Speaker 1: Now here's a highlight from Coast to Coast AM on iHeartRadio.
Speaker 2: And welcome back to Coast to Coast George Nori with you.
Speaker 2: Josh Wynn is a professor of astrophysics at Princeton University.
Speaker 2: His research group explores the properties of planets around other
Speaker 2: stars and tries to understand how planets form and evolve
Speaker 2: and make progress on the age old question of whether
Speaker 2: there are planets capable of supporting life out there. His
Speaker 2: latest book is called The Little Book of Exoplanets. Josh,
Speaker 2: it's a great book, by the way, Welcome to the program.
Speaker 3: Thank you very much, and I've been looking forward to
Speaker 3: this conversation.
Speaker 2: These exo planets. How many have been discovered so far?
Speaker 3: Well, NASA maintains the closest thing we have to an
Speaker 3: official list of exoplanets, and I checked just before the
Speaker 3: program and the official number is five thousand, five hundred
Speaker 3: to two.
Speaker 2: That's amazing, it is.
Speaker 3: Yes, it's one of the most rapidly advancing fields of astrophysics.
Speaker 2: Considering thirty years ago. Do you know any of them?
Speaker 1: Right? That's right.
Speaker 3: Yes, it's a new field. It's very much technology driven
Speaker 3: and it was only in the mid nineteen nineties, when
Speaker 3: technology advanced to the point that we could start discovering
Speaker 3: planets around distant stars, well outside the Solar System.
Speaker 2: What percent would you guess that a star, wherever it
Speaker 2: may be, would support planets.
Speaker 3: Yeah, that's a good question. So there are too many
Speaker 3: stars for us to search them all, right, there's maybe
Speaker 3: one hundred billion stars in the Milky Way. So what
Speaker 3: we do is we search the nearest brightest stars, those
Speaker 3: are the ones where it's easiest to find planets, and
Speaker 3: we do it kind of a census, and based on
Speaker 3: what we've seen so far, it seems likely that at
Speaker 3: least for Sun like stars, most or all of them
Speaker 3: have some kind of planets. To be a little more specific,
Speaker 3: if you pick a random sun like star, there's at
Speaker 3: least a thirty percent chance that it has one of
Speaker 3: the types of planets that we can detect today. And
Speaker 3: we can't detect all kinds of planets. Some planets are
Speaker 3: much harder to find than others. Planets that are very
Speaker 3: small are difficult for us to find. Planets that are
Speaker 3: in very wide orbits are difficult for us to find.
Speaker 3: So there's like a one in three chance that it
Speaker 3: will have a detectable kind of planet, and that leaves
Speaker 3: plenty of room for the others that probably have the
Speaker 3: types of planets we're only just beginning to be able
Speaker 3: to detect.
Speaker 2: And Josh, of those planets that might be out there,
Speaker 2: what percent do you think might be earth like, Well.
Speaker 3: It kind of depends on what you mean by earth like.
Speaker 3: The one thing you need to know about exoplanet science
Speaker 3: is that we can only learn a very limited amount
Speaker 3: of information about each planet. So if we have a
Speaker 3: planet in the Solar System like Mars, I can show
Speaker 3: you beautiful images of the surface of Mars and it'd
Speaker 3: see mountains and valleys, and you can look for water
Speaker 3: at the ice caps and so forth. For exoplanets, they're
Speaker 3: so hard to detect that we have none of that
Speaker 3: kind of detailed information. Most of the time. All we
Speaker 3: know is the size of the planet, the overall size,
Speaker 3: the mass, and we know how far away it is
Speaker 3: from the star that it's orbiting, We know how fast
Speaker 3: it's moving in its orbit, and we might be able
Speaker 3: to measure the shape of its orbit. That's about it.
Speaker 3: So when you say earth like planet, many of your
Speaker 3: listeners are probably thinking about a planet that has continents
Speaker 3: and oceans, maybe breathable air, that sort of thing. We
Speaker 3: have no way at the moment of knowing whether those
Speaker 3: things are true for any exoplanet. But if we just ask, okay, well,
Speaker 3: what about planets that are the same size as the
Speaker 3: Earth and that orbit a star like the Sun and
Speaker 3: are about the right distance from the star to have
Speaker 3: the same surface temperature as the Earth. That's kind of
Speaker 3: a working definition of Earth like based on things that
Speaker 3: we can measure today, And the answer is that they're
Speaker 3: probably not. We actually struggle to detect such planets. That's
Speaker 3: kind of right on the limit of our technology right
Speaker 3: now to detect planets as small as the Earth. But
Speaker 3: it seems to be that maybe ten of Sun like
Speaker 3: stars have such a planet.
Speaker 2: Josh, how does a planet even form?
Speaker 3: That's a great question, and that is one of the
Speaker 3: big questions that motivates this field. Planets and stars. They
Speaker 3: didn't just pop into existence with the Big Bang. They
Speaker 3: had to form the universe. The early universe was just
Speaker 3: a kind of formless sea of atoms, and somehow, in
Speaker 3: a there some process must have created the Sun and
Speaker 3: the planets and other stars and their planets. And the
Speaker 3: current theory is that This happens mainly due to gravity.
Speaker 3: When we look around the galaxy, we see lots of
Speaker 3: clouds of material, mostly hydrogen gas, but all kinds of
Speaker 3: other stuff is mixed in there too, And every now
Speaker 3: and then, one of those gigantic clouds of gas starts
Speaker 3: contracting under its own gravity. Gravity, as you know, is
Speaker 3: an attractive force. Everything attracts everything else with the force
Speaker 3: of gravity.
Speaker 2: And it's universal, right, and.
Speaker 3: It's universal as far as we can see, And so
Speaker 3: that will cause the cloud to start shrinking under its
Speaker 3: own gravity. And what happens is that if it contracts
Speaker 3: strong enough and gets to be small enough and dense enough,
Speaker 3: then the material can ignite and become a star. It
Speaker 3: can start nuclear fusion reactions that give stars their power sources.
Speaker 3: But it doesn't just all collapse into a point like
Speaker 3: a star. Instead, what happens is the material ends up
Speaker 3: swirling around this new born star like a vortex. And
Speaker 3: that spinning pattern of material, that disk of material that
Speaker 3: surrounds a young star that is supposed to be where
Speaker 3: the planet's formed. The planets kind of congeal out of
Speaker 3: this material that swirls around a newborn star for several
Speaker 3: million years, so that is the essence of the modern
Speaker 3: theory of planet formation. You form a star by contracting
Speaker 3: a giant cloud of gas under its own gravity, and
Speaker 3: then the material that doesn't quite make it down all
Speaker 3: the way to the star swirls around for a long time,
Speaker 3: brillions of years in fact, and that gives enough time
Speaker 3: for small objects within that spinning disk to conglomerate and
Speaker 3: join together and get larger and larger and become planets.
Speaker 2: And in our Solar system, Josh, the one planet that
Speaker 2: didn't get its act together and form is probably what
Speaker 2: they call the asteroid belt, now right.
Speaker 3: Yeah, that's right. So there are actually two places in
Speaker 3: the Solar System where we see a lot of small debris,
Speaker 3: asteroids and other objects of similar size. One of them
Speaker 3: is between Mars and Jupiter. That's the asteroid belt that
Speaker 3: you just referred to. Probably what happened there is we're
Speaker 3: looking at the material that would have come together under
Speaker 3: its own gravity to become a planet. But Jupiter is
Speaker 3: right next door, and Jupiter is a very massive planet,
Speaker 3: and that means that its gravity stirs up the material
Speaker 3: in the asteroid belt and probably prevented it from forming
Speaker 3: a full fledged planet. The other region that's like that
Speaker 3: is out beyond Neptune. There's another zone where we find
Speaker 3: lots of small, rocky and icy bodies. That's called the
Speaker 3: Kuiper Belt. That's right. Probably what happened there is that
Speaker 3: that material might have become a planet eventually too. But
Speaker 3: everything happens so slowly out there. The further you are
Speaker 3: from the Sun, the weaker the Sun's gravity, and the
Speaker 3: slower all of the motions are out there, and so
Speaker 3: they're just they couldn't get it together quickly enough to
Speaker 3: form a planet.
Speaker 2: Josh, you mentioned the Big Bang, and I got to
Speaker 2: tell you, I have interviewed so many scientists on this
Speaker 2: program over the years. I still don't understand the Big Bang.
Speaker 2: How something would start from nothing? Have you come up
Speaker 2: with your own thoughts about that?
Speaker 3: Yeah, I don't know what came, why something started from nothing.
Speaker 3: I think that's one of the large kind of imponderable
Speaker 3: questions that we have today. But I do know the
Speaker 3: evidence for the Big Bang, the fact that we have
Speaker 3: pretty good reason to think that the universe is expanding.
Speaker 3: That is the when we look at distant galaxies, we
Speaker 3: see that the distances between galaxies are growing with time,
Speaker 3: and that means that if we trace back the clock
Speaker 3: about thirteen point seven billion years I think is the
Speaker 3: current estimate for the age of the universe, that the
Speaker 3: universe was an extremely dense state, that all of the
Speaker 3: matter that we see and spread all over in distant
Speaker 3: galaxies was actually quite close to each other. So it
Speaker 3: was a very hot, dense sea, as I call it
Speaker 3: before of atoms. There's actually a lot of very solid
Speaker 3: evidence for that, and the evidence can take us all
Speaker 3: the way back to the first few seconds after the
Speaker 3: Big Bang. We understand we think the conditions at that
Speaker 3: moment in the early universe's history, and the reason is
Speaker 3: that when we look around the universe, we see it's
Speaker 3: mostly hydrogen, but there's also some helium. Hydrogen and helium
Speaker 3: are the simplest kind of atoms that there are, and
Speaker 3: so there's three quarters of the universe is hydrogen and
Speaker 3: the other quarter is mostly helium. And the only way
Speaker 3: to make sense of that is to suppose that these
Speaker 3: elements formed in that early, hot, dense phase of the universe.
Speaker 3: And if you calculate, well, what would be the elements
Speaker 3: that formed from a hot, expanding fireball with the conditions
Speaker 3: that we think existed in yearly Universe. You get the
Speaker 3: right answer, You get that, well, there should be about
Speaker 3: three quarters hydrogen and most of the rest is helium,
Speaker 3: with a little bit of lithium and so forth. So
Speaker 3: the evidence can take us back to the first few seconds.
Speaker 3: But then if you ask me, well, what about beforehand,
Speaker 3: that's where we have to go off of the path
Speaker 3: of the evidence and start speculation.
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