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Sensitivity analysis. Elements of the simulation are based wholly on proven, low-level physics (for example, calculating the amount of heat absorbed by a given

by saulrh 15y ago

Sensitivity analysis. Elements of the simulation are based wholly on proven, low-level physics (for example, calculating the amount of heat absorbed by a given amount of CO2 from a given amount of sunlight) whenever possible, and when that's infeasible the modelers test a range of possible values to see what happens. For example, you can't exactly calculate the density of condensation nuclei in the atmosphere (used for calculating cloud formation behavior), so they just ran the simulation with a bunch of believable values. Another example is pretty clearly laid out in the first sentence of the "results" section: We performed simulations with 5, 10, 20 and 30 bar atmospheric pressure and 1:1, 1:2 and 1:10 orbit-rotation resonances for both rocky and ocean planets (see Table 1).

jerf 15y ago
There is not enough data in a vague orbit and vague size (in a dataset that until recently contained a spurious planet) to feed a simulation like this, which means that the simulation was, mathematically necessarily (and I do not use this term lightly), made up from nearly whole cloth. And then we have no way to verify anything that it did say, assuming it even started from the correct place, especially with regards to stability on geologic time. Even an 99.9999999%-per-hour perfect simulation will still diverge on geologic time scales. For all we know, an atmosphere with a mountain range here will freeze out in a century, whereas a mountain range there could in fact result in a stable atmosphere over geologic time. This is all information-theoretic necessity. This is entertainment, not science. That may be all the scientists claimed. It's still a fun result, even if I wouldn't put my grandchildren on a flight to Gliese on the strength of it. I'm reacting against the certainty expressed in the article.
- saulrh 15y ago
  Ok, I think I see what you mean now, and I agree with you. They've shown that the distribution assuming some set of priors includes some particular, interesting outcome. This is the first planet we've ever seen where we can say that given how much information we have about it, though, which means that it's still cool.
- robryan 15y ago
  Yeah, we can still look at some extremely broad possibilities how how such a planet atmosphere could behave based on the little we know about the planet. Then the simulation gives some guide onto how each of these would play out. Sure it's very speculative, but one step up from no data at all, which is the best we have now. At least have an idea of the size, the orbit and the sunlight intensity that would be hitting the planet.

by saulrh 15y ago

jerf 15y ago

There is not enough data in a vague orbit and vague size (in a dataset that until recently contained a spurious planet) to feed a simulation like this, which means that the simulation was, mathematically necessarily (and I do not use this term lightly), made up from nearly whole cloth. And then we have no way to verify anything that it did say, assuming it even started from the correct place, especially with regards to stability on geologic time. Even an 99.9999999%-per-hour perfect simulation will still diverge on geologic time scales. For all we know, an atmosphere with a mountain range here will freeze out in a century, whereas a mountain range there could in fact result in a stable atmosphere over geologic time. This is all information-theoretic necessity. This is entertainment, not science. That may be all the scientists claimed. It's still a fun result, even if I wouldn't put my grandchildren on a flight to Gliese on the strength of it. I'm reacting against the certainty expressed in the article.

saulrh 15y ago
Ok, I think I see what you mean now, and I agree with you. They've shown that the distribution assuming some set of priors includes some particular, interesting outcome. This is the first planet we've ever seen where we can say that given how much information we have about it, though, which means that it's still cool.
robryan 15y ago
Yeah, we can still look at some extremely broad possibilities how how such a planet atmosphere could behave based on the little we know about the planet. Then the simulation gives some guide onto how each of these would play out. Sure it's very speculative, but one step up from no data at all, which is the best we have now. At least have an idea of the size, the orbit and the sunlight intensity that would be hitting the planet.