars. As you go below about a
tenth of the solar-mass, you get so-called
brown dwarfs, okay? There's a limit below which
the hydrogen in the core can't fuse, the
temperatures are too low. And these things
aren't really stars. They're kinda the
failed stars, okay? So the last 20 years,
we've been finding more and more of these failed stars but there's been
a surprise, okay? So this is from about a
tenth of the solar-mass down to about a hundredth
of a solar-mass. This is about 10 Jupiters. Recently, we've been starting to see very, very low-mass
things in the field. And now we're starting to put some estimates on their density. By the way, I'm sorry, there's
the hydrogen burn limit. Now, when I squint,
this is a paper that just came out by Jonathan
Gagné I'm co-author on. If I squint and I look at this, you could just about
fit a line through here. I wouldn't place any bets on it. The line I've picked is
actually the mass function for planets orbiting
stars, okay? It goes roughly as the mass
to the minus one power. You have many fewer
massive planets than you do low-mass planets. If you fit that
function through here, these could be planets
that are floating in space that are not orbiting a star. These could be the
so-called rogue planets. And I think I'm
starting to see data from a few different
surveys now that I think there's a convincing
case to made, that there's a
separate population. These things fundamentally
formed different from stars. The physics of gas and dust
on the scales of light-years, and gravity winning
out over gas-pressure and magnetic-field
pressure, that forms stars and the brown dwarf
population, okay? But below that,
there seems to be this whole different population. And these could be planets
that have been stripped from their stars and
just roaming in space. So we keep talkin' about,
you know, Alpha Centauri as the nearest
destination in space. We could very well find
things that are on the order of the sizes of Jupiters or
Saturns or Neptunes floating. There could be many more
targets, just not stars, between us and Alpha Centauri and these would be dimly
glowing in the infrared. So there's our rogue planet. The James Webb Space Telescope is gonna be launching in 2019. This is gonna be the successor to the Hubble Space Telescope. It's gonna be studying
planets that pass in front of their stars. Some of the missions like
Kepler and TESS and K2 are feeding targets
into the plans for JWST. What we want is
nearby bright stars that have planets
passing in front of them and we can measure the
spectra of those planets. And so there'll be
some interesting extrasolar planetary
science coming out of JWST. But beyond JWST, what
we really wanna see is the small pale dots, the
pale blue dots next to stars. And so this is one of the
concepts that's being worked on. And in fact, here at JPL, there's a so-called
starshade, okay? The idea of a starshade
is you launch a telescope and then you launce a
separate spacecraft, okay? And the model they have is
about 34 meters in size, pretty big. But you can wrap it
up inside of a rocket and let it unfurl in space. And this starshade, you
would put between what star you wanted to look at
and your telescope. And so the starshade would
essentially form a little shadow and you have to keep your
spacecraft in that shadow and then look for the
dim little planets whose light is not passing
through the starshade, okay? Lots of technical challenges, but there's a path ahead and
there's currently proposals now to construct the starshade. And there's actually a demo in one of the
buildings here at JPL. So this is what it
would look like. This is an earlier concept
where the starshade would actually launch
with a telescope. One of the proposals
on the table now that's being considered is you
launch the WFIRST spacecraft in the mid-2020s and
then a few years later, you would launch a
separate starshade mission and the starshade would
move about 80,000 kilometers away from the spacecraft. Right here, they show like
they're close together. They won't be close together. And the starshade
has its own fuel. And so it would sort of
park in front of a star, WFIRST would look at it or
whatever future mission comes up and you would study the
planets, the faint planets. And basically if you
wanna get down to things that are about
the size of Earth, this is really the next
step you have to take. Right now, we're not, this
is gonna be a ways ahead of the 2020s. I'll show a few slides
on Proxima Centauri b, 'cause you've probably heard
about this in the media. So Proxima Centauri's the
nearest star to the Sun. It's about four
light-years away. And it was a great discovery,
middle of last year. And this was a
ground-based discovery. There were some
astronomers in Europe that used a ground-based
telescope with a spectrograph. And they were
measuring the motions of Proxima Centauri
very closely. And what they decided to
do was observe it night after night, after night,
after night, after night for months, okay? They took a lot of
telescope time to do this. It was worth it, okay? So what they found on the
velocity signal of the star was this little 11-day ripple at the
one-meter-per-second level. Okay, this is one
meter per second. Actually, I'm not allowed
to walk over the rug here. One meter per second. This is an Earth-sized
planet tugging on a little star about a
tenth of the size of our Sun. So, this is the art
for Proxima Centauri b. This is Proxima Centauri,
the little faint star. It's actually a triple system. Our nearest stellar
neighbor is a triple, okay? Our Sun is a little bit of
an oddball as a single star. Lots of stars come in doubles,
triples, quadruples and up. So the art here
actually shows this. There's two sun-like
stars very far away, about 10,000 astronomical
units away from the star. And then here's the
little red-dwarf star of Proxima Centauri. So these are the designations, Alpha Centauri A, B and C and then the so-called proper
names, Rigel Kentaurus. This was the foot
of the centaur, Proxima Centauri
was the nickname for the dim red dwarf
discovered about 100 years ago. This is just showing a
comparison of the size of those stars
compared to the Sun. Alpha Centauri A is a little
bit bigger than the Sun. Alpha Centauri B is a little
bit smaller than the Sun. Proxima Centauri's about a
tenth the size of the Sun. And there could be planets around Alpha Centauri
A and B, too. There was a purported
planet a few years ago around Alpha Centauri B,
so far that seems to have not been confirmed. But so far Proxima
Centauri b looks good. This was showing a
comparison of the Sun and Mercury's orbit. Okay, our innermost
planet along with, on this side, Proxima
Centauri, dim little red dwarf. If you can see, its
luminosity's very tiny. It's about .0015
times the energy that the Sun is putting out. This is the habitable
zone for Proxima Centauri and lo and behold,
Proxima Centauri b, it orbits its star in 11 days, but this star is so dim
that if you wanna look for a place that
has liquid water, you have to move this
close to the star, okay? You're campin' real
close to the fire to keep that water liquid. Now we don't know, this planet
is probably a rocky planet based on its mass. We don't have an
estimate of the radii, we don't have an
estimate of the, we haven't seen the
atmosphere or anything yet. So right now, there's a
bit of speculation on that. By the way, eventually,
these planets'll need names. Eventually your kids and
your grandkids and beyond, some of these objects are
gonna be so interesting that they may have
their own proper names. You think of the planets
in our own solar system. So this is the first attempt the International
Astronomical Union did. Last year, there was a contest
opened up to the public called the Name
Exoworlds Contest. And so there was a few
dozen of these exoplanets were actually named and you
saw a few of those in the talk. And so some of these are like, there's a very
nice example here. The mu Aire system is
known as Cervantes, Quijote, Dulcinea,
Rocinante, Sancho. So some of them have
interesting themes based on characters from books. The contest was, there was
entries from all over the world. You had to be in an astronomical
organization to apply, so, but there was classrooms
and amateur astronomy clubs that contributed. And so there was a
lot of great entries and so these are the
ones that won out. There was 600,000 votes from
all over the world for these. So this was the first
attempt of the IAU at this but I suspect we'll be doing
more of this in the future. I just wanted to
look back at Earth. There's this great
picture the Voyagers took, Voyager 1 took in 1991. This was the Earth
as seen from tens of astronomical units
away from the Sun. Oops. Oh, it didn't show
the other one. Okay, I have another one,
there was a picture that was just taken this
week from Mars. From one of the Mars orbiters. It shows the Earth and the
Moon as seen from Mars. But at the end of the day, we'd like to also understand
the Earth in the context of the other planets. We only have one Earth, we
can't run the experiment of forming the Earth
and we probably shouldn't be tweaking too much with the chemistry of the
atmosphere and the oceans. Just a suggestion. I like the Earth the way it is. But we get to see all
the different examples of how physics and
chemistry comes together to form other planets. So this is sort of
a, it's January, this is the state of
the galaxy report. This is, I'm gonna
give you a few results. These are basically
extrapolating from what we know now, okay? We don't have a complete
census of all these objects. This is just from what
we've been able to gather from some of these systems. First off, exoplanets
are ubiquitous, okay? Nearly every star you see in
the night sky has planets. This is amazing, okay? This is one of
the terms that was in the so-called Drake equation. How common are planets? We now know planets
are very, very common. Sun-like planets, sorry,
Sun-like stars typically have five or more planets. There could be even more. This is only down to the size
of about half an Earth, okay? So most of those stars
not only have planets, they probably have
several planets. The super-Earths
and mini-Neptunes, these things sort
of intermediate between the size of
the Earth and Neptune, they seem to be more common
than the rocky planets. They especially
seem to be common around the very
lowest-mass stars. That may be a hint
why the aliens haven't got here, yet, alright? The planets, if there's
a lot of these planets that have these big
gaseous envelopes, they may not be conducive
for forming life. But anyway, so those
intermediate-sized planets seem to be very common. Planets form over a wide
range of stellar properties. It seems like everywhere we go in parameter space is a
function of stellar mass, luminosity, age. We see planets around
very youngest stars. The oldest planetary
system we've seen so far is 11 billion years old, okay? The universe is 13
billion years old. This is one of the, we've seen a system with
a full set of planets that formed less than 2 billion
years after the Big Bang. We see the planets as a variety, varying by chemical composition around the very metal-rich stars and around the very
metal-poor stars. We're starting to see some
trends like the planets that, the stars that have more metals
seem to form more Jupiters. So that might be telling us
something about the conditions for forming planets. And also the
multiplicity of the star. We see planets around
one-star systems, two-star systems,
triples quadruples, so the planets are
very resilient. The incidents of the exo-Earths. This is still being worked on. If we called the so-called
exo-Earths rocky planets, rock-dominated planets
between about half the size of the Earth and 1.5 times
the size of the Earth. I picked that
upper limit because if you
go bigger than that it looks like the
planets start to get very thick
gaseous envelopes and they become less Earth-like. If you go much below
about Earth-mass in size, you start to have, the lower gravity starts to, you start to lose atmosphere. It would turn into
something more like Mars. So, we're sort of
looking at things within about half the
size of the Earth in size and orbiting in their
habitable zones. So how many are there? This is still being debated. There's still, people
are still taking the data and trying to
statistically combine it. And the answers
are coming up over, there's a bit of a range, here, by about a factor of 10 or so. But the answer's probably
something like a half, okay? There's probably about half
a planet per Sun-like star where you've got a rocky planet. That's not to say that's the
incidence of planets with life. There's a lot of things that can go wrong with those planets. They may have the right size,
they may be in the right place but there may be
other conditions that preclude life on them. I wanted to show this plot
I had made several years ago and I just updated it last Fall. This is kinda the
Moore's Law for planets. This is showing the
year going back to 1989 and this is the number of
planets but its logarithmic. It goes one, 10, 100, 1,000. And the remarkable thing is
over the last three decades, this doubling time
hasn't varied that much. About every 27 months the
number of exoplanets doubles. And actually if you
look at the missions that are coming
ahead, we'll probably be discovering tens of
thousands of planets with those missions
and this trend looks like it'll continue at least
well through the 2020s. So there is a characteristic
doubling time scale. The interesting thing is
once you start finding these, now you're gonna
start finding planets that are more and
more similar to Earth. You're starting to find
things that are within a small parameter-range of
the characteristics of Earth. And hopefully, we'll be able
to get the spectra of those. So, I'm gonna put this slide up, these are a few links to
the Exoplanets Program: exoplanets.nasa.gov. We have the NASA
Exoplanet Archive down at the Caltech campus at the
so-called MechSci Institute. This is a shout-out to the
Kepler and K2 Exoplanet Mission. They have a lot of great
graphics from that mission. And I'm gonna show
a little example for a minute or two here of
the so-called NASA Eyes app. This is an app you can
download that lets you fly around the galaxy and
visit the exoplanets. So, I'm going to switch
the screen to Eyes on, whoops, Eyes on Exoplanets. And I have to move my computer
without destroying it. And now, we're gonna
fly around the galaxy. So this is, this is
the NASA's Eyes app. And you can rotate
around the galaxy. So these highlighted
stars all have exoplanets. The Sun is at the center
of this distribution. And you see this big plume
of objects our there. That's the Kepler field. The Kepler Mission stared
at 100 square degrees of sky for a few years and discovered
thousands of planets in one direction. So all those results I
showed you from that mission, it was just from that
tiny patch of sky in the constellations
Cygnus and Lyra, okay? The TESS Mission is
gonna map the whole sky and there'll be
thousands more exoplanets to be found. And I wanted to show this
has a little animation. This'll fly us to
Proxima Centauri in the nearest
exoplanetary system. So if you look hard enough,
you'll see the Sun flying by. We're zooming in to
Proxima Centauri, the star, and then this is
the little planet that was discovered in 2016. And we can, you can sort
of change the orientation. It tells you about the planet, tells you the mass of the star, how many planets
are in this system. And you can get
information about these. And so there's a nice app here, you can go visit the
planetary systems. And with that, I'll thank
you very much for your time and I'll open up to questions. (audience applauding) So there's a microphone
in the center of the room. So I ask if you, if
you ask a question please use the microphone. - Can I go?
- Yep. - Hi, great
presentation, thank you. I had a question
about Hot Jupiters. I was wondering
how it's possible that they form around
Sun-like planets. - That's a very good question. So, as soon as they were
discovered about 20 years ago, the theorists went to work
trying to explain how they form. There's a couple
different ideas. One of them, I would say
the idea that probably has the most merit is
that there are Jupiters that form far out, just
like our Jupiter did but they were able to, they had gravitational
interaction with their inner disk, there was a torque between
the disk and the planet. And the planet can actually
slowly change its trajectory. But, you can tweak
the initial conditions on these experiments and
you may get a Jupiter that travels all the way
in and runs into the star. You may get ones that
move in and then stop. You may get ones that
don't move at all. And so there seems to a
range of stopping points. It's possible that
our Jupiter moved in, cleared out, there really
isn't that much matter in the inner part of our solar
system compared to Jupiter. In fact, Jupiter's
existence itself may be why there's so little
mass in the inner planets. There's a model
called the Grand Tack where Jupiter and Saturn
and the other planets, the outer planets were
migrating a little bit and Jupiter may have swept out
some of the region near us. It's conceivable the planets
could have formed in situ. It's a little hard to
believe because we think that if you have ice, ice
sticks together a lot better than rock, especially hot rock. And so the conditions for
these planets accreting out of that disk, it
can go much, much faster if you have a lot of ice. And so you need to be
a couple times further the nearest Sun-distance
where water becomes an ice and carbon monoxide,
carbon dioxide, these things are very
good at forming ices that stick together. So, but there's been some
planets where they think they may have a
large rocky core. You may need tens of
Earth-masses to form these along with a hydrogen-,
helium-rich envelope. So, we may be seeing, there
may be a variety of mechanisms. The other hint is some of
the hot-Jupiter systems have stellar companions. Those stellar companions
could have altered the orbits of those Jupiters. And if they were sent in on
sort of comet-like orbits, the torques from the star itself would actually circularize
them and bring them closer to the star. So, there may be a few
different physical mechanisms. - Thank you.
- Yep. - It was probably a really
good reason for this, but why does the starshade
have to be so big and far away rather than smaller and just closer to the lens? - I think the answer is the, so you need the, the position of the
starshade with respect to the spacecraft,
you need to get within a couple meters, right? It has to be very, very, basically about as
much wiggle-room as I have on this
rug up here, okay? And this is one of the
technical challenges, is keeping the orientation
of the starshade and the spacecraft so close. - [Audience Member] I guess
it has to be big enough to create a shadow, also? - Yeah, you have to,
you want the spacecraft to be in the shadow that
the starshade is creating. So it's not purely
the geometric size. There's some other
optical complications that you have to
take into account. But the model they're
working with now, we're talking tens
of meters in size. - [Audience Member]
Cool, thank you. - Mm-hm. - Then, as a follow-up
question to that, is the starshade, is it the
same idea as a coronagraph? Is it the same thing and as
kind of a follow-up to that, is that how much, how well
does it blot out the light? How, like, what planets,
how far would those planets be away from the star such
that we could see them? - That's a great question. So, if I had some more
time, I would've talked a little bit more
about the coronagraph. So the coronagraphs
are essentially little, miniature starshades you have
inside of your telescope. You can blot out the star
within your telescope. And you have to create, you have to make them
in certain shapes that have to be very
precisely machined. How dark can they get? I think the answer for
the internal coronagraph in WFIRST, I think
now's 10 to the minus-- - Nine.
- Nine? Yeah, so, something on the
order of a part in a billion. So, you're getting
down to seeing things like Jupiter around
the nearby stars. The other thing to
consider is the so-called inner-working angle. And so for the set-ups
that we're taking about, for the telescopes that
we're talking about, the inner-working
angle's on the order of a tenth of an arcsecond. So something like one over few
ten-thousandths of a degree. And so if you wanna
see, you know, planets like Jupiter,
Neptune, et cetera, you'd have to look around
just the nearby stars. If you move the
star too far away, that angular separation
gets too small. - And then, a follow-up to that, is does the starshade,
would that move so that you could look
at multiple stars? - Yes. Yeah, I think people would
scream if it only looked at one star. - [Audience Member]
I would think so. - The idea is the starshade, so you would launch
your telescope, your telescope would
observe the star for days or weeks on end, but you need to
integrate all that signal to get the faint light
from the planets. And then the starshade
would, has some fuel, and it would move to
its next orientation. And it may take days or weeks to get to that next orientation. In the meantime, you
have a space telescope which can do other things. It can look for
microlensing events or study dark energy
and galactic structure. There's lots of other
astrophysics you can do in the down time. Not really down time, but, in between observing
the exo-Earths, okay? - One more question. So with respect to
circumbinary stars, have we found any
planets that orbit within the boundary of two, of
a binary system or are they-- - Yes.
- all on the outside? - Alpha Centauri's
a perfect example. That's an Earth-sized planet
orbiting a little red dwarf. If you go 10,000
astronomical units away, you've got two Sun-like
stars orbiting each other, Alpha Centauri A and
B go around each other about every 80 years. And they, themselves, there's dynamically-stable zones around each of those about
the size of Mars' orbit where there could be planets. So all three bodies
could have planets. - Thank you. - It looks like we have some, whoops, sorry. We have some questions
from the internet. It is known what the
effect of dark matter is on gravitational
lensing if any. Okay, so when we're
talking about dark matter, the dark matter seems
to be distributed on very large scales. We're talking
thousands-of-light-years scales. The dark matter is
probably everywhere but it's very, very low-density and particle physicists
have not been able to detect it, yet. But we don't think its having
an influence on the scale of planetary systems,
on those scales. Where we really need to
worry about dark matter if you will, is on
the scales of galaxies and galaxy-clusters. And that's where it
seems like we're missing, we're missing much of the
matter in the universe. The next question is: how can information be
discerned about any one planet using the wobble
method where there are likely multiple planets
causing their star to wobble? That's a great question. You need to watch
them for a long time. If you were watching, if you're our Sun, if
you were an astronomer who was tens of light-years away and you're watching our Sun, Jupiter is tugging on our Sun, Jupiter has a 12-year period. Saturn's a pretty big planet. It has a 30-year period,
so it's tugging on the Sun. And then the Earth
and the Venus, Earth and Venus are
both tugging on the Sun. And so you actually get a
fairly-complicated pattern and you need to monitor
them over many years, okay? And this is, you know, teasing out the signals
over very long time-scales, this is technically challenging. We're used to thinking
of these missions in terms of years,
but we may need to, you know, to properly
characterize the masses of the planets further out, we may need missions
that last decades, so. You need to do, you need
to do computer modeling and try different
solutions until you get one that statistically looks right. Yes? - Yeah, I just
wanted to say that if you go to that top link, the website, exoplanets.nasa.gov there is a lot of good
things to read there and some good videos that
will help you understand the coronagraph
and the starshade and what the strengths and
difficulties are for each. - Yes. Barely scratch the
surface with graphics for the coronagraph
and the starshade, so I definitely
encourage you to go to exoplanets.nasa.gov. Any other questions? - My question is
how will we know when we've found a planet
that may have life on it? What are you looking for? - That is a great
question (laughing) and is a whole talk in itself. There's the so-called
biosignatures. I mean, we're obviously
looking for planets similar to Earth that
would have, you know, features like oxygen,
you know, some CO2, maybe see methane. There's a lot of discussion now. What are the unique
chemical signatures that you would
see in a spectrum? Because what we're
finding is there may be abiotic reasons for having
oxygen-rich atmospheres that may not require,
you know, photosynthesis. So, right now, people
are studying how do you, what chemical signatures
do you look for that are unique? You'd look for chemicals
that are out of equilibriums. If you start seeing
oxygen, CO2, methane in certain abundances,
you might ask, well why is there so
much methane there. Oh, there's cows there, right? (audience chuckling) So, you know, if we look
at a planet like Mars, you see CO2, and
Venus, you see CO2. You would would
know that there's a very strong greenhouse
effect in Venus' atmosphere from the depths of the
carbon dioxide feature. We have some CO2, little bit, just enough to
warm up the planet on the order of 14 Celsius. You know, there's
different things you'll be able to tell from
the chemical signatures. So that's a whole
talk in itself. And we've, some of
the larger planets, some of the larger
transiting planets, people may be able to tease out the chemistry and see
evidence of certain molecules. A few of the
directly-imaged planets, the giant planets,
they're also seeing things like methane and
hydrogen in the atmospheres. - [Audience Member] Thank you. - In addition to the, sort
of the unusual-mass planets that we don't really see based
on the solar system model that we have, have we seen
any super-dynamic systems where there's multiple
orbital planes, so you have one planet
over here, you know, several on one angle, you know, and very eccentric
comet light orbits or is it all very sort of
conventional, what we see here? - Ah, so that's been one
of the other surprises. We look at our own solar system, the planet orbits tend
to be fairly circular. There's a few exceptions. You know, Mercury's
is a little eccentric. But most of the
planets like Earth's, Earth's orbit is
circular to about 2%. Most of the planets
in the solar system, their orbits are
circular to about 5%. A lot of the systems
we're seeing, a lot of the ones
that Kepler's seeing that are very close in
tend to be very circular. But there are ones on
very eccentric orbits. A lot of the Doppler-spectroscopy-detected
systems, some of them are on
very eccentric orbits. They've seen Jupiter-like
planets on comet-like orbits. They've also detected
planets orbiting very close to their star going
the opposite way of the star's rotation. Bah, how do you do that? (laughing) You know,
they've had to, you know, that's a
whole can of worms in terms of dynamical
simulations. You must've had a very complex, it must've been multiple
planets, some collisions. You know, how do you get a
system where one of the planets is going the wrong way? And at a very steep angle
with respect to its star? So, they're not all
nice and circular like our solar system. And that's actually
an open question, is just how unique
is our solar system in terms of the dynamics? - Thanks. - Another question with
respect to the orbits. I guess for us to be able
to detect the planets, they have to cross
the line between us and their sun?
- Yep. - And so how much
of a coincidence is that that there are orbits
that have that property and how often are they
completely misaligned such that they never
cross that line? - Well, most of them are not
passing in front of the star so we have to be, you know, with missions like
Kepler, literally, you're looking at
over 100,000 stars and we're only seeing a few
thousand where the planets are passing in
front of the star. So, statistically, you
have to take into account that it's less likely that
you would see the planets pass in front of the star
as you get further away. There's just a lot more, if you started varying the
orientations of the orbits, you know, 99.99% of the
time, you're not gonna see it passing in front of the star. So this is one of the
reasons the Kepler Mission's been so sensitive to the planets that are very close in. So, its, you know, those
are the ones we can see. What we're doing is we're, based off of those statistic, we're trying to figure out what
the distribution looks like for all the planets, taking into account the
ones that we can't see. One of the frustrating aspects of the planet-detection
techniques is they all probe slightly
different parameter space. Like the transit method,
you're very sensitive to planets very close in
and you get the radii. And occasionally,
you can get the mass if the planets are
tugging on each other. With radial velocity,
it's tougher to get the low-mass planets, but you can detect the
planets further out. Microlensing, you're
very sensitive to bigger, or to planets at a
wide range of masses but mostly very far
away from their star. They all cover different
parameter spaces and so we're trying
to piece together what the distribution of
planetary properties is building off the strengths of
these different techniques. But no single technique's gonna
give you the whole answer. Any other questions? Okay, I'll take one more. - Hello, I'd like
to keep it short. I just had a question. You vaguely touched on Planet 9? And I guess digesting data to
see if it really was a planet or just debris. Do you think you'd be
able to give us a heads-up on a timeline, possibly or when
we would know more about it? - (laughing) There's
other people down the road to talk to about that. I would say what
looks interesting is that we're finding
there's a whole belt of objects out past
Neptune's orbit, the so-called Kuiper Belt. Over the past two
and a half decades, been finding more
and more objects out past Neptune's orbit. Pluto and a few of
the dwarf planets just tend to be
the biggest ones, Eris, Makemake, Haumea. There's thousands of these
big objects out there. And as you go further out, out, sort of 40, 50
astronomical units, you're starting to see
a little bit of clumping in the orbital
properties of some of the very, very
distant objects. And it looks a little,
it's interesting. There's not many of them, but their properties are
starting to clump up. Why would they be clumped up? It's almost like there's
preferred orbits. Now, this is for a very
low number of objects, but over time, they've
been finding more of these objects, very far out. Things on orbital-time
scales of thousands of years. These spend most of their time hundreds to thousands
of astronomical units away from the Sun. We can only catch them
when they're very close. Very close, out past
Pluto, you know? 40, 50 astronomical units out. That's when they're bright
enough that we can see them with our telescopes. They're very dim,
they're very slow-moving. And so, it's only been
the last few years they've been able to piece
together a few of these and they're starting to say, hm, there's some
interesting properties. You know, that the orbits
are starting to clump up. Well, what would produce a
clumping up of those properties? And so, you know, I'm starting, I was skeptical initially, I'm starting to take it a
little bit more seriously when there's results
from multiple teams that are working
on the dynamics. They're doing simulations
and are starting to come to some
similar constraints. And so, I think what the
hypothesis at this point is you're talking about
an object that's probably about 600 astronomical
units away from the Sun, probably something like
five or 10 Earth-masses, maybe something intermediate
between the Earth and Neptune in size. Am I 100% sure
they're gonna find it? No. (chuckling) We've been burned
too many times. But it's, when I see multiple
teams doing these simulations and coming to
similar conclusions and starting to say, it's probably in that
region of the sky. You know, then they'll
actually show a plot and they'll say, it's probably
in this banana-shaped region of the sky and we
think we know the mass and we think we know the
radius and the orbital period. Then, I start to
take that seriously. The reason it hasn't
been discovered yet, if it is real, is
because the region of sky where it is is
probably, is very big. And it's probably so faint,
even if it's something the size of Neptune and it's
600 times further away than the Earth-Sun distance, we're talking about
something that's about, in magnitude parlance,
24th, 25th magnitude. This is just many, many
factors of 10 dimmer than most the things
you're used to looking at with a telescope. So it takes up a lot
of telescope time, you need wide-field images and they need to be deep. And that means a lot
of time on telescopes and you have to
convince astronomers to give you that time to carry out that study. But now that there's
been multiple teams, there's multiple teams searching and there's multiple teams
coming to similar conclusions about where on the
sky it might be. I would not be, I
would not be shocked if next week there
was an announcement but it could be in a few
years, it may disappear. Maybe there's some
observational bias we hadn't thought of in
the orbital properties of these very distant objects
that may be effecting the, that may be allowing
astronomers just to find ones that have certain properties. But my money now is they're
probably gonna find one. And it's probably gonna be
something smaller than Neptune. - [Audience Member] Thank you. - And when they do, we
need to build a probe and send it there
as fast as we can. And along the way, we can
take pictures of exoplanets. So, okay, that may not go
over well with some people but we should definitely
build a probe to Planet 9. Send a probe to Planet
9 if it's discovered. - [Audience Member] Thank you. - Okay, I think we'll close
up the questions there. And thank you very
much for your time, I hope you enjoyed the talk. (audience applauding) (quiet audience chatter) (cheerful chiming music)
