What does it really mean for a planet to be "habitable"?

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A reliable test: they will almost certainly have a Starbucks.


This guy seems to take a more severe interpretation of ‘habitable’ than ‘in the habitable zone’ but then uses Venus as an example of an inhabitable planet that’s in the zone. Gotcha! So will he only accept habitable as a description if there’s a nitrogen-oxygen atmosphere, breathable by humans, or are we forgetting the plans to create floating habitats in the high atmosphere of Venus?

I’m sure there’s another layer of ‘gotcha’ over and above my technology enabled interpretation of the term. Mars is not habitable, until we have habitats there, ‘oh but would you walk around outside unaided?’ Well, no but that goes for Shanghai during particularly smoggy days as well so…

A perfect simulacrum of atmosphere, weather, gravity, viruses, not overly dangerous sea and land animals. Oh and also we get to go in guns blazing and displace the indigenous aliens, it wouldn’t be truly perfect unless we get to take it by force.

Have you seen the state of their secondary schools and colleges, I could never bring myself to live in such a place!

Edit, took too long to edit my comment and @Boundegar got the starbucks reference in first!


I’d go for defining “habitable” as “possible to terraform”. I’d go even for “can be good for long-term survival if the amount of technology for that is not overwhelming”, where “overwhelming” stays undefined (and runs the risk of considering an icy Jupiter moon habitable via a sealed base with a nuke reactor for power).

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I’m reminded of the robot probes in Larry Niven’s Known Space stories that are programmed to look for inhabitable points rather than inhabitable planets, so we end up sending colonies to such places as Plateau, where the only inhabitable area is a plateau projecting above an atmosphere that is otherwise too thick for humans to live on (I don’t think Niven is specific, but my head-canon is that the concentration of oxygen is toxic on the planet’s mist-hidden surface); and Canyon, which has the opposite problem that the only inhabitable area is a deep canyon (imaginative names these planets have!) where the air is just thick enough for humans to breathe, but the rest of the planet has too thin an atmosphere.

But then I wonder how much of Earth’s surface is strictly speaking inhabitable if you’re being conservative about it. Too liberal in your programming and you could list areas such as Antarctica and Mount Everest as inhabitable, merely because humans have visited and survived there. But by that criteria, the Moon is inhabitable. And then recall that the Moon is within the “habitable” zone, which brings us back to the video’s point.

I’d say an inhabitable planet is one where there’s somewhere that a human can survive for an arbitrary period with just the clothes on her back, has some chance of finding or growing food, and can find other resources for her other needs. So, the Himalayan Plateau is inhabitable, but the peak of Mt Everest is not; Antartica is not, but the Arctic is… but only because it has neighbouring land and sea that can support life; the seas of Earth I’d give a pass to, but the oceans of Waterworld, probably not.


I think it becomes habitable when you land a Kerbal on it with some kind of base, no?


I would just like for scientists to find something living somewhere other than here. If they find a bacterium on Titan or a worm on Europa, I’d be in awe for the rest of my life. Would it be carbon-based? DNA-based? Can complexity emerge without oxygen or did some other biochemical pathway evolve?

Considering the weird and inhospitable places we find life around here I have to believe that life can thrive anywhere. Look at waterbears. Those things can survive in the radiation-drenched, freezing cold vacuum of space.

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That strikes my ear very oddly. I mean, “alien” in common discourse means any living creature (or AI/robot/gas-thing) that didn’t originate on earth. But if we go to another planet with indigenous inhabitants, it would seem very strange to call them aliens on their own turf… I’d just call them natives/indigenous, rather than alien. They’re not really aliens until they come to us.

I’d bet in this kind of future ever comes, that our insistence on calling all the non-earth-originating species aliens in the galactic UN would be seen as tribalistic or isolationist and insensitive.

Just a weird thought.


So why they are squatting on our planet?


Given our history of peace and brotherly love even among conspecifics, It’s a trifle hard to imagine human interaction with the galactic UN that doesn’t either involve our being declared a rogue life form by the security council; or our being given a seat on the security council, and carefully never chided for tactlessness, because we have just that many nukes/deployable singularities/discrete volume hadron nullifiers/etc. and a distinct air of being willing to take advantage of that…


Yeah, I’ve always had the feeling that if we ever meet a more advanced alien race, there’d only be two outcomes:

1.) They’d recognize us for the natural racists we are, and would figure out that we aren’t worth the trouble to bring into the larger interstellar community. So they’d either destroy us (because we’re ants), or do something to cut us off from the rest of interstellar civilization.

2.) We’d have slipped by under the radar long enough to have the upper hand in superweapons and one of our more fearful people in power would deploy said weapons and either destroy us, destroy whoever we made contact with us, or kick off a war big enough that nobody from anywhere would survive.

Of course, this could be in the far future at a point where we’ve gotten our act together. But I suspect that if an advanced species arrived in orbit tomorrow and said hello, there’d be a nuclear war between our superpowers out of sheer paranoia.

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Barring some sort of advance in superluminal communication or travel; a nice game of galactic thermonuclear war would likely be even less fun than a nice game of global thermonuclear war.

Aside from any xenophobia issues surrounding the fact that the colony-sentiences of Tau Ceti V are way more Xenos than even the godless communist ruskies are; speed of light delays make negotiation deeply problematic.

Earth’s circumference is ~40,000 kilometers. Accounting for sub-optimal cable routing, let’s say that any two terrestrial negotiators are separated by that much cable(in practice, it’s likely to be much less; but a bit more than an as-the-crow-flies direct cable link, unless the negotiating parties have giant pots of money to spend on laying fiber). The speed of light in optical fiber is lower than in vacuum(this is actually one of the few reasons that some of the pre-fiber microwave tower infrastructure is still in place: the bandwidth sucks; but speed of light in air is a bit higher), varying slightly by fiber type; but the usual estimate is 200,000km/s. So, ignoring any additional delays from switching equipment and repeaters; negotiator A can get a message to negotiator B in ~.2 seconds. Negotiator B can consider(however long that takes), and respond at the same speed. In informal chit-chat or ‘heartbeat’ signalling, the round-trip time will be noticeable enough to be less pleasant than face-to-face(nearly half a second); but minimal.

In galactic diplomacy, by contrast, things get tedious real fast: you’ll be communicating mostly through vacuum, so we can use distances in light years as a decent approximation; but that means that our cheery hello to even Proxima Centauri will take 4.2 years, and their reply as long. The 50-closest known objects list runs from 4.2 to just over 16 light years; with with the galaxy as a whole estimated as having a diameter of 100,000+ light years.

Diplomacy gets hairy enough when the ‘well, the next administration is likely to be more/less favorable than this one, so let’s stall/hurry whatever the process is’; but “our envoy’s message won’t even reach them before every one of us in this room is dead of old age; and their response, if any, might well reach a society we’d barely recognize” is a whole different game.

Especially nail-biting, of course, because (while no weapon based on physics-as-we-know-it could travel any faster than a message, and any remotely plausible one would travel more slowly) all the grim game theory behind first and second strikes and MAD and deterrence doesn’t go away, it just gets more obnoxious as the distances and times get longer(and, unlike ICBM launches between planetary neighbors, which are hard to hide; coming up with an estimate of “How many of my neighbors modified an asteroid to reduce its radar signature, covered it with carbon black, and shoved it toward me at 10% the speed of light?” or “are the skies strangely silent because space is big; or because some now-long-dead-asshole released the Berzerker probes back when my ancestors were still unicellular goo?” are the sort of exercises that are good for keeping you up at night; but not really so good for being answerable.


“Autochthon” and “indigene” are alternatives. Maybe “native”, if you’re being either unPC or ironic.

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To be serious for a moment; I, personally, would just call them whatever they’d like to be called, and if I’m referring to them as a species, I’d call them by their species name, or the appellation they coined for planet they came from, as long as it’s pronounceable by human anatomy (bearing in mind this my default conception is that this happens in the far future, and I could be uploaded and be able to replicate whatever sound is recordable via whatever advancements in sound reproduction and recording)

At the moment I take the same position regarding names and prounouns that I figured out when my cousin switched genders Transitioned from male to female, when I was 16*. The policy being: “It’s polite, civil, and honors a person’s personhood to call people by the names and gender they tell you they are. If unsure, then apologize and ask.” Which is wonderful when I forget cis-gender people’s names. Since I’m giving myself permission to ask people their names.

I re-read and it seemed really judgemental, which isn’t what I meant, so I made it a little more PC, and decided to put the emphasis on how I acted, rather than onto her.

Seriously, it’s not that big a deal to me now, but it was back when I was a stupid teenager, still clinging to conservatism, and thinking that her transition was an insult “to the way god made her”. Ugh.

If I could go back in time, I’d hurt my younger self’s feelings so badly by constantly pointing out how stupid he was.


But here we’re talking about beings who are incapable of naming themselves by virtue of being hypothetical (…there may be an SF story in that). You’re also assuming that they’ll have a name for themselves that we can pronounce, or that they have a established system for transliterating alien-to-English. Or that they care what we call them.

Or should I be habitually calling Japanese people 日本人 in English? I don’t insist that 日本人 pronounce, say, “English” properly.

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If I was the one to have discovered Japan, and figured out how to communicate with the Japanese via their language, I’d call them what ever they said they were.

What I’m saying is: Call someone how they’d like to be called. Otherwise, don’t make up new names for something/someone that already has a name. Especially if they are sentient and call themselves something already.

Also, I don’t care what people call me. As long as it’s honest. You can call me Shirley, but you can’t call me late to dinner.

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And I’m not wholeheartedly disagreeing with this as a principle. But the principle breaks down in detail, both in the general — “Igirisu” is almost how the Japanese would pronounce “English” if they made a serious effort to pronounce it like an Englishman, but isn’t quite right — and in the specific case here, where the aliens don’t have a name.

Sure, call the Alpha Centaurians “Trisolarians” if that’s what they collectively prefer, but when we don’t know if there are any Trisolarians, let alone whether there are any aliens at all, we need generic words to describe the classes of beings that may or may not exist on other planets, just like we use group words for “transpeople”, “transmen” and “transwomen” rather than naming each individual every time we want to talk about the group as a whole. I notice you didn’t name your cousin here, instead just used a generic word describing your familial relationship; was that out of disrespect?

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