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Hello, I'm Dr. Ruth Angus. I'm an astronomer and an associate curator and professor of astrophysics at the American Museum of Natural History. Let's answer some questions from the internet. This is exoplanet support. 22 minutes asks, "Scientists believe there is a super Earth at the edge of the solar system, but the way things are going around here, even a slightly above average Earth would be welcome." Agreed.
A super Earth is a cool name for what is actually a slightly pedestrian thing, which is just a planet that is a little bit more massive than the Earth. Do we have a super Earth beyond Neptune? Maybe. So, we talk about planet 9, a potential ninth planet in our solar system. If it exists, we think that it might be tugging on other objects out there right at the edge of the solar system. If it's out there, it's extremely far away, therefore very faint because it doesn't reflect much sunlight. And it's also moving extremely slowly. Nobody's found it yet, but it's hypothesized.
Real scientists asks, "How do we find exoplanets? Even though the idea of exoplanets has been around for a long time, they have only been confirmed in the last 30 years. They are really hard to find." They are really hard to find. So, there are a couple of main ways that we detect them. We can't directly image them. Most of the time, they're just too faint compared to their host star. And trying to photograph an exoplanet is like trying to photograph a firefly next to a lighthouse. Instead, what we have to do is try to figure out the presence of a planet based on the influence it has over its host star. One of the main techniques we use to find exoplanets is called the transit method. This is where
a planet passes in front of its host star and blocks out a little bit of light. If we measure the brightness of a star at repeating intervals, we can actually see the star seem to get a little bit more dim as the planet passes in front of it and then it brightens again once the planet has passed all the way past it. We've found more than 3,000 planets this way. There's another technique that is also pretty successful and it's called the radial velocity method or sometimes the Doppler method or sometimes the wobble method. This is where we actually see the star moving in space. We can't see what's pulling on it, but we can see that the star moves and we infer that there's a planet
orbiting it, dragging it around with its gravity. What we can do is actually measure the Doppler shift of the stars light. When the star is moving towards us, its light is blue shifted and when it's moving away, its light is redshifted. So, we infer that the star is moving and it's being yanked around by a planet. Casey Hall asks, "My toddler makes me read about space, watch things about space, talk about space. I'm just out here pretending I have any clue. Sorry, but WTF is an exoplanet." Well, I also have a toddler, so I can totally relate. An exoplanet is just a planet outside of our own solar system. It's a planet that orbits another star. And we found thousands of these exoplanets. We're up
to over 6,000. They're everywhere in our galaxy. Probably every star has an exoplanet. Financial sun 6933 asks, "Is a planet orbiting two suns at once actually possible IRL?" Yes, it is. And we have found planets just like this. This is actually a pretty unlikely configuration and they're very difficult to find. So these are called circumbinary planets. The star itself, the double star is called a binary. Kepler 16b, for example, is a circuminary planet. It's one of the first ever discovered. If you've seen Star Wars, like the original film on Tatooine, there's an image of two suns rising. So Tatooine is actually a circuminary planet. It orbits both stars
at the same time. So binary stars, stars that have another star for a companion, are actually the most common type of star in the galaxy. Most stars are binaries. Our sun is actually slightly unusual in that we don't have another sun. Star talk radio asks, "What is the most extreme exoplanet?" We could talk about the hottest exoplanet which orbits its star extremely close in and it's basically as hot as a star is. It's so hot in fact that on its day side molecular hydrogen like H2 molecules are actually split apart. We could also talk about planets that are extremely eccentric. Most exoplanets sort of orbit in a circular way like the Earth is has a very circular orbit but some planets
don't. They all bit in a sort of oval shape like an ellipse. And these planets have extreme temperature swings. There are some planets that are actually kind of disintegrating as we watch. So these are planets very close to their host star that have a big extended puffy atmosphere which actually seems like it's kind of being blown away from the planet. A few different options for extreme planets there. Fluorescent light bulb asks, "Explain like I'm five. What makes the Earth so gosh darn livable? How is it different from the other planets in our solar system or viewable planets in our galaxy? We have liquid water here because Earth's in the habitable zone and also because it's
small and rocky and it has a discernable surface, but there are a lot of other qualities that make Earth pretty perfect for habitability and life. It has a pretty strong magnetic field and that magnetic field shields us from solar radiation. Earth also has an atmosphere which we think is essential for life. Plate tectonics we think might be important for life because plate tectonics allow us to actually almost moderate the amount of carbon that's in the atmosphere. And this kind of keeps the planet in equilibrium and it actually solves something called the faint young sun paradox. Our sun used to be fainter and dimmer. And yet the planet Earth has sort of always maintained roughly the same average
temperature. As the planet gets warmer, there's more rain, more evaporation, more weathering of rock and rock weathering removes carbon. Another thing that makes our planet special is that we have a large moon which actually stabilizes Earth and without it axial tilt might change and it would send the seasons sort of totally out of whack and the Earth itself would experience massive climactic swings. Overall, we're at a pretty steady state and we think that this is probably a prerequisite for life. Courtney W. Rocket asks, "Have we discovered any habitable planets yet? because I'd really just like to start over. Unfortunately, we haven't discovered anything that we know for
sure is habitable. So, what makes a planet habitable? The main thing we think is the existence of a liquid water on the surface. This means a planet has to be about the right distance from its star to be the right sort of temperature for liquid water. It also means that the planet has to be relatively small like Earth because big planets like Jupiter, Saturn, they tend not to have a discernable surface. They're actually mostly made of gas. But there are a lot of other criteria probably that make a planet habitable. For us on Earth, we have a stabilizing moon which stops our orbit from changing too much. We have a magnetic field which prevents solar radiation from irradiating the surface
of Earth. We have an atmosphere. We have plate tectonics. Have we found planets in this habitable region? The distance that makes liquid water possible? Yes, we have. Most of these planets, however, orbit stars that are very different from our sun. Most of these planets orbit little stars, M dwarfs or K dwarfs. K dwarfs are a little smaller than the sun and M dwarfs are a lot smaller than the sun. The problem with that is that M dwarfs are very magnetically active. Think solar flares. They have coronal mass ejections which are storms of harmful high energy particles leaving their surfaces and potentially blasting these exoplanets. The James Webb Space Telescope has been looking for signs of
atmospheres on habitable zone exoplanets orbiting mwarfs. And so far, it hasn't found any. So, we're now starting to wonder whether actually maybe the star has to be just right as well for a planet to be habitable. Evan Slayers asks, "Which exoplanet do you think has the greatest chance of harboring life?" # AskNASA. One of the main targets in the search for life is the Trappist one planetary system. The problem with Trappist one is that it is a very active mdwarf star with a extremely strong magnetic field and the planets orbiting Trappist 1 are blasted with its radiation. Now Trappist 1 has three planets in the habitable zone and we don't yet know whether or not they
have atmospheres but the James Web Space Telescope is working on it. I think a better candidate is a star called TOI700. It has two exoplanets in its habitable zone and it is also an M dwarf, so it's a small star with a strong magnetic field. TOI700D and E are probably my bet for the place most likely to have life. Ty 700 is old, really old. Old stars tend to be more stable, more peaceful, more sanguin, more calm, a bit like our own son. And so TOI700 doesn't have so much strong radiation blasting its planets. A Reddit user asks, "Explain
NAM 5. If the sun is getting hotter in billions of years, does that mean that planets further away from us may become suitable for life while Earth may not?" Yes, the sun is getting hotter and the habitable zone in our solar system is moving outwards. And it's actually been doing this for a really long time. And in a billion years from now, the Earth's oceans might evaporate and the Earth itself will not be habitable. Humans have only been around for like 300,000 years. So, we've got a lot of time to figure it out. It does mean that Mars is going to get warmer and is going to move into the habitable zone even more and it will stay in the
habitable zone for quite a long time. Job Megan's one asks, "Can't help but wonder if an alien civilization would have detected Earth the same way we detect exoplanets. There's actually a zone that's called the Earth transit zone, which is like a plane, which is where an alien would have to be able to look back at the sun and see the Earth transit. Probably if there are aliens out there scanning the skies looking for Earth-sized exoplanets, they might have spotted us if they live in that Earth transit zone. If an alien has seen us, why haven't they said hello yet? It takes a really long time for light to travel across space. So, it could be that distant aliens haven't
really noticed our presence yet because human technology hasn't been around for all that long in the grand scheme of things. Black Auntie asks, "How do we know what exoplanets look like?" We could know its mass because we can measure the radial velocity or Doppler shift of the star as the planet orbits. And if you have radius, you have size, and you have mass, then you know something about the density of your planet. Maybe a planet's around the right density to be entirely made of water. Or maybe it's around the right density to be extremely heavy, like mostly made of metals and rock. Mostly, I've talked about exoplanets transiting their stars, so passing in front of the star. But planets can also pass around
the back. And if they're extremely hot and they [snorts] glow brightly in infrared, we can actually see when they pass behind the star because we lose their signal. And we can even map the hot spots on the surface of a planet and we can figure out what the winds might be doing and understand relatively speaking what they might look like. So some of those exoplanets that we've discovered are actually pretty bizarre looking. Proud Reaction 224 asks, "Explain like I'm five how scientists can figure out the composition of exoplanet atmospheres."
Often the way we do this is by observing a planet as it transits its host star. Most of the light coming from the star is going to pass directly through space into our telescopes. But some of the light is going to filter through the planet's atmosphere on its way to our telescopes. And as it does that, as it passes through a planet's atmosphere, it's changed. Gas molecules in the atmospheres of planets absorb light at certain distinct wavelengths. Carbon dioxide, for example, removes certain colors. Oxygen removes certain colors. And we can infer the presence of these molecules in the atmosphere of an exoplanet by seeing where those colors are missing as a planet passes in front
of its host star. It's much easier to do this for a big puffy planet because you get more light passing through the atmosphere. For planets like Earth, the atmosphere is actually just a teeny tiny layer on top of the rocky core and so you don't really get very much starlight passing through the atmosphere. It's really difficult to do this for Earthlike planets. Prince of Atheism asks, "Just learned there's an exoplanet nearly the size of our sun. I wonder are there planets bigger than stars?" The maximum size for an exoplanet is about the size of Jupiter. You could try adding mass to Jupiter, but what you would actually do is just increase its density and not its size. The smallest
stars, M dwarfs, can be extremely small, about as small as Jupiter. So, can you get a star that's smaller than a planet? Actually, in certain circumstances, perhaps you could. So some Jupiterized planets that are very close to their host star are actually irradiated so strongly that they are so hot that they actually puff up a little bit. So you can get a planet that is a little bit bigger than Jupiter. Adam Aloa asks, "What does it take for us to be able to take images of exoplanets?" You need to have a planetary system that is relatively nearby. You have to block the
light from the star using something called a coronagraph. When we're trying to get these really, really high resolution images from the ground, the atmosphere makes it difficult. You know, when you look at a star, you can see it twinkling. That is because the light from that star passes through a column of air that's turbulent, winds, etc., right? And as it lands on the telescope, that twinkling messes up your observations. Basically, you can't resolve really small distances in your images. So, what you can do is shine a laser through the atmosphere that allows you to predict the motion of the air and then the starlight falls on a mirror that you distort to counteract the variations in the air. And this is
called adaptive optics and it allows you to focus light really extremely precisely and get these precise images of exoplanets. Zad Shall asks, "So the web telescope already detected water in the form of steam on an exoplanet already, and I wonder if we will detect signs of life like methane soon. Water is a really common molecule in the galaxy, it turns out, and a lot of exoplanets do have water. You also asked about methane. So, methane is a molecule that's produced by life, and it's something that we call a bio signature gas. The problem with methane and a number of other single molecules is that there are lots of ways to make methane
that actually doesn't have to involve life at all. So methane on its own is not a perfect bio signature. And now the consensus is that we actually probably want to look at a combination of two different molecules. So for example, methane and oxygen together because the two methane and oxygen should not naturally coexist. If they are seen together, it's basically a sign that methane and oxygen have to be constantly produced perhaps by something like life. Peter Corus asks, "Which exoplanet fascinates you most?" One of my favorite exoplanets is called 55 Canank E. The planet is a super Earth. It's more massive than the Earth. It orbits extremely close to its host star. It whizzes around every few hours. Its
whole year is shorter than an Earth day. And it's so hot that we think it's actually a lava world. And yet, it's held on to an atmosphere. That atmosphere is probably constantly being outgassed. So, it's being replenished. Maybe it's being stripped away at the same time. It's almost like a beacon of hope for me because it shows that planets can outgass new atmospheres and recreate them even when their host star is doing everything it can to strip those atmospheres away. Sugar and blots asks, I have recently heard that astronomers have found an exomoon. I am quite scientifically illiterate. So what exactly is an exomoon and could it affect us on Earth?
An exomoon is a moon in another solar system. We have tons of moons in our solar system. We're up to like basically 900 or something like that moons. So, if our solar system has so many moons, it would be surprising if other planetary systems didn't have any. Moons also present another interesting possibility for life. So, in our own solar system, we have icy moons, Europa and Enceladus. And these moons are actually warmer than they should be. They're outside the habitable zone, but they have liquid oceans under an icy crust. The reason for that is that they orbit massive planets that have strong tidal forces. So, we're actually we think maybe there's life on our own icy moons in our
own solar system. And if icy moons could be a place for life to hang out, then there's lots of opportunities for icy moons to exist elsewhere in the galaxy and another potential host for life. Heather JS asks, "WTF? No one's concerned about rogue planets. Rogue planets are these solitary planets that don't have a host star. They probably once did, but interactions maybe with other planets in the planetary system has sent the planet outwards. So, we think that there are thousands and thousands, maybe millions or billions of rogue planets out there in space." John Alog asks, "How does finding planets in habitable zones affect SETI? Do we point instruments at these planets?" SETI is
the search for extraterrestrial intelligence. This is really more about techno signatures rather than bio signatures. It's searching for things like narrowband radio emission. It's searching for potentially laser signals. It's searching for also things called Dyson spheres. A Dyson sphere is where the entire star is covered in solar panels. It would look like a very dim object that's very bright in infrared. There's a lot of space to cover. There's a lot of stars to look at. And so in fact, SETI's really only covered like a very small number of stars, but it's still searching. Myth and Dear's Ghost asks, "How do we know that exoplanets
aren't sunspots or star spots? Spots on the surface of a star, like our sunspots on our own sun, are two-dimensional for the most part. So, as a star rotates, you can see a spot coming into view. And that spot actually makes the star a little bit more dim overall, just like a planet does. A planet is a solid object, and it passes in front of its star without being forcehortened on the limb. So variations in starlight caused by spots tend to be smooth because as spots round the corner they almost disappear. They sort of flatten whereas planets as they trans transit they sharply block the stars light. So transits tend to look like very sharp dips. When we search for planets using the Doppler method the star itself actually has a Doppler
signal. And this is a massive problem. Our earth orbiting the sun actually makes the sun move a little bit because both the earth and the sun orbit the center of mass of the earth sun system. The earth is dragging it around as it orbits. But it's doing that very slowly. The sun itself has its own Doppler signal. It's shifting and roing and pulsating. And that signal can be larger. And a lot of the time when we find exoplanets using the Doppler method, they turn out not to be real. They turn out just to be interference from the spots. If you've seen the movie Project Hail Mary, 40 Erodani, the planet that Rocky is from was thought to be a real planet when Andy Weir was
writing the book. And it later turned out that it was probably not a real planet. It was probably just some spots on the surface of the star that acted like a planet. And unfortunately, Rocky's home world might not be real, but it still lives on in our hearts and minds. Brat asks, "Interstellar, how is it possible for the waves to be so big on the water planet if the gravity is stronger?" The water planet in Interstellar is a planet that's orbiting a black hole and it has extremely strong tidal forces and it's tidily locked to the star. Tidal locking happens a lot. The moon is actually tidily locked to the Earth. The moon's rotational period, how fast it spins, is exactly the same
as its orbital period, how long it takes to go around the Earth. So, it always shows the same face to the Earth. This water planet that orbits a black hole is the same. It has these big tidal bulges on each side, on the side facing the black hole and on the side away from the black hole because the planet's distorted into this football or rugby ball shape. And the waves on the planet are created by these tidal forces. The tidal bulges actually should stay put. They shouldn't move around. So you'd have a shallow part of the planet and you'd have a deep part of the planet and you wouldn't necessarily have waves like traveling and rippling across the planet like you do in the film. If the planet
wasn't quite tidily locked, if it was moving around just a little bit, perhaps you could get some sort of sloshing back and forth of the ocean and maybe you could make these kinds of exotic waves. Um, maybe that is what Kitthornne was going for in the science. Um, I'm not totally sure. Those are all the questions for today. Thank you for watching Exoplanet support.
