NIST Colloquium Series: Strange New Worlds, by Phil Plait


[MUSIC] And I’m really excited
to introduce Phil today. Phil is known as the bad astronomer, and he earned his PhD in astronomy from
the University of Virginia in 1995. During the 1990s, Phil worked on the Cosmic background
explorer mission, which was COBE. And later was part of
the Hubble Space Telescope team at NASA Goddard Space Flight Center where he worked on the space
telescope imaging spectrograph. In 1993, while working on his dissertation on the
rings of debris around Supernova 1987a, Dr. Plait harnessed the power of a novel
technology called the World Wide Web. And began publishing articles aimed
at carrying one of his pet peeves, the proliferation of inaccurate,
wrong or just plain made up misinformation about astronomical
topics in popular culture. And I think this is a timely topic for
today. Dr. Plait’s internet postings expanded
into the Bad Astronomy blog and into his book,
Bad Astronomy: Misconceptions and Misuses Revealed from Astrology
to the Moon Landing Hoax. [LAUGH] Doctor Plait’s second book,
Death From The Skies, There Are Ways The World Will End,
was published in 2008, investigates numerous astronomical
phenomena, such as black holes and supernovae, by charmingly
describing hypothetical scenarios in which these events will
extinguish all life on earth. If you are interested in either of
these books, they are available for sale out in the hallway
through the Boulder Bookstore. In addition, to his books, Doctor Plait’s
online and live action work has proliferated in myriad ways as his Bad
Astronomer blog has continued at various locations from Discover magazine, Slate
magazine, and most recently Syfy Wire. In 2010,
he hosted the three part documentary series Phil Plait’s Bad Universe on the Discovery Channel based on concepts
from the Death From The Skies book. And in 2015 wrote and
presented a 46 episode series of videos about astronomy for the YouTube
educational series Crash Course. Dr. Plait has also appeared on many other
programs such as Nova, How the Universe works on the Science Channel and
the Late Late show with Craig Ferguson. We’re fortunate in that Phil
lives the Boulder area. And when not writing about all things
space, he enjoys raising goats, horses and experiencing the wonderful
environment that we all live in out here in the Rocky Mountains. So with that, I’d like to give
Phil a warm welcome to Boulder. [APPLAUSE]
>>Thank you, thank you, that was, we’re out of time. Sorry, wow,
I didn’t know I did all that stuff. Yeah, I do live in Boulder,
it’s really nice. Although I’m kind of envying Gaithersburg
now cuz their seats look a lot more comfortable.>>[LAUGH]
>>Look at that, it’s like the Regal Theater
up here in Longmont, that looks great,
you’ll be very comfy falling asleep. And they’re wondering where I’m,
I don’t even know if they can see me. They can?
Okay, so you have to look over here. If I’m making this pose,
yeah hi, yeah there you go. That means I’m looking at you so
stay awake please. So it is a great pleasure to be here. I visited the National Institute
of Standards and Technology when I was I think
in third grade in Maryland. And I remember some of it,
but it was a long time ago. So it’s pretty neat to be here
again as an invited speaker, especially giving a talk about
one of my favorite topics. And I’ve given talks on people who
think the moon landings are fake, and that the face on Mars is real. And the Maya predicted
the Apocalypse in 2012. And it is so
nice to talk about a real science topic that has actual data, is a brand new
field, and is super, super exciting. Because this is something,
when I was a kid raised as a nerd. And it’s also great to talk in front
of a crowd of actual, you know, professional nerds, this is great. But as somebody who grew
up with Star Trek and all those other great shows to be able
to talk about planets is such a joy. And we had to no idea about any
of this stuff when I was a kid, it was just all in our imagination,
really. And now we are discovering
these new worlds and actually starting to figure out
a little bit about what they’re like. And we can compare them to our own planet. And so that’s why, I have this talk called
Strange New Worlds, because they are, these ones that we’re finding. But finding these planets,
what we call exoplanets, planets orbiting other stars,
alien worlds orbiting alien stars. Even though we’re doing this
because of the love of science, just being able to find these things and
learn as much as we can about them. You ask any astronomer about that, what
they’re doing, a planetary scientist and they’ll talk about all that,
this joy of discovery and all that. But in the back of their head,
all right, what are they thinking about? They’re wondering if they’re gonna
find planets that can support life. And can there be life like us out there? That’s always, even if you’re not
thinking about it consciously, that question is always
floating out there. And so
I wanna talk about how these planets work, how we find them, what they’re like,
and then compare them to the Earth. And the question I want the answer to
all of this is, is the earth special? And it turns out, the answer is
a little bit difficult to answer, it depends on what you’re asking. And so as a true scientist who
hasn’t actually published on this, which allows me to say whatever I want.>>[LAUGH]
>>I don’t have to worry about the referees
hanging over my shoulder. The answer to this question
is Earth special is yes, no, maybe, it’s complicated. It depends on what you mean
when you ask that question. That is a very broad question
is the Earth special. And as you start to drill down into it,
you find that the answer completely changes depending
on what you’re talking about. So let’s start with the Earth. Here’s our planet, I love this picture. This is taken from the Discovery
satellite, which is in orbit around the sun about 1.5,
1.6 million kilometers toward the sun, faces the Earth, takes a picture
every hour or something like that. This was Al Gore’s Triana satellite,
do I have that right? But it was rescoped, renamed and it does this amazing job of taking
pictures of our changing world. And this is sort of the picture you
always see, because we are very northern hemisphere and
western hemisphere biased I think. So you tend to see pictures
like this of the Earth. You’d see Africa, Saudi Arabia in there,
Mediterranean Sea. This is a very typical view, except
it’s not, it’s the view you see a lot. It might be a stereotypical view, but really what’s a more
typical view of the Earth? And that would be this,
that hardly looks like Earth, it’s not what you’re familiar with. There’s barely any land visible in there,
and I apologize to the people in Gaithersburg that I can’t send my
laser pointer over the Internet. But I’m going to point out a few things. At the bottom left there’s Australia. At the upper right,
you can see the west coast of the US. There’s Baja, California and
the Sea of Cortez. [SOUND] and that’s it. Hawaii is in here someplace but
it’s too small and maybe cloudy to see. That’s it.
As far as land goes that’s all you see. The rest of this is the Pacific Ocean. This is a far more typical
view of the Earth, right? 74% something like that of
the Earth is covered in water. And it’s hard to grasp how big
the Pacific Ocean is until you’ve seen it. I’ve lived in the San Francisco area and
I flew to Australia a few years back, and we left
San Fransisco Airport and in five minutes, we were over the Pacific Ocean,
and 12 hours later, I was over Australia and did not see
a lick of land in that entire time. Basically, the entire hemisphere
of the Earth is ocean, and that’s kinda staggering
when you think about it. It’s a lot of water. This is what defines our planet. It’s not just that it’s a water planet,
it’s that water exists on the surface in three different states of matter. Liquid, obviously, also, gaseous, the clouds you’re seeing there are water
vapor, so water can exist as a gas. And although you can’t
really see it too well, at the bottom of this
picture is Antarctica, a little sliver of it there below that
cloud, and that’s water in a solid state. And so this turns out to be relatively
important for life on Earth. We need to have a water cycle where water
can evaporate, move across some place where there’s not water and then rain
down, and that way life can propagate and exist in different places on the Earth
where otherwise it may not be able to. And water is important as far as we
know to life, we’re carbon based, all of our biology, all of our
chemistry is based on molecular carbon. Carbon is able to create complex molecules
that can do all kinds of interesting things, including reproduce themselves. So you can have a long molecule like
DNA and it can replicate itself, and that is sort of the fundamental
basis of life on Earth. So water is important. Does that make Earth special? And again, [SOUND] you can answer
that in a few different ways here. But let’s look at the solar
system just as a drawing here. This is a lovely little drawing,
not to scale, thank God. It would be very unpleasant on Earth. The sizes are to scale. That is the size of the sun and
the planets to scale there. And you can see the sun on the left and
Mercury, Venus, and then Earth, Mars and then a big jump to Jupiter,
Saturn, Uranus and Neptune. So there you have it. All of the planets in the solar system, every single planet’s up there,
ending with Neptune. I’m not afraid to dive into
controversial politics in this talk, at least passively aggressively. When you look at these planets,
it’s pretty easy to categorize them in different ways and
the most obvious one is size, right? You’ve got the four
giant outer planets and the four smaller,
rocky terrestrial planets. So if you ask is there a special in
terms of size, the answer is kinda. Half the planets in our solar system are
not at all like Earth, half kind of are. Mercury’s pretty small and rocky and hot. Mars is pretty small and rocky and cold. Venus is sort of the same
size as the Earth but it has this tremendously thick atmosphere,
super hot on the surface. It rains sulfuric acid there. It’s a lot more like Maryland
than Boulder actually.>>[LAUGH]
>>Anybody getting up and leaving? No, okay, good, and so
in the solar system, earth is kind of unique. As far as we know we are the only planet
that has liquid water on its surface. Now there are other places
that have ice on their surface including Mercury which
has ice in its poles. There are craters that are deep
enough at the poles so that the sunlight never reaches in there. These are called cold traps. And if ice gets in there it stays there
and possibly for billions of years. So it is possible to have water on
the surface of your planet as long as it’s in the frozen state. That’s not terribly helpful when we’re
thinking about Earth like conditions. So as far this sort of general overview
goes, yeah, the earth is kind of special we’re the only ones that have this
sort of conditions on the surface. But is this the only way planets are? Is this it for
every planetary system in the galaxy? Well, when I was a kid we didn’t know. When I was kid we knew of nine planets and
then there were eight for a while, but it turns out we started discovering
other planets around other stars and that allowed us to do
that thing that every 5th grade English teacher likes to teach,
and that is compare and contrast, right? As we’re finding these other systems,
do they look like us, or do they not look like us,
and what does that mean? And it turns out that once you start to
discover these objects, an interesting thing happens in that you can start
to do what I think of as zoology. If you see all these animals in front
of you, you want to start categorizing them as these have four legs, these have
six legs, these don’t have any legs, these swim, these do this, these do that,
and when you start to categorize things, you start to learn more about how they
interact, how they behave on their own, and maybe how all of these
things came to be up from simple up to the complicated life systems
that we see now through evolution. Planets don’t really evolve like that, but
same principle, the more of them you see, the more of them you
can figure things out. Is the earth unique? And that’s the question. Let’s see if we can find the answer. So first of all how do
we find these planets? It turns out this is really hard
until suddenly it becomes super easy. When I was a kid I used to read
a lot about efforts to look for planets around nearby stars, Alpha
Centauri, for those of you who were big into astronomy like I was, of VB8B,
Van Maanen’s Planet, all these things. People were looking for
these planets orbiting nearby stars using different methods, and
they could never quite do it. It’s really, really delicate precise work. And it turns out what you really
need are digital detectors. And once you start to put those
on the back ends of telescopes, you can start doing a lot
more precision measurements. And I’m gonna skip, actually,
the first method we used to actually find a planet and go straight to
the transit method, which is far and away the most successful method. Basically, what you do is you look at
a star and stare at it for a long time. And what you hope is that if there’s
a planet orbiting that star, and the orbit of that planet is seen edge
on from Earth, so it’s not face on, it’s not doing this, but
we’re seeing it edge on, then once every orbit it’s gonna
pass in front of that star. And what will happen is if it does
that you get a mini eclipse, and the star light drops a little bit. So if you can measure very precisely the
brightness of a star every whatever amount of time, every day, every hour, whatever,
and you [SOUND] you just keep measuring it, if that planet happens to transit
pass in front of that star, you get a mini-eclipse, and you get a little dip
in the sunlight, just like this animation. So here’s a star, and we’re gonna
plot brightness versus time, and as the planet goes around [SOUND]. Right it blocks the light from that star. As the planet goes around the star from
our angle it goes through phases like the moon does. It goes from crescent to full. I can play this again. Sorry, it doesn’t loop. Here we go. There it’s new, first quarter, full. Well, you only get half of that. There we go, maybe I did that wrong. Here we go. And so as you do this, the measurements, there’s a little bit of
noise in the measurements. But overall, you see sort of that
dip in the light from the star. That is a transit. The amount of information
you can glean about a planet from something as simple as
this is really quite stunning. If you know how big that star is,
and it turns out we can do this. There are very complicated methods to
determine exactly how big a star is. As that planet passes in front,
if the planet’s really big, it’s gonna block more of that light,
so you got a deeper transit. If the planet’s smaller, it blocks less of
the light and the transit is shallower. So right away, if you know the size of
the star by how much light is blocked, you can get the size of the planet. Now you can’t necessarily get the mass of
the planet, I’ll get to that in a moment. But there are other tricks you
can do that tell you things like what the orbit of that planet is. The time it takes for it to cross the star tells you how
long it takes to orbit the star. And if you know how long
it takes to orbit the star, you know how far from the star it is. And that tells you right away
sorta kinda how hot the planet is. Now, that depends on a lot of things. If the planet has an atmosphere or
not or a lot of other stuff, but it gives you an idea. It’s like the minimum temperature
of this planet is 1,000 degrees, probably not the best place to look for
life. On the other hand, if it’s in an Earth-like orbit around
a Sun-like star that becomes interesting. There are other things you
can tell from this as well. I won’t go into detail, but
you can read about this if you want. But you can learn about
the atmosphere of the planet, you can learn a little bit
about the star itself. Just a huge amount you
can learn from this, as long as your measurements
are accurate enough. And this is far and
away the most popular, so to speak, the most successful way of planet
finding that we’ve got right now. Now the first way that we found planets,
at least, although the story gets complicated, is using what’s called
reflex velocity or radial velocity. Now as a planet is orbiting a star,
that planet has mass. It has gravity. Not much, I mean, it’s orbiting a star,
a gigantic massive object. But the planet still does
have some amount of gravity. So as the planet is going around the star,
it’s tugging on that star. So as the planet makes, let’s call it
a circle, a big circle around the star, the star is making a little circle
as well, in the opposite sense. So as this thing’s going this way,
they’re kinda tugging around each other. And you can think of this,
if you’re standing with somebody who, say, is a kid,
somebody who’s much smaller than you. Face each other, hold hands,
and swing that kid around. That kid’s gonna make a big circle around
you, but they’re pulling on you as well. So you’re gonna kinda make a circle around
them as well, around your center of mass, right, where you’re balancing. Astronomers call that the barycenter
because why call it the center mass, which is obvious. Call it the barycenter and
confuse people instead. That’s how we like to do things. So you can see that on
the graphic on the left. So the stars making a little circle. Now that circle typically is way
too small to see with a telescope. You can take a million measurements
of a star and it’s not gonna look like it’s making that circle, simply
because this system is really far away. It’s trillions of
kilometers away at least. And that circle it’s making is very,
very tiny. However, ah-ha. This is the cool part. If the orbit is edge on like it
is on the right-hand animation, then what you’re doing is that star,
you’re seeing it moving back and forth. The back and
forth isn’t the important part. It’s that it’s moving towards you for
half the orbit and moving away from you from
the other half of the orbit. And so if you point a telescope at
this thing and measure the light from the star extremely carefully,
you can see a Doppler shift in its light. This is the same thing you get
if you’re standing on a road and a motor cycle goes by and
it goes [NOISE] right? The pitch changes, the pitch is higher
as it’s moving towards you, and lower as it’s moving away. That’s the Doppler shift. The same thing happens with light. An object’s moving towards you,
the wavelength of the light shrinks, and we call that blue shifting. If it moves away from you, the wavelength
increases and we call that red shifting. It’s a very, very small effect because
it depends on the velocity of the star. And the star is making this little
circle that may take it weeks or months to move around. And so the typical velocity of a star as
it’s moving in this little circle is like 10’s or 100’s of meters per second. It’s not very much. However, we are really, really good at
building telescopes and spectrographs and you can measure this for
a lot of these stars. And the more massive the planet is,
and the closer it is to the star, the bigger that effect is. And so,
the very first planets that we found were these planets that are very
close into their star and very massive, simply because those are the
easiest things to find using this method. The joke is it’s where
the light is better. A cop is walking down the street at night
and there’s a kid under a street light on his hands and knees and
the cop says, what are you doing? And the kid says I’m looking for
a quarter I lost. And the cop says well,
where did you lose it? The kid says over there. And the cop says,
why are you looking here? Because the light is better. All right, dumb joke, yes. However, that’s how astronomers think. So, we looked at stars,
a bunch of them and found a lot of planets
orbiting stars this way. And it turns out these
are massive planets, much more massive than Jupiter and they’re
orbiting their star extremely close in, such that their orbits
are measured in days. Now, Mercury is the closest planet to
the Sun, and its orbit is 88 days long. And yet we’re talking about planets
here which are orbiting their star in four days, five days, something like that. So they’re very close in,
really yanking on that star hard and making it much easier to
see this Doppler shift. So that’s why this is
called the reflex velocity. The star is moving in reflex to
the planet moving around it and it’s the velocity that’s important. So finding these hot
Jupiters was a big surprise, nobody was expecting to see these because
they don’t exist in our solar system. Ding, a-ha! Answer to our question right away. Is our solar system unique? No, or I should say yes. It’s not unique in that
other solar systems exist, so we are finding planets
around other stars, hooray! So we’re not the only planet,
solar system in the galaxy. We didn’t know. It seems like solar systems are easy
to make, because ours exists. And there doesn’t seem to be anything
special about the Sun, necessarily. Lots of stars like it. But without knowing for
sure, we just didn’t know. So now we know. Is our solar system unique? No, other ones exist. Is it unique in its structure? Maybe, we don’t have planets like
this in our solar system and yet these were the ones that we
were finding lots of at first. Well, we were finding them
cuz they’re easy to find. As we got better at this, we started finding lower mass
planets farther out from their star. And the beauty of this is that
the shift that you see in the star’s light depends
on the mass of the planet. And suddenly, if you have an edge on
system like this and it’s transiting as well, you now have the size of the planet
and you have the mass of the planet. And if you divide basically the size
by the mass or the mass by the size, you get the density. And now we have the density. That tells you very much good
things about your planet. Look a Jupiter, right? Jupiter’s a big planet, but
its density is very low. It’s only about as dense as water, about
one gram per cubic centimeter, on average. The Earth is about 5.5
grams per cubic centimeter. And look at the Earth, it’s got its
huge iron core, got a lot of rock and a very thin atmosphere. Jupiter also has a very large core, but it’s mostly atmosphere that dominates it,
so its density is very low. So without even physically seeing this
planet, if you can get its mass and its size, you can tell right away, is this
thing a solid terrestrial like planet, or is it a giant gaseous, gas giant? Hope that wasn’t a confusing phrase for
you. And that’s amazing that you can do this. Now, the thing about a transit is
that Jupiter orbiting the Sun, Jupiter is about a tenth
of the width of the Sun. So, you put Jupiter up next to the Sun,
Sun’s about ten times wider, but it’s blocking an area, and
that goes as the diameter squared. So since the Jupiter is
a tenth the size of the Sun, it actually blocks one-one hundredth
of the Sun’s surface when it transits. So that would be a 1% transit. Typically, that the kinds of transits you
see with these Jupiter-size planets around Sun-like stars. That’s a 1% drop in the light. That’s super easy to detect. I have an 8″ telescope at home that
is an off-the-shelf telescope. If I buy an off-the-shelf camera,
I could actually point this thing at quite a few of the stars that
have these planets and detect them. These were sitting in
front of us all this time. It wasn’t until we could prove that
this happened, that this took off, and then NASA launched the Kepler Space
Telescope, and then that was a huge boom. Kepler has discovered over
2,000 planets this way. A bunch of ground based telescopes have
discovered lots of planets this way. We now know, between this method and
the transit method, the reflex velocity method, and a handful
of others that are less efficient. We now know of almost 4,000 planets
orbiting other stars, 4,000. The first one was discovered in 1992, a three-planet system orbiting a pulsar,
a dead star. It’s not a Sun-like star,
those planets were pretty weird, it’s not, it’s cool but it wasn’t
really what we were looking for, but the first planets orbiting a Sun-like
star were discovered in 1995. And then, it took a couple of more years,
we started finding more and more, and now we’re finding these
things almost everyday. It’s pretty rare that a new planet
isn’t added to the roster, basically, every week, and
we’re really close to 4,000 up to now. The Kepler mission’s over,
but now we have TESS, which is
the Transiting Exoplanet Survey Satellite. I always have to think about that. And that is, Kepler stared at
one spot in space for years, looking at a hundred something thousand
stars, looking for planets around them. TESS is a survey instrument. It’s sweeping the sky. And it’s looking at brighter stars, looking under the assumption that
brighter stars tend to be closer to us. So it’s looking for
nearby planetary systems. And it launched not that long ago. And it’s already discovering
them hand over fist, although it has neither hands nor fists. But it’s finding lots of planets. This is a very exciting
time to be into this stuff. There is a third method, which I have
to talk about, because it is so cool. As an amateur astronomer myself and somebody who’s always loved looking
through telescopes or getting optimal data from telescopes, it turns out that in some
special cases you can see these planets. They’re not detected indirectly
like these other two methods. In this case, you take a picture and
there’s a planet there. This is Beta Pictoris,
a relatively nearby, very young star, that in the middle,
there’s a little piece here. This is a picture taken in November 2003,
in the infrared, and the star itself has been blocked. That star shows you where it is. And there is a planet, that’s
Beta Pictoris B, Beta Pic B as we call it. Picture taken six years later, this is where is was in 2003 at the upper
left at about the 11 o’clock position. Six years later it’s down here
at about the 5 o’clock position, something like that. That’s because we’re seeing
it orbiting it’s star. We’re seeing it orbiting its star. I’ve known about this for 15 years now and it still makes the hair on the back
of my neck stand up, so cool. The bottom picture shows
the two of them together, another picture taken in March of 2010. And you can see it’s moved a little
bit from its 2009 position. It’s basically orbiting the star. We’re seeing it almost but
not quite edge on, very disappointing. It was supposed to transit last year and
it didn’t. If it had transited its star then we’d be
able to determine a lot more about it, its size and its density and all that. Unfortunately, we didn’t, but you can see, there’s a picture of Saturn’s orbit there
for comparison at sort of the same angle, and that’s how this planet is moving
around its star, you can see that. This has been done for many other stars,
HR8799 is another great system. Again, the stars in the center
are blocked out, and we name the planets in order of discovery,
so its B, C and D. There’s no A for historical reasons. So D is actually closer in, but it wasn’t discovered at first
because it was harder to detect. B was a first one founding
even though it’s further out. A picture taken a little bit later
actually shows, oops, four of them, but I have an animation of this, this is a
bright enough star easy enough to detect, you can see B, C, D, and E,
I can’t remember which one is which. But here’s one here here very faint. And the three brighter ones on
the other side, I can play that again. You take enough images,
you can string them together and get a movie of the motion of these
planets orbiting their star. [LAUGH]
>>Love this, that is science fiction, baby. That is Star Trek right there,
and that’s for real. Now, the reason we can see these
planets is that the star and the planets are very young. They’re only a few million years old,
and that makes them very hot. They’re still cooling from
their initial formation. And hot things glow in the infrared,
and we have detectors that can detect infrared, the star is not nearly
as bright in infrared, and that makes the planet look
brighter in comparison. Typical planets are a billionth as
bright as a star in optical light, but it may only be a millionth
as bright in infrared. And that still sounds like a small number
but that’s It’s a thousand times better. And so you can do stuff like this. And that, to me, is amazing. We’d actually directly imaged
over a dozen planets, this way. Pretty phenomenal stuff, I love it. So where does this put us,
as far as uniqueness goes? Well, let’s talk about what
makes the Earth unique. Exoplanet astronomers and
astrobiologists, which is a real thing. That is a real thing that NASA does now
that you would have been laughed out of your grant money. I don’t know, 20 years ago, 30 years ago,
calling yourself an astrobiologist. Now you can get a PhD in it.>>[LAUGH]
>>And there’s this concept called the Habitable
Zone, you’re probably familiar with this. And that is, basically, how close or far you can be from a star,
such that conditions are temperate. You can have liquid water on
the surface of whatever this thing is. This is a,
if I can quote Pirates of the Caribbean, this is more of a guideline than a rule. I see a lot of Michael Bay
fans in the audience. Okay, so the idea is that if
you’re too close to the star, you’re too hot and water will boil away. If you’re too far away,
it’s too cold, it’ll freeze. And you want to be in that
zone that’s just right. A lot of people call
this the Goldilocks zone. That’s what we were calling it for a long
time, actually, and then somebody came up with habitable zone, which is
actually much harder to pronounce. However, I’m not a big fan of
calling it the Goldilocks zone, because it should really be
called The baby bear zone, right? Goldilocks is the one who
walks into this house and says, this porridge is too hot,
this porridge is too cold. Baby bear’s is just right, and so we should really call
this the baby bear zone. But this is very typical
European colonization thinking. That this white girl is going to
go into somebody else’s cabin and steal all their stuff and
we’re going to name it after her.>>[LAUGH]
>>All right, great, and if that gives you a flavor of my politics,
congratulations.>>[LAUGH]
>>This is a government facility, I should probably shut up.>>[LAUGH]
>>But I can’t, so this idea that you can have this
habitable zone is a nice guideline. The reason it’s a guideline is because
look at our own solar system, Venus and Mars are on the edges of
the sun’s habitable zone. The Earth’s pretty much in the middle,
relatively speaking. So Venus in on the inner edge, but it’s
not habitable because of its atmosphere. It has a lot of carbon dioxide in its
atmosphere that traps a lot of heat. And it had a runaway greenhouse effect and now it’s hot enough to melt lead on
the surface of Venus, more or less. Very, very hot, completely uninhabitable,
kinda, maybe I’ll get back to that. Mars is very small, has very little
atmosphere and it’s very cold. If you could swap Venus and Mars and wait
a billion years or something like that. It’s entirely possible that Mars
would get a thicker atmosphere, Venus might lose some of its atmosphere. And they would be habitable and we’d have
three habitable planets in our system, but as it is, they’re not. So just because a planet’s in the
habitable zone doesn’t make it habitable. Anymore than just because a planet is
Earth sized doesn’t make it Earth like. Venus is very close to being
Earth’s size and mass, but it is an entirely different planet. So you have to be careful about
the terminology you use here, now, this is the habitable
zone in our solar system. There are different kinds of stars, there
are hotter stars, there are cooler stars, a hotter star has a much
larger habitable zone. It’s just the way the math works out,
and so you can actually, the inner edge is probably farther out. Of course, than the inner edge for our habitable zone because
the star itself is hotter. You have to be farther away
before it’s cool enough. But at that point you can be much
farther out from the star and still be in that habitable zone. As stars get cooler,
that habitable zone shrinks and starts to huddle much closer to the star. And when you’re talking about M dwarfs,
these little dinky red dwarfs. Those have a habitable zone
that’s very close to the star, do we see planets in the habitable
zones of their stars, right? Is Earth unique in being the only planet
sitting right at that great spot in the middle of a star’s habitable zone? Does that make the Earth special? And the answer is, no, no, no, no, we find lots of planets in
the habitable zones of their stars. You look at G stars, like the Sun, that’s
just the term that astronomers use for stars like the Sun. And this is an old plot,
this is from a couple of years ago, but it’s beautiful the way it’s displayed,
so I still use it. We have a lot more of these
than what’s shown here, but Kepler-452b, it is the 452nd star
in the catalog that Kepler used. It has another name, but as far as
the Kepler catalog goes, 452nd star. That Kepler looked at and
found a planet around, b makes it the first one
discovered around that star. And it is in the habitable
zone of Kepler 452. K Stars, a little bit cooler than the Sun,
kind of more orange than the Sun is, and we found a bunch of those. And then around red dwarves, what we
call M Stars, a bunch of those, too. This is an old, like I said, this is
an old graphic, we know tons of them. It turns out M Stars are really
good at making planets that can orbit around
their habitable zone. The interesting thing about this graph is
that although the distances are not to scale, the sizes are. All right, so
we know that the Earth is not unique, because there are other stars that
have planets in their habitable zone. But now, when you look at this plot,
you realize, hey, the Earth’s not unique. We’re discovering lots of planets that
are roughly the same size as the Earth. But do you notice anything about all
these planets compared to the Earth? Are you awake?>>[LAUGH]
>>Come on, it’s the National Institute of Standards, you guys have to automatically
go, well, if you categorize them. It’s a little bit hard to
tell from this plot, but they’re all bigger than the Earth. By the time you start looking at
planets around the size of the Earth, it gets pretty tough to see them. The Earth blocks about one
10,000th of the Sun’s light, if it were to transit the Sun
seen from another star. And so now you’re talking about 100th
of a percent drop in the starlight. We can do that, but it’s tough,
and as planets get smaller, it gets harder to detect them. And so these planets are all
bigger than the Earth, and it turns out planets bigger than
the Earth, we call them super-Earths. They don’t have a cape,
that’s not the way you can tell.>>[LAUGH]
>>But that it turns out, there are a lot of these
out there in the sky. Here is just a drawing representing
some of the super-Earths we’ve found. Just to give you a size comparison, and
you can see Kepler-62 has quite a few planets surrounding it,
at least four, for b, c, d and e. And these planets are all
bigger than Earth. Once they get about twice
the width of the Earth, and if they’re also dense like the Earth,
there’s rock and metal. Their gravity gets so strong,
we think, that as they form, they’re able to draw in more
material much more rapidly. And so you get kind of this jump as
a planet gets bigger, it’s Earth, Earth, super-Earth, super-Earth. Once it gets about twice as big, suddenly, it can grow in size hugely as it’s
forming and it becomes more like Neptune. And so planets that get that big,
we start to call them mini Neptunes. This is not a hard and fast rule, it’s just a guideline to have
us understand what we’re seeing. So, now that we can start to see
lots of different kinds of planets, we know that super-Earths are out there,
how does this stack up? When we start to look at all these
planets that we can determine their size, how many of each kind
of size are we finding? And it turns out, you can plot that, this
is one of like two plots in this talk, so I apologize if you don’t like math. But this is really easy to read,
basically, size goes left to right, left hand side of the plot is small,
right hand side is big. Up and down is just how many of them
we’ve seen, so, bottom is zero, top is a lot, doesn’t matter what
the number is, it’s just more. And what you see is,
Mars size planets, you see hardly any. Well, does that mean that there are very
few Mars size planets out there? No, it means they’re really hard to find,
the light is not good there, to use that metaphor again,
these are tiny planets. They do not affect their star much,
whether they’re blocking the light or tugging on it. So they’re much more difficult to find,
we have found a few. We’ve even found some,
I think one of them is about Mercury size, very marginal detection. But there could be lots of them out there,
we’re just not finding them. Once you start to get
to Earth-sized planets, we’re starting to get more complete in
our surveys, we’re finding lots of those. But then you see a big jump to
super-Earths and mini Neptunes. Far and away, the most planets we’re
finding are somewhere between the size of Earth and Neptune. And then when you get to Neptune’s size,
there’s a sudden drop. And something bigger, something getting
closer to Jupiter, there are even fewer. And Jupiter and super-Jupiter,
we find not that many. And here’s the thing,
if there’s a Jupiter system and it’s an edge on system, yeah,
we’re going to find it. It’s super easy to find, like I said, I
could do this with my backyard telescope. So our surveys are telling us that there
really aren’t that many Jupiter or super-Jupiter planets out there. Stars don’t make them as easily as
they make these super-Earths and mini Neptunes, that’s a real effect. So basically stars make those middle
sized planets really, really well, how many of those do we
have in our solar system? None. There’s none. The most common type of planet
maybe in the entire universe, and our solar system doesn’t have one. That’s interesting, is that important? Maybe. If we find planet nine, this hypothetical
planet orbiting way out past Neptune, that’s been talked about a lot recently,
that may be a super-Earth. And so, we may have one in our system,
but the thing is If it’s that far out, it’s almost impossible to detect
using any of our methods. So what we’re finding here are
super-Earths that are relatively close in to their star, and
our solar system doesn’t have one. There is an idea that we used to,
that there were some super-Earths, maybe as many as five, orbiting the sun
between the Sun and the orbit of Mercury. They weren’t stable,
they crashed into each other and basically smashed themselves to pieces. Most of those pieces blew away,
but then the debris settled in and formed the four inner
planets of our solar system. And so we’re sort of a second generation
planet formed from the debris of the first generation super-Earths. But that wouldn’t have been
possible if we didn’t have those super-Earths in the first place,
and we don’t have them now. So not having super-Earths
is telling you something. We don’t know what, exactly. Maybe we used to have them,
and maybe we never did, but right away this is telling you, yeah, our solar system is special in some way
that we don’t have these types of planets. That’s amazing to me. So we’re getting a better handle, now,
on whether the Earth is unique or not. However, Are we being too picky? Was Goldilocks too, well we know Goldilocks was too picky,
she’s really picky. Let the hot porridge cool for
a couple of minutes. Come on, how hard is that to do? But maybe we’re being too picky about
what we want for conditions for life. Now Jupiter, Is a huge gas giant,
mostly atmosphere, probably not habitable in the way we think
of it, but it has these giant moons. That’s Europa there, and
that’s Io, the volcano moon. Europa is an interesting moon,
here’s a close-up shot of it. It’s an icy moon,
we’ve known that for a long time. When we got up close to it it
has these cracks in it, and as probes investigated it more, we realized
that it actually has a subsurface ocean. Basically as it orbits Jupiter, the gravity of Jupiter compresses and
flexes the moon, and that creates a huge amount of friction
inside the moon, which warms it up. It’s mostly water ice,
when you warm up water ice you get water. So we think there’s an ocean under there, and even a core of rocky material,
which is very interesting because that means there are minerals there
that can interact with the water. And we think that might be salt water, which is possibly how
life on Earth originated. The conditions under Europa’s surface
may be very similar to conditions that existed on Earth when life arose. So, you don’t need even to be in
a habitable zone, maybe, to have life. We know that there’s liquid water
that exists on these icy moons, and we’ve seen it in fact. We didn’t see it in Europa,
we’ve inferred it. But this is Enceladus, a moon of Saturn. It has these parallel bluish streaks
in this picture at the bottom, this is all ice. Interestingly, it doesn’t
have very many craters on it. It’s a very old moon, if it doesn’t have
craters on it, that means the surface has probably been repaved some time recently,
hundreds of millions of years ago. That indicates that maybe there’s
tectonics or some sort of geological process which is pouring liquids over the
surface which then cover up the craters. And you’ve got these big stripes here,
these are actually cracks in the ice, and Cassini discovered that there is
water spewing from these things. These are geysers,
seen backlit by the Sun. You can actually see the shadow of
the curve of the moon there, and these are geysers shooting out into space. Cassini flew through those geysers and found that there’s dust in them and
organic molecules. Now, not life molecules,
but carbon-based molecules, which means that the ingredients for
life are under the surface of Enceladus. It, too, has a liquid water
ocean under the surface. How common is this, and this was
kind of a surprise in the 70s when it was first thought of for Europa
then the 90s and 2000s with Enceladus. But it turns out this may be very common. This is, Rhea, yes Rhea, a moon of Saturn,
Titania and Oberon, moons of Uranus I believe,
Triton around Neptune, Eris and Sedna, these are gigantic Pluto roughly
sized objects out past Neptune. All of these objects may have liquid water
under their surface for various reasons. So it turns out having liquid water
is not a unique property of Earth, at all, even Pluto. This shocked me when we got
the close-up pictures of Pluto, and you see this heart-shaped feature,
Sputnik Planitia, Sputnik Planum. And the western lobe here, the left-hand
side of the heart, Tombaugh Regio, is very smooth, and it turns out
it’s been repaved recently too. I would have thought that Pluto
is a frozen ball of rock and ice. And it turns out no,
there is still heat in its interior, there is still liquid under its surface. This tells you that this stuff
is everywhere, everywhere. Is there life there? Don’t know, I’d love to know. We don’t know, but
the conditions look interesting. But now, wait a minute,
are we talking about liquid or are we talking about water? Because if you need just
a liquid of some kind, it turns out there are other
types of liquid as well. This is a Cassini shot of Saturn with the
moon Titan there silhouetted against it. Titan has a very thick nitrogen
atmosphere that’s too thick for optical light to penetrate,
but Cassini has radar. And it could beam this radar down to
the surface, have it bounce back up, and it could map out the topology,
the surface features. And near the north pole of, I believe this
is the north pole of Titan, this gigantic moon that’s basically about as big as
Mercury, it’s a planet-sized moon. It found these areas that were
not reflecting its radar, and the only thing that doesn’t reflect
radar is liquid, it absorbs it. And so this became very interesting,
and then as the images got better and better you started to see that yeah,
this looks a lake, right? There are tributaries feeding into it that
get bigger and bigger as they get closer. And it turns out yeah, this is a lake
of liquid methane on Titan, and Titan has a methane cycle. This stuff evaporates,
it forms methane clouds, they move over to the surface
where it’s dry, it rains down and then forms these rivers that
flow back into the lakes. Can you have life based on
methane instead of water? I don’t know, why not? Nature is surprising, nature knows a lot
more about how it works than we do so it’s constantly surprising us. There could very well be some sort
of life based on this cycle, and not based on water. Now, it’s very cold on Titan,
water there is so hard that it’s basically like granite. If you made a snowball here on Earth and
brought it to Titan, it would turn into rock as hard as
the top of the Rocky Mountains here. You don’t wanna get in
a snowball fight like that. But it’s just telling you conditions are
very different, and yet eerily Earth-like, so we’re not even unique that we
have liquid water on our surface. Is there another way we can look at
the Earth, and the answer is yes. Here is Mars, It’s very dry,
very cold, very thin atmosphere. Huge evidence, conclusive evidence that it used to
have a lot of water on its surface. There are dry channels of rivers, there’s even indications that there
was a standing ocean on Mars. That’s a little bit controversial,
but I’m fairly convinced by it. So Four billion years ago, something like
that, Mars might have looked like this. And it may have had oceans,
thicker atmosphere, weather. Mars three and a half billion years ago, something like that, was more
Earth-like now than Earth was then. Earth then was still too hot. Mars was already like this. And so could life have
originated on Mars back then? Absolutely, there is no reason
not to think it could’ve. So we don’t know, but it might’ve. And you probably of panspermia. This idea that life may
have started on Mars. Giant asteroid hits Mars, blows debris
up into space and it falls to Earth. And becomes us eventually. We may be Martians,
that is entirely possible. It’s unlikely, I think conditions on
Earth were fine for life to arise, just later than Mars. But the point is, we can’t be prejudiced. We can’t just look at a habitable zone. We can’t just look for liquid water. We can’t even just think about now. Planets, a long time ago,
may have been Earth-like a long time ago, even if they aren’t now. Are we ready to answer the question I
posed at the beginning of this talk? Yeah, and it’s the answer I gave you. Spoilers, right? Is Earth special? Yes, no, maybe, it’s complicated, right? It depends on what you
mean by the question. Are we special in our
position in the solar system? No, there are lots of planets
in the habitable zone. Are we special in our size? No, a lot of Earth-like planets. Are we special in that we look
like other solar systems? Yeah, we don’t look like
a lot of other solar systems. There are other solar systems that look
like us, but they’re in the minority. Most of them have these super-Earths. Are we special in having liquid water? On our surface, yes, on our planet, no. Are we special in time? Maybe, the Sun is a certain age and
the Earth is a certain age. And it takes a little while for
life to arise. We know of other stars that are the same
age as the Sun, or even older. We have seen planets around these stars. Maybe they had life on them once,
maybe they did, maybe they don’t now. Maybe they never did, we don’t know. We’re just beginning to do this. This is by far my favorite
picture of our planet ever taken. The Rosetta spacecraft, a European Space Agency mission, that went
to the comet 67P/Churyumov–Gerasimenko. Just rolls off the tongue. 67P, the rubber ducky comet, you’ve seen
a million pictures of this thing, right? It passed by the Earth and used our gravity to assist it to get
where it needed to go to visit the comet. And as it passed the Earth and went sort
of on the other side of the Earth so the Earth was between it and the Sun,
it got this beautiful crescent shot. And you can see that gorgeous blue color,
this is a natural color image. What your eye would have seen if
you had been there with it, and you weren’t gasping for breath and dying. And that’s what you would have seen. You see clouds here, you see that liquid
water, you see that gaseous water. We don’t know, we still don’t know if there are any
Earth-like planets out there. There are Earth-size planets out there, there are planets that have
maybe Earth’s temperature. There are lots, and lots, and lots of planets that have any one of
these unique features that Earth has. But we don’t know if
they have all of them. And does this make us unique? We don’t know, for me it does. Right now it’s the only Earth we have. It’s the only Earth we know. It’s the one we live on, it’s our home. And so as far as I’m concerned to
answer the question, is Earth special? The answer’s yes. Thank you very much.>>[APPLAUSE]
>>Okay, did I run horribly long? I have no idea.
>>[INAUDIBLE]>>Okay, I’m willing to take questions, if you’re willing to hear my answers.>>Hi.
>>Hi.>>I want to ask, is there been a time
when during the transit method for a large planet there’s been some glimmer of a refraction indicating
an atmosphere on the edge of these?>>Yeah,
it turns out that in an exoplanet, especially these Jupiters,
especially these hot Jupiters. When they pass in front of the planet, if they were solid they would just block
the star’s light and that would be it. But if they have a thick atmosphere
it’s possible that some of that light from the star will pass through that
atmosphere on its way to our telescopes. Atmospheres will absorb
certain colors of light. For example carbon dioxide is opaque
to certain wavelengths of infrared. That’s why we have a greenhouse effect. That’s why carbon dioxide
is a greenhouse gas. It traps, the Earth takes light Sun,
warms the planet up. The Earth turns around and
emits thermal infrared light, but the carbon dioxide won’t let it out. So if you were looking at the Sun, you would see lots of thermal
infrared light coming from the Sun. But if you look at the Earth,
it’s not as much as you expect, because it’s being blocked
by the carbon dioxide. So if some of that light from the star
passes through the atmosphere of that planet, some of that
light will get blocked. And so if you look at a star when
the planet’s not transiting, to give you a nice template, then look
at it when the planet is transiting. And suddenly you see certain
wavelengths of light are missing. And it’s like, that’s hydrogen,
that’s helium, that’s carbon dioxide. That can tell you what’s in
the atmosphere of the planet. That is a very,
very difficult observation. That is right on the edge of what
we can do, but it has been done. The James Webb space telescope,
which will launch any decade now.>>[LAUGH]
>>I worked on it in 1996 when it was still on paper,
literally on paper. We were drawing pictures of it to
figure out what we were doing. But that’ll launch hopefully
in the next couple of years, that should be able to
do that sort of method. It’s much tougher for
an Earth-like planet, but for these Jupiter-size planets,
it’s a lot easier. And so, yeah, you can detect them. And in fact, to go another step on this, I
talked about these moons orbiting Jupiter. I should be clear that if there
are moons orbiting these other planets they may be habitable too. If you find a Jupiter-size planet
in the habitable zone of a star, it’s a gas giant. You can’t live there. But if it has big moons then these moons might be able
to have life on their surface. Because they’re in the habitable
zone of this planet. And we have not 100% sure
discovered an exomoon yet. But there is one orbiting a planet that
Kepler observed that appears to be a moon of a gas giant. It’s a big moon, it’s about
the size of Neptune if it’s real. There’s astronomers
right now working on it. I’m literally expecting them to make
their announcement any week now. Their data is really,
really close to being done. I’m hoping that they’ve
actually discovered it. It’d be the first moon of a planet
orbiting another star ever detected. But we, no reason not to expect that. There’s, even if you say there are nine
planets, ten planets in our solar system, whatever, there are hundreds of moons. So moons outnumber
planets by a huge number. And if exoplanets exist, exomoons do too. And if they can be habitable there could
be trillions of habitable worlds in our galaxy. How about that?>>[LAUGH]
>>Sweet, come on, one question. Anybody in Gaithersburg have a question? They might have to do sign language. I don’t know if-
>>Yeah, they’re not there.>>Here we go.>>Is it on?>>Hello.>>There you go.>>Thank you, this is great.>>Thanks. So when I look up at the night sky, how many of these stars have
planets that we’ve looked at? What kind of percentages
are we talking about?>>Right, that’s the thing that stuns me,
that these planets are so easy to find. And the thing is,
the transit method Depends on geometry, you have to have that orbit
almost exactly edge on. Because if it’s tilted even a little bit,
and the planet’s far enough out, it’ll just miss the star
from our point of view. So when you say, we’ve looked at X
number of planets, or X number of stars, 100,000 or whatever, and
we’ve found 1,000 planets. How many are we missing? And this leads up to the answer to your
question, and it turns out, a lot. The majority are orbiting face on or
at an angle and we just don’t see them. And depending on your numbers,
if you say one out of every 100 stars, we find has a planet. But we’re missing 90% of them, then suddenly your numbers become one
in ten or something of that order. It’s not one in a million, and
it’s probably not every star, although we expect most
stars have planets. But most stars have planets and
you look at our solar system and there are eight, nine,
ten, whatever planets. This means that even if your typical
solar system is, let’s just say ten, because that’s a nice round number. And one out of every
ten stars has planets, that means there are as many planets
as there are stars in the Milky Way. And the Milky Way has 200 billion stars,
something like that, and our galaxy is a big one. But this is telling you that on average,
there’s one planet per star. And you look at all these other galaxies
and you realize that there could be sextillions of planets in the universe,
that’s staggering. So when you go out and look up at the
night sky and you see a few hundred stars, yeah, some of them will have planets. And in fact there are naked eye stars that
we have found that have planets orbiting them, and that to me is also amazing. These stars I grew up with and
now I can say, I have a friend who does
exoplanet research. And she has a table of exoplanets known,
and she has crossed that with
known planets in Star Trek. Which makes me happy because that
means there are bigger nerds out there than I am. And she has actually listed planets
around, when Star Trek is mentioned, the name of the star and the planet. Then she can cross-check that. And it turns out, yeah, there are quite
a few Star Trek planets that are real, including Spock’s home world, Vulcan. We have found a planet
around 40 Eridani A, which is canonically Spock’s star,
so Vulcan exists, which I love. Yes, in Gaithersburg,
from across the country.>>Hi, thanks.>>Hi.>>So if we were to start considering
life on methane system planets or moons, do we have any sense
what that life might be like? If we’re carbon based, what would that be?>>I don’t know, it could be carbon based. It’s hard to say, I mean, if you’re in a sea of carbon-based
molecules, can you have carbon-based life? I don’t know, but life wants a liquid
because liquids are really good. That if you throw a lot of glop in them,
you can shake it up and that glop can interact. If it’s just sitting on a rock, these two
molecules, they’re never going to meet. But if they’re in a liquid floating
around, they can get together and do what molecules do, and
be fruitful and multiply. So it may not be that it’s
important what the liquid is, unless it’s corrosive or
something like that. Liquid methane, in the absence of oxygen,
is fairly stable, if you have oxygen, it’s fairly unstable. Yikes, that would be a very interesting
thing to see through a telescope. Titan is on fire, but it’s just that
it would be a slower chemistry, right? It’s much colder, so the chemical
reactions may not happen as rapidly. But on the other hand it may
be more stable than water, I mean, water has a pretty wide
temperature range it exists as a liquid. But if you’re at the hot end,
it can start to break things up, and so maybe methane is even better
at these cold temperatures. You can have even bigger molecules
that can be more sophisticated, so it might even be better for life. I am totally making this up on the spot, I am an astronomer who studies how stars
explodes, this isn’t even my field. I’m just an educated layman
when it comes to exoplanets, a little bit more than that because I’ve
studied some of the physics behind this. So I’m pulling this out of my hat,
I’ll say that.>>[LAUGH]
>>But it’s entirely possible that you could have life based on methane liquid,
which, what that looks like, I don’t know. And science fiction authors
have written about that. And to add to that I remember
watching Star Trek as a kid and thinking, you can’t have
planets around a binary system. That would never work, or you can’t have
a green sky, or you can’t have this, you can’t have that. And it turns out, yeah,
you can have all those things. Every time we find a planet
around a binary system, the headlines are always the same. Another Tatooine has been found,
like, okay fine, Star Wars, it’s okay, I mean,
it’s not Star Trek, it’s okay.>>[LAUGH]
>>But it turns out, yeah, we find planets in systems that you might have
thought initially that could never be. And it turns out, no, we find planets orbiting one of
the stars in a binary system. And we find them orbiting in big orbits
around both of them, and it’s just, all these weird systems. There is this one called
TRAPPIST-1 you may have heard of, it’s a little red dwarf. It has seven Earth-sized planets
all orbiting the star closer in than Mercury orbits the sun. Three of those planets are in
the habitable zone of that dwarf star, that system is something
I’ve thought is ridiculous. Having two planets,
they could both have civilizations. That was another thing in Star Trek,
where you have two warring civilizations, and it’s like, yeah,
I always thought that was silly. It turns out, maybe not, I mean,
the warring part, maybe, but the idea of two planets that could
support life in the same system, sure. No reason that couldn’t exist,
life could be everywhere.>>Thank you.>>Okay, well, thank you all very much.>>[APPLAUSE]

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  • I like the tie.

  • Thank you for posting this! Phil is one of my favourite astronomers to listen to. I gave a similar talk to my local astronomy society a couple of years ago, and it's lovely to see some of the progress made since then.

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