Newly Discovered Planet is Just Like Earth

Its mass indicates that it is probably a rocky planet with a definite surface and enough gravity to hold on to an atmosphere.

Gliese 581 has two previously detected planets that lie at the edges of the habitable zone where the atmosphere is just the right temperature for liquid water to exist - one on the hot side (planet c), the other on the cold face (planet d).

While some astronomers still think planet d may be habitable if it has a thick atmosphere, others are skeptical. The newly-discovered planet g, however, lies right in the middle of the habitable zone.

The planet is tidally locked to the star, meaning that one side is always facing the star and basking in perpetual daylight, while the side facing away from the star is in perpetual darkness.

One effect of this is to stabilize the planet's surface climates, according to Vogt. The most habitable zone on the planet's surface would be the line between shadow and light (known as the 'terminator').

It comes as astronomers make a case for expanding the habitability zone of a planet to include a larger set of criteria so as not to exclude other possibilities of alien life. Experts report that there are already more than 700 exoplanets discovered, but only a few are in the habitable zone.

According to The International Business Times, scientists are saying that limiting the search for extraterrestrial life in Earth-like planets could exclude other possibilities of alien life.