"55 Cancri e" is a planet 40 light-years away from Earth that was discovered in 2004. It has a mass 7.8 times greater than that of Earth and is 26 times closer to its parent star than Mercury is to the Sun. Because of its close proximity to the star, it was thought that the planet was a barren wasteland with no source of water. New observations by the Spitzer Space Telescope may have lead us to the conclusion that this is untrue.

Because of its size, 55 Cancri e had been labeled a "super-Earth" and it was first estimated that this super-Earth was a dense planet of solid rock. Now scientists believe that "about a fifth of the planet's mass must be made of light elements and compounds--including water." These light elements must be present in a "supercritical" fluid state, which is described as a "liquid-like gas".

This information shows us that not every planet similar to the size of Earth is like the Earth. We can't assume that every planet reacts the same way the Earth would under certain conditions.

http://science.nasa.gov/science-news/science-at-nasa/2012/13jan_rethink/