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We get a lot of questions about planetary habitability (just to name a few). This search will give you these and many, many more. I enjoy answering these, as Astronomy is one of my passions and I've learned quite a lot about it. As such, I answer quite a lot of these questions. If I don't answer one, it's generally because there was at least one superb answer before me - often more than one, actually - which I then read, upvote, comment on, and move on.

On the answers I write to some of them, I find myself repeating a few key points:

  • Calculating the habitable zone's inner and outer radii
  • The lifetime of the central star and whether or not it could support life
  • Calculating planetary temperature
  • Investigating whether such a planet could form (if applicable)

. . . and so on.

Most cases have something unique about them - whether it be that the planet is shaped like something other than a sphere or whether it is entirely covered by snow - but most ask about whether or not the planet would be habitable, which can be analyzed by the points I listed above, as well as a number of other things.

This question led me to write a loooong answer that addressed a bunch of these, but there's still a lot that's left out.


The point of all this is that I'd prefer to write much shorter answers in the future and not have to rehash all of this stuff. All of it is necessary framework to consider, but I think that sometimes people see some of it in my answer, say "Bleah, math and too many words" and skip it to move on to greener pastures.

I'd like to create a canonical "general habitability" question and answer that can be referenced in the future, so I don't have to keep bringing up these points time and time again. It would mean I (and others) could be much more concise and focus on the essential aspects of future questions, allowing me (and them) to go into more detail on the minute aspects of each scenario.

I was going to cover all of the points I described above and more in an answer, with mathematics in the relevant sections and links aplenty. If it was needed, I could add in some points about moons and other objects, which would be helpful.

Is this question and answer acceptable, or should I not post it?

If so, I'll post it either today or tomorrow (most likely tomorrow).


By the way, we appear to have a tag, which has been unfortunately only used on three questions (as of this posting). It should probably be used more!


There was an issue previously with this question. I only came across it now. I realized that there's a chance that this question will suffer the same fate, in which case I totally understand if mine is closed. Still, I think that it should be kept open because, unlike CAgrppa's question, the material covered in mine has been reiterated time and time again, and will certainly prove useful in the future.

Again, though, I understand if the community wants to close it.


The question has been split up into two questions: one about the star, the other about the planet. Others may be added if necessary.


There are now multiple answers on the planet question dealing with different aspects of the planet.

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  • $\begingroup$ Since there has been a downvote of the actual question, would the downvoter - if you read this - write an answer explaining your objections. I would appreciate any feedback, negative or positive. $\endgroup$ – HDE 226868 Feb 8 '15 at 1:02
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    $\begingroup$ +1 Great idea. We need a few good wikis. $\endgroup$ – Serban Tanasa Feb 8 '15 at 17:45
  • $\begingroup$ Your point about tags is a tough one - most SE sites, especially early, struggle with getting questions properly tagged. $\endgroup$ – corsiKa Feb 11 '15 at 21:32
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    $\begingroup$ This would probably have to be broken down into a series of wiki's. Star Type/Habitable Zone, Atmosphere, Gravity...among others. The sub-topics could be their own wiki's, I think habitability is just to big a topic. (Hence the downvote) $\endgroup$ – James Feb 18 '15 at 17:56
  • $\begingroup$ @James Glad you explained. I've already split it up into the star and planet; I think that splitting it up into many more would just be too complicated. I'm not going into a lot of detail, just the essential bits. I don't want to address every habitability question that could be asked, just the overarching ones. Thanks for explaining the downvote. I appreciate it. $\endgroup$ – HDE 226868 Feb 18 '15 at 19:28
  • $\begingroup$ I think if you limit this to only solar system level info then it works just fine. When you start getting into climate/weather/atmosphere/landmass etc I think it gets to be too much. If that is the plan then I totally agree it is a good idea. $\endgroup$ – James Feb 18 '15 at 19:47
  • $\begingroup$ @James I'm probably going to keep it there. There also hasn't been a huge amount of contributions in the past few days - i.e. everyone forgot about it - and I don't know enough to write up good stuff on lower-level effects. $\endgroup$ – HDE 226868 Feb 18 '15 at 19:48
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Absolutely.

While the existence of this question would not preclude the existence of other habitability questions, it would be useful to have it as a general guide to point people to. I would suggest it should be CW-ed so that it's easy for other people with knowledge to edit it and add bits to it - it just needs a bit of a check every now and then to make sure it hasn't become nonsensical.

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  • $\begingroup$ I thought community wiki would be a good idea, too. I'll most likely do that. $\endgroup$ – HDE 226868 Feb 7 '15 at 23:23
  • $\begingroup$ @HDE226868 Mainly because I'd like to contribute ;) I'm sure it would be good for everyone else though. $\endgroup$ – ArtOfCode Feb 7 '15 at 23:24
  • $\begingroup$ I hope to see your contributions! $\endgroup$ – HDE 226868 Feb 7 '15 at 23:25
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I like the idea of having various canonical questions to point people to, but also want to raise a point of concern here. The question touches on and brings together several disciplines, which isn't at all bad by itself, but it is also very broad. The sheer length of the answer itself (even ignoring the images) is a good indication that maybe the question is trying to bite off too much. The answer is easily four screenfuls or so tall even on a high-resolution monitor, and even so, there are still parts of it that aren't filled out or fleshed out. On most sites in the Stack Exchange network, a question prompting an answer of that length would immediately fail the so-called "book test":

Your questions should be reasonably scoped. If you can imagine an entire book that answers your question, you’re asking too much.

That's often a problem with canonical questions in general, especially for as broad (subject matter wise) a site as ours: answers risk getting overwhelming.

Instead, I think we should have several different questions (or at the very least, several different answers, each clearly labelled) each of which focuses on a different aspect. One of those could be "I have a planet at distance X from a star, how do I know its temperature?". Another could be "how does the luminosity of a star vary over its lifetime?". A third could be "what range of atmospheric compositions would allow life as we know it to form?". And so on.

That approach does have the downside that it doesn't offer as clear-cut a "close as duplicate" target for any given question. However, it's a lot more digestable for the person who wants an answer to their specific question.

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Yes I think it could be useful to have that. Tim B asked questions like these already. As you said, the topic as already been covered in most angles possible and only the details are changing. Therefore it becomes repetitive.

After seeing the question on the main SE, I realize that it's a good idea as long as the scope is relatively focused. Right now, the answer lack consistency probably because the topic is too broad and some parts are just a series of ideas with no descriptions.

About habitation,: it does not feel appropriate. Habitability would suit better. Habitation is more a synonym of a house, the physical place where we live.

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  • $\begingroup$ I completely forgot about TimB's questions. Thanks. $\endgroup$ – HDE 226868 Feb 7 '15 at 23:16
  • $\begingroup$ I agree. There is a great question about designing fictional religions too. $\endgroup$ – Dronz Feb 9 '15 at 4:46
  • $\begingroup$ Part of the reason it's a bit loose is that most sections haven't been developed yet. Splitting it up will certainly help. $\endgroup$ – HDE 226868 Feb 9 '15 at 16:12

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