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?
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."