- 2 hours ago
Astronomer and Associate Curator of Astrophysics at the American Museum of Natural History Dr. Ruth Angus joins WIRED to answer the internet’s burning questions about exoplanets. What is the most extreme exoplanet? Have we discovered any habitable planets yet? How are the waves on Miller’s planet (Interstellar) so big? Answers to these questions and many more await on Exoplanet Support.Image Credit: HR 8799 Orbiting Exoplanets by Jason Wang (Caltech)/Christian Marois (NRC Herzberg), licensed under Creative Commons Attribution 3.0 Unported (CC BY 3.0).Source: https://commons.wikimedia.org/wiki/File:HR_8799_Orbiting_Exoplanets.gifLicense: https://creativecommons.org/licenses/by/3.0/No modifications made.For information about the American Museum of Natural History, visit https://amnh.org or connect with the Museum on YouTube: https://www.youtube.com/c/AmericanMuseumofNaturalHistory.
Category
🤖
TechTranscript
00:00Hello, I'm Dr. Ruth Angus. I'm an astronomer and an associate curator and
00:04professor of astrophysics at the American Museum of Natural History.
00:08Let's answer some questions from the internet. This is Exoplanet Support.
00:1622 Minutes asks,
00:18Scientists believe there is a super Earth at the edge of the solar system,
00:22but the way things are going around here, even a slightly above average Earth would be welcome.
00:26Agreed.
00:27A super Earth is a cool name for what is actually a slightly pedestrian thing,
00:32which is just a planet that is a little bit more massive than the Earth.
00:36Do we have a super Earth beyond Neptune? Maybe?
00:41So we talk about Planet Nine, a potential ninth planet in our solar system.
00:46If it exists, we think that it might be tugging on other objects out there,
00:52right at the edge of the solar system.
00:54If it's out there, it's extremely far away, therefore very faint,
00:59because it doesn't reflect much sunlight.
01:00And it's also moving extremely slowly. Nobody's found it yet, but it's hypothesized.
01:07Real Scientists asks,
01:09How do we find exoplanets?
01:11Even though the idea of exoplanets has been around for a long time,
01:14they have only been confirmed in the last 30 years.
01:17They are really hard to find.
01:19They are really hard to find.
01:21So there are a couple of main ways that we detect them.
01:24We can't directly image them most of the time.
01:28They're just too faint compared to their host star.
01:31And trying to photograph an exoplanet is like trying to photograph a firefly next to a lighthouse.
01:36Instead, what we have to do is try to figure out the presence of a planet
01:41based on the influence it has over its host star.
01:44One of the main techniques we use to find exoplanets is called the transit method.
01:50This is where a planet passes in front of its host star and blocks out a little bit of light.
01:56If we measure the brightness of a star at repeating intervals,
02:00we can actually see the star seem to get a little bit more dim as the planet passes in front
02:05of it,
02:05and then it brightens again once the planet has passed all the way past it.
02:09We've found more than 3,000 planets this way.
02:12There's another technique that is also pretty successful,
02:16and it's called the radial velocity method, or sometimes the Doppler method,
02:20or sometimes the wobble method.
02:22This is where we actually see the star moving in space.
02:26We can't see what's pulling on it, but we can see that the star moves,
02:30and we infer that there's a planet orbiting it,
02:33dragging it around with its gravity.
02:36What we can do is actually measure the Doppler shift of the star's light.
02:40When the star's moving towards us, its light is blue-shifted,
02:43and when it's moving away, its light is red-shifted.
02:46So we infer that the star is moving, and it's being yanked around by a planet.
02:53Casey Hall asks,
02:55My toddler makes me read about space,
02:57watch things about space, talk about space.
02:59I'm just out here pretending I have any clue.
03:01Sorry, but WTF is an exoplanet.
03:04Well, I also have a toddler, so I can totally relate.
03:07An exoplanet is just a planet outside of our own solar system.
03:11It's a planet that orbits another star,
03:13and we've found thousands of these exoplanets.
03:15We're up to over 6,000.
03:18They're everywhere in our galaxy.
03:20Probably every star has an exoplanet.
03:24Financialsun6933 asks,
03:26Is a planet orbiting two suns at once actually possible IRL?
03:30Yes, it is, and we have found planets just like this.
03:33This is actually a pretty unlikely configuration,
03:35and they're very difficult to find.
03:37So these are called circumbinary planets.
03:40The star itself, the double star, is called a binary.
03:43Kepler-16b, for example, is a circumbinary planet.
03:46It's one of the first ever discovered.
03:49If you've seen Star Wars, like the original film,
03:52on Tatooine, there's an image of two suns rising.
03:55So Tatooine is actually a circumbinary planet.
03:58It orbits both stars at the same time.
04:00So binary stars, stars that have another star for a companion,
04:06are actually the most common type of star in the galaxy.
04:10Most stars are binaries.
04:12Our sun is actually slightly unusual in that we don't have another sun.
04:17StarTalk Radio asks,
04:19What is the most extreme exoplanet?
04:21We could talk about the hottest exoplanet,
04:24which orbits its star extremely close in,
04:28and it's basically as hot as a star is.
04:31It's so hot, in fact, that on its dayside,
04:34molecular hydrogen, like H2 molecules, are actually split apart.
04:38We could also talk about planets that are extremely eccentric.
04:42Most exoplanets sort of orbit in a circular way,
04:46like the Earth has a very circular orbit,
04:48but some planets don't.
04:50They orbit in a sort of oval shape, like an ellipse.
04:53And these planets have extreme temperature swings.
04:57There are some planets that are actually kind of disintegrating as we watch.
05:01So these are planets very close to their host star,
05:05that have a big, extended, puffy atmosphere,
05:08which actually seems like it's kind of being blown away from the planet.
05:13A few different options for extreme planets there.
05:17Fluorescentlightbulb asks,
05:18Explain like I'm five, what makes the Earth so gosh darn livable?
05:22How is it different from the other planets in our solar system,
05:24or viewable planets in our galaxy?
05:26We have liquid water here because Earth's in the habitable zone,
05:29and also because it's small and rocky, and it has a discernible surface.
05:33But there are a lot of other qualities that make Earth pretty perfect for habitability and life.
05:39It has a pretty strong magnetic field, and that magnetic field shields us from solar radiation.
05:47Earth also has an atmosphere, which we think is essential for life.
05:51Plate tectonics, we think, might be important for life,
05:54because plate tectonics allow us to actually almost moderate the amount of carbon that's in the atmosphere.
06:01And this kind of keeps the planet in equilibrium, and it actually solves something called the faint young sun paradox.
06:08Our sun used to be fainter and dimmer, and yet the planet Earth has sort of always maintained roughly the
06:16same average temperature.
06:17As the planet gets warmer, there's more rain, more evaporation, more weathering of rock, and rock weathering removes carbon.
06:26Another thing that makes our planet special is that we have a large moon which actually stabilizes Earth.
06:31And without it, axial tilt might change, and it would send the seasons sort of totally out of whack,
06:37and the Earth itself would experience massive climactic swings.
06:42Overall, we're at a pretty steady state, and we think that this is probably a prerequisite for life.
06:49Courtney W. Rocket asks,
06:51Have we discovered any habitable planets yet? Because I'd really just like to start over.
06:56Unfortunately, we haven't discovered anything that we know for sure is habitable.
07:00So what makes a planet habitable? The main thing, we think, is the existence of liquid water on a surface.
07:08This means a planet has to be about the right distance from its star to be the right sort of
07:13temperature for liquid water.
07:14It also means that the planet has to be relatively small, like Earth.
07:19Because big planets like Jupiter, Saturn, they tend not to have a discernible surface.
07:24They're actually mostly made of gas.
07:26But there are a lot of other criteria, probably, that make a planet habitable.
07:32For us on Earth, we have a stabilizing moon, which stops our orbit from changing too much.
07:39We have a magnetic field, which prevents solar radiation from irradiating the surface of Earth.
07:46We have an atmosphere.
07:48We have plate tectonics.
07:49Have we found planets in this habitable region, the distance, that makes liquid water possible?
07:57Yes, we have.
07:58Most of these planets, however, orbit stars that are very different from our Sun.
08:04Most of these planets orbit little stars, M-dwarfs or K-dwarfs.
08:09K-dwarfs are a little smaller than the Sun and M-dwarfs are a lot smaller than the Sun.
08:12The problem with that is that M-dwarfs are very magnetically active.
08:17Think solar flares, they have coronal mass ejections, which are storms of harmful, high-energy particles, leaving their surfaces and
08:27potentially blasting these exoplanets.
08:30The James Webb Space Telescope has been looking for signs of atmospheres on habitable zone exoplanets orbiting M-dwarfs, and
08:39so far it hasn't found any.
08:41So, we're now starting to wonder whether, actually, maybe the star has to be just right as well for a
08:48planet to be habitable.
08:50Evan Slayers asks,
08:52Which exoplanet do you think has the greatest chance of harbouring life?
08:57Hashtag ask NASA.
08:58One of the main targets in the search for life is the TRAPPIST-1 planetary system.
09:04The problem with TRAPPIST-1 is that it is a very active M-dwarfs star,
09:09with an extremely strong magnetic field, and the planets orbiting TRAPPIST-1 are blasted with its radiation.
09:16Now TRAPPIST-1 has three planets in the habitable zone, and we don't yet know whether or not they have
09:21atmospheres,
09:22but the James Webb Space Telescope is working on it.
09:25I think a better candidate is a star called TOI-700.
09:30It has two exoplanets in its habitable zone, and it is also an M-dwarfs, so it's a small star
09:36with a strong magnetic field.
09:37TOI-700-D and E are probably my bet for the place most likely to have life.
09:44TOI-700 is old, really old.
09:47Old stars tend to be more stable, more peaceful, more sanguine, more calm, a bit like our own sun.
09:55And so TOI-700 doesn't have so much strong radiation blasting its planets.
10:01A reddit user asks, explainnicam5, if the sun is getting hotter in billions of years, does that mean that planets
10:08further away from us may become suitable for life, while Earth may not?
10:12Yes, the sun is getting hotter, and the habitable zone in our solar system is moving outwards.
10:18And it's actually been doing this for a really long time, and in a billion years from now, the Earth's
10:24oceans might evaporate, and the Earth itself will not be habitable.
10:28Humans have only been around for like 300,000 years, so we've got a lot of time to figure it
10:32out.
10:32It does mean that Mars is going to get warmer and warmer, and is going to move into the habitable
10:38zone even more, and it will stay in the habitable zone for quite a long time.
10:43JobMegans1 asks, can't help but wonder if an alien civilization would have detected Earth the same way we detect exoplanets.
10:51There's actually a zone that's called the Earth transit zone, which is like a plane, which is where an alien
10:58would have to be to be able to look back at the sun and see the Earth transit.
11:03Probably, if there are aliens out there scanning the skies, looking for Earth-sized exoplanets, they might have spotted us
11:12if they live in that Earth transit zone.
11:14If an alien has seen us, why haven't they said hello yet?
11:18It takes a really long time for light to travel across space, so it could be that distant aliens haven't
11:24really noticed our presence yet,
11:27because human technology hasn't been around for all that long in the grand scheme of things.
11:34BlackAnti asks, how do we know what exoplanets look like?
11:38We could know its mass, because we can measure the radial velocity or Doppler shift of the star as the
11:45planet orbits.
11:45And if you have radius, you have size, and you have mass, then you know something about the density of
11:52your planet.
11:53Maybe a planet's around the right density to be entirely made of water.
11:57Or maybe it's around the right density to be extremely heavy, like mostly made of metals and rock.
12:03Mostly I've talked about exoplanets transiting their stars, so passing in front of the star.
12:08But planets can also pass around the back, and if they're extremely hot and they glow brightly in infrared,
12:16we can actually see when they pass behind the star, because we lose their signal.
12:21And we can even map the hot spots on the surface of a planet, and we can figure out what
12:29the winds might be doing,
12:30and understand, relatively speaking, what they might look like.
12:34So some of those exoplanets that we've discovered are actually pretty bizarre looking.
12:42ProudReaction224 asks,
12:43Explain like I'm 5 how scientists can figure out the composition of exoplanet atmospheres.
12:48Often the way we do this is by observing a planet as it transits its host star.
12:54Most of the light coming from the star is going to pass directly through space into our telescopes.
13:00But some of the light is going to filter through the planet's atmosphere on its way to our telescopes.
13:06And as it does that, as it passes through a planet's atmosphere, it's changed.
13:12Gas molecules in the atmospheres of planets absorb light at certain distinct wavelengths.
13:18Carbon dioxide, for example, removes certain colours. Oxygen removes certain colours.
13:24And we can infer the presence of these molecules in the atmosphere of an exoplanet
13:29by seeing where those colours are missing as a planet passes in front of its host star.
13:34It's much easier to do this for a big puffy planet because you get more light passing through the atmosphere.
13:40For planets like Earth, the atmosphere is actually just a teeny tiny layer on top of the rocky core.
13:46And so you don't really get very much star light passing through the atmosphere.
13:50It's really difficult to do this for Earth-like planets.
13:54PrinceOfAtheism asks,
13:55Just learned there's an exoplanet nearly the size of our Sun.
13:58I wonder, are there planets bigger than stars?
14:01The maximum size for an exoplanet is about the size of Jupiter.
14:05You could try adding mass to Jupiter, but what you would actually do is just increase its density and not
14:11its size.
14:12The smallest stars, m-dwarfs, can be extremely small, about as small as Jupiter.
14:19So can you get a star that's smaller than a planet?
14:23Actually, in certain circumstances, perhaps you could.
14:26So some Jupiter-sized planets that are very close to their host star are actually irradiated so strongly that they
14:35are so hot that they actually puff up a little bit.
14:38So you can get a planet that is a little bit bigger than Jupiter.
14:43Adam Aloka asks,
14:45What does it take for us to be able to take images of exoplanets?
14:49You need to have a planetary system that is relatively nearby.
14:52You have to block the light from the star using something called a coronagraph.
14:57When we're trying to get these really, really high-resolution images from the ground, the atmosphere makes it difficult.
15:04You know when you look at a star, you can see it twinkling?
15:07That is because the light from that star passes through a column of air that's turbulent, winds, etc.
15:14And as it lands on the telescope, that twinkling messes up your observations basically.
15:20You can't resolve really small distances in your images.
15:24So what you can do is shine a laser through the atmosphere that allows you to predict the motion of
15:32the air and then the starlight falls on a mirror that you distort to counteract the variations in the air.
15:40And this is called adaptive optics and it allows you to focus light really extremely precisely and get these precise
15:48images of exoplanets.
15:51Zayad Shalabi asks, so the Webb telescope already detected water in the form of steam on an exoplanet already.
15:59And I wonder if we will detect signs of life like methane soon.
16:03Water is a really common molecule in the galaxy, it turns out.
16:08And a lot of exoplanets do have water.
16:11You were also asked about methane.
16:12So methane is a molecule that's produced by life and it's something that we would call a biosignature gas.
16:20The problem with methane and a number of other single molecules is that there are lots of ways to make
16:27methane that actually doesn't have to involve life at all.
16:29So methane on its own is not a perfect biosignature.
16:34And now the consensus is that we actually probably want to look at a combination of two different molecules.
16:41So for example, methane and oxygen together, because the two methane and oxygen should not naturally coexist.
16:49If they are seen together, it's basically a sign that methane and oxygen have to be constantly produced, perhaps by
16:58something like life.
17:00Peter Corliss asks, which exoplanet fascinates you most?
17:05One of my favourite exoplanets is called 55 Cancri e.
17:09The planet is a super Earth. It's more massive than the Earth.
17:13It orbits extremely close to its host star. It whizzes around every few hours.
17:20Its whole year is shorter than an Earth day.
17:23And it's so hot that we think it's actually a lava world.
17:26And yet it's held on to an atmosphere.
17:29That atmosphere is probably constantly being outgassed.
17:32So it's being replenished. Maybe it's being stripped away at the same time.
17:36It's almost like a beacon of hope for me.
17:38Because it shows that planets can outgas new atmospheres and recreate them,
17:45even when their host star is doing everything it can to strip those atmospheres away.
17:51Sugar and Blots asks, I have recently heard that astronomers have found an exomoon.
17:57I am quite scientifically illiterate.
17:59So what exactly is an exomoon and could it affect us on Earth?
18:03An exomoon is a moon in another solar system.
18:06We have tons of moons in our solar system.
18:09We're up to like basically 900 or something like that moons.
18:12So if our solar system has so many moons, it would be surprising if other planetary systems didn't have any.
18:19Moons also present another interesting possibility for life.
18:23So in our own solar system we have icy moons, Europa and Enceladus.
18:27And these moons are actually warmer than they should be.
18:31They're outside the habitable zone, but they have liquid oceans under an icy crust.
18:36The reason for that is that they orbit massive planets that have strong tidal forces.
18:43So we're actually, we think maybe there's life on our own icy moons in our own solar system.
18:49And if icy moons could be a place for life to hang out,
18:53then there's lots of opportunities for icy moons to exist elsewhere in the galaxy.
18:57And another potential host for life.
19:01Heather JS asks, WTF, no one's concerned about rogue planets?
19:05Rogue planets are these solitary planets that don't have a host star.
19:10They probably once did, but interactions maybe with other planets in the planetary system
19:14has sent the planet outwards.
19:17So we think that there are thousands and thousands, maybe millions or billions,
19:22of rogue planets out there in space.
19:27John Olog asks, How does finding planets in habitable zones affect SETI?
19:32Do we point instruments at these planets?
19:34SETI is the search for extraterrestrial intelligence.
19:38This is really more about techno signatures rather than biosignatures.
19:41It's searching for things like narrow band radio emission.
19:45It's searching for potentially laser signals.
19:48It's searching for also things called Dyson spheres.
19:52A Dyson sphere is where the entire star is covered in solar panels.
19:56It would look like a very dim object that's very bright and infrared.
20:01There's a lot of space to cover.
20:02There's a lot of stars to look at.
20:04And so in fact, SETI's really only covered like a very small number of stars,
20:09but it's still searching.
20:11Myth and Dears Ghost asks, How do we know that exoplanets aren't sunspots or star spots?
20:17Spots on the surface of a star, like our sunspots on our own sun,
20:21are two-dimensional for the most part.
20:24So as a star rotates, you can see a spot coming into view,
20:30and that spot actually makes the star a little bit more dim overall,
20:34just like a planet does.
20:35A planet is a solid object, and it passes in front of its star without being foreshortened on the limb.
20:43So variations in starlight caused by spots tend to be smooth,
20:48because as spots round the corner, they almost disappear, they sort of flatten.
20:53Whereas planets, as they transit, they sharply block the star's light.
21:00So transits tend to look like very sharp dips.
21:03When we search for planets using the Doppler method,
21:07the star itself actually has a Doppler signal.
21:11And this is a massive problem.
21:13Our Earth orbiting the sun actually makes the sun move a little bit,
21:17because both the Earth and the sun orbit the centre of mass of the Earth-Sun system.
21:24The Earth is dragging it around as it orbits.
21:27But it's doing that very slowly.
21:29The sun itself has its own Doppler signal.
21:32It's shifting and roiling and pulsating.
21:35And that signal can be larger.
21:37And a lot of the time when we find exoplanets using the Doppler method,
21:41they turn out not to be real.
21:43They turn out just to be interference from the spots.
21:47If you've seen the movie Project Hail Mary,
21:50Forti Eridani, the planet that Rocky is from,
21:53was thought to be a real planet when Andy Weir was writing the book.
21:57And it later turned out that it was probably not a real planet.
22:00It was probably just some spots on the surface of the star that acted like a planet.
22:06And unfortunately, Rocky's homeworld might not be real.
22:09But it still lives on in our hearts and minds.
22:13Brat asks,
22:15Interstellar, how is it possible for the waves to be so big on the water planet if the gravity is
22:20stronger?
22:20The water planet in Interstellar is a planet that's orbiting a black hole,
22:24and it has extremely strong tidal forces.
22:27And it's tidally locked to the star.
22:29Tidal locking happens a lot.
22:31The moon is actually tidally locked to the Earth.
22:34The moon's rotational period, how fast it spins,
22:37is exactly the same as its orbital period, how long it takes to go around the Earth.
22:42So it always shows the same face to the Earth.
22:46This water planet that orbits a black hole is the same.
22:49It has these big tidal bulges on each side,
22:52on the side facing the black hole, and on the side away from the black hole,
22:56because the planet's distorted into this football or rugby ball shape.
22:59And the waves on the planet are created by these tidal forces.
23:05The tidal bulges actually should stay put.
23:07They shouldn't move around.
23:08So you'd have a shallow part of the planet,
23:11and you'd have a deep part of the planet,
23:12and you wouldn't necessarily have waves, like,
23:15traveling and rippling across the planet like you do in the film.
23:18If the planet wasn't quite tidally locked,
23:21if it was moving around just a little bit,
23:23perhaps you could get some sort of sloshing back and forth of the ocean,
23:27and maybe you could make these kinds of exotic waves.
23:30Maybe that is what Kip Thorne was going for in the science.
23:33I'm not totally sure.
23:35Those are all the questions for today.
23:37Thank you for watching Exoplanet Support.