 Whether or not a tide @-@ locked planet with the orbital characteristics of Gliese 581g is actually habitable depends on the composition of the atmosphere and the nature of the planetary surface . A comprehensive modeling study including atmospheric dynamics , realistic radiative transfer and the physics of formation of sea ice ( if the planet has an ocean ) indicates that the planet can become as hot as Venus if it is dry and allows carbon dioxide to accumulate in its atmosphere . The same study identified two habitable states for a water @-@ rich planet . If the planet has a very thin atmosphere , a thick ice crust forms over most of the surface , but the substellar point remains hot enough to yield a region of thin ice or even episodically open water . If the planet has an atmosphere with Earthlike pressures , containing approximately 20 % ( molar ) carbon dioxide , then the greenhouse effect is sufficiently strong to maintain a pool of open water under the substellar point with temperatures comparable to the Earth 's tropics . This state has been dubbed " Eyeball Earth " by the author . 
