Gliese 581d in the habitable zone

This time using a 3-dimensional global climate model...
Gliese 581d is the first discovered terrestrial-mass exoplanet in the habitable zone

Needs around 10 bar of carbon dioxide in the atmosphere.

We can not check possible composition due lack of transit but in my opinion considering low density of kepler 11 planets and low metallicity of host star is very unlikely planet d as terrestial planet simply next minineptune with around 2.0g/cm3 density

I tend to agree with you there.

I am not sure about possibility of creating co2 in atmosphere of water ,ice planet but with deep 500km ocean I dont expect any life.Planetary biology give HZ between 0.1-0.15 AU around this star-so this planet require at least 5.0 g/cm density and 10 bar co2 in air -very unlikely.

Although I am not sure http://arxiv.org/abs/1105.0021

On the cold edge of the habitable zone the gaseous H₂/He atmosphe might actually be helpful to habitability (provided there is not so much that it exceeds the critical pressure). Gliese 581d remains a potentially-habitable planet either way...

Potentially habitable -ok but what composition of 581d you meant lazarus??

He's talking about a composition that has a gaseous-to-solid boundary (like your typical terrestrial planet), as opposed to a gradual transition from gaseous to solid (like a mini-Neptune or gas giant).

Lazarus wrote:

(provided there is not so much that it exceeds the critical pressure)

Critical point.
"A critical point specifices the conditions (temperature, pressure, and sometimes composition) at which a phase boundary ceases to exist."