Earth 2
The search is on to find a second earth.The exact circumstances that have led to our planet being habitable by life include the fact that we are of a certain size,a certain distance from our sun and have an atmosphere rich in hydrogen.Whilst there is a potential for life to form on other planets, taking forms we could never fathom or even imagine at this stage,the biggest chances of their being intelligent life would be on planets that resemble our own.