Gliese 436b transmission spectrum: featureless

Knutson et al. (2014) "A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b"
http://www.nature.com/nature/journal/v505/n7481/full/nature12887.html

Cloud-free hydrogen-dominated atmosphere ruled out to 48σ. Alternatives are clouds or a high molecular weight, hydrogen-poor atmosphere.

Lazarus wrote:

... ruled out to 48σ...

Goodness.

Well, I don't suppose the alternative to a cloudy atmosphere is particularly likely.

So water dominated atmosphere?

If it's the cloud-free hydrogen-poor atmosphere then I'd guess water is a likely alternative, yes.

But my money's on clouds, in which case a hydrogen-dominated atmosphere similar to Uranus and Neptune is still a possibility.

The gory details now on arXiv...

Knutson et al. "A featureless transmission spectrum for the Neptune-mass exoplanet GJ 436b"
http://arxiv.org/abs/1401.3350