It’s time for school! The Astro101 series will cover some of the most important questions in astronomy. In today’s lesson, we’ll have: How did the solar system form? What is a “planet” and who decided that? Just how much space is in space? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
Class is in session. Now, all cultures have known about five of the planets since basically forever. And it's it's easy to spot a planet on the sky. It it's the things that don't twinkle. It's the stars that aren't quite behaving exactly as stars should.
Now, the reason the stars twinkle is because there is a thin beam of light passing through our atmosphere and our atmosphere is a very complicated place with lots of hot air layers and cold layers and all shifting around and that bends the path of light. So if, if a light is passing through a cold layer and then hits a warm layer, it's gonna shift its path and then back to cold, blah blah blah, it's gonna wiggle around, it's gonna twinkle. And planets don't twinkle because they're close enough that they don't appear as a tiny dot of light. They appear as actually a small disc of light. So all that light is still getting twinkled up, but when you take a disc of light and just mix it up on the inside, it it still looks like a disc, and so the planets don't twinkle.
So immediately, you start to notice some weird things on the sky. And then planets do this other weird thing, which is change their position relative to the stars. As you track them night by night by night, they'll be close to another star, and then they'll get really close to it, and then they'll move far away from it, and then they'll be in between stars, and they'll approach another star, and on and on and on. And then sometimes they even go backwards. That's right.
Like, overnight tonight, you can see a steady progression of the movement of the planets, and then sometimes, they retrace their steps like they drop something, and then they continue on their way. We call this retrograde motion. The normal direction of motion is called prograde motion, by the way, but this is called retro grade motion. And I know it like, it's still in my news feed. I get, like, Mars is in retro grade.
And I was like, it means nothing. It just means now we know that it has to do with us catching up in our orbit and then passing them. So from our point of view, looking out to the distant stars, it looks like the planet is moving backwards, but that's just the same way, like, a racer on a racetrack running around will, from their point of view, the other racers that they're beating are moving backwards because they're going faster than them. But, you know, for thousands of years, we didn't know that. So we thought retrograde was really important.
And I've spoken about this transition speaking of going from not knowing anything to starting to know something. I I I did an episode about Kepler's laws way back when. That was a really fun episode. And the main thing I wanna communicate is that figuring out the motions of the planets to the ability necessary to actually predict their motions is really hard. And it's especially hard if you don't have that bird's eye view.
You can't shoot up a billion miles above the solar system and see, oh, yeah, I get it. All the planets are orbiting around. Now it's really easy. You don't get that when you're stuck to the surface of the Earth. And so people like Kepler had to figure it out from just observation, observation after observation.
And how did they do it? With everybody's favorite word, spreadsheets. Look at the work of Kepler or his mentor, Tycho Brahe. It is like, even the books they publish are just mostly spreadsheets. You know, on this night, at this time, this planet was in this position.
And then this night, at this time, this planet was in it, on and on and on and on. It is incomprehensible, and they didn't have, like, digital spreadsheets like we did. It was literally handwritten records. And then the the genius of people like Kepler, I can't imagine it to just look at tables upon tables of handwritten numbers and figure out a pattern in those tables of numbers. Like, that is a stroke of insight.
That is a stroke of genius. That is not something that I would have the patience to do. But, you know, Kepler was a different kind of guy as we explored in that episode, and so he was perfectly able to do it. And he came up with, well, a lot. He wrote, like, 15 book no.
Just I think he wrote two books total. And out of those two books, we get distilled three essential, what we call Kepler's laws, three essential rules for planetary motion. One is that Kepler realized he wrote a whole bunch. I need to interrupt myself. He wrote a whole bunch of stuff that we just, like, pretend doesn't exist anymore because we just it, like, looks like total nonsense, and it largely is, and it's not really useful for modern astronomy.
Three things survived, and those three things were pretty important. One is that the planets do not move in circles around the sun. They move in ellipses around the sun. The second is that this this law or a rule that we call equal area in equal time. So basically, it says when when a planet is on the path of its ellipse and it's closer to the sun, it's gonna move faster.
Then when it's farther away from the sun and that part of the ellipse is gonna move slower. So when it's really far away, it's gonna move nice and slow, and then it dives in for a nice speedy pass by the sun, then it gets nice and slow again, then nice and fast. That's basically what it's saying. And then Kepler realized or discovered a relationship between the distance of a planet from the sun and the speed of its orbit. He had no idea why planets moved in ellipses, in this equal area and equal time, and the relationship between the orbital period and the distance, he had no clue.
At the same time that Kepler was figuring all this out based on spreadsheets, Galileo went ahead and invented the astronomical telescope. He saw all sorts of cool stuff. I'd love to do an episode on Galileo, by the way. Just feel free to ask. A very, very interesting figure.
He saw the phases of Venus. Like, you know, you're used to the phases of the moon with crescents and gibbuses and full and and new. He saw the exact same thing with Venus, which was quite a bit of surprise. He saw moons of Jupiter, and he saw well, he saw the rings of Saturn, but he didn't really have the resolving power to know what they were. He just saw two lumps on either side of Saturn.
And then as he watched it over the course of the months months, those lumps would disappear and then reappear, and that was, like, really annoying and really confusing. But then eventually, with later observations, we realized that they were rings that he was seeing. After the invention of the telescope, yeah, we observed planets, we observed moons, and then there was a lot of focus on comets for a couple hundred years. Like, it seemed like every astronomer after the invention of the telescope was really a comet hunter, and then over the course of hunting for comets, accidentally make major groundbreaking discoveries like the discovery of a new planet. Of course, people were interested in comets because comets were interesting and random and strange and unexplained, so of course, you're gonna be interested in comments.
It took until Newton, a hundred years after Kepler, to actually put some explanation on the motion of the planets. He figured out universal gravity, which I went to into in-depth about why universal gravity, that concept is so dang important. If you haven't gotten the point by now, I'm just gonna keep on trying because I don't know what else to do. Universal gravity is one of the most groundbreaking realizations William Herschel in 1781, as he was comet hunting, discovered the planet Uranus. In fact, you can actually see Uranus with the naked eye.
So people have been seeing the planet for thousands of years, but it was too small and too dim to realize that it was a planet. In 1846, a bunch of astronomers spotted Neptune. In eighteen o one, shortly, just twenty years after Herschel discovered Uranus, Giuseppe Piazzi discovered Ceres when he was, wait for it, comet hunting. And as time goes on from the eighteen hundreds and on, we we get more and more powerful telescopes. We get more and more powerful techniques.
We get more We start to bring in photographs, that technology, that wonderful technology into the field of astronomy. Things like just really go nuts. And in our solar system, we'd start to discover smaller and smaller things, and things that are further and further away. And then we start categorizing them. We start putting them into buckets.
We start putting labels on them. We start trying to to classify things. At first, it was easy. Planet was just a wonder. In fact, planet comes from the Greek word for wonder, and that was all you needed.
Comets were weird and distinct enough. That was our solar system. We had planets, and we had comets. And then there were a bunch of stars that were really far away. Ceres, though, brought some trouble.
At first, maybe it's a planet, but then we discovered many smaller things in the same orbit, and there was an entire belt of, well, let's just call them asteroids, so Ceres got demoted to asteroid after being called a planet first. And then once we start introducing the concept of asteroids, we get into the weeds of solar system classification, And since this is an episode about the solar system, well, welcome to the weeds. Short version is it's a mess. There are so many objects of so many different sizes in so many different orbits that it's downright impossible to create a simple category system. There are bound to be overlaps and special cases and exceptions because because nature doesn't care about our naming conventions and categories.
But we keep trying to categorize all the objects in our solar system, put them into nice little buckets because that represents our understanding of the solar system. The categories are our understanding of the solar system. When we just have planets, that encapsulates in our entire knowledge of the solar system. When we have planets and asteroids, it means we understand a little bit more. If we have planets and dwarf planets and minor planets and small solar system bodies and Kuiper Belt and trans Neptunia, it means we know more about the solar system.
So, of course, with time, the classification and categories are gonna change, and we're just gonna have to deal with it. So let's start with planets. Up until 02/2006, there was no official definition. Why bother? A planet is a planet.
Duh. We've got comets, asteroids, planets. How is this so hard? But then we started to find a lot of things in the outer solar system just like we started to find things in the asteroid belt, but now this is further out, and we're faced with a frightening possibility of having thousands of planets in the solar system, and that really upset some people. And it's a valid argument.
Like, there's the one argument is, like, we can't have 10,000 planets. Kids are gonna have to memorize all the names, and that's gonna take forever. That's dumb because we have hundreds of billions of stars, and we don't memorize all star names. In fact, most don't even have names. But the worry was, could you have a category that is able to distinctly describe 10,000 objects?
Like, yes, there are hundreds of billions of stars, but a star is defined as an astrophysical body that is capable of nuclear fusion in its core. Boom. There. You have a nice simple straight definition. Doesn't matter how many of there are, but there's a simple thing that sets stars apart from everything else.
Now if you're going to say that there are 10,000 planets, that's fine. What's your simple definition of planet that encompasses 10,000 objects? Or in this what happened in 02/2006, do you need a separate classification system? Do you need planets to be over here and maybe be few in number and then something else over there with a lot in number? And in 02/2006, there is a meeting of the International Astronomical Union, which is the International Professional Astronomer Club, I guess, and they took a vote.
Now there are a lot of shenanigans about this, what happened in 02/2006. It was an IAU meeting over in Hawaii, I believe. Astronomers are always really good at picking conference locations, and 02/2006 did not disappoint. In 02/2006, I was not a member of the IAU. I was still a I just started being a graduate student, and so I I wasn't a member.
Years later, I would join, and I've been to a few IAU meetings. But IAU meetings, to give you a sense of it, are huge. They're multi day affairs, hundreds, if not, like, a thousand or more sign astronomers showing up at the same beach town. There are different days and parts of a day devoted to different subjects like, okay, Tuesday afternoon, it's supernova. Okay.
Wednesday morning, we're gonna do some cosmology. And, apparently, what happened at this IAU meeting oh oh, but and I do need to mention that anyone can be a member. Any astronomer, any professional astronomer or student can be a member of the IAU. And if you're a member of the IAU, you get to vote on certain things, like, hey. Let's define the word planet.
Now I need to say, if you were to present to me at a meeting of the IAU in Hawaii a proposal for the definition of planet, okay. I guess. I'm a cosmologist. I study, like, the big bang and the large scale structure of the universe. I have no idea if Pluto should be a planet, but I would be allowed to have a vote because that's the rules of the IAU.
So a lot of people voting on the definition of planet, the what went down in 02/2006, were not actual planetary scientists. If you're an expert on supernova, you have no real opinion on whether Pluto should be a planet, what the definition of planet is. You have no particular thoughts about it because it's not your specialty, but you still get a vote. And it turns out what happened apparently is that the planetary science, the people who care about the definition of planet, they had their time at the conference earlier in the week, and then most of them went home. And then the very last day of the conference, there was a surprise agenda item.
In the last day of the conference, you know almost everyone who is still there is just at the beach bar. But there's a surprise agenda. I'm, hey, everyone. We're gonna vote on the definition of planet. Like, this afternoon, go.
And then there was a vote, and then we defined planet. And Pluto got kicked off the list of planets. Some people disagree with that, with how it was handled. Some people disagree with the vote itself. Some people disagree with the definition.
Say, hey. Hey. If I was there, I would have voted against it. If all my friends would have voted against it too, and this thing would have never passed. What's up with that?
So there's allegations of shenanigans when it comes to the definition of a planet, but here's the definition that we have right now. One, in order to be a planet, you have to orbit the sun. Two, you have to be large enough to make yourself round. You need to be big to have a lot of gravity so you can pull in on yourself so you don't have all weird lumpy features. And three, you have to clear your orbit.
In other words, you have to dominate the orbit. You have to be the biggest thing in that belt around the sun. So if we look at the Earth, the Earth is pretty big. There's there's a few rocks sharing our orbit, but essentially nothing. Same for Jupiter, but this is where Pluto failed.
And in fact, this definition was explicitly designed to make Pluto and all of its friends fail so that we wouldn't have a thousand planets. Pluto shares its orbit with lots of smaller objects enough that it hasn't really dominated that orbit according to the arbitrary standards of this definition. And, yes, it is totally arbitrary because it was designed to demote Pluto from planet hood. A lot of people take issue with that definition because, one, that is a definition that is, like, outside the control of that object. Like, for example, if you were to swap places of Pluto in the Earth, then Pluto would get to be a planet because our orbit is nice and clear, but the Earth would not because there's a bunch of junk in that orbit.
So the argument goes, why should you define a planet based on other things that are in its orbit that it may or may not be able to control? And this was all tuned specifically to eliminate Pluto and basically any planet outside the orbit of Neptune. It just seems arbitrary. I tend to agree with that definition personally or I tend to agree with that argument. I do think personally that Pluto should be a planet, but, hey.
I wasn't there. I did that the meeting in 02/2006, so I didn't get to vote. And this is life, and we have to live with it. We have eight planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, and then we have a bunch of other stuff. I'll get to the other stuff in a second.
When it comes to the planets, I have to be completely honest. When it comes to the solar system, if you were an alien species, you would care about Jupiter and Jupiter only. Why? Because Jupiter is by far the biggest planet. It's two and a half times more massive than all the other planets combined.
That is big. That is the vast majority of material, the vast majority of mass in the solar system is locked up inside of Jupiter. For all intents and purposes, our solar system is Jupiter and everybody else is just a rounding error on those calculations. It's massive enough that it affects the orbit of just about everybody else in at least some subtle way. It's so large that you can fit 1,300 earths inside of it.
It's made of mostly hydrogen and helium, but some under other interesting things like ammonia that give it some color. Its interior is this crazy quantum mechanical soup called metallic hydrogen. It has the most violent magnetic environment in the entire solar system. Like, magnetic fields way stronger than the earth, stronger even than the sun, and that traps charged particles and massive belts around it. Like, we have a we have an orbiter around Jupiter right now called the Juno probe, and it's not gonna last long because of this massive particle storm that Jupiter is constantly able to create.
It's big. And after Jupiter, we're all just basically peanuts. Even Saturn, the number two planet, is just 30%, one third the mass of Jupiter, and Saturn is huge, and it's still tiny compared to Jupiter. It does get those awesome rings, though. Uranus and Neptune, the other two giant planets, they're not even 5% the mass of Jupiter.
5%. They're nothing. They're tiny. So tiny we don't even call them gas giants anymore. We call them ice giants, mostly because they're not made of primarily hydrogen and helium.
They're made of other things, and they have a slightly different formation process than Jupiter and Saturn. So they get to be called ice giants instead of gas giants. We don't own much about Uranus and Neptune because we had the Pioneer probes and the Voyager probes and then nothing for forty years. I'm sorry, but this is just a big this one sticks in my craw. Like, we have no planned missions to the ice giant worlds.
All the nice high resolution pictures we have came from the Voyager spacecraft four decades ago. Jupiter and Saturn get multiple probes, and Mars gets, like, every probe every year. Meanwhile, Uranus and Neptune are hanging out there being all cold and lonely. I feel bad for them. I'd like to visit.
Continuing on in our tour of the solar system starting with the things that matter, which is Jupiter and Jupiter alone, and then moving on to things that don't, like Saturn, Uranus, and Neptune, come the rocky planets. The rocky planets sit on nice close tight orbits. If you're looking from a distance, it would look like we are impossibly close to our sun, and the giant planets are at least somewhat reasonable in their maintaining their distance from the sun. Mercury is crazy. It is one eighteenth the volume of the Earth, has this weird orbit orbital resonance between its spin rate and its orbital rate.
Guess why it has that? It's because of Jupiter, because Jupiter just can't leave anyone alone. Venus rotates backwards, which is just weird, and nobody likes it. Earth, well, we know Earth and Mars. Everyone's obsessed with Mars.
There. That is the Paul Sutter Ask a Spaceman survey of our solar system. It's almost impossible to capture the scale of the solar system in a model. Like, if you're trying to make a scale model of the solar system, good luck. Either you have to keep the relative sizes, but you have to cheat on the distances.
Like, if you wanna show how much bigger Jupiter is compared to Earth, you need to put them right next to each other. But if you wanna show, like, relative distances from the sun, you have to cheat on sizes and make the planets way bigger than they really are. Like like, if you're building a scale model and you're like, okay, Mercury is gonna be one foot away from the sun and Venus is gonna be two feet and then Earth is gonna be four feet. And and and like that, your your planets are like the size of a grain of rice or like a speck of dirt in that scale model. It's just it's just crazy the kind of scales we're talking about in the solar system.
Like, most of this is just completely, totally empty space. The planets in the sun take up almost no volume at all. Like, less than a tenth of a percent of the volume of the solar system is composed of planets. The rest is just empty nothingness. It is so hard.
It is so hard to communicate the absolute desolation of space of how you can just go and go and go and go and go and there be absolutely nothing. Nothing. And then more nothing. That's how empty it is. Did you feel that pregnant pause and how full of nothing would and you'll stretch that out for, like, nine years because it takes years to go to the outer solar system.
You could travel at tens of thousands of miles per hour, and it takes years to get to the outer planets. It also takes years to get inwards because here in our orbit on Earth, we're going really fast. And if you wanna get inwards, you have to go slower, and it takes forever to slow down. So it basically takes forever to go anywhere, which is slightly depressing if you think about it too much. We know from surveys of exoplanets that our solar system isn't very special.
The more we learn about alien star systems, the more we learn just how kinda average we are, but we still wanna know why and how our solar system formed. Why? Because science, and we live here. I mean, when you tour a new house, you like to know when was it built? What kind of materials are made?
What's it like? This is our source, and we live here. We'd like to understand it. The best current guess is called the Nice model because where else are you going to have a conference about the formation of the solar system? Like I said, astronomers are very good at conference locations.
This conference was in Nice, France, and they all agreed on this model. Now it's a it's a broad brush model. There are a lot of details that we don't fully understand. We think that the rocky planets formed roughly where they are through slowly gluing together pebbles of material that steadily grew larger into something we call planetesimals, and the planetesimals start crashing into each other. And then it all just kinda sorted out to become the planets, the inner rocky planets.
We think of the giant planets though. When you're far away from the sun, you get a slightly different formation process, and that's because it's cold enough that you don't just have rocks hanging around and banging against each other, you also have ices. And so you can build up a really big mass really quickly. You can build a nice big heavy core when you're in the outer parts of the solar system. And from that core, you can start sucking down any material that comes nearby, like like hydrogen or helium or ammonia or methane or anything else.
And we think that those giant planets just ballooned up really, really, really quickly. We don't think, however, that those giant planets formed in their present location. We think that originally those giant planets were further out and also more widely spaced. We need that because we need them to be big. And in order to be big, you need a lot of material.
And if you're all crammed up next to each other, you're all trying to compete for the same plate of food. And so we think the planets formed the giant planets formed further away from each other where they could have their own their own buffet. But then we think that the planets started once they formed, once they grew up a lot of mass, there was still a lot of material left in the solar system. They started interacting with that material in very interesting gravitational ways. We think the planet started to move.
There may have been even a fifth giant planet in the solar system that got ejected during this process. We don't know exactly how it moved, these planets moved. They could have moved in concert, moving towards the inner solar system. Jupiter may have swung close, like, to the orbit of Mars and then scooted back out. But over time, we think these planets spread out.
The last to move were Uranus and Neptune that migrated to the outer solar system. In that process, they kicked out a lot of debris into rings and belts and clouds surrounding our solar system. And then once things settled down, it was just the way it was for the next few billion years. But those are just the planets, the formation of the planets. What about the little guys?
We call them dwarf planets. This is a new category invented in 02/2006, and it's basically all the things that might have qualified for planethood, but we decided not to let them because we didn't want 10,000 of them. So Pluto got demoted to dwarf planet. Ceres in the asteroid belt got promoted from asteroid to dwarf planet. So now the argument is that Pluto and Ceres are more alike than, say, Pluto and Mercury.
You can take either side of that debate. I will not fight you. There are a few other dwarf planets that we know of in the outer solar system like Haumea and Makemake. This is the category that might eventually be filled up with 10,000 members. I've talked about Pluto before, and I'd love to do an episode on Ceres, so just ask.
But today is not that day. Those are the dwarf planets. There might be 10,000 of them. Most don't have names, and most haven't been discovered, and there's a lot of them. And then there's the rest.
The asteroids, the comets, the minor planets, the centaurs, the trans Neptunian objects, the plutoids, the small solar system bodies, yes, that's a real phrase, the Trojans, the Patreons. That's right. The most important part of the solar system are the Patreons. That's patreon.com/pmsutter, where you can keep this show going. I really do appreciate it.
I really do. All these definitions of asteroids, centaurs, trans Neptunian objects, plutoids have all sorts of confusing overlapping definitions, and honestly, to me personally, it's not worth getting into. Maybe if this was a real astronomy class, I would teach it to you so I'd have something to put on your Friday quiz. But for this show, it's not really worth getting into, mostly because it changes every few years and mostly because nobody can agree. There are all these overlapping definitions, like, some things are small solar system bodies, and that's it.
Some things are both dwarf planets and trans Neptunian objects and plutoids. Some are neither. Like, it's it's the brief sketch is that asteroids are the large ish rocks hanging out between the orbit of Mars and Jupiter. It's a place where you might expect another rocky planet to form, but because Jupiter is right next door, its gravitational influence keeps anything from forming. So it just keeps ripping apart.
I mean, there isn't a lot of stuff. If you were if you were to take all the asteroid belt mass, you'd have something like like half of Mars, if I remember right, off the top of my head as I'm recording this episode. It's small. It's just or maybe even half a Mercury. It's just not a lot of material, but still it'd count if it weren't for Jupiter being a bully.
There's some other objects called centaurs, which are just random rocks hanging out amongst the giant planets. There are trans Neptunian objects, which is anything past the orbit of Neptune. There are plutoids, which are a dwarf planet past the orbit of Neptune. So Ceres is a dwarf planet but not a plutoid, and Pluto is a dwarf planet and is also a plutoid. There are the Trojans, which are rocks that share orbits with planets.
There's this delicate balancing act of gravity that you can get where you can have leading and trailing clumps of objects in a stable orbit. So Jupiter has a bunch of Trojans. Earth has a few Trojans. And then there are the comets, which are like asteroids, but also have some icy material in them. So if you wanna consider an asteroid as a dry comet or a comet as a wet frozen asteroid, be my guest.
Comets originate in something called the scattered disk or the Oort cloud, which is like the asteroid belt but further away. Oh, yeah. That Oort cloud is all the remnants of the formation of the solar system, really tiny objects. We're talking, like, five Earth masses total spread out over two light years of volume. And then there are the moons.
Lots and lots of moon. Mostly just tiny little rocks because guess what? We have no definition of moon. So if you orbit a planet, guess what? You get to be a moon.
But if you are big enough to be roundish, and then of those, there are a few that really stand out. I'd I'd like to share some of the notable moons like the moon. The moon is actually the largest moon. I I'm talking about our moon, by the way. Our moon is the largest moon relative to its planet in the solar system.
It's only beaten by Charon and Pluto, but Pluto is not a planet, so it doesn't count. We have a giant moon. It's, like, 10% the mass of Earth. Like, no. No one else even comes close.
Yeah. Jupiter has some big moons, but, like, Saturn could be a moon of Jupiter, and that would still be lame. Europa, I could talk forever about Europa. In fact, I did an episode on Europa. It's about the size of our moon, liquid water ocean, super cool, space sharks, the whole deal.
That last part is not proven yet. You've got Titan, the largest moon of Saturn, where you have the methane seas, possible water, ocean underneath the crusty layers. Such a weird, weird, weird, weird and wonderful world. You've got Triton, which is the largest moon of Neptune, which we think was a plutoid, a dwarf planet out there, and then got captured by Neptune. So by studying Triton, we get a sense of what some dwarf planets are like out there in the Kuiper Belt, and that's it.
We've got planets. We've got moons. We've got dwarf planets. We've got asteroids. We've got comets, and we've got other and all sorts of interesting and complicated and sometimes not interesting overlapping layers.
Oh, and I guess there's the sun, which we kind of need to make a solar system, but we'll save that for next time. Class dismissed. Thank you so much for listening. Go ahead and buy my book. That's How to Die in Space, a Journey Through Dangerous Astrophysical Phenomena.
And, oh, yes. I talk about the solar system and how dangerous it is. You can check it out on Amazon or at Barnes and Noble. And of course, please please please keep the contributions going. That's patreon.com/pmsutter.
It is your contributions that make this show possible. I'm not joking around. So I'd like to thank my top Patreon contributors this month. Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, Nudiru, Chrissy, Robert m, Nate h, Andrew f, Chris l, Cameron l, Nalia, Aaron s, Tom b, Scott m, Billy t, and Rob h is your contributions and everyone else's that make it possible and for which I'm eternally grateful. Thank you so much for listening.
Keep those questions coming. Hashtag ask a spaceman. Ask a spaceman@gmail.com. Ask a spaceman dot com or at Paul Mattsutter and all social channels. And if you get a chance, leave a review on iTunes.
It it really helps promote the show visibility. I do appreciate it, and I'll see you next time for more complete knowledge of time and space.