I'm not quite sure if this is the right place for this question, but I'm fairly certain I read about it in a sci-fi book. There was a planetary habitability rating based on 10 categories. I think a few of those categories were liquid water, breathable atmosphere, and plate tectonics. I believe anything that scored 7 or above was either habitable or easily terraformable. Earth rated a 9 on this scale, missing only one of the 10 categories, I can't remember which one. Does this sound familiar to anyone else?

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    Not sure, but habitability is a fun word to say out loud.
    – NominSim
    Sep 7, 2012 at 15:28
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    Earth is lacking in the "chocolate forest" category. Sep 7, 2012 at 15:51
  • @GorchestopherH - That's part of the 11 category ideal world scale ;)
    – SaintWacko
    Sep 7, 2012 at 15:57
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    Despite my Heinlein answer below, I think that Halderman's Forever War is a better candidate. I think there is a comment about Sanctuary begin a more habitable world than Earth at some point, but I haven't got access to a copy for reference just now. Sep 7, 2012 at 16:09
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    If you have not read Forever War, then you should put it on you to-read list. However you feel about Dr. Halderman's politics it is part of the canon, and a fine piece of literature in its own right. Sep 7, 2012 at 16:38

1 Answer 1


Heinlein's Friday featured such a scale mentioned in passing.

Friday is browsing random clasified adds and draws Georges' attention to a call for colonists...

We are about to abandon a pioneer party on a virgin planet type T-13. Guaranteed sex ratio 50-40-10±2% Median bio age 32±1. No temperament test required No Assessments-No Contributions-No Rescue
System Expansion Corporation
Division of Demography and Ecology
Luna City GPO lock box DEMO
or punch Tycho 800-2300

I called that one back and reread it. How would it feel to tackle a brand-new world side by side with comrades?-people who could not possibly know my origin. Or care. My enhancements might make me respected rather than a freak-as long as I did not flaunt them.
"Georges, look at this, please."
He did so. "What about it?"
"It could be fun-no?"
"No! Marjorie, on the T scale anything over eight calls for a large cash bonus, lavish equipment, and trained colonists. A thirteen is an exotic route to suicide, that's all."

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    Ah, I love that book. That scale doesn't quite fit the bill, though. First, it goes up to at least 13, second, higher numbers are worse than lower numbers, and third, it isn't explained in any depth.
    – SaintWacko
    Sep 7, 2012 at 16:04
  • @SaintWacko Yeah. See my comment on the question for a possibly better candidate. Sep 7, 2012 at 16:10

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