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Comment by qntty | Hacker News Reader

Here are some other planets we've found with comparable similarity. Note that earth-like similarity does not imply that it is habitable.

http://phl.upr.edu/projects/habitable-exoplanets-catalog/dat...

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A few zones some think need to overlap and be dialed-in to come close to offering a habitable place:

water habitable zone

ultraviolet habitable zone

photosynthetic habitable zone

ozone habitable zone

planetary rotation rate habitable zone

planetary obliquity habitable zone

tidal habitable zone

astrosphere habitable zone

Pretty sure these all apply for Mars and Venus and they're dead planets. Not sure why everyone is assuming some exo-planet must have life when the two other examples we have don't.

The earth similarity index for venus is 0.44, and for mars is 0.70

I understand, but that's a synthetic benchmark. We actually have no idea why Earth has life and other planets don't and similarity to Earth may not be a big factor (see theories on life in Europa's seas for example or non-carbon based life).

I just feel everyone gets excited over nothing solely because its extra-solar. Our own solar system is fairly diverse. If life was common, we'd probably be seeing more of it here.

maybe life is common enough, but doesn't typically overlap in time. Maybe life on mars or venus died out a billion years ago.

We'll have a better picture when we study our solar system in more detail. Maybe 100 years? I agree that speculation this early in the game isn't enough to get excited over.

quite a few of those are not relevant for habitability. for example tides, really? or you wouldn't survive if day would have 40 hours???

I think it's more like if the day was 100 msec that you have to worry about. Also, if the day is too slow, then one side of the planet bakes while the other side freezes. Think of the rotation axis as a spit roaster.

Nice metaphor :)

They are relevant, you're just misinterpreting. None of these are meant to imply "X must be like Earth for the planet to be habitable," they mean "X is an important factor for habitability and must be considered in our models if we want them to be meaningful, unlike the ESI which captures a mere handful of variables".

For example, "tidal habitable zone" doesn't mean "we need [ocean] tides to survive," it means "tidal heating effects have an enormous impact on planetary conditions". For example, an Earth analogue in orbit around a tiny red dwarf in a seemingly "habitable zone" would be subject to tidal heating effects which would bake the surface, whereas a similar planet in a similar orbit around a sun-like yellow dwarf would not.

Similarly, "rotation rate habitable zone" doesn't mean "the planet must have a ~24 hour day", it means "all else being equal, a planet's rotation rate can greatly affect habitability," mostly due to weather patterns and air/heat circulation. By including rotation rate in our models, some planets previously thought to be inhabitable may turn out not to be, and vice versa.

I'd put magnetosphere in that list

I'd put it up fairly high on the list...

http://www.windows2universe.org/glossary/plasmaspheric_gain....

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