First, a climate conducive to life on Earth depends upon the extraordinarily narrow orbital parameters that define a continuously habitable zone where water can exist in a liquid state.

Instead the IAU definition makes life more complicated for astronomers, he said, because the notion of whether an orbital neighborhood has been cleared remains hazy.

To sustain life, a planet must have a mass similar to that of earth, liquid water on its surface, an atmosphere and a similar orbital distance from its star as that of the earth from the sun.