Why is the TRAPPIST-1 system so fascinating? Is it really habitable? How are we figuring all this out? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPT (AUTO-GENERATED)
I love talking about exoplanets. Which if you haven't tuned into the latest astro jargon yet, exoplanets are planets orbiting other stars. They are extrasolar planets, hence exoplanets. I mean, I'm sure our home solar system has so many cool things going for it. There are four giant planets, there are liquid water oceans under frozen icy moons, there's a planet with this giant magnificent ring system.
Oh, yeah. There's that one planet with life on it too. There's lots of cool stuff happening in our own solar system, but I've said this before and I'll say it again in including right now. The worlds that we are discovering around other stars are unlike anything we could have possibly ever imagined. The best sci fi authors in history haven't even come close to what's actually out there in the real universe just a few dozen light years away.
And that's just crazy to think about like, I want you to imagine right now in your head, close your eyes, I don't care if you're driving, close your eyes. Imagine a crazy complicated super exotic alien system. One, nature already has that. It's real. It exists.
And two, nature has something even cooler. Case in point in the subject of today's episode, the Trappist one system, which is a family of planets orbiting a star just about 40 light years away. First, I want to talk about the name Trappist one. Its original name TRAPPIST one is not the original name for this star 40 light years away. Its original name is are you ready for this?
I'm gonna tell you the whole thing. 2MassJ23062928DashO502285. Doesn't exactly roll off the tongue. I'm glad they switched it to the name Travis, and I'll get to why in a bit. But let me break down this name and why it's important.
The 2MASS, two m a s s, stands for two micron all sky survey. It was a survey taken decades ago back in the late sixties, I think. And the two micron is a clue that what we're about to talk about is weird and wild and also kind of wonderful. Two microns, this is the wavelength. This is the wavelength of light that the survey was taken in, and this wavelength of light is in the infrared.
It's not the visible portion of the electromagnetic spectrum. It's the infrared. That means that this star that is only 40 light years away cannot be seen with the naked eye. It was only discovered through a survey of the infrared portion of the electromagnetic spectrum. It's 40 light years away folks, and you can't see it with the naked eye.
In fact, you can't really see it or it's hard to see it, very hard to see it with a regular telescope. You have to switch to an infrared telescope to see it. What kind of star could that possibly be? It's a small red dwarf star. That's what.
And it's dim. Not just a little bit dim. It is dim. I'll get to the details in a second. It's also small.
It's also tiny. It's also red. It's also infrared. It is a small red dwarf star. But the name.
But we don't call it two mass j whatever whatever whatever anymore. We call it Trappist one, and that's because a gang of astronomers in Belgium, A Few Years ago, decided to go hunting for exoplanets because, you know, it's it's a kind of a cool thing to do in astronomy. And they were also very fond of a beer made by the local Trappist monastery because who isn't? And so they decided to call their planet hunting telescope the TRAPPIST telescope, and then they worked out an acronym to fit the word TRAPPIST, and they came up with Transiting Planet and Planetesimal Small Telescope. Okay.
Like, if it kinda sort of forms the word TRAPPIST, I suppose, if you've had enough of their beer. And what do you know? Using the Trappist Telescope Observatory, they found a bunch of planets orbiting the star to mass j blah blah blah blah blah. And if you had the option of naming a star after a beer, I think you would take it too and so the star was renamed Trappist one because this is the first time they found planets orbiting around a star using the Trappist Observatory, hence Trappist one. And yes, I am perfectly aware of the fact that I'm devoting an entire episode to the family of planets around the Trappist one star several years after the discovery.
You're just gonna have to live with that. Okay? Anyway, back to the star itself. Don't worry. We're gonna dig into the planets because they're weird and wild and wonderful, like I said.
But I want to talk about the star itself because that's part of the weirdness. I've talked about red dwarf stars before in other episodes about how they're tiny, they're red, and they're dim, but Trappist one is ultra tiny, ultra red, and ultra dim. This star is barely bigger than Jupiter. It's barely bigger than Jupiter. It's much more massive.
It's massive enough to trigger nuclear fusion in its core, but its size is not much bigger than the planet Jupiter. And even though it has enough mass to ignite nuclear fusion in its core, it's not even a tenth of the mass of the Sun and it has just point 2% of the volume of the Sun. So our Sun is gigantic compared to this thing. Because it's so small, because it's so feeble, it emits light almost entirely in the infrared portion of the electromagnetic spectrum. Its surface temperature is less than half the surface temperature of the sun, so it's mostly infrared with just a little bit of red leaking into the visual spectrum.
So if you were to look at it with your naked eye, it would appear as very, very red, but a dim, almost brownish red, like, almost barely there red. If you were to put on infrared goggles, it would light up like a star, I guess. I ran out of metaphor. It would light up light up like a red dwarf star. In the infrared button visual, it's just nothing.
The total luminosity, which this is another astronomy jargon word, luminosity is the total light output of a star or the energy output of a star. The total luminosity across the entire electromagnetic spectrum is less than a tenth of a percent of the Sun. So this star, this red dwarf star, Trappist one, puts out less than a tenth of a percent the amount of light that our sun does. In the visual part of the electromagnetic spectrum, remember most of that energy coming off Trappist one is in the infrared. The visual part, the part that you can actually see with the eyeballs compared to the sun is point 003%.
So visually, it looks about a thousandth as bright as the sun. It's about a thousand times dimmer than the sun. Hence, we couldn't see this star until we started doing massive infrared surveys despite the fact that it's basically right next door in our galactic neighborhood. This star is much much older than the Sun. It's twice as old as the Sun.
It's about 8,000,000,000 years old, and it will probably live to for over ten trillion years, because, yeah, red dwarfs are awesome in that way. They don't need to burn a lot of hydrogen to keep themselves stable, to keep themselves warm, to counteract the collapse of gravity from their own weight, because there isn't a lot of stuff going on. There isn't exactly a lot of weight to fight against, so they can hold it up a lot longer than something like our sun. And the way red dwarfs are constructed, they can circulate their material from the core to the outer reaches of their atmospheres, So they have a lot more hydrogen available in the gas tank than something like our sun does. And so these two things combined give them extremely long lifetimes.
So even though our sun at four and a half billion years is halfway through its life cycle, this star, Trappist one, at eight billion years is barely even out of diapers. It's not even out of diapers. It you it's not potty trained yet. That's how young this star is compared to its total lifetime. But we don't care so much about the star.
It is, after all, just another red dwarf in the galaxy. It is by far the most common kind of star in the Milky Way, but, you know, whatever. What we care about are the planets, and there are seven of them. They have names. Well, they have labels.
The closest one to the Trappist one star is called planet b, and then next one out is c, and then d, e, h, I. Oh, no. Not I. I went too far. It's just b through h.
There's only seven planets. So Trappist one b is the name or the label for the planet that orbits closest to the Trappist one star, and Trappist one h is the name of the planet that orbits furthest from the Trappist one star. For once, an astronomical naming system that actually makes sense even if it's unoriginal and boring, but, hey, it's logical, so we're gonna take it and not complain. All these planets, by the way, all seven of them are Earth like, which hold up here. We hear this word a lot in exoplanet discussions.
Earth like. This term can be confusing and or aggravating because really what it means is that these plants are about the same size as the Earth. That's when an astronomer says we discovered an Earth like exoplanet, it means we found a planet that is about the same size as the Earth. So Venus is Earth like. Mars is Earth like.
In this very strict narrow, definite jargon definition of the word Earth like, it is not what you might imagine the word Earth like to actually mean, which is somewhere maybe livable and warm and where you can take a summer vacation to. I'm sorry. I am not in charge of jargon as much as I try. Earth like means about the size of the Earth. So there are seven planets orbiting this red dwarf star, and all seven of them are about the size of the Earth.
What makes this even more interesting is that three of them orbit within the habitable zone of the star. The habitable zone of a star, and it's different for every single star, is the range of orbits where you're not too close, where the extreme heat from the star boils off all your water, and you're not too far from the star where the lack of extreme heat from the star makes all your water freeze up. It is the range of orbits where liquid water, if conditions are right, can be, well, liquid. That is the definition of the habitable zone. It does not really tell you a lot.
For example, in our own solar system, Venus, Earth, and Mars are all in the habitable zone of our sun, but I wouldn't exactly call Venus habitable. There is liquid water in the outer parts of the solar system far outside the habitable zone. They're locked under shells of ice in the moons around the gas giants. So again, this is not the most helpful jargon term, but it's the only one we got. In around Trappist one, there are three planets out of seven in the habitable zone.
Four of these planets, the other four by the way contribute to Patreon. That's patreon.com/pmsutter. It is their contributions, these four planets orbiting Trappist one and yours combined that keep this show going. Thank you to you and to them for their contributions. The smallest planet, it has a radius about three quarters of that of the Earth, and the largest is just a titch over.
It's like 15% wider than the Earth. So, yeah, definitely Earth like. More Earth like than Mars, by the way. How do we know that Trappist one has a family of planets? How do we know their sizes?
We get this through the transit method. The transit method relies on really really lucky chances. Where if you stare at a star long enough, and if that star happens to have some planets around it, and if those planets happen to have orbits that just happen to line up and cross your line of sight to that star, then as you're staring at that star, it will dim just a tiny little bit as that planet blocks some tiny fraction of that light. And then when the planet leaves the line of sight, the star resumes full brightness. And then you wait a few days or a few months or a few years depending on the orbit, and it happens again and again and again.
This relies on lucky chances because the orbits have to be aligned just right. You know, the planets have to cross their star right when we're looking. We get over this by studying, like, thousands of stars at once, and then we get lucky with a few of them. And that is what these Belgian astronomers figured out with their TRAPPIST telescope. They saw not just one transit, but seven different transit events repeating over and over and over again.
And they were able to get the sizes of these planets through the transit method itself. When that planet starts to cross in front of the face of the star, we see a little dip in brightness. And then that dip will get bigger and bigger. The star will appear to get dimmer and dimmer as the planet moves into view, almost like it's an eclipse. It's it's like a miniature version of an eclipse.
The star will get dimmer, and then it will bottom out because now the entire planet is in front of the star. It's blocking as much light as it can, and then on its way out, it'll do the exact same thing but in reverse. So by looking at how long it takes for the star to do its niming, we can figure out the width or diameter of the planet. So that's how we know these planets exist. That's how we know how big these planets are.
And there's something really cool about how these planets orbit their sun. I'd mentioned that three of them are in the habitable zone, just like there are three planets in the habitable zone around our sun, but that doesn't give the full picture. Remember, this is a red dwarf star. This is not a bright star. This is not a big star like our sun.
This is a tiny star, and this is a very dim star. If you want to be in the habitable zone of a dim star, you have to be close. And I mean close, Like, within your personal bubble close, uncomfortably close, jam packed subway car close, closer than Mercury is to our own sun. That's right. All seven planets in the Trappist one system are closer to their star than Mercury is to our sun.
To give you a sense of how close this is, the nearest planet, little b, Trappist one b, its entire orbit takes one and a half days, Earth days. One and a half days. Thirty six hours. Thirty six hours that planet whips around its star. In the farthest one planet, h all the way out there takes nineteen days.
Mercury's, the closest planet to our Sun takes eighty eight days to orbit. Eighty eight. These planets are ridiculously close and compact in their system. They are so tightly packed that they are visible from each other. You can stand on the surface of one of these planets, look up and see the surfaces of the others, And if everything's just right, you can see the surfaces of all the others better than you can see the surface of our own moon.
Plus, there's that red dwarf star eating up a good chunk of your sky. This is a truly alien world. Right? The size is relatively easy. The distance is relatively easy to get from transit observations, but we really want to know about the density.
Why do we want to know density? Because density tells us what a planet is made of. Because there's only so many things in the universe. There's only so many different ingredients. There's hydrogen, there's helium, there's water, there's carbon, there's silicon, like, we have a list of the elements and the most common molecules.
Each one has a different density. Each one has a different, fraction in the primordial soup. Like, if you're gonna make a star system, you basically know from observations of the interstellar medium and how stars form, that there's gonna be a certain fraction of hydrogen, a certain fraction of helium, a certain fraction of carbon, a certain fraction of water, etcetera, etcetera. So, when you measure the density of a planet, you get a much clearer picture about what a planet is made of. If the density is very very low, then you're probably looking at a gas giant.
Lots of hydrogen, lots of helium, lots of light stuff. Remember like Saturn, it is less dense than water. And if you're looking at something super dense, very very dense, then you know this is like an absurdly rocky planet with lots of iron and heavy metals and nickel and things like that. We want to know if these planets have a similar density to the Earth, but this is a pretty hard number to get because in order to get the density, you need the mass. Now we know the size of these plants, we know their widths, but we don't know how heavy they are from transit observations.
It takes more observations. It needs something called, feel free use this jargon word whenever you want, TTV or Transit Timing Variations. The gist of it, I'm not gonna go into detail. The gist is that as these planets orbit their star, they all have their own masses, and they're all like subtly and gently poking and nudging and tweaking each other very, very subtly changing their orbits. I'm just tiny like like if you're planet b and you're over here and then planet h is over on the same side of the star as you, it might give you a little tug.
And if planet h is on the opposite side, it might give you a little tug in the opposite direction. So by watching transit after transit after transit after transit, you can start to build up a picture of their orbits and you can start to build up a picture of their tiny little influences on each other. It's kind of a hard problem, gives but it does give us our best estimates of their masses. Once you have the mass, you take their volume. Mass divided by volume, you get the density.
And the densities of these seven worlds are, well, weird and wild and wonderful. The least dense one has a density about half that of the Earth, and the most dense one, the densest one is just a tish above Earth density. So here we have seven worlds all in close orbit, all roughly the same mass, all roughly the same size, and all roughly the same density of the Earth. And what are these densities telling us? Well, they definitely do not have thick gassy atmospheres, like gas giant style thick, like really really gassy, like they've got a problem gassy because the densities are too high for that.
But all the densities are generally smaller than the Earth's, suggesting that there's a lot of and again, here I am with another lame, unhelpful astronomy jargon word. The unhelpful astronomy jargon word that we're using today. What we already have, like, what? Habitable zone, Earth like. Now we have volatiles.
I swear I'm not making this up. In astronomy circles, a volatile doesn't mean what you think it means. A volatile means that it is a kind of element that doesn't stick around for long. It could mean a form of gas. It could mean a form of liquid.
It could mean a form of solid. I I know that doesn't really narrow it down. It generally means light stuff. It generally means waters and ices and gases. Like, it's the big thing.
So if you're not a rock, alright, if you're not iron or silicon or magnesium, you're gonna be a volatile. I'm sorry. Okay. Let's just move on. The fact that the densities are pretty low or lower than the Earth suggests that they have more volatiles than the Earth.
So they probably have more liquids and gases than the Earth does. Not enough to make them a gas giant or, like, mini gas giant, a gas dwarf. I don't I don't know. What we think is happening is that there's a lot of water. I just skip and go right to the punchline.
We think that there's a lot of water. In some of these planets, we think that up to 5% of the mass of these worlds is in water. To give you a sense of how much water that is, the Earth is less than point 1% water. So there is a lot of water we suspect on these worlds. Could they be water worlds or locked in ice?
We're not exactly sure. But let's let's break this down planet by planet. Once you combine the density information, which with where they are in the solar system, you can start to make a best guess about what this water is doing and what these planets are doing. When it comes to the close ones one b and one c, we think they have very rocky cores and very thick atmosphere, something like Venus. It's too close for water to hang out for long.
One d is the lightest planet, and it's really hard to tell. It could be a rocky planet with a very large atmosphere, or it could be an ocean world. We're just like a giant liquid water ocean miles and miles and miles deep covering the entire world, or it could be completely encased in ice or some combination thereof. The outer worlds, f, g, and h, definitely most likely water because there's water everywhere, but it's so far out from the star that is probably ice. So they probably have super thick ice layers on their surfaces.
Maybe with liquid water underneath, it's it's very hard to tell, but probably thin atmosphere is just because they're so far out. One e is very interesting. It has slightly higher density than the Earth. So it doesn't have, like, a super thick liquid water ocean because that the math doesn't work out. It doesn't have a super thick gas in the atmosphere because that math doesn't work out.
It has some sort of maybe reasonable Earth like atmosphere. That's interesting, isn't it? I'll get back to that in a little bit later. First, someone answer a question. How did this system form?
Well, we don't really know. There there welcome to modern astronomy. There are two ways to make a planet, folks. You can if you're trying to make a rocky planet, you generally have a picture where you have a bunch of tiny little pebbles gluing onto each other and slowly building up over the course of a long time. Or if you're trying to make a gas planet, there there are instabilities, and where a a big section of a protoplanetary disk can just very quickly collapse and form a big envelope around something.
That's how you build a gas giant. These planets are weird because they couldn't have formed in the same way that planets in our solar system form. It like, the same processes that form the rocky planets of our solar system doesn't work, because they're too close into the star for that kind of process to work. But they're obviously not gas giant planets, so what we think may have happened is that these planets started out further away. They formed further away where they able to build up a lot of material and then some process brought them in close to the star.
So the upshot is that these worlds didn't form like anything in our solar system. They didn't form like the terrestrial planets in our solar system, and they didn't form like the giant planets of our solar system. Some sort of maybe hybrid approach, because that's our best guess, and our other models of how planets form just don't work. How did they get so much water? Well, that is definitely a big question, because that much water doesn't exist that close to a star when you're forming a star.
Like, most of the water, like, Earth got a bunch of water from cometary impacts later in its life. It lost the water that it formed with because our sun is big and bright and hot. Maybe these planets formed way farther out again, that's this piece of evidence that suggest these planets form farther out. They formed far out from their star where they could build up a lot of ice, get a lot of water, and then migrate in and then some of it melted. Is that realistic?
I don't know. It's our best guess. We got nothing better going on right now. But the million dollar question on everyone's mind is this. We have Earth like planets.
Some of them are in the habitable zone of the star. One of them is very similar to the earth in terms of density. Are there little creatures on there staring up at their blood red star? And the consensus is it's hard to tell if it's likely or not. One e, Trappist one e is by far the closest to Earth in density, so it might have an atmosphere similar to ours or not.
It is in the habitable zone of the star, but it is on the far edge in in context. It's the equivalent of being in our solar system somewhere between Earth and Mars. So maybe that's good, maybe that's bad. There is this issue, like, even if life got a start on one of these worlds like Trappist one e, there is this issue that it's not exactly the friendliest place for life. One of the issues is what's called tidal locking.
When you have a small thing orbiting a big thing in a really close orbit, you end up synchronizing your rotation and your orbit so that one side always faces the star, and one side always faces away. Like the moon is tidally locked with the Earth, we only ever see the same side of of the moon. We never get to see the far side unless we go there, but we can't see it from the Earth. We suspect that all these planets are tidally locked because they're so dang close to their star. There may be some possibilities where they're not, but it seems like a very small chance.
So even though these habitable zone planets, these three of them, are in the habitable zone, that's only on average. If one side of the planet is constantly facing the star, it's just gonna get a full blast of sunlight all the time. It's gonna be too hot, while the other side is in permanent night and it's gonna always be too cold. So even though on average, it's great, the average of negative a hundred on one side and a hundred on the other might be zero, but, like, you don't wanna live in either one. Maybe life could flourish in the terminator zone.
All the plant, you know, that twilight period, which is just permanent on these plants. You just pick a spot, and there's your twilight forever, where things can be just right. Who knows? Who knows? We have no experience with life in this context, so we don't have any idea.
The other issue is the star itself. Red dwarf stars are massively temperamental. I mean, they are just cranky. In fact, while we were observing in these Trappist one planets, we saw a surge of 50% in brightness just randomly from the star just being like, you know what? I'm gonna be brighter today.
Blah. Flares are much more common on red dwarf stars than something like our sun. And because those planets are so close in, they get the full blast. They can't avoid it. They have no distance.
They have no space between them and their stars, so they just get it. Anytime that star is mad, they get yelled at, and it's just nasty. There's a lot of UV heating during those flares that could have removed a lot of water, so these plants could have even had more water in their past, and then something like one e, the most Earth like one, could have had all its water stripped away. Who knows? Again, just who knows?
On the other hand, even though it's a kind of a nasty place with the tidal locking, extreme temperatures, flares, etcetera, etcetera, These planets are twice as old as the Earth and they'll remain in their habitable zones for trillions of years. So even though life may have a tough go at it on one of these planets, They sure do get a lot more chances than the Earth does. But could you just imagine what the experiences must be like on these worlds like Trappist-1e? The sun is red. It's dim but intense in this very weird combination.
It's beating down in the infrared. It's looming large, like, far larger than the sun is in the Earth's sky. If you watch carefully, you can see massive star spots blot out half its face as at a time. That's a warning that you have to hunker down because a giant flare and storm is on its way. That star is not alone in your sky.
There are other planets in the system that appear larger than the moon does to us. The star stays fixed. It doesn't travel across the sky. If you're on the day side, the sun is in one spot, and that's it. You're tidally locked.
But if you're on the dark side, you are locked in permanent night. But the planets in your solar system around Trappist one will move over the course of days and even hours. You can watch them dance in and out, entering your horizon and leaving the horizon back and forth. Like, just paint that picture. Like, the experience on these planets is unlike anything you could possibly imagine on Earth or even in our entire solar system.
The TRAPPIST one system is a potential home for life, and we're gonna hunt for it with instruments like the James Webb Space Telescope should it ever launch. It's hard to explain. It's full of mysteries, and it's also beautiful and wonderful. And it's only 40 light years away. Thanks to Ron r for the question that led to today's episode, and, of course, thank you to all my Patreon contributors.
That's patreon.com/pmsutter, especially my top ones this month. Shout outs to Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, Nuder Dude, Chris c, Robert m, Nate h, Andrew f, Chris l, Cameron l, Nalia, Aaron s, Kirk t, and James h. It is your contributions and everyone else's that keeps this show going. That's patreon.com/pmsutter. Go to iTunes, leave a review.
Those are always super helpful, and I really appreciate it. Shoot me some questions. Askaspaceman@gmail.com. Go to ask a spaceman dot com. Hit me up on social media with the hashtag askaspaceman.
I love it when you send me questions. I just love it. I love interacting with all of you. It is a real treat. It is a real pleasure, and I will see you next time for more complete knowledge of time and space.