First habitable exoplanet discovered?

[jerf]

"After its discovery, it was generally believed that any atmosphere thick enough to keep the planet warm would become cold enough on the night side to freeze out entirely, ruining any prospects for a habitable climate.... To test whether this intuition was correct, Wordsworth and colleagues developed a new kind of computer model capable of accurately simulating possible exoplanet climates.... To their surprise, they found that with a dense carbon dioxide atmosphere -- a likely scenario on such a large planet -- the climate of Gliese 581d is not only stable against collapse, but warm enough to have oceans, clouds and rainfall."

Question. How the bloody hell do you validate a computer model of how an atmosphere unlike anything we can observe in our solar system works? Did someone fly out there and verify it before publishing? And I'm supposed to believe your computer model iterates correctly over geologic time? Really? Really?

(Obligatory-but-totally-serious that this is still cool work not counting the computer model part, and to be honest I don't really care either way what the computer model says; I would be equally skeptical if they produced a model that claimed any outcome at all.)

[mturmon]

It appears that radiative transfer modeling is a specialty of the LMD at CNRS in Paris, which is the home institution of the authors:

http://en.wikipedia.org/wiki/GEISA

The state of the art in radiative transfer modeling is surprisingly advanced. For more, see:

http://en.wikipedia.org/wiki/Atmospheric_radiative_transfer_...

For instance, the use of RTMs for retrieving estimates of gas concentrations on Earth is routine. This idea is what the global CO2 maps produced by AIRS

http://airs.jpl.nasa.gov/science/geophysical_science/

are based on. You can sense back-scattered radiation, which tells you about the CO2 concentration in the air below the satellite. A good RTM is what allows the inversion of radiation into gas concentration.

Another related data point is that lots of investigators have been working for years on climate of Jupiter and Saturn using some of the same ideas. There are conference sessions about this topic, e.g.

http://www.agu.org/meetings/sm05/sm05-sessions/sm05_SA24A.ht...

I'm not saying that this means the authors are right, just that there's more valid science here than you might guess.

[saulrh]

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).

[fhars]

By making predictions that can be checked with the next generation of telescopes. That's how science works: look at what you have, figure out what you still want to know and design an experiment that can discriminate between different alternatives.

[jules]

Especially since researchers aren't able to accurately simulate Earth's climate over a smaller timescale, despite having much much better data about the current climate. Heck, for that planet they don't even know the composition of the atmosphere.

[danssig]

Welcome to science today. To their credit, at least when we find out the model was missing some key information they will update it and update their theories.

[DavidSJ]

The actual paper: http://arxiv.org/pdf/1105.1031

[D_Alex]

Great! Let's go and check it out!

[pjscott]

It's 20 light years away, so that could take a while. (I still want to do it, though.)

[Rariel]

Great. Now all we have to do is wait until Zefram Cochrane invents the warp drive in 2063. :-)

[troels]

Actually, being just 20 lyrs away, sub-warp speed would be sufficient for us to get there. Well, not us, but our grand children anyway.