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Speaker 1: Hey, Kelly, do you prefer to have like a huge,

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Speaker 1: spacious house with lots of rooms or a cozy little house?

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Speaker 2: Oh? So I like to have spacious land, but the

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Speaker 2: house can be like whatever size we've got, like a

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Speaker 2: nice size house. It's not huge or anything, but we've

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Speaker 2: got a lot of land and we love that space.

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Speaker 2: What about you?

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Speaker 1: I agree, I think big houses can be too big.

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Speaker 1: We moved here from a little Chicago apartment into a

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Speaker 1: huge southern California house where like the bedroom was as

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Speaker 1: big as our old apartment. It just feels like too

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Speaker 1: much space.

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Speaker 2: How can a house be too big? What do you mean?

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Speaker 2: That sounds great?

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Speaker 1: It's like too big to have a conversation across you know,

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Speaker 1: we want the kids to come down for dinner, we

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Speaker 1: end up like texting them. It's ridiculous, all right.

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Speaker 2: Well, so even in my tiny house, I text Zach

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Speaker 2: from like the other room. But we don't have to

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Speaker 2: worry about that with our kids because they're like younger

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Speaker 2: and super andredic so they're more like quantum particles. They're

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Speaker 2: like simultaneously in every part of the house at once.

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Speaker 1: That's a great analogy because kids also have their wave

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Speaker 1: functions collapse eventually when they're exhausted.

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Speaker 2: You know, Usually it's my wave function that collapses first,

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Speaker 2: and I can just hopefully get them in the like

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Speaker 2: area of their bedroom beforehand. But lots of collapsing, Yes.

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Speaker 1: Check out our upcoming book, Quantum Parenting by Daniel and.

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Speaker 2: Count I'm not sure anyone should be following my lead

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Speaker 2: or at least paying for my advice, but but hopefully

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Speaker 2: I'm doing something right.

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Speaker 1: Hi. I'm Daniel. I'm a particle physicist and a professor

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Speaker 1: at UC Irvine.

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Speaker 2: And I'm Kelly Wienersmith. I'm a parasitologist adjunct with Race University.

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Speaker 1: And as much as I used to like to travel

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Speaker 1: all around the world, these days, I really like being

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Speaker 1: a homebody. I like having a comfortable place to sit

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Speaker 1: on my couch and read great novels and look at

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Speaker 1: pictures of my travels around the world. How about you, Kelly,

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Speaker 1: are you traveling a lot these days? Are you sticking

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Speaker 1: close to home?

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Speaker 2: You know, COVID squashed a bunch of my travels and

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Speaker 2: they haven't picked up too much. Again. I like getting

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Speaker 2: out of the house, but I also just really like

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Speaker 2: being at home with my family and my bugs.

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Speaker 1: And As much as I like looking up at the

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Speaker 1: stars and thinking about space travel, I'm not really very

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Speaker 1: excited about going into space myself. I'd rather stay here

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Speaker 1: where the atmosphere is nice and warm and there's plenty

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Speaker 1: of fresh water while other people break new ground. Amen,

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Speaker 1: and welcome to the podcast. Daniel and Jorge explain the

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Speaker 1: universe in which we mostly cast our minds, not our bodies,

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Speaker 1: out into the universe to try to understand what's out there,

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Speaker 1: how does it all work, and is it possible to

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Speaker 1: sustain in life anywhere else in this vast and glittering

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Speaker 1: cosmos other than our cozy couches. My friend Jorge and

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Speaker 1: usual co host can't be here today, but I'm very

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Speaker 1: happy to be talking to our regular guest host, Kelly. Kelly,

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Speaker 1: thank you very much for connecting to us from your

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Speaker 1: comfortable couch.

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Speaker 2: Well, thanks, I'm actually in my comfortable barn, but I'm

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Speaker 2: excited to be connecting on such an interesting topic.

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Speaker 1: And today we are thinking about couches and barns, but

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Speaker 1: not here on Earth where everybody's comfortable. We're thinking about

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Speaker 1: out in space. It feels like the standard trope in

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Speaker 1: science fiction is to think about the future of humanity

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Speaker 1: as out in the stars, And of course lots of

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Speaker 1: people talk about how it's vital that humans get off

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Speaker 1: this planet and establish colonies or outposts in other places

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Speaker 1: in the Solar System and maybe even around the galaxy

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Speaker 1: to avoid being extinguished by one single rock from space.

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Speaker 2: Do you think that's a good argument I'm going to

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Speaker 2: derail us real early.

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Speaker 1: I think that depends on whether you mean good for

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Speaker 1: humanity or like good for the galaxy. It might be

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Speaker 1: best if we're knocked out at the table early on

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Speaker 1: before we do any more damage.

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Speaker 2: M fair enough. I hear that argument from ecologists a lot.

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Speaker 1: I mean, there might be fascinating bits of life here,

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Speaker 1: and they're all over the Solar System or all over

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Speaker 1: the galaxy, and we don't exactly have the greatest history

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Speaker 1: about treating local ecosystems with respect. So from the point

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Speaker 1: of view of like nascent life in other places of

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Speaker 1: the galaxy, it might be best if we just stay

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Speaker 1: where we are.

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Speaker 2: It might be especially if they're bacteria, since I'm not

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Speaker 2: sure we would have a ton of respect for bacteria

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Speaker 2: on another planet.

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Speaker 1: But as a booster for humanity, of course, I want

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Speaker 1: my kids to survive and their kids to survive, and

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Speaker 1: also your kids, and you know other people's kids too,

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Speaker 1: And I want us to all have cozy places to

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Speaker 1: live and fun places to run around. Then yeah, I

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Speaker 1: think it makes absolute sense for us to think about

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Speaker 1: places to live other than Earth, because our time here

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Speaker 1: is limited, even if we do take good care of it.

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Speaker 2: Yeah, you know, humans make a lot of misis, but

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Speaker 2: I still remain pro human. So yes, I like this

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Speaker 2: plant b argument.

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Speaker 1: Way to take a really controversial opinion there.

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Speaker 2: I know people who aren't super pro human, but I

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Speaker 2: think my species has some good features.

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Speaker 1: I think so too. I've got a soft spot for

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Speaker 1: humanity over here, and Earth does seem like a very

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Speaker 1: wonderful and comfortable place to live. But it's important that

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Speaker 1: we think about other places that we might be able

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Speaker 1: to survive, places where humanity might be able to get

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Speaker 1: a foothold and even flourish. Places of course, other than Earth.

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Speaker 1: Even if a meteor doesn't hit the planet, and even

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Speaker 1: if we don't boil the oceans with climate change, eventually

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Speaker 1: the Sun will get brighter and larger and will boil

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Speaker 1: our oceans for us and may even envelop the Earth

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Speaker 1: in its outer layers. So if we're thinking really really

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Speaker 1: long term. It's important that we find another place for

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Speaker 1: humans to run around.

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Speaker 2: Well, so, just before we scare everybody, because I think

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Speaker 2: a theme is going to be that technology is nowhere

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Speaker 2: near or prepared for us to inhabit another planet. We've

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Speaker 2: got like a couple billion years before the Sun consumes

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Speaker 2: the Earth or whatever.

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Speaker 1: Right, calculations vary, but we have at least a cool

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Speaker 1: billion years. So yeah, this is not something we need

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Speaker 1: to plan for next week. You don't need to cancel

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Speaker 1: your travel plans, your kids can finish high school, all

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Speaker 1: that kind of stuff, but it is something that we

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Speaker 1: need to be thinking about. You know, humans also have

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Speaker 1: a record for kicking the can down the road, so

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Speaker 1: it's important to be aware of these things well before

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Speaker 1: we actually need to take any action.

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Speaker 2: Well and frankly, it's fun, what a fun project to

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Speaker 2: start on. So yeah, let's let's get started for the

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Speaker 2: fun of it.

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Speaker 1: That's right. And something that's very exciting in the last

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Speaker 1: couple of decades is that we've been able to discover

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Speaker 1: planets around other stars. Until about twenty years ago, we

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Speaker 1: only really knew about planets in our Solar system. Out

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Speaker 1: of all the stars out there in the cosmos. We'd

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Speaker 1: never seen a planet orbiting another star. But now we

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Speaker 1: have the technology to discover those planets and to think

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Speaker 1: about which ones might actually be homes for humanity. A

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Speaker 1: common way of thinking about this is identifying the habitable zone,

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Speaker 1: a region around those stars where there's enough heat enough

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Speaker 1: solar radiation to keep people warm and toasty on the surface.

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Speaker 2: Fun aside here the people who think about how many

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Speaker 2: generations you would need to get to one of these

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Speaker 2: habitable planets outside of our you know, neighbors, you know,

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Speaker 2: farther out past Mars or whatever they call their field

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Speaker 2: arc eology, because it's like your arc to get there

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Speaker 2: you're or maybe Zach is the one who came up

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Speaker 2: with that name. Anyway, it makes me laugh.

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Speaker 1: So you're not sure if that's a scientific term or

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Speaker 1: just a joke invented by your husband, whose job is

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Speaker 1: control science.

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Speaker 2: This is my life. Everything blurs. I don't know, but

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Speaker 2: I'm always having fun.

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Speaker 1: Well. A lot of the planets that we have found

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Speaker 1: about in other stars are pretty big, because big planets

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Speaker 1: are easier to find. A lot of these planets are

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Speaker 1: close to their Sun or very very massive, and so

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Speaker 1: it makes some of us wonder like, is it possible

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Speaker 1: to live on a really big planet or are there

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Speaker 1: other small planets out there that we might live on.

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Speaker 2: Is it the case that the smaller the planets we

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Speaker 2: can live on, the more options we would have, or

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Speaker 2: is it more complicated because science.

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Speaker 1: We'll get into that at the end of the episode,

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Speaker 1: whether there are more small or large planets available. But

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Speaker 1: today on the podcast, we're going to be digging deep

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Speaker 1: into one extreme of possible habitats for humanity. So on

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Speaker 1: today's episode, we'll be answering the question what's the smallest

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Speaker 1: habitable planet size?

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Speaker 2: Ooh, you know what I'm wondering.

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Speaker 1: Are you thinking about The Little Prince?

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Speaker 2: No, I have no idea what you're talking about. That's

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Speaker 2: not what I'm thinking about at all.

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Speaker 1: Well, you've never read the book The Little Prince.

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Speaker 3: No.

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Speaker 1: This is a famous story about a little prince who

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Speaker 1: lives on a tiny little planet. He can like see

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Speaker 1: the curvae, he can like run around the whole planet

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Speaker 1: in about two minutes.

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Speaker 2: WHOA, that sounds lonely.

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Speaker 1: Wow, waited just like pan famous literature Crime and Punishment

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Speaker 1: sounds depressing.

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Speaker 2: I mean that's Russian literature, right you don't need to

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Speaker 2: take the class. It's just that's depressing.

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Speaker 1: You know. I think you should put out a book

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Speaker 1: with one word reviews of famous literature.

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Speaker 2: Well, you know, if you're interested in brief reviews, you

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Speaker 2: can check out zax a Bridge Beyond the Point of

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Speaker 2: Usefulness series where he did that for Shakespeare and it

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Speaker 2: was hilarious.

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Speaker 1: All right, But today we are talking about tiny little

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Speaker 1: places to live. The Earth is small compared to many

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Speaker 1: planets like Jupiter and many planets we've discovered around other stars.

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Speaker 1: But it's really also very, very big, and there's lots

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Speaker 1: of much smaller chunks of rock, even in our Solar system,

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Speaker 1: and you might wonder whether it's possible to have life

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Speaker 1: on those little bits of carbon. And so, as usual,

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Speaker 1: I was wondering what people had thought about this question,

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Speaker 1: if people imagine living on tiny little rocks, or if

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Speaker 1: people thought that Earth was basically the smallest thing that

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Speaker 1: could keep an atmosphere and maintain habitable conditions. So I

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Speaker 1: went out there and asked folks who listen to the

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Speaker 1: podcast their thoughts on this question. I really value hearing

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Speaker 1: everybody's opinions before I prepare the podcast helps me align

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Speaker 1: the episode with what people already know. If you would

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Speaker 1: like to share your thoughts for an upcoming episode, please

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Speaker 1: don't be shy. We want to hear your voice right

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Speaker 1: to me. Two questions at Danielandjorge dot com. So think

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Speaker 1: about it for a moment before you hear these answers.

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Speaker 1: What do you think is the smallest habitable planet size?

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Speaker 1: Here's what some listeners had to say.

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Speaker 3: I think that the smallest planet for humans to inhabit

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Speaker 3: would be one that would support our kind of life

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Speaker 3: without a need of lots of artificial equipment like astronaut suits.

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Speaker 3: So it would need to be big enough to hold

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Speaker 3: its atmosphere only through gravity.

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Speaker 1: It's on gravity.

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Speaker 4: This question gives me real the little Prince vibes. If

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Speaker 4: we're talking habitable in terms of life as we know it,

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Speaker 4: then I believe we have to have an atmosphere, which

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Speaker 4: means it has to have the mass to retain one

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Speaker 4: like Mars is about half our mask, but it has

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Speaker 4: lost that atmosphere due to solar wind or sheer mass issues.

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Speaker 4: So maybe there's a way to have a smaller mass

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Speaker 4: where it lives something lives deep in the rock or whatnot.

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Speaker 4: But I believe you would need some sort of liquid water,

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Speaker 4: liquid methane or whatnot, which would require again an atmosphere.

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Speaker 4: So my thing would be the requirement of an atmosphere

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Speaker 4: would be a minimum.

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Speaker 2: So those were some great answers, and I think that

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Speaker 2: they point to an important question that you need to

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Speaker 2: clarify before we move on. Does smallest habitable planets? How

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Speaker 2: much technology and equipment are we allowed to use? Do

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Speaker 2: we make it habitable by like making pressurized domes where

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Speaker 2: we provide the atmosphere, or are you talking about habitable

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Speaker 2: with like no help from technology. You could PLoP a

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Speaker 2: naked person down and they would survive.

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Speaker 1: Yeah, you're right, And we could spend like forty five

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Speaker 1: minutes even just discussing like the definition of habitable. And

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Speaker 1: as we'll discover, the literature on this question is begetting

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Speaker 1: more and more sophisticated as people add more conditions to

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Speaker 1: the definition of habitable. You know, people when they were

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Speaker 1: first thinking about habitable planet, they were just like, is

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Speaker 1: there roughly the sun's amount of sunlight? And then as

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Speaker 1: time goes on and on, they add conditions like, you know,

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Speaker 1: is the gravity okay? And is there liquid water on

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Speaker 1: the surface, and can you breathe. And you know, personally,

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Speaker 1: when I think about a habitable planet, I'm imagining my

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Speaker 1: kids running around and touching grass. You know. I can't

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Speaker 1: really imagine raising kids and living in like a glass

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Speaker 1: bubble on the surface of a desolate asteroid. Though technically

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Speaker 1: that does make something habitable, right You put down a

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Speaker 1: habitat on something, and principle you can inhabit it. But

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Speaker 1: I'm imagining sort of a warmer, cozier future for humanity,

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Speaker 1: one where you can like grow crops and go outside

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Speaker 1: that a breathing apparatus. What do you think that is.

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Speaker 2: The future I would want to inhabit if I was

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Speaker 2: not living on the Earth, But I wouldn't want to

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Speaker 2: leave all the amazing tiny little signipet gall wasps that

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Speaker 2: we have on Earth. But maybe that makes me weird,

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Speaker 2: But certainly I've talked to a lot of people who

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Speaker 2: would be totally fine living in pressurized habitats and going

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Speaker 2: outside only after like breathing oxygen and putting on a spacesuit.

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Speaker 2: So I think there's a lot of variability and what

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Speaker 2: people think they would be happy dealing with, although I'd

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Speaker 2: argue that maybe those people after like three or four

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Speaker 2: years of living like that might not be so enamored

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Speaker 2: of the idea anymore. But maybe I'm wrong, and maybe

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Speaker 2: I just have very high standards. I do like a

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Speaker 2: lot of space.

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Speaker 1: I suspect you're right. And I notice in science fiction

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Speaker 1: where people do live in like glass bubbles, they are

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Speaker 1: all these like soft focus memories of walking through fields

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Speaker 1: of wheat on Earth, you know, or dipping their toes

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Speaker 1: in water, or in that recent show Silo where everybody

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Speaker 1: lives underground in this survival tube, they're all like nostalgia

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Speaker 1: about walking along the beach, And you know, I get

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Speaker 1: it that sounds pretty terrible. But you know, if we

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Speaker 1: are thinking about just technically habitable, like could we put

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Speaker 1: a colony there and have people survive, Like for example,

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Speaker 1: Elon Musk, I think is imagining on Mars. He might

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Speaker 1: have like longer term plans to terraform Mars by nuking

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Speaker 1: the polar ice caps and releasing more atmosphere.

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Speaker 2: Such a good idea, Yeah, but he's.

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Speaker 1: Always thinking shorter term, right, can't we get people there

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Speaker 1: in the next ten years or so. He's definitely not

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Speaker 1: planning to have people be able to walk around, And

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Speaker 1: of course we're lucky enough to know somebody who's something

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Speaker 1: of an expert on whether it's possible to build habitats

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Speaker 1: on Mars or other Solar System bodies. That's you, Kelly,

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Speaker 1: that's right you and zactually has wrote a book about

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Speaker 1: this called Literally a City on Mars. So tell me,

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Speaker 1: do you think it's possible with current or near future

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Speaker 1: technology to build something so that humans could make essentially,

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Speaker 1: you know, any rock out there habitable? No? Is that

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Speaker 1: the whole book? No, it's a short pamphlet, a bridge

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Speaker 1: to beyond usefulness.

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Speaker 2: Now, actually the book is over four hundred pages long,

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Speaker 2: so that's a much more nuanced argument.

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Speaker 1: Is it, just like no on four hundred different pages? No, no, no, no.

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Speaker 2: No no no no no no no no no no

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Speaker 2: no no no no no no.

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Speaker 1: What are the major obstacles?

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Speaker 2: Well, so it depends on who you talk to. Everybody

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Speaker 2: has their favorite obstacle. And actually it was very interesting

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Speaker 2: going through the space medicine literature because you'd find multiple

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Speaker 2: different titles that were of the form blank is the

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Speaker 2: biggest barrier to living on space. But everybody would have

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Speaker 2: different blanks, and one of them would be like, you know,

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Speaker 2: the way microgravity messes with vision, and another would be

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Speaker 2: space radiation. And so there's like a lot that we

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Speaker 2: don't know. But in terms of technology, in my mind,

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Speaker 2: the thing that we really don't know is how to

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Speaker 2: create closed loop ecosystems that don't break and are like

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Speaker 2: reliable on a planet like Mars. So you know, for example,

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Speaker 2: so you want to be able to grow food on Mars,

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Speaker 2: and you want to be able to like use those

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Speaker 2: plans to sort of clean your atmosphere. But right now,

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Speaker 2: you know, we don't have ecological systems figured out to

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Speaker 2: the right level of detail to know exactly how many

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Speaker 2: plants you need. For example, there was this simulation that

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Speaker 2: happened in China that had the amazing acronym Lunar Palace.

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Speaker 2: Like they are clearly rivaling NASA's acronym game Watch out, guys.

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Speaker 1: Wait, Lunar Palace is the name of it. And also

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Speaker 1: every letter stands for something.

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Speaker 2: So Lunar No, this was a simulation for the Moon,

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Speaker 2: but palace it all stood for something.

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Speaker 1: So just to be clear, you're not just talking about

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Speaker 1: having an outpost where we're sending supplies from Earth. You're

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Speaker 1: talking about like a self sustaining colony. Is that right?

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Speaker 2: Well, so you know, if you're talking about Mars, for example,

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Speaker 2: habitable kind of requires self sustaining because the orbital window

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Speaker 2: only opens every two years and a lot of food

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Speaker 2: is not shelf stable for that long, and like so

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Speaker 2: you sort of need to be able to pack as

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Speaker 2: little as possible because it's still pretty expensive to ship

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Speaker 2: stuff to Mars, and you need to have redundancy, and

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Speaker 2: you need to have you know, you need to have

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Speaker 2: all of this stuff working in a way that won't break.

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Speaker 2: And at the moment, you know, resupplies to the ISS

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Speaker 2: happened pretty often when things break, but that's not going

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Speaker 2: to happen on Mars. So you need to make sure

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Speaker 2: that you've got this all figured out before you leave. Otherwise,

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Speaker 2: y'all did so like.

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Speaker 1: A big fancier version in the ISS would not qualify

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Speaker 1: as a real habitat right, We like outfitted an asteroid

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Speaker 1: with a bigger version of the ISS and space panels,

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Speaker 1: but still required a lot of resupply from Earth. That

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Speaker 1: feels like just an extension of Earth, right, because then

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Speaker 1: if Earth goes out, if Earth gets hit by a meteor,

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Speaker 1: then obviously that's going to die out.

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Speaker 2: Well, and I don't think that's a problem. Initially, I

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Speaker 2: think relying on resupply from Earth for a while is fine,

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Speaker 2: and you're certainly going to need that as you're trying

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Speaker 2: to get towards self sustaining. But when you're out as

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Speaker 2: far as Mars, you already need to have a lot

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Speaker 2: of this stuff figured out because you are going to

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Speaker 2: be on your own for years. And at the moment,

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Speaker 2: we don't have that kind of stuff figured out. And so,

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Speaker 2: like you know, that Lunar Palace sim that I was

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Speaker 2: talking about, they actually had they had a crew of

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Speaker 2: three guys, and they didn't have enough oxygen for the

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Speaker 2: three guys, so they had to swap out of the

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Speaker 2: guys for smaller women, and then they had enough oxygen

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Speaker 2: for everybody. And like that's where we are right now. Like,

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Speaker 2: if you're on Mars and you're like, shoot, we should

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Speaker 2: have brought two shorter people, like you're just out of luck.

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Speaker 2: You can't just be like breathe less guys.

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Speaker 1: You can make people shorter. I guess you know. Sorry,

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Speaker 1: you gotta lose some height there, buddy.

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Speaker 2: We got to take off one of your arms. Pal

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Speaker 2: too much aerobic respiration happening. So anyway, that's where we

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Speaker 2: are right now, Like, we don't know how to keep

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Speaker 2: these systems stable, even on Earth for periods of time

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Speaker 2: of less than two years and so, and there's not

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Speaker 2: a lot of money going into that because it's not

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Speaker 2: like exciting science, and so I don't think we can

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Speaker 2: do this now if we start investing in it heavily

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Speaker 2: and then your future I think we could, And some

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Speaker 2: people are doing that science, but not on the scale.

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Speaker 2: I think we need to be like creating settlements on Mars,

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Speaker 2: for example.

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Speaker 1: How much of that is the context and how much

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Speaker 1: of that is just like we don't know how to

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Speaker 1: get things started. Say, for example, we found a copy

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Speaker 1: of Earth, you know, a rocky planet with our atmosphere

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Speaker 1: and our temperature and flowing water and all that kind

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Speaker 1: of stuff, but barren of life, completely sterile. Could we

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Speaker 1: get agriculture, etc. Started? Or is it just really hard

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Speaker 1: to boot up a whole ecosystem?

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Speaker 2: I mean, it's hard to boot up a whole ecosystem.

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Speaker 2: So for example, in Biosphere Too, they tried to boot

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Speaker 2: up a whole ecosystem and in some cases it went

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Speaker 2: like hilariously wrong. I'm sure it wasn't hilarious for them,

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Speaker 2: but so like these scorpions that they didn't mean to

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Speaker 2: bring along, they did bring along, and it turns out

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Speaker 2: that these scorpions are like deadly, and so they had

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Speaker 2: to figure out what to do with the scorpion.

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Speaker 1: Wait, doesn't that problem solve itself? I mean, scorpions are

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Speaker 1: eaten in some parts of the world, right, can't you

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Speaker 1: turn that problem into your afternoon snack?

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Speaker 2: Sure, but like I would rather that my snacks didn't

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Speaker 2: have the chance to kill me. You know, like if

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Speaker 2: I had to choose between meal worms and scorpions that

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Speaker 2: could kill me, I'd go with the meal worms. And

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Speaker 2: those are probably gonna be your early choices for protein

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Speaker 2: on space something like that. I mean, so like, for example,

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Speaker 2: agriculture on the Moon would be hard because there's hardly

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Speaker 2: any carbon there. And so in our theoretical or hypothetical situation,

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Speaker 2: are you saying that all of the stuff that plants

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Speaker 2: need to grow is already on Earth, but just like

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Speaker 2: microbes haven't shown up yet.

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Speaker 1: Yeah, exactly, I'm wondering, in like the best case scenario,

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Speaker 1: a planet with all the resources we need, but without

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Speaker 1: life having gotten started, could we like bring enough of

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Speaker 1: our ecosystem with us to actually make that livable.

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Speaker 2: I would bet we could. I bet that there would

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Speaker 2: be some things that get sort of out of balance,

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Speaker 2: and there could be some difficult moments where, you know,

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Speaker 2: like an insect that we brought to help us out

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Speaker 2: sort of does something we weren't expecting, and then we

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Speaker 2: have to figure out how to control it. Like I

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Speaker 2: imagine there'd be some tense moments. But that sounds like

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Speaker 2: a much easier project to me than trying to like

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Speaker 2: garden in the perchlorate laden soil that you find on Mars. Yeah,

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Speaker 2: that would be better, but that doesn't happen in our

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Speaker 2: solar system, I.

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Speaker 1: Don't think, all right, So it sounds like building a

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Speaker 1: technological habitat in an otherwise completely unfriendly to life situation

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Speaker 1: is currently far outside of our technical abilities. Though you know,

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Speaker 1: maybe in one hundred or five hundred years or a

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Speaker 1: thousand years, we would be able to build habitable bubbles

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Speaker 1: that could go anywhere, and making this question of habitability

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Speaker 1: sort of irrelevant. Until then, though, we do need to

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Speaker 1: find places where we can get a foothold where we

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Speaker 1: could bring our ecosystem and boot it up and provide

439
00:21:22,000 --> 00:21:25,640
Speaker 1: you know, fields for playing baseball and soccer for our

440
00:21:25,680 --> 00:21:28,960
Speaker 1: great great grandchildren, so that can have some kind of life.

441
00:21:29,119 --> 00:21:31,840
Speaker 2: Okay, so let's take a break and then we'll move

442
00:21:31,880 --> 00:21:35,840
Speaker 2: on to talking about what kind of characteristics this small

443
00:21:35,880 --> 00:21:38,560
Speaker 2: habitable planet would need to have in order for us

444
00:21:38,600 --> 00:21:40,399
Speaker 2: to be able to dip our toes in the ocean

445
00:21:40,480 --> 00:21:56,960
Speaker 2: or run our hands through fields of wheat. Okay, we're back,

446
00:21:57,080 --> 00:22:01,719
Speaker 2: soll right, Daniel, smallest habitable planet, tell me more about

447
00:22:01,880 --> 00:22:04,159
Speaker 2: what kind of characteristics it would need to have. So

448
00:22:04,320 --> 00:22:06,960
Speaker 2: I'm usually thinking about things like, you know, can you

449
00:22:07,000 --> 00:22:10,720
Speaker 2: grow plants? But as a non biologist, I bet you're

450
00:22:10,720 --> 00:22:13,560
Speaker 2: going to tell me that's something other than biology matters,

451
00:22:13,880 --> 00:22:15,919
Speaker 2: which is hard to imagine, but give me a shot.

452
00:22:16,560 --> 00:22:20,000
Speaker 1: No, I think that can you grow plants is essentially

453
00:22:20,040 --> 00:22:22,880
Speaker 1: the requirement number one, because that brings together a lot

454
00:22:22,920 --> 00:22:25,320
Speaker 1: of the other issues. I think the basic requirements for

455
00:22:25,440 --> 00:22:29,080
Speaker 1: building a habitat are like liquid water on the surface,

456
00:22:29,560 --> 00:22:32,760
Speaker 1: meaning you have water and it's not presently being boiled

457
00:22:32,800 --> 00:22:36,760
Speaker 1: off the surface into the atmosphere or freezing into giant

458
00:22:36,840 --> 00:22:40,119
Speaker 1: ice sheets. Right. You want that water to last for

459
00:22:40,280 --> 00:22:45,119
Speaker 1: like a long time, things like billions of years, so

460
00:22:45,160 --> 00:22:47,240
Speaker 1: that either life can evolve or so that we can

461
00:22:47,320 --> 00:22:49,639
Speaker 1: like detect it and travel to it and have it

462
00:22:49,720 --> 00:22:52,199
Speaker 1: like still be there. We don't want to find some

463
00:22:52,320 --> 00:22:54,200
Speaker 1: planet with water on it and then when we get

464
00:22:54,200 --> 00:22:55,879
Speaker 1: there it's a frozen wasteland.

465
00:22:55,960 --> 00:22:57,800
Speaker 2: But does it need to be flowing? So like on

466
00:22:57,840 --> 00:23:01,440
Speaker 2: Mars it was flowing at some point and near the equator,

467
00:23:01,520 --> 00:23:06,000
Speaker 2: you definitely might under ground have water that isn't frozen.

468
00:23:06,359 --> 00:23:09,679
Speaker 2: Is flowing important or just like water that is accessible.

469
00:23:09,840 --> 00:23:11,960
Speaker 1: I think if we're making a wish list, then definitely

470
00:23:11,960 --> 00:23:14,600
Speaker 1: flowing water is a lot easier. I mean, if you

471
00:23:14,640 --> 00:23:17,880
Speaker 1: need to burn energy and use technology just to get

472
00:23:17,920 --> 00:23:21,640
Speaker 1: frozen water out of the ground and available to your crops,

473
00:23:21,960 --> 00:23:24,000
Speaker 1: then it's going to make everything much much more difficult.

474
00:23:24,119 --> 00:23:25,720
Speaker 1: So I think it might be possible with places on

475
00:23:25,800 --> 00:23:28,480
Speaker 1: frozen water, but I think that sounds a lot less comfortable.

476
00:23:28,560 --> 00:23:30,760
Speaker 1: So let's put flowing water on our wish list.

477
00:23:30,880 --> 00:23:34,080
Speaker 2: And from the perspective of psychology, we all love flowing water.

478
00:23:34,680 --> 00:23:37,560
Speaker 1: We do exactly. Nobody wants to dip their toes in

479
00:23:37,640 --> 00:23:38,560
Speaker 1: a frozen.

480
00:23:38,240 --> 00:23:40,960
Speaker 2: Lake, right, That's right, that's right.

481
00:23:41,240 --> 00:23:43,399
Speaker 1: So we need flowing water on the surface. We also

482
00:23:43,480 --> 00:23:47,000
Speaker 1: need an atmosphere. We need this planet to have an atmosphere,

483
00:23:47,080 --> 00:23:50,320
Speaker 1: meaning there's an envelope of gas that surrounds it, and

484
00:23:50,359 --> 00:23:53,280
Speaker 1: that envelope is sticking around. It's not like boiling off

485
00:23:53,320 --> 00:23:57,240
Speaker 1: into space or getting zapped off by solar radiation. You

486
00:23:57,280 --> 00:23:59,520
Speaker 1: know that it's going to be there for us to breathe.

487
00:23:59,840 --> 00:24:02,119
Speaker 2: It needs to be a certain composition, right, Like if

488
00:24:02,119 --> 00:24:04,760
Speaker 2: it's all carbon dioxide, it doesn't matter if it's being

489
00:24:04,800 --> 00:24:06,640
Speaker 2: held to the surface exactly.

490
00:24:06,720 --> 00:24:08,760
Speaker 1: All of carbon dioxide will poison us and also lead

491
00:24:08,760 --> 00:24:11,959
Speaker 1: to a runaway greenhouse effect. So we need a certain

492
00:24:12,080 --> 00:24:15,080
Speaker 1: mixture of atmosphere to be there. And all this in

493
00:24:15,119 --> 00:24:18,159
Speaker 1: the end comes down to gravity on the planet. Like

494
00:24:18,160 --> 00:24:20,520
Speaker 1: in order to have liquid water, you need temperature. In

495
00:24:20,600 --> 00:24:23,800
Speaker 1: order to have that temperature, you need an atmosphere because

496
00:24:23,800 --> 00:24:27,160
Speaker 1: the atmosphere is what keeps the solar radiation on the surface.

497
00:24:27,359 --> 00:24:29,160
Speaker 1: You know. I see this on Twitter from politicians who

498
00:24:29,160 --> 00:24:32,959
Speaker 1: don't understand any better. They're confusion about like why space

499
00:24:33,080 --> 00:24:36,360
Speaker 1: is cold because you're going towards the Sun. Like if

500
00:24:36,400 --> 00:24:38,000
Speaker 1: you lift off the surface of the Earth, why does

501
00:24:38,040 --> 00:24:40,080
Speaker 1: it get colder and colder if you're getting closer and

502
00:24:40,080 --> 00:24:43,760
Speaker 1: closer to the Sun. Right? Is this confusuency sometimes on

503
00:24:44,240 --> 00:24:46,880
Speaker 1: social media. And the answer is that space is very

504
00:24:46,960 --> 00:24:49,560
Speaker 1: very cold. It just happens to be warm here because

505
00:24:49,560 --> 00:24:52,080
Speaker 1: we're under a blanket. So imagine that you're like camping

506
00:24:52,200 --> 00:24:54,280
Speaker 1: and you're under a thick blanket and there is a

507
00:24:54,320 --> 00:24:56,720
Speaker 1: fire there. But if you crawl a lot from under

508
00:24:56,760 --> 00:24:58,920
Speaker 1: your blanket, you're going to get very very cold before

509
00:24:58,960 --> 00:25:00,120
Speaker 1: you get close to the fire.

510
00:25:00,320 --> 00:25:02,359
Speaker 2: But you got to be careful about that planket. Because

511
00:25:02,440 --> 00:25:06,000
Speaker 2: Venus got too many blankets, they overheated exactly.

512
00:25:06,440 --> 00:25:08,760
Speaker 1: So you need that atmosphere and you have to have

513
00:25:08,760 --> 00:25:11,399
Speaker 1: that atmosphere be the right situation, not too thick, not

514
00:25:11,520 --> 00:25:14,439
Speaker 1: too thin. And to keep that atmosphere on your planet,

515
00:25:14,560 --> 00:25:17,960
Speaker 1: what you need is gravity, right, You need gravity to

516
00:25:18,080 --> 00:25:20,480
Speaker 1: hold that gas to the planet because in the end,

517
00:25:20,560 --> 00:25:23,480
Speaker 1: what else is keeping it there. Atmospheres don't hang out

518
00:25:23,560 --> 00:25:25,840
Speaker 1: just because they think the planet is cool. They don't

519
00:25:25,840 --> 00:25:28,240
Speaker 1: like hop from planet a planet looking for the best

520
00:25:28,240 --> 00:25:29,080
Speaker 1: place to hang out.

521
00:25:29,200 --> 00:25:31,159
Speaker 2: Ours would have left us a long time ago.

522
00:25:32,280 --> 00:25:35,360
Speaker 1: It's gravity that keeps our atmosphere here, and it's gravity

523
00:25:35,359 --> 00:25:38,600
Speaker 1: that determines its composition. What's going to boil off into space?

524
00:25:38,680 --> 00:25:41,160
Speaker 1: What isn't going to boil off into space? And gravity

525
00:25:41,200 --> 00:25:43,879
Speaker 1: is also directly important, Right, you can't live in a

526
00:25:43,920 --> 00:25:46,080
Speaker 1: place with too high gravity. If we land on a

527
00:25:46,119 --> 00:25:49,359
Speaker 1: planet that has like ten g of gravity, ten times

528
00:25:49,359 --> 00:25:51,760
Speaker 1: our normal surface gravity, it's not going to be a

529
00:25:51,840 --> 00:25:53,840
Speaker 1: lot of fun. You can't like walk through that field

530
00:25:53,920 --> 00:25:56,240
Speaker 1: of wheat and when you're grassed through it, right.

531
00:25:56,520 --> 00:25:57,639
Speaker 2: No smoosh.

532
00:25:57,680 --> 00:26:00,000
Speaker 1: And so in the end, it all comes down to gravity.

533
00:26:00,200 --> 00:26:02,480
Speaker 1: If you have enough gravity, then you can have a

534
00:26:02,520 --> 00:26:05,280
Speaker 1: blanket of an atmosphere, and you can keep enough solar radiation,

535
00:26:05,600 --> 00:26:08,359
Speaker 1: and then you can keep your water liquid. And so

536
00:26:08,480 --> 00:26:11,159
Speaker 1: the gravity of the planet really is crucial, which is

537
00:26:11,160 --> 00:26:14,840
Speaker 1: why I think this question is interesting the smallest habitable planet,

538
00:26:14,920 --> 00:26:18,000
Speaker 1: because often when people think about the habitable zones the

539
00:26:18,040 --> 00:26:21,760
Speaker 1: goldilocks region around a star, they imagine that it's defined

540
00:26:21,800 --> 00:26:24,040
Speaker 1: by the star. Right, you find the star, You know

541
00:26:24,119 --> 00:26:26,399
Speaker 1: the brightness of the star. Now you can calculate the

542
00:26:26,520 --> 00:26:29,640
Speaker 1: region in which that star gives off about as much

543
00:26:29,760 --> 00:26:33,000
Speaker 1: solar radiation as our star. And so when you talk

544
00:26:33,040 --> 00:26:35,520
Speaker 1: about the habitable zone of a star, you're kind of

545
00:26:35,520 --> 00:26:39,320
Speaker 1: ignoring the planetary characteristics. But it turns out the planetary

546
00:26:39,400 --> 00:26:42,639
Speaker 1: characteristics are super important. Right if you're on a tiny,

547
00:26:42,680 --> 00:26:46,320
Speaker 1: little rock inhabitable zone. It's not going to have an atmosphere,

548
00:26:46,320 --> 00:26:47,679
Speaker 1: it's not going to be habitable.

549
00:26:47,960 --> 00:26:51,280
Speaker 2: And so, because science is never straightforward, is there an

550
00:26:51,359 --> 00:26:55,360
Speaker 2: interaction between like the size to get the gravity right

551
00:26:55,400 --> 00:26:57,479
Speaker 2: and how close you are, So like, if you are

552
00:26:58,160 --> 00:27:02,040
Speaker 2: too close, you need to have more gravity because the

553
00:27:02,040 --> 00:27:05,600
Speaker 2: solar wind is trying to kick your atmosphere away, and

554
00:27:05,640 --> 00:27:08,320
Speaker 2: so like size varies depending on how close you are,

555
00:27:08,800 --> 00:27:11,119
Speaker 2: or is this one of those amazing instances in science

556
00:27:11,119 --> 00:27:12,560
Speaker 2: where it's not that complicated.

557
00:27:12,720 --> 00:27:16,000
Speaker 1: Unfortunately, your pessimistic instincts I think are correct here. For

558
00:27:16,040 --> 00:27:19,080
Speaker 1: a given mass and volume of planet, it's sort of

559
00:27:19,119 --> 00:27:22,359
Speaker 1: a little window where it's well suited. If you look

560
00:27:22,400 --> 00:27:25,439
Speaker 1: at the Earth, for example, the Earth, if it was

561
00:27:25,560 --> 00:27:28,600
Speaker 1: like five percent closer to the Sun, it would not

562
00:27:28,600 --> 00:27:31,280
Speaker 1: have liquid oceans. The Sun would boil away our oceans

563
00:27:31,320 --> 00:27:34,159
Speaker 1: and we'd get a runaway green house effect sort of

564
00:27:34,320 --> 00:27:36,440
Speaker 1: like Venus. And if we were a couple percent further

565
00:27:36,480 --> 00:27:39,080
Speaker 1: from the Sun, then our oceans would freeze and we

566
00:27:39,119 --> 00:27:42,639
Speaker 1: would be globally glaciated. So the size and mass of

567
00:27:42,680 --> 00:27:46,399
Speaker 1: your planet really does determine where around that star you

568
00:27:46,480 --> 00:27:48,000
Speaker 1: can survive dikes.

569
00:27:48,160 --> 00:27:52,200
Speaker 2: Okay, so it's complicated. Is it even more complicated?

570
00:27:53,880 --> 00:27:57,520
Speaker 1: There is one additional crazy complication, which is that the

571
00:27:57,560 --> 00:28:00,320
Speaker 1: mass of a planet and its volume are not a

572
00:28:00,359 --> 00:28:04,000
Speaker 1: simple connection. It's not like if you want a bigger planet,

573
00:28:04,160 --> 00:28:06,240
Speaker 1: you just got to like add more stuff to it.

574
00:28:06,600 --> 00:28:08,879
Speaker 1: Like if you want to make Earth bigger, you couldn't

575
00:28:08,960 --> 00:28:11,359
Speaker 1: just like add a layer of rock to the Earth

576
00:28:11,640 --> 00:28:14,480
Speaker 1: and then you'd have like a larger planet, because adding

577
00:28:14,520 --> 00:28:18,280
Speaker 1: more stuff means more gravity, and more gravity means it

578
00:28:18,320 --> 00:28:21,879
Speaker 1: gets more compressed. So in order to make the Earth bigger,

579
00:28:21,920 --> 00:28:24,239
Speaker 1: you need to add a lot more stuff because then

580
00:28:24,240 --> 00:28:26,919
Speaker 1: the Earth gets more and more dense. So this is

581
00:28:27,080 --> 00:28:30,600
Speaker 1: complicated relationship between the mass and the density of a

582
00:28:30,640 --> 00:28:33,920
Speaker 1: planet that determines in the end the surface gravity, which

583
00:28:33,960 --> 00:28:36,480
Speaker 1: remember is the crucial thing to determining whether you can

584
00:28:36,480 --> 00:28:38,360
Speaker 1: hold an atmosphere and keep liquid water.

585
00:28:38,640 --> 00:28:42,640
Speaker 2: Okay, so the answer to this episode, what is the

586
00:28:42,720 --> 00:28:47,360
Speaker 2: smallest habitable planet is going to be It's complicated, and

587
00:28:47,400 --> 00:28:50,400
Speaker 2: I'm totally down for that answer as a scientist. Okay,

588
00:28:50,400 --> 00:28:53,200
Speaker 2: So it depends then probably also like what you know,

589
00:28:53,200 --> 00:28:57,480
Speaker 2: if you have mostly metals versus if you have other stuff,

590
00:28:57,520 --> 00:29:00,360
Speaker 2: that probably determines the size that can hold an atmosphe.

591
00:29:00,640 --> 00:29:03,840
Speaker 1: Right, it does exactly. It depends on how much the

592
00:29:03,880 --> 00:29:07,320
Speaker 1: atoms squeeze together. What is like the structural strength. Because

593
00:29:07,320 --> 00:29:10,120
Speaker 1: if you're building a planet out of like diamond, for example,

594
00:29:10,480 --> 00:29:12,920
Speaker 1: it wouldn't take as much diamond to make a large

595
00:29:12,960 --> 00:29:16,040
Speaker 1: planet because diamond is super duper strong. And if you're

596
00:29:16,040 --> 00:29:19,000
Speaker 1: building that planet out of like oatmeal or something much

597
00:29:19,000 --> 00:29:23,320
Speaker 1: more compressible, or helium, which is very compressible, right, then

598
00:29:23,360 --> 00:29:26,320
Speaker 1: it takes a lot more. And it's really fascinating if

599
00:29:26,360 --> 00:29:29,280
Speaker 1: you look at the connection between the mass of planets

600
00:29:29,320 --> 00:29:33,400
Speaker 1: and their density, a very weird relationship. Like Earth turns

601
00:29:33,400 --> 00:29:36,280
Speaker 1: out to be the densest planet in the Solar System

602
00:29:36,840 --> 00:29:41,080
Speaker 1: because it's close to the largest rocky planet size. As

603
00:29:41,120 --> 00:29:44,360
Speaker 1: you keep adding stuff to rocky planets, they get denser

604
00:29:44,440 --> 00:29:47,320
Speaker 1: faster than they get larger, and so it's hard to

605
00:29:47,360 --> 00:29:50,160
Speaker 1: grow a rocky planet a lot bigger than Earth. It's

606
00:29:50,160 --> 00:29:54,680
Speaker 1: like this maximum size probably around ten thousand kilometer in radius,

607
00:29:54,720 --> 00:29:57,120
Speaker 1: which is only like an Earth and a half. So

608
00:29:57,160 --> 00:29:59,560
Speaker 1: we're like up there, sort of closest to the limit

609
00:29:59,600 --> 00:30:02,840
Speaker 1: of the life largest possible rocky planet you could ever build.

610
00:30:03,360 --> 00:30:06,600
Speaker 1: The other planets like Jupiter, they're much more massive, but

611
00:30:06,640 --> 00:30:09,479
Speaker 1: they're much less dense than the Earth because they're made

612
00:30:09,520 --> 00:30:10,920
Speaker 1: of really compressible stuff.

613
00:30:11,040 --> 00:30:13,200
Speaker 2: You know, I was prepared to be impressed by all

614
00:30:13,240 --> 00:30:15,080
Speaker 2: of that, but now that you've mentioned that you could

615
00:30:15,120 --> 00:30:18,440
Speaker 2: have a planet made out of compressed oatmeal, I'm totally

616
00:30:18,520 --> 00:30:21,440
Speaker 2: depressed because I'd rather live there. But okay, all right,

617
00:30:21,440 --> 00:30:22,280
Speaker 2: that's all interesting.

618
00:30:22,480 --> 00:30:24,040
Speaker 1: And so what you want to do in the end

619
00:30:24,240 --> 00:30:27,280
Speaker 1: is have the right surface gravity, and so you need

620
00:30:27,400 --> 00:30:30,080
Speaker 1: enough gravity to hold onto your atmosphere. But there's also

621
00:30:30,160 --> 00:30:32,920
Speaker 1: a maximum amount of gravity, right, Like, if you have

622
00:30:32,960 --> 00:30:35,480
Speaker 1: too much gravity for people, then they just can't even

623
00:30:35,480 --> 00:30:37,520
Speaker 1: walk around and live on the planet. And studies I

624
00:30:37,720 --> 00:30:40,440
Speaker 1: read suggest that people could live comfortably up to like

625
00:30:40,680 --> 00:30:43,200
Speaker 1: one and a half G, like one and a half

626
00:30:43,280 --> 00:30:46,520
Speaker 1: times Earth's gravity would be comfortable for people to live on.

627
00:30:46,600 --> 00:30:48,560
Speaker 2: How about in the other direction, My sense is that

628
00:30:48,640 --> 00:30:52,440
Speaker 2: we don't know what the lowest gravity humans could remain

629
00:30:52,480 --> 00:30:55,680
Speaker 2: healthy in. Is Is that your sense as well?

630
00:30:55,720 --> 00:30:58,240
Speaker 1: I think biologically you're right, we know something about the

631
00:30:58,320 --> 00:31:01,000
Speaker 1: highest gravity people could tolerate, but we don't know anything

632
00:31:01,040 --> 00:31:04,040
Speaker 1: about this lower end. People wonder if we could live

633
00:31:04,080 --> 00:31:07,120
Speaker 1: in basically zero G for a lifetime and I know

634
00:31:07,160 --> 00:31:09,040
Speaker 1: in your book you guys talk about like whether you

635
00:31:09,040 --> 00:31:11,400
Speaker 1: can reproduce and whether babies can develop and all this

636
00:31:11,480 --> 00:31:14,280
Speaker 1: fun stuff in space. But I think here we should

637
00:31:14,280 --> 00:31:17,200
Speaker 1: just focus on, like could you build a planet that

638
00:31:17,360 --> 00:31:21,320
Speaker 1: has lower than Earth gravity and still keep water on

639
00:31:21,360 --> 00:31:25,040
Speaker 1: the surface and an atmosphere and high enough temperatures and

640
00:31:25,080 --> 00:31:26,000
Speaker 1: all that kind of stuff.

641
00:31:26,040 --> 00:31:29,320
Speaker 2: We'll put those rails on the conversation. Okay, So we're

642
00:31:29,360 --> 00:31:33,560
Speaker 2: gonna focus on how do you maintain an atmosphere and

643
00:31:33,760 --> 00:31:37,440
Speaker 2: what gravity do you need before humans are squished or

644
00:31:37,920 --> 00:31:41,240
Speaker 2: their will to live is squished, And after we get

645
00:31:41,280 --> 00:31:43,520
Speaker 2: back from the break, let's talk about the history of

646
00:31:43,560 --> 00:31:46,120
Speaker 2: how we've thought about that and the what we know

647
00:31:46,200 --> 00:32:01,680
Speaker 2: so far about the math behind this question. All right, Daniels, So,

648
00:32:01,880 --> 00:32:05,520
Speaker 2: I have been reading books from decades and decades ago

649
00:32:05,560 --> 00:32:08,640
Speaker 2: where people talk about going out and inhabiting space. When

650
00:32:08,640 --> 00:32:11,440
Speaker 2: did we start thinking about this question mathematically as opposed

651
00:32:11,480 --> 00:32:13,720
Speaker 2: to just sort of like chatting about it over beer

652
00:32:13,840 --> 00:32:14,160
Speaker 2: or tea.

653
00:32:14,360 --> 00:32:16,640
Speaker 1: It's really interesting to dig into that history and think

654
00:32:16,680 --> 00:32:19,640
Speaker 1: about what people were thinking about decades and decades ago.

655
00:32:19,640 --> 00:32:22,480
Speaker 1: I love that the earliest study that I found is

656
00:32:22,520 --> 00:32:25,880
Speaker 1: a book from nineteen sixty four written by a guy

657
00:32:26,080 --> 00:32:30,600
Speaker 1: Dole at Rand Corporation thinking about habitable planets for man.

658
00:32:31,160 --> 00:32:33,880
Speaker 1: So this is, you know, very early space age. We

659
00:32:33,920 --> 00:32:37,040
Speaker 1: hadn't even landed on the Moon. He's already like thinking

660
00:32:37,040 --> 00:32:40,040
Speaker 1: about these calculations. And this book is really fun because

661
00:32:40,080 --> 00:32:42,600
Speaker 1: he brings together a lot of really early science from

662
00:32:42,600 --> 00:32:45,880
Speaker 1: all sorts of different areas, you know, atmosphere, chemistry, and

663
00:32:46,040 --> 00:32:49,600
Speaker 1: planetary geology to think about how to put a planet together.

664
00:32:50,160 --> 00:32:52,960
Speaker 1: And so it's very forward thinking for its time. It's

665
00:32:53,000 --> 00:32:55,040
Speaker 1: also sort of simplistic from the point of view of

666
00:32:55,080 --> 00:32:58,320
Speaker 1: modern studies, which have gone progressively more and more sophisticated

667
00:32:58,400 --> 00:33:00,080
Speaker 1: as time goes on. But you know, you got to

668
00:33:00,120 --> 00:33:01,520
Speaker 1: start from somewhere.

669
00:33:01,160 --> 00:33:03,520
Speaker 2: And this is so sixty four. That would be like

670
00:33:03,600 --> 00:33:07,000
Speaker 2: before the Venera probes that the Soviet Union sent out

671
00:33:07,080 --> 00:33:10,440
Speaker 2: landed on Venus and like immediately got squished and boiled.

672
00:33:10,720 --> 00:33:13,200
Speaker 2: So is this like back when we still thought like

673
00:33:13,360 --> 00:33:16,040
Speaker 2: Venus could potentially be habitable. Is that sort of playing

674
00:33:16,080 --> 00:33:17,360
Speaker 2: into the way he thinks about things?

675
00:33:17,600 --> 00:33:20,040
Speaker 1: Yeah, exactly. I think his question was like, how does

676
00:33:20,080 --> 00:33:23,280
Speaker 1: this work? What do our calculations suggest? And he started

677
00:33:23,320 --> 00:33:25,840
Speaker 1: from a pretty simple model. He was like, let's just

678
00:33:25,880 --> 00:33:28,920
Speaker 1: imagine a big blob of rock, and let's calculate the

679
00:33:28,960 --> 00:33:31,440
Speaker 1: gravity on the surface and then try to estimate whether

680
00:33:31,480 --> 00:33:34,040
Speaker 1: it can hold onto an atmosphere. Then think about the

681
00:33:34,080 --> 00:33:37,719
Speaker 1: solar radiation, how much energy would be absorbed by that atmosphere,

682
00:33:37,760 --> 00:33:40,280
Speaker 1: and could you have liquid water on the surface. So

683
00:33:40,360 --> 00:33:43,000
Speaker 1: he makes this specific list of requirements in his book

684
00:33:43,240 --> 00:33:45,280
Speaker 1: about what it would take to be habitable, and he

685
00:33:45,360 --> 00:33:47,920
Speaker 1: requires basically what we've been talking about, which is reasonable

686
00:33:47,960 --> 00:33:51,200
Speaker 1: amount of gravity, a reasonable temperature, and liquid water on

687
00:33:51,280 --> 00:33:51,840
Speaker 1: the surface.

688
00:33:52,120 --> 00:33:53,920
Speaker 2: Okay, cool. And what does he decide what is the

689
00:33:53,960 --> 00:33:55,280
Speaker 2: smallest tabitable planet.

690
00:33:55,400 --> 00:33:58,680
Speaker 1: His model suggests that a planet a little bit smaller

691
00:33:58,680 --> 00:34:02,080
Speaker 1: than Earth, something with like half of Earth's gravity, only

692
00:34:02,160 --> 00:34:06,040
Speaker 1: like twenty percent of Earth's mass and like sixty percent

693
00:34:06,120 --> 00:34:10,480
Speaker 1: of Earth's radius would be sufficient to maintain those conditions

694
00:34:10,920 --> 00:34:13,839
Speaker 1: that you would have an atmosphere on the surface, and

695
00:34:13,880 --> 00:34:16,760
Speaker 1: you would have enough atmosphere to keep the solar radiation

696
00:34:17,160 --> 00:34:20,000
Speaker 1: so that water could be liquid on the surface. So

697
00:34:20,040 --> 00:34:21,280
Speaker 1: this is something pretty small.

698
00:34:21,440 --> 00:34:24,239
Speaker 2: Yeah, okay, that's cool. So that probably opens up a

699
00:34:24,239 --> 00:34:27,880
Speaker 2: lot of possibilities when we get out past our solar system.

700
00:34:28,120 --> 00:34:30,799
Speaker 2: How have his calculations held up over time.

701
00:34:31,000 --> 00:34:34,040
Speaker 1: So his calculations were a great first step of course

702
00:34:34,080 --> 00:34:35,920
Speaker 1: in this field. But as always when you make a

703
00:34:35,960 --> 00:34:39,080
Speaker 1: first step, you make approximations, and so later studies have

704
00:34:39,160 --> 00:34:42,160
Speaker 1: dug into some of those approximations and those assumptions and

705
00:34:42,200 --> 00:34:44,640
Speaker 1: try to make them more realistic. For example, he assumes

706
00:34:44,680 --> 00:34:48,040
Speaker 1: a very simple atmosphere. He assumes it's optically very thin,

707
00:34:48,360 --> 00:34:51,040
Speaker 1: has a very fixed amount of reflection, and that like

708
00:34:51,080 --> 00:34:54,000
Speaker 1: what's happening on the surface in terms of clouds and

709
00:34:54,280 --> 00:34:57,759
Speaker 1: water vapor being formed isn't changing the reflection at all.

710
00:34:58,000 --> 00:35:01,880
Speaker 1: So he for example, ignores you know, greenhouse feedback effects

711
00:35:02,040 --> 00:35:04,000
Speaker 1: and all sorts of stuff like that, which really do

712
00:35:04,160 --> 00:35:04,920
Speaker 1: change the answer.

713
00:35:05,200 --> 00:35:08,719
Speaker 2: Yeah, I wouldn't want to move to another planet based

714
00:35:08,760 --> 00:35:12,960
Speaker 2: on these calculations. I remain impressed, but I'm not going

715
00:35:13,000 --> 00:35:13,840
Speaker 2: to sell my house.

716
00:35:14,239 --> 00:35:16,359
Speaker 1: So then in the nineties this was picked back up again,

717
00:35:16,640 --> 00:35:19,520
Speaker 1: and there's a paper by Casting at All that really

718
00:35:19,560 --> 00:35:22,400
Speaker 1: do consider the presence of liquid water and this greenhouse

719
00:35:22,440 --> 00:35:25,760
Speaker 1: effect and allow the possibility of a runaway greenhouse effect

720
00:35:25,760 --> 00:35:27,960
Speaker 1: in their calculations, and they rule out some of the

721
00:35:28,080 --> 00:35:31,719
Speaker 1: possibilities that Dole allowed. But more recently there was a

722
00:35:31,719 --> 00:35:35,440
Speaker 1: really fascinating study by a group at MIT and Harvard

723
00:35:35,560 --> 00:35:38,040
Speaker 1: that trying to make these calculations much more realistic.

724
00:35:38,320 --> 00:35:40,759
Speaker 2: And does that mean that they needed supercomputers and all

725
00:35:40,840 --> 00:35:43,239
Speaker 2: kinds of fancy stuff. How did they make it more realistic?

726
00:35:43,600 --> 00:35:46,000
Speaker 1: You don't really need fancy computers. You just need to

727
00:35:46,000 --> 00:35:48,719
Speaker 1: take this model that you're building in your mind and

728
00:35:48,760 --> 00:35:52,000
Speaker 1: make it more realistic, add more wizzes and bangs to it.

729
00:35:52,080 --> 00:35:54,960
Speaker 1: This is a really interesting and sort of philosophically important

730
00:35:55,040 --> 00:35:57,400
Speaker 1: step in science. When you're trying to answer a question,

731
00:35:57,640 --> 00:36:00,120
Speaker 1: you have to decide like which details are important and

732
00:36:00,160 --> 00:36:02,879
Speaker 1: which details are irrelevant. And in the end, when we're

733
00:36:02,920 --> 00:36:05,720
Speaker 1: doing science, we're never answering questions about like the actual

734
00:36:05,840 --> 00:36:09,160
Speaker 1: universe out there, some specific planet. We're always building a

735
00:36:09,160 --> 00:36:11,839
Speaker 1: little POI model in our mind, one where we have

736
00:36:11,920 --> 00:36:15,480
Speaker 1: mathematical equations that we know how to wrangle with and

737
00:36:15,560 --> 00:36:18,640
Speaker 1: answering questions about that and then wondering how well does

738
00:36:18,680 --> 00:36:21,440
Speaker 1: that apply to the real universe out there. And so

739
00:36:21,520 --> 00:36:24,120
Speaker 1: the history of this field is like making those models

740
00:36:24,239 --> 00:36:27,080
Speaker 1: more and more sophisticated, bringing them what we think is

741
00:36:27,160 --> 00:36:30,640
Speaker 1: closer and closer to reality. And so, for example, the

742
00:36:30,800 --> 00:36:34,240
Speaker 1: recent study by MIT and Harvard include an important effect,

743
00:36:34,719 --> 00:36:38,160
Speaker 1: which is that as the planet gets lower and lower mass,

744
00:36:38,280 --> 00:36:42,000
Speaker 1: the atmosphere grows in size, Like you can have the

745
00:36:42,000 --> 00:36:44,560
Speaker 1: same amount of atmosphere, but it can get more fluffy.

746
00:36:44,640 --> 00:36:47,279
Speaker 1: And as the atmosphere gets hotter, it can also get

747
00:36:47,400 --> 00:36:51,120
Speaker 1: large because a hot atmosphere means those little particles are

748
00:36:51,120 --> 00:36:53,960
Speaker 1: moving around faster, which means that they can get further

749
00:36:54,120 --> 00:36:56,400
Speaker 1: from the planet. And this that's important effect on the

750
00:36:56,480 --> 00:37:00,600
Speaker 1: temperature of the planet because like a larger atmosphere more

751
00:37:00,680 --> 00:37:04,839
Speaker 1: solar radiation and also emits more solar radiation. So they

752
00:37:04,840 --> 00:37:08,759
Speaker 1: have this more nuanced model of how planetary atmospheres work,

753
00:37:09,000 --> 00:37:13,000
Speaker 1: how they grow and shrink, how they emit and absorb radiation,

754
00:37:13,239 --> 00:37:15,680
Speaker 1: and this lets them do more realistic modeling of what

755
00:37:15,719 --> 00:37:17,160
Speaker 1: these planets would actually be like.

756
00:37:17,320 --> 00:37:19,360
Speaker 2: Oh so, I wonder how much research on the greenhouse

757
00:37:19,400 --> 00:37:21,880
Speaker 2: effect on Earth has helped with being able to do

758
00:37:22,160 --> 00:37:24,680
Speaker 2: models like this, or maybe even the other way around.

759
00:37:24,719 --> 00:37:27,319
Speaker 2: Maybe studying the greenhouse effect on Venus helps with our

760
00:37:27,360 --> 00:37:29,920
Speaker 2: greenhouse effect models on Earth, or maybe they're both helping

761
00:37:29,920 --> 00:37:30,279
Speaker 2: each other.

762
00:37:30,640 --> 00:37:34,279
Speaker 1: Yeah, exactly. It's really fascinating. What they found is that

763
00:37:34,320 --> 00:37:37,040
Speaker 1: Earth mass planets can also get too hot. You can

764
00:37:37,080 --> 00:37:40,239
Speaker 1: get this runaway greenhouse effect if you're too close to

765
00:37:40,280 --> 00:37:43,319
Speaker 1: the Sun, even if you're Earth mass, right. But there's

766
00:37:43,560 --> 00:37:46,440
Speaker 1: this interesting wrinkle which is that smaller planets can actually

767
00:37:46,440 --> 00:37:50,480
Speaker 1: avoid this runaway greenhouse effect because their atmospheres can get

768
00:37:50,480 --> 00:37:53,440
Speaker 1: bigger and they can emit more. So this helps balance

769
00:37:53,440 --> 00:37:56,279
Speaker 1: the absorption. As the temperature on the planet goes up,

770
00:37:56,440 --> 00:37:58,600
Speaker 1: the sort of the gap between how much you're emitting

771
00:37:58,600 --> 00:38:01,480
Speaker 1: and how much you're absorbing also goes up, and so

772
00:38:01,520 --> 00:38:04,080
Speaker 1: it helps like release some of that energy into space.

773
00:38:04,640 --> 00:38:07,760
Speaker 2: That's really interesting. Could we blow part of Venus off

774
00:38:08,040 --> 00:38:09,160
Speaker 2: and make it habitable?

775
00:38:09,719 --> 00:38:12,720
Speaker 1: Yeah, that's exactly the point. So if Venus was smaller,

776
00:38:12,760 --> 00:38:15,040
Speaker 1: it might not have this greenhouse effect because it would

777
00:38:15,040 --> 00:38:17,560
Speaker 1: allow its atmosphere to be a little fluffier because the

778
00:38:17,600 --> 00:38:20,320
Speaker 1: gravity would be weaker, and that would help it radiate

779
00:38:20,360 --> 00:38:22,200
Speaker 1: more energy out into space.

780
00:38:22,560 --> 00:38:25,399
Speaker 2: Well, okay, so I'm definitely not recommending that we do this,

781
00:38:25,920 --> 00:38:29,200
Speaker 2: but maybe Elon Musk you could imagine him saying something like,

782
00:38:29,640 --> 00:38:32,320
Speaker 2: what if we blow off a part of Venus to

783
00:38:32,400 --> 00:38:35,160
Speaker 2: make it smaller, and then maybe it would become habitable

784
00:38:35,160 --> 00:38:36,799
Speaker 2: at enough time, although you'd have to make sure that

785
00:38:36,840 --> 00:38:38,960
Speaker 2: none of the parts of Venus you blew off it Earth.

786
00:38:38,960 --> 00:38:41,080
Speaker 2: That would be embarrassing exactly.

787
00:38:41,160 --> 00:38:43,200
Speaker 1: And then you also have to worry about like disrupting

788
00:38:43,200 --> 00:38:47,319
Speaker 1: the atmosphere with your planet exploding nuclear weapons. I think

789
00:38:47,360 --> 00:38:49,440
Speaker 1: there's a lot of details to nail down there before

790
00:38:49,440 --> 00:38:50,640
Speaker 1: you pitch that to investors.

791
00:38:51,760 --> 00:38:53,279
Speaker 2: Yeah, but none of those details are fun.

792
00:38:56,600 --> 00:38:59,000
Speaker 1: And in this paper they do this fun calculation where

793
00:38:59,000 --> 00:39:01,800
Speaker 1: they think about how long water can exist on the

794
00:39:01,840 --> 00:39:04,359
Speaker 1: surface of this planet. Because as the planet gets really

795
00:39:04,400 --> 00:39:07,440
Speaker 1: really small, it's not as good at holding onto its water.

796
00:39:07,760 --> 00:39:11,280
Speaker 1: The water then becomes vapor and then increases the greenhouse effect.

797
00:39:11,400 --> 00:39:13,799
Speaker 1: So they do this calculation where they determine like how

798
00:39:13,880 --> 00:39:16,560
Speaker 1: long water will be liquid on the surface for these planets,

799
00:39:16,640 --> 00:39:18,960
Speaker 1: and they do it at a whole range of sizes

800
00:39:19,200 --> 00:39:23,200
Speaker 1: and distances from the star and local surface temperature. It's

801
00:39:23,239 --> 00:39:24,080
Speaker 1: really fascinating.

802
00:39:24,200 --> 00:39:27,120
Speaker 2: So if they were to find a planet in another

803
00:39:27,160 --> 00:39:30,360
Speaker 2: solar system and they ran this model on it to

804
00:39:30,440 --> 00:39:32,759
Speaker 2: give you a yes, no, this is going to be habitable,

805
00:39:33,680 --> 00:39:38,600
Speaker 2: would you sell your house and trust these calculations and

806
00:39:38,680 --> 00:39:40,720
Speaker 2: go move out there, or do you think we need

807
00:39:41,120 --> 00:39:44,760
Speaker 2: a couple more decades of adding additional variables to these models.

808
00:39:44,840 --> 00:39:47,120
Speaker 1: I'm pretty sure the authors of this paper would not

809
00:39:47,200 --> 00:39:50,279
Speaker 1: bank on these results. Ok No, I mean I think so.

810
00:39:50,320 --> 00:39:52,000
Speaker 1: I think this is part of the process, you know,

811
00:39:52,160 --> 00:39:54,640
Speaker 1: and it's informing our understanding, and it's giving us a

812
00:39:54,680 --> 00:39:57,319
Speaker 1: sense for what's out there, and it's also helping to

813
00:39:57,440 --> 00:40:01,560
Speaker 1: inform what we're looking for deciding. What they find in

814
00:40:01,600 --> 00:40:04,160
Speaker 1: this paper is that you can live on a pretty

815
00:40:04,200 --> 00:40:06,959
Speaker 1: small planet if your planet is like forty percent water

816
00:40:07,000 --> 00:40:09,640
Speaker 1: by mass. They do a calculation and they suggest that

817
00:40:09,719 --> 00:40:12,920
Speaker 1: a local gravity of just one and a half meters

818
00:40:12,960 --> 00:40:15,920
Speaker 1: per second squared, which is like, you know, fifteen twenty

819
00:40:16,000 --> 00:40:19,680
Speaker 1: percent of Earth gravity, would be enough to keep liquid

820
00:40:19,719 --> 00:40:22,200
Speaker 1: water on the surface and the atmosphere and everything else

821
00:40:22,239 --> 00:40:22,640
Speaker 1: we need.

822
00:40:22,840 --> 00:40:25,040
Speaker 2: Wow, that's pretty tiny. That's very cool.

823
00:40:25,280 --> 00:40:28,279
Speaker 1: It's pretty small. I mean, it's like fifty percent of

824
00:40:28,320 --> 00:40:31,359
Speaker 1: the size of mercury. It's about twice the size of

825
00:40:31,400 --> 00:40:34,799
Speaker 1: our moon. So that's a lot smaller than the earlier calculations.

826
00:40:35,040 --> 00:40:38,640
Speaker 1: These planets benefit from having the like fluffy atmosphere effect,

827
00:40:38,880 --> 00:40:40,920
Speaker 1: which helps prevent the runaway greenhouse effect.

828
00:40:41,200 --> 00:40:45,200
Speaker 2: Interesting, So did the authors note that there's like anything

829
00:40:45,320 --> 00:40:47,680
Speaker 2: that they know they should have included in the model,

830
00:40:47,680 --> 00:40:50,239
Speaker 2: but it was just getting too complicated, or are they like,

831
00:40:50,320 --> 00:40:52,719
Speaker 2: this is all the stuff that we think is important

832
00:40:52,840 --> 00:40:53,239
Speaker 2: so far.

833
00:40:53,440 --> 00:40:55,920
Speaker 1: No, they definitely understand that this is just one step

834
00:40:55,960 --> 00:40:59,440
Speaker 1: in the process of building more and more sophisticated models

835
00:40:59,719 --> 00:41:04,759
Speaker 1: of alien planet atmospheres. You know, for example, they ignore clouds, right,

836
00:41:04,800 --> 00:41:08,120
Speaker 1: They're only thinking about a few atmospheric species and they're

837
00:41:08,120 --> 00:41:11,719
Speaker 1: not including the effect of like having clouds in the atmosphere. Also,

838
00:41:11,760 --> 00:41:15,680
Speaker 1: for example, not thinking about tidal forces. Tile forces are

839
00:41:15,719 --> 00:41:19,160
Speaker 1: the effect of having a different gravitational force from the

840
00:41:19,200 --> 00:41:22,000
Speaker 1: Sun on one side of the planet and the other.

841
00:41:22,400 --> 00:41:24,719
Speaker 1: So mercury, for example, is very close to the Sun,

842
00:41:24,760 --> 00:41:27,240
Speaker 1: it is much stronger gravity on one side of mercury

843
00:41:27,280 --> 00:41:29,960
Speaker 1: than on the other side of mercury, which squeezes and

844
00:41:30,000 --> 00:41:33,400
Speaker 1: compresses mercury and gets internal heating the same way like

845
00:41:33,520 --> 00:41:36,880
Speaker 1: Jupiter has tidal heating of all of its moons. And

846
00:41:36,920 --> 00:41:40,120
Speaker 1: so this is something they completely ignore in their calculations,

847
00:41:40,520 --> 00:41:42,680
Speaker 1: and they're very upfront about that, and in their paper

848
00:41:42,719 --> 00:41:45,560
Speaker 1: they're like, here's you know, future work. And so there's

849
00:41:45,600 --> 00:41:47,719
Speaker 1: definitely going to be more studies of this kind of thing,

850
00:41:47,800 --> 00:41:51,759
Speaker 1: especially as we discover alien planets and learn about their

851
00:41:51,800 --> 00:41:55,279
Speaker 1: atmospheric signatures by looking through telescopes and seeing what kind

852
00:41:55,280 --> 00:41:57,600
Speaker 1: of light they emit and looking at that spectra, we're

853
00:41:57,600 --> 00:42:01,040
Speaker 1: going to be discovering planets that probably disagree with all

854
00:42:01,080 --> 00:42:03,040
Speaker 1: these calculations that are going to make us go back

855
00:42:03,120 --> 00:42:04,719
Speaker 1: and figure out how to modify them.

856
00:42:04,800 --> 00:42:08,400
Speaker 2: And have we identified any planets yet that meet the criteria,

857
00:42:08,600 --> 00:42:11,120
Speaker 2: for example, that are laid out in this particular paper

858
00:42:11,200 --> 00:42:12,320
Speaker 2: that might be habitable.

859
00:42:12,520 --> 00:42:16,120
Speaker 1: So one disadvantage of our methods for finding exoplanets is

860
00:42:16,120 --> 00:42:19,200
Speaker 1: that they're very good at finding really big planets and

861
00:42:19,360 --> 00:42:23,080
Speaker 1: very good at finding planets close to their star, because

862
00:42:23,120 --> 00:42:25,160
Speaker 1: those are the ones that like block the light from

863
00:42:25,200 --> 00:42:27,440
Speaker 1: the star of the most or make that star wiggle

864
00:42:27,520 --> 00:42:30,879
Speaker 1: the most, and those are two best techniques for finding exoplanets.

865
00:42:31,200 --> 00:42:32,680
Speaker 1: So what that means is that a lot of the

866
00:42:32,680 --> 00:42:36,040
Speaker 1: exoplanets we have found are really big and really close

867
00:42:36,080 --> 00:42:38,200
Speaker 1: to their star, which is like, not what we're looking

868
00:42:38,200 --> 00:42:40,440
Speaker 1: for at all. Nobody wants to move to like a

869
00:42:40,480 --> 00:42:43,160
Speaker 1: hot jupiter, even though that sounds like a fun dance club.

870
00:42:44,920 --> 00:42:45,960
Speaker 2: It does, I'd go there.

871
00:42:46,480 --> 00:42:49,680
Speaker 1: But there's a lot of work in understanding what are

872
00:42:49,680 --> 00:42:51,759
Speaker 1: the exoplanets that are out there that we're not as

873
00:42:51,800 --> 00:42:55,200
Speaker 1: good at finding. We had astronomers on the show recently

874
00:42:55,239 --> 00:42:57,560
Speaker 1: talking about like how to extrapolate. If you know that

875
00:42:57,600 --> 00:43:00,160
Speaker 1: you have a bias in your sort of sampling method,

876
00:43:00,400 --> 00:43:02,719
Speaker 1: then you can try to unfold that bias and say, well,

877
00:43:02,719 --> 00:43:04,520
Speaker 1: what's out there that I'm not seeing? Like if you

878
00:43:04,560 --> 00:43:06,200
Speaker 1: walk through the woods and write down all the animals

879
00:43:06,280 --> 00:43:08,839
Speaker 1: you see, that's not necessarily all the animals that are

880
00:43:08,880 --> 00:43:11,160
Speaker 1: in your woods, right, because you imagine there's something that

881
00:43:11,200 --> 00:43:13,080
Speaker 1: you can't see or something that run away from you.

882
00:43:13,160 --> 00:43:15,720
Speaker 1: And so if you know that the scale of that effect,

883
00:43:15,719 --> 00:43:18,000
Speaker 1: you can like invert it to try to estimate, like

884
00:43:18,040 --> 00:43:20,440
Speaker 1: what's out there that you're not seeing. So we do

885
00:43:20,480 --> 00:43:22,640
Speaker 1: the same thing with planets and try to estimate, like,

886
00:43:22,719 --> 00:43:25,960
Speaker 1: what is the true population of planets, not just the

887
00:43:25,960 --> 00:43:27,120
Speaker 1: ones that we can.

888
00:43:27,000 --> 00:43:30,560
Speaker 2: See, And is it additionally complicated by the fact that

889
00:43:30,560 --> 00:43:32,439
Speaker 2: they're far away and the light takes a long time

890
00:43:32,480 --> 00:43:35,040
Speaker 2: to get to us, and by the time we're analyzing it,

891
00:43:35,080 --> 00:43:36,880
Speaker 2: maybe the planet is no longer habitable.

892
00:43:37,080 --> 00:43:39,879
Speaker 1: It is in fact complicated by that and the fact

893
00:43:39,920 --> 00:43:42,879
Speaker 1: that we don't really understand how solar systems form. Right,

894
00:43:42,880 --> 00:43:45,480
Speaker 1: if we had a great model for solar system formation,

895
00:43:46,080 --> 00:43:48,880
Speaker 1: then we could make a very confident prediction for what

896
00:43:48,920 --> 00:43:51,720
Speaker 1: the distribution of planets are out there. But it's very chaotic,

897
00:43:51,920 --> 00:43:54,080
Speaker 1: very complicated. You and I have talked about it. Even

898
00:43:54,080 --> 00:43:56,200
Speaker 1: the history of our own Solar system is not one

899
00:43:56,239 --> 00:43:58,920
Speaker 1: that we understand very well. We think Jupiter moved in

900
00:43:59,080 --> 00:44:01,520
Speaker 1: and then got pulled out again, and Saturn followed it,

901
00:44:01,560 --> 00:44:03,480
Speaker 1: and there may have been another planet that was lost.

902
00:44:03,800 --> 00:44:07,319
Speaker 1: It's very chaotic and sensitive to initial conditions, which makes

903
00:44:07,320 --> 00:44:10,279
Speaker 1: it very hard to model, sort of ab initio, what

904
00:44:10,320 --> 00:44:12,960
Speaker 1: these solar systems should look like. But we have found

905
00:44:12,960 --> 00:44:16,839
Speaker 1: some small planets. There's a planet called Kepler thirty seven B,

906
00:44:16,880 --> 00:44:20,560
Speaker 1: which is like the smallest exoplanet ever found. Its radius

907
00:44:20,640 --> 00:44:23,759
Speaker 1: is like thirty five percent of the Earth's radius, so

908
00:44:23,840 --> 00:44:26,680
Speaker 1: it's like a little bit larger than the Moon. Though

909
00:44:26,760 --> 00:44:29,279
Speaker 1: based on its orbit around its Sun, they estimate its

910
00:44:29,280 --> 00:44:32,560
Speaker 1: service temperature is like seven hundred kelvin, which is like

911
00:44:32,680 --> 00:44:36,600
Speaker 1: eight hundred degrees fahrenheit, So there'll be no dipping your

912
00:44:36,640 --> 00:44:39,560
Speaker 1: toes in the water around on Kepler thirty seven B.

913
00:44:39,719 --> 00:44:44,120
Speaker 2: There no toes on Kepler thirty seven B's.

914
00:44:43,160 --> 00:44:48,520
Speaker 1: Right, yeah, exactly, But you know, it is fascinating to

915
00:44:48,600 --> 00:44:51,080
Speaker 1: think that there might be smaller planets than we ever

916
00:44:51,120 --> 00:44:54,439
Speaker 1: imagined possible that are habitable. Then when we look out

917
00:44:54,440 --> 00:44:57,200
Speaker 1: into those solar systems and imagine where we might live,

918
00:44:57,200 --> 00:45:01,200
Speaker 1: we don't just have to look for other earth bigger earths,

919
00:45:01,239 --> 00:45:03,280
Speaker 1: or slightly smaller earth. That there might be a whole

920
00:45:03,400 --> 00:45:05,960
Speaker 1: range of planets out there, and you know, the experience

921
00:45:06,000 --> 00:45:09,200
Speaker 1: of living on those planets could be very different. Imagine

922
00:45:09,239 --> 00:45:12,160
Speaker 1: living on a planet where like the curvature is much

923
00:45:12,239 --> 00:45:14,759
Speaker 1: more visible. Right, You're like out on the ocean and

924
00:45:14,800 --> 00:45:17,000
Speaker 1: you could like see the curvature of your planet.

925
00:45:17,200 --> 00:45:19,440
Speaker 2: I think Phil Plait recently wrote a book that's all

926
00:45:19,440 --> 00:45:21,759
Speaker 2: about like imagining what it would be like if you

927
00:45:21,800 --> 00:45:23,879
Speaker 2: were living on another planet and sort of looked out

928
00:45:23,880 --> 00:45:26,440
Speaker 2: at like their atmosphere that has different color sunsets and

929
00:45:26,480 --> 00:45:27,440
Speaker 2: different curvatures.

930
00:45:27,640 --> 00:45:30,120
Speaker 1: Yeah, that sounds super awesome. Imagine if you lived on

931
00:45:30,160 --> 00:45:32,439
Speaker 1: a small planet that had a moon, and that moon

932
00:45:32,560 --> 00:45:35,479
Speaker 1: was tidly locked, and you were tidally locked tho would

933
00:45:35,480 --> 00:45:37,359
Speaker 1: mean you could only see the moon from like one

934
00:45:37,480 --> 00:45:40,360
Speaker 1: side of the planet. These effects are much more likely

935
00:45:40,440 --> 00:45:43,680
Speaker 1: on a small planet than a larger planet with small moons,

936
00:45:44,200 --> 00:45:46,320
Speaker 1: and so the whole experience of living on those planets

937
00:45:46,400 --> 00:45:47,680
Speaker 1: could really be very different.

938
00:45:47,920 --> 00:45:51,200
Speaker 2: You are maybe sort of kind of making me think

939
00:45:51,239 --> 00:45:53,040
Speaker 2: that it might be fun to leave my house for

940
00:45:53,120 --> 00:45:57,120
Speaker 2: another planet. That does all sound pretty awesome. Now, now,

941
00:45:57,160 --> 00:46:01,160
Speaker 2: do these planets have different wasps that haven't been described yet?

942
00:46:01,200 --> 00:46:03,080
Speaker 1: Because then I'm in you mean, like, are there weird

943
00:46:03,120 --> 00:46:05,800
Speaker 1: alien parasites that might suck the brains out of your children?

944
00:46:05,880 --> 00:46:06,560
Speaker 1: Is that you're asking?

945
00:46:06,760 --> 00:46:10,000
Speaker 2: No, No, not at all. I'm hoping that they're sucking

946
00:46:10,080 --> 00:46:12,320
Speaker 2: the brains out of each other and I can take notes,

947
00:46:12,400 --> 00:46:15,640
Speaker 2: but that they're not well adapted to me. I would

948
00:46:15,719 --> 00:46:17,000
Speaker 2: like to be at the top of the food chain

949
00:46:17,040 --> 00:46:17,600
Speaker 2: there as well.

950
00:46:17,840 --> 00:46:20,880
Speaker 1: Well, maybe you'll enjoy spicy wasps, you know, on your salad.

951
00:46:20,960 --> 00:46:23,880
Speaker 1: We all have to make compromises when we're camping on exoplanets.

952
00:46:24,120 --> 00:46:27,120
Speaker 1: So so far we found about five thousand planets, mostly

953
00:46:27,200 --> 00:46:29,880
Speaker 1: hot Jupiters, but a smattering of smaller ones. And we

954
00:46:30,000 --> 00:46:33,200
Speaker 1: hope that as our ability to find these planets improves,

955
00:46:33,320 --> 00:46:37,239
Speaker 1: we might find smaller and smaller, rocky planets, maybe even

956
00:46:37,320 --> 00:46:40,440
Speaker 1: ones that have everything we need to travel there and

957
00:46:40,560 --> 00:46:44,040
Speaker 1: boot up our ecosystem on its surface. Let's hope that

958
00:46:44,080 --> 00:46:46,160
Speaker 1: we bring small enough people so they don't use up

959
00:46:46,200 --> 00:46:46,960
Speaker 1: all the oxygen.

960
00:46:49,040 --> 00:46:51,200
Speaker 2: Yes, it would be nice if we could have interchangeable people,

961
00:46:51,239 --> 00:46:54,120
Speaker 2: but yes, small people is a good decision.

962
00:46:54,320 --> 00:46:56,399
Speaker 1: And thanks all the listeners for coming along with us

963
00:46:56,400 --> 00:47:00,560
Speaker 1: on this journey to imagine small habitable planets might one

964
00:47:00,680 --> 00:47:04,360
Speaker 1: day send our great great great great great grandkids to

965
00:47:04,560 --> 00:47:06,880
Speaker 1: run along in And thanks Kelly for joining us on

966
00:47:06,920 --> 00:47:07,720
Speaker 1: today's episode.

967
00:47:07,760 --> 00:47:09,600
Speaker 2: Thanks for having me. As always, it was a ton

968
00:47:09,640 --> 00:47:10,120
Speaker 2: of fun.

969
00:47:09,960 --> 00:47:20,040
Speaker 1: All right, tune in next time. Thanks for listening, and

970
00:47:20,120 --> 00:47:22,839
Speaker 1: remember that Daniel and Jorge Explain the Universe is a

971
00:47:22,880 --> 00:47:27,440
Speaker 1: production of iHeartRadio. For more podcasts from iHeartRadio, visit the

972
00:47:27,520 --> 00:47:31,680
Speaker 1: iHeartRadio app, Apple Podcasts, or wherever you listen to your

973
00:47:31,719 --> 00:47:32,520
Speaker 1: favorite shows.